A Neuropsychological Theory of Positive Affect and Its Influence on Cognition

Abstract

Positive affect systematically influences performance on many cognitive tasks. A new neuropsychological theory is proposed that accounts for many of these effects by assuming that positive affect is associated with increased brain dopamine levels. The theory predicts or accounts for influences of positive affect on olfaction, the consolidation of long-term (i.e., episodic) memories, working memory, and creative problem solving. For example, the theory assumes that creative problem solving is improved, in part, because increased dopamine release in the anterior cingulate improves cognitive flexibility and facilitates the selection of cognitive perspective.

Full text

Psychological
Review
1999,
Vol. 106,
No. 3.
529-550
Copyright
1999
by the
Americ an Psychologica l Associ ation, Inc.
0033-295X/99/S3.00
A
Neuropsychological
Theory
of
Positive Affect
and
Its
Influence
on
Cognition
F.
Gregory Ashby
University
of
California, Santa Barbara Alice
M.
Isen
Cornell University
And
U.
Turken
University
of
California, Santa Barbara
Positive affect systematically influences performance
on
many cognitive tasks.
A new
neuropsycholog-
ical
theory
is
proposed
that accounts
for
many
of
these effects
by
assuming that positive
affect
is
associated with
increased
brain dopamine levels.
The
theory predicts
or
accounts
for
influences
of
positive
affect
on
olfaction,
the
consolidation
of
long-term (i.e., episodic) memories, working memory,
and
creative problem solving.
For
example,
the
theory assumes that creative problem solving
is
improved,
in
part, because increased dopamine release
in the
anterior cingulate improves cognitive
flexibility
and
facilitates
the
selection
of
cognitive perspective.
Feelings permeate people's daily lives.
For
example, many
cognitive
processes
are
performed
in the
presence
of
some affec-
tive
or
emotional
state.
Somewhat surprisingly,
a
large
amount
of
research
has
shown convincingly that even moderate
fluctuations
in
positive feelings
can
systematically
affect
cognitive processing
(for
reviews,
see
Isen,
1993,
1999).
For
example, Isen
and
others
have
shown that mild positive
affect,
of the
sort that most people
can
experience every day, improves creative problem solving (e.g.,
Estrada, Young,
&
Isen,
1994;
Greene
&
Noice,
1988;
Isen,
Daubman,
&
Nowicki,
1987; Isen, Johnson,
Mertz,
&
Robinson,
1985), facilitates recall
of
neutral
and
positive material (Isen,
Shalker, Clark,
&
Karp,
1978; Nasby
&
Yando, 1982;
Teasdale
&
Fogarty,
1979),
and
systematically changes strategies used
in
decision-making tasks
(Carnevale
&
Isen, 1986; Estrada, Isen,
&
Young,
1997;
Isen
&
Geva,
1987;
Isen
&
Means,
1983;
Isen,
Nygren,
&
Ashby,
1988;
Isen, Rosenzweig,
&
Young, 1991).
Despite these pervasive
and
well-documented
effects,
there
are
few
theories
of how
positive
affect
influences cognition. There
is
almost
no
mention
of
positive
affect
in the
neuroscience literature,
F.
Gregory Ashby
and And U.
Turken, Department
of
Psychology,
University
of
California, Santa Barbara; Alice
M.
Isen, Johnson Graduate
School
of
Management,
Cornell
University.
This research
was
supported
by
Grant
SBR-9514427
from
the
National
Science Foundation
and by a
grant
from
the
Olfactory Research Fund.
We
thank Lisa Aspinwall, Jonathan Cohen, Martha
Denckla,
Christine
Duvauchelle, Ami r Erez, Carlos Estrada, Aaron Ettenberg, Barbara
Fredrickson,
Jon
Horvitz,
Dan
Levine,
Loy
Lytle,
Read
Montague,
An-
thony
Phillips,
and
Norman White
for
their
helpful
comments
and
sugges-
tions.
Correspondence concerning this article should
be
addressed
to F.
Gregory Ashby, Department
of
Psychology, University
of
California,
Santa Barbara, California
93106.
Electronic mail
may be
sent
to
ashby@psych.ucsb.edu.
and
with
few
exceptions, cognitive psychologists have ignored
positive
affect
in
their
own
theories
of
human cognition.
Although
there
is
little
mention
of
positive
affect
in the
neuro-
science
literature, there
is
considerable mention
of a
number
of
topics that seem closely related
to
positive
affect.
For
example,
there
is a
huge literature
on the
neurobiology
of
reward
(for
reviews,
see
Beninger,
1983;
Liebeman
&
Cooper, 1989; Wise,
1982; Wise
&
Rompre,
1989).
In
humans, reward
often
induces
positive
affect.
In
fact,
one of the
most common methods
for
inducing
positive
affect
is to
administer
a
noncontingent reward
to
experimental
participants (i.e.,
by
giving
an
unanticipated
gift).
Thus,
it is
possible that many
of the
behavioral
influences
of
positive
affect
are
mediated
by the
same neural mechanisms that
mediate reward.
The
neuroscience literature
on
reward
has
focused
on
the
neurotransmitter dopamine.
For
example,
it has
been shown
that
rewards,
and
events that signal reward, elicit release
of
dopa-
mine
from
several brain stem sites (for reviews,
see, e.g.,
Be-
ninger,
1991;
Bozarth,
1991;
Phillips,
Blaha,
Pfaus,
&
Blackburn,
1992; Phillips, Pfaus,
&
Blaha, 1991),
and it is
well known
that
dopamine antagonists (i.e., neuroleptics) disrupt reward signals
and
render reinforcement ineffective (e.g., Wise, 1982).
This
article describes
a
theory
that
was
developed
from
the
initial
hypothesis that many
of the
behavioral
and
cognitive
effects
of
positive
affect
are
mediated
by the
dopamine system. More
particularly,
when developing
the
theory,
we
began with
the
fol-
lowing
two
assumptions. First,
we
assumed that positive
affect
is
associated with increased brain dopamine levels, although
we did
not
assume that dopamine causes
the
pleasant feelings associated
with
positive
affect.
Second,
we
assumed that
at
least some
changes
in
cognitive processing that have been observed
in
posi-
tive
affect
conditions
are due to the
increased brain dopamine
levels associated with positive
affect.
For
example,
we
present
evidence
that
creative problem solving
is
improved because con-
ditions
of
positive
affect
are
associated with increased dopamine
529

530
ASHBY,
ISEN,
AND
TURKEN
levels
in
frontal
cortical areas
(i.e.,
prefrontal cortex
and
anterior
cingulate).
A
number
of
researchers have proposed hypotheses related
to
the
theory developed here.
For
example, Depue
and his
colleagues
have
argued that
the
genetically determined sensitivity
of the
brain
to
dopamine
is
positively correlated with
the
personality trait
of
extroversion
or
positive
affectivity
(Depue
&
lacono,
1989;
Depue, Luciana,
Arbisi,
Collins,
&
Leon,
1994).
Others have
discussed
the
neural mechanisms
of
moods
and
emotions (e.g.,
Derryberry
&
Tucker,
1992)
and
their possible neurochemical
correlates (e.g., Panksepp,
1986,
1993),
and
there even have been
occasional proposals that positive
affect
is
associated with dopa-
mine release (e.g., Phillips,
1984;
Phillips
et
al.,
1992). However,
to our
knowledge,
we are the
first
researchers
to
propose that
the
resulting increased dopamine
release
could mediate
the
effects
of
positive
feelings
on
cognition. Moreover,
the
theory
we
propose
addresses
the
impact
of
mild, induced positive
affect,
allowing that
the
dopamine
effects
we
consider need
not be
genetic.
The
theory developed
in
this article describes some
of the
neural
pathways
and
structures
(and
neurotransmitter systems) that
we
believe
are
most heavily responsible
for
mediating
the
neural
effects
of
positive
affect
and its
influence
on
cognition.
The
resulting
theory
has a
number
of
advantages over current theoret-
ical
approaches
to the
study
of
positive
affect.
First,
of
course,
it
provides
a
neuropsychological account
of a
number
of
well-
documented
positive
affect
phenomena. Second,
it
predicts
influ-
ences
of
positive
affect
on
tasks that previously have
not
been
investigated
in the
positive
affect
literature
(e.g.,
working memory
and
odor perception tasks). Third,
it
describes
a
variety
of
tasks
in
which
positive
affect
is
predicted
not to
affect
performance (e.g.,
visual
perception tasks). Fourth,
it
ties results
from
the
positive
affect
literature
to
previously unrelated neuropsychological litera-
tures.
For
example,
the
theory contrasts cognitive processing
in
healthy
people under positive
affect
conditions
with
cognitive
processing
in a
variety
of
neuropsychological patient groups (e.g.,
Parkinson's disease, schizophrenia, major depression). Thus,
in
addition
to
providing
a
coherent account
of
current data
on the
influences
of
positive
affect
on
cognition,
the new
theory suggests
many
new
avenues
of
research.
The
next section
of
this article briefly reviews
the
literature
on
the
influences
of
positive
affect
on
cognitive organization
and
creative problem solving.
The
third section contrasts
the
effects
of
positive
affect
with those
of
arousal
and
negative
affect.
The
fourth
section introduces
the
dopaminergic
theory
of
positive
affect
and
reviews
the
evidence bearing
on the
central postulate
of
that
theory, namely, that dopamine
and
positive
affect
are
closely
related.
The
fifth
section elaborates
the
theory
and
examines
pre-
dictions
and
preliminary tests
from
a
variety
of
cognitive tasks.
The
sixth section considers some documented influences
of
posi-
tive
affect
that
are
beyond
the
scope
of
this article,
and the
seventh
section considers some
of the
neuropsychological implications
of
the
theory. Finally,
we
close with some brief conclusions.
Positive
Affect
and
Creative Problem Solving
It is now
well recognized that positive
affect
leads
to
greater
cognitive flexibility
and
facilitates creative problem solving across
a
broad range
of
settings. These
effects
have been noted
not
only
with
college student samples
but
also
in
organizational settings,
in
consumer contexts,
in
negotiation situations,
in a
sample
of
prac-
ticing
physicians asked
to
solve
a
diagnostic problem,
with
ado-
lescents,
and in the
literature
on
coping
and
stress, just
to
name
a
few
(e.g., Aspinwall
&
Taylor,
1997;
Camevale
&
Isen,
1986;
Estrada
et
al.,
1994, 1997;
Fiske
&
Taylor,
1991;
J. M.
George
&
Brief,
1996;
Greene
&
Noice,
1988;
Hirt,
Melton, McDonald,
&
Harackiewicz,
1996;
Isen,
1984, 1987, 1993, 1999;
Isen
&
Baron,
1991; Isen
&
Daubman,
1984;
Isen
et
al.,
1985, 1987;
Kahn
&
Isen,
1993;
Mano,
1997;
Showers
&
Cantor,
1985;
Staw
&
Bar-
sade,
1993;
Staw, Sutton,
&
Felled,
1994;
Taylor
&
Aspinwall,
1996). This research suggests that positive
affect
increases
a
per-
son's
ability
to
organize ideas
in
multiple ways
and to
access
alternative cognitive perspectives.
In
some
of
these studies, natu-
rally
occurring positive
affect
or
optimism
was
examined,
but in
dozens
of
experiments supporting these conclusions, participants
were assigned randomly
to
either
a
neutral
or a
positive
affect
condition,
and
positive
affect
was
induced
in a
variety
of
simple
ways.
The
agreement
of the
results obtained
in
these
different
settings, using diverse methods
and
measures, adds
to the
strength
of
the
findings.
The
most common methods
for
inducing
positive
affect
in
neutral
affect
participants
are to
give them
a
small unanticipated
gift
(less
than
$1
in
value)
or to
have them watch
a
comedic
film,
read
funny
cartoons,
or
experience success
on an
ambiguous task.
The
simple nature
of
these methods indicates
that
the
effects
can
be
prompted readily,
by
small things
in
people's lives. Thus,
by
positive
affect,
we
mean
a
seemingly mild increase
in
positive
feelings
brought about
by
commonplace, everyday events.
A
more detailed examination
of
this literature indicates that
positive
affect
has
predictable consequences
in
different
types
of
tasks. First,
in
word association, people
in a
positive
affect
group
have been shown
to
respond
to
neutral words (but
not to
negative
words) with
a
broader range
of
first
associates than
do
neutral
affect
controls (Isen
et
al.,
1985). Similarly,
in a
study with
adolescents, positive
affect
increased verbal
fluency,
and
adoles-
cents
in the
positive
affect
condition gave more category words
and
more unusual examples
of the
category than
did
adolescents
in
the
neutral
affect
control condition (Greene
&
Noice, 1988).
A
similar
finding,
with
adults,
was
obtained
by
Hirt
et al.
(1996).
Second,
people
in
positive
affect
conditions
are
able
to
classify
material more
flexibly
and are
better able
to see
ways
in
which
nontypical
members
of
categories
can
fit
or be
viewed
as
members
of
those
categories
(e.g., Isen
&
Daubman,
1984;
Isen,
Niedenthal,
&
Cantor,
1992;
Kahn
&
Isen, 1993). This
effect
has
been
found
for
items
in
natural categories, such
as
those used
by
Rosch
(1975;
Isen
&
Daubman, 1984);
for
products
in a
mildly pleasant class
of
snack foods (Kahn
&
Isen,
1993);
for
person types
in
positive
but
not
in
negative person categories (Isen
et
al.,
1992);
and for the
perception
and
classification
of
human social groups (enabling
a
socially distinct "out-group"
to be
integrated
and
perceived
as
part
of
a
superordinate,
mutual
"in-group";
Dovidio,
Gaertner,
Isen,
&
Lowrance,
1995). Thus, positive
affect
has
been shown
to
enable
people
to see
more similarities among items
or
people during
the
categorization
process. Positive
affect
also
can
result
in
more
perceived
differences
if
people
are
asked specifically
to
focus
on
differences
and to find
ways
in
which items
differ
from
one
another
(Isen,
1987,
p.
234;
Murray,
Sujan,
Hirt,
&
Sujan,
1990).
This
is
probably because positive
affect
fosters cognitive elabora-
tion (e.g., Isen
et
al.,
1985), which
has
been
found
to
influence

POSITIVE
AFFECT
531
perceived
similarity
and
difference
as a
function
of
contextual
factors,
such
as the
question posed (Tversky
&
Gati, 1978).
Third,
people
in
positive
affect
conditions have been shown
to
perceive
an
interesting assigned
task,
but not a
dull one,
as
richer
and
more varied than
do
control participants
(Kraiger,
Billings,
&
Isen,
1989).
In the
organizational behavior literature, task richness
is
closely related
to the
complexity, variety, diversity,
and
inter-
estingness
of the
task.
The
influence
of
positive
affect
on
perceived
task
richness
can be
seen
as
reflecting
an
ability
on the
part
of the
positive
affect
participants, again,
to see
additional associations
and
aspects
of
interesting things.
Fourth, positive
affect
increases
the
likelihood
that people will
pursue
a
problem-solving approach that leads
to
improved outcomes
for
both parties
in an
integrative
bargaining task
(Carnevale
&
Isen,
1986).
To
reach
the
optimal agreement
in
such
a
task,
people
must
make tradeoffs
of
differing
values,
see new
possibilities,
think inno-
vatively,
and
reason
flexibly
about
how
these tradeoffs might
be
made. Obvious compromises
or
simple yielding will
not
result
in
satisfactory
outcomes (for greater detail, see, e.g.,
Pruitt,
1983).
Fifth,
positive
affect
has
been found
to
increase variety seeking
among safe, enjoyable products
but not
among risky
or
dangerous
alternatives.1
Specifically, Kahn
and
Isen (1993) reported that
people
in a
positive
affect
group showed more switching among
alternative
choices
in a
food category
(e.g.,
soup
or
snacks) than
did
controls
and
included
a
broader range
of
items
in
their choice
sets,
as
long
as the
circumstances
did not
make potentially
un-
pleasant
or
negative
features
of the
items
salient.
Thus,
there
is
evidence that positive
affect
promotes enjoyment
of
variety
and of
a
wider range
of
possibilities,
but
only when
the
situation
does
not
prompt people
to
think
of
unpleasant outcomes.
Finally, positive
affect
has
been shown
to
improve performance
on
several tasks that typically
are
used
as
indicators
of
creativity
or
innovative
problem solving (Isen
et
al.,
1987).
In one of
these
tasks,
the
so-called candle problem (Duncker, 1945),
a
person
is
given
a
candle,
a box of
tacks,
and a
book
of
matches
and is
asked
to
attach
the
candle
to the
wall
so
that
it
will burn without dripping
wax
on the
table
or the floor. To
solve
the
problem,
the
person
can
empty
the box of
tacks, tack
the box to the
wall,
and
then
use the
box as a
platform
for the
candle. Thus,
the
person must
use one of
the
items (the box)
in an
unaccustomed way.
In
three studies
from
two
different
laboratories, using both
college
students
and
adoles-
cents (eighth graders), positive
affect
participants performed sig-
nificantly
better
than controls
on
this task (Greene
&
Noice, 1988;
Isen
et
al.,
1987). Such responding
can be
seen
as
involving
cognitive
flexibility, or the
ability
to put
ideas together
in new but
useful
ways—a
classic definition
of
creativity (e.g., Koestler,
1964).
It
also
has
been referred
to as
"breaking set"
or
overcoming
"functional
fixedness" (Duncker, 1945;
Wertheimer,
1945).
A
second
task
that
has
been
used
to
study
the
influence
of
positive
affect
on
cognitive
flexibility or
creativity
is
based
on the
Remote Associates
Test
(M. T.
Mednick, Mednick,
&
Mednick,
1964),
which
was
designed
in
accord with
S. A.
Mednick's
(1962)
theory
of
creativity.
In
this test, which
in its
full
form
was
designed
to
measure individual differences
in
creativity, participants
are
presented with three words
and a
blank line
and are
asked
to
respond with
a
word that relates
to
each
of the
three words given
in
the
problem.
An
example
is the
following:
mower atomic foreign
.
(The correct answer
is
power.)
Seven items
of
moderate
difficulty
from
the
Remote Associates
Test
have been used
in the
research
on
the
influence
of
affect.
Several studies have
found
that
positive
affect
improves accuracy
in
this test,
not
only
in
college students
but
also
in a
sample
of
practicing
physicians
(Estrada
et
al.,
1994;
Isen
et
al.,
1987).
To
summarize
the
research
described
so
far, more
than
25
experiments,
from
at
least
10
different
topic areas, using varied
affect
inductions
and
diverse measures
of
cognitive
flexibility,
have indicated that randomly assigned positive
affect
enhances
people's
ability
to see
alternative cognitive perspectives.
In
addi-
tion, several studies investigating naturally occurring positive
af-
fect
in
applied settings
(or
positive
affectivity)
have reported
compatible results, namely, that this variable
is
associated with
creative problem solving
(e.g.,
J. M.
George
&
Brief, 1996; Staw
&
Barsade,
1993; Staw
et
al.,
1994)
and
promotes
flexible and
effective
coping skills
(e.g.,
Aspinwall
&
Taylor, 1997; Taylor
&
Aspinwall,
1996). Thus,
in
both laboratory
and field
studies using
a
diverse
set of
measures
and
assessing
a
wide variety
of
contexts,
positive feelings have been shown
to
lead
to
cognitive elaboration
and
flexibility,
giving
rise to
more thoughts, more nontypical
thoughts,
and
innovative solutions
to
problems.
In
positive
affect,
thinking
is flexible so
that both usual
and
unusual
aspects
and
senses
of
concepts
may be
accessible.
As
indicated
in our
review,
a
number
of
studies investigating
the
impact
of
induced
affect
have reported significant interactions
between positive
affect
and the
task materials
or
conditions.
In
many
studies, positive
affect
has
been
found
to
increase cognitive
flexibility
only
when
the
situation
is
neutral
or
positive
in
emo-
tional content,
or at
least minimally engaging
or
involving. Thus,
positive
affect
does
not
improve performance
on all
tasks,
so the
effects
that have been reported
do not
simply reflect
an
increased
global motivation
or
activation
on the
part
of
people
in the
positive
affect
conditions
nor
some general increase
in
nonsystematic pro-
cessing, because such effects would tend
to
equally
affect
all
stimuli
or
situations. Rather, they suggest that positive
affect
enables
flexible
thinking about topics that
people
want
or
have
to
think
about. Typically, these would include topics people expect
to
enjoy,
but
there also
is
evidence
that
people
in
positive
affect
want
to
think about
a
wide range
of
serious tasks
and not
j ust about
games
or
fun. These tasks include diagnostic problems
in the
case
of
physicians
and
medical students (e.g., Estrada
et
al.,
1994; Isen
et
al.,
1991),
and
problem-solving, negotiations that
are
otherwise
acrimonious,
and
product
choice
and
categorization
in the
case
of
college
students (e.g., Carnevale
&
Isen, 1986; Isen
et
al.,
1985,
1987; Kahn
&
Isen, 1993).
There also
is
evidence that positive
affect
can
promote attempts
to
cope
with negative events
or
information,
and
studies have
shown
that under conditions
of
positive
affect,
people
are
less
defensive
and can
better focus
on
needed negative
information
(Aspinwall,
1998; Isen
&
Geva, 1987;
Trope
&
Neter, 1994; Trope
&
Pomerantz, 1998). Such coping cannot
be
assessed
in
studies
in
1
As we
discuss later, positive
affect
also
has
been
found
to
have
adaptive
effects when situations
are
unpleasant
or
negative
and to
foster
attention
to
negative material when that would
be
useful.
However, these
effects
are
different
from
variety seeking, which occurs
only
in
safe,
enjoyable
contexts.

532
ASHBY,
ISBN,
AND
TURKEN
which
there
is no
need
or
benefit
to
elaborating
on
negative
information.
Unless
the
negative information
is
useful
or
impor-
tant,
people
in
positive
affect
will most likely
not
engage
it
carefully,
which
may
play
a
role
in
producing
the
observed statis-
tical
interactions
between
affect
and
valence
of the
material.
How-
ever, accumulating evidence indicates that when
the
information
is
useful
or
important, positive
affect
facilitates careful processing
of
negative
as
well
as
positive information.
Positive
Affect
Versus Arousal
and
Negative
Affect
Some studies showing
an
impact
of
positive
affect
on
cognitive
flexibility
also indicate that positive
affect
is
distinct
from
negative
affect
and
affectless
"arousal"
in its
ability
to
facilitate flexible
responding (e.g.,
Isen
et
al.,
1987).
It is
important
to
note,
at
least
briefly,
the
evidence that positive
affect
and
arousal
do not
appear
to
have identical
effects,
because
at one
time,
affect
and
arousal
were thought
to be
synonymous
(e.g.,
Duffy,
1934, 1941),
and
even
now, there
is
some
confusion
regarding this point. There
are
two
common ideas about
how to
manipulate arousal.
One is
through
exercise (e.g., Zillmann, 1979),
and the
other
is
through
the
induction
of an
emotional state (e.g., LeDoux,
1996).
Typi-
cally,
this emotional state would involve negative
affect
such
as
fear
or
anger,
but
according
to
some views, arousal increases with
either
positive
or
negative
affect.
Thus,
if the
increase
in
cognitive
flexibility
observed with positive
affect
is
simply
an
arousal
effect,
then induced
negative
affect
also
should facilitate
cognitive
flexibility.
Some studies have included conditions
or
measures intended
to
address this question.
For
example,
in two
sets
of
experiments,
positive
affect
participants reported more positive
affect,
but not
more arousal
or
alertness, than neutral
affect
control participants
on
a
manipulation-check questionnaire that followed
the
affect
induction
(Isen
&
Daubman, 1984; Isen
&
Gorgoglione, 1983).
In
addition,
the
behavioral results
of
these experiments correlated
better
with
the
affect-induction
treatments than with
the
reported
levels
of
arousal.
In
another series
of
studies, Isen
et al.
(1987)
asked
four
groups
of
participants
to
solve
the
candle problem
and
to
complete
a
subset
of
items taken
from
the
Remote Associates
Test.
One
group served
as
neutral
affect
controls. Positive
affect
was
induced
in a
second group.
In a
third, exercise group, partic-
ipants
stepped
up and
down
on a
cinder block
for 2 min
before
the
test, which increased their heart rates
by
about 60%. Finally,
a
fourth
group,
a
negative
affect
group, viewed
a few
minutes
of the
film
Night
and
Fog,
a
French documentary
of the
World
War II
German
death camps.
As
expected,
the
positive
affect
participants
performed
better than
the
control participants
on
both
the
candle
task
and the
Remote Associates Test items. Equally important,
people
in the
exercise
and
negative
affect
groups
performed
no
better
than
the
control participants
on
either test. Thus, again, Isen
et
al.
found
evidence that, unlike positive
affect,
arousal
does
not
improve
creative problem solving.
There
is
other evidence against
the
hypothesis that
the
effects
of
positive
affect
on
cognitive
flexibility
are due to
arousal. First,
current
theories
do not
predict that arousal increases creativity
because arousal
is
thought
to
increase
the
likelihood
of a
dominant
response, rather than
an
innovative response (Berlyne, 1967; East-
erbrook, 1959). Second, reconceptualizations
of the
"arousal"
con-
cept
suggest that
it may not be a
unitary
construct
and may
need
to
be
investigated
differently
from
the way it has
been
addressed
in
the
past (e.g.,
Dienstbier,
1989; Lacey, 1967, 1975;
Neiss,
1990;
Venables, 1984).
Third,
a
recent trend
in the
affect
literature
has
attempted
to
disentangle arousal
and
pleasantness
by
conceptual-
izing
affect
as
having
two
orthogonal
dimensions—pleasantness
and
arousal (e.g.,
Lewinsohn
&
Mano, 1993; Mano,
1997).
This
work investigated
effects
of
pleasantness
and
arousal separately,
for
example,
by
comparing
the
influences
of
pleasant-arousing,
pleasant-nonarousing,
unpleasant-arousing,
and
unpleasant-non-
arousing
conditions
or
affects.
On the
other hand, even though they
may
be
logically independent, pleasantness
and
arousal
may be
empirically
correlated.
Indeed, research
has
indicated that,
espe-
cially
up to a
point, arousal
can
have
a
pleasant
and
facilitating
effect
on
task performance (e.g., Berlyne, 1967; Yerkes
&
Dodson,
1908).
However, there
is
considerable
evidence that arousal
is
associated with increased activity
in
neurotransmitter
systems
other than
dopamine
(e.g.,
norepinephrine
and
acetylcholine). And,
as
noted,
the
empirical
effects
of
arousal
or
negative
affect
are
different
from
those
of
positive
affect.
Thus,
in
sum, there
is
substantial reason
to
believe
that
affect
and
arousal
are not
syn-
onymous,
as was
once proposed (e.g.,
Duffy,
1934, 1941),
and
that
the
increases
in
cognitive flexibility
and
creative problem solving
reported
in so
many articles
are
indeed
due to
positive
affect,
not
simply
to
increases
in
arousal.
The
last section reviewed many studies that examined
the in-
fluence
of
positive
affect
on
cognition. There
is
also
a
large
literature
on
negative
affect, which
indicates
that
the
impact
of
negative
affect
is
more complex
and
difficult
to
predict than
is the
case
for
positive
affect
(for reviews, see, e.g., Isen, 1987,
1990).
Even
so,
referring
to
these
different
emotional states
as
"negative
affect"
and
"positive affect" suggests they might represent
two
ends
of the
same continuum.
If
this were true, then performance
under
negative
affect
conditions could
be
predicted
from
the
theory developed
in
this article
by
simply assuming that
in
nega-
tive
affect
conditions, people have lower brain dopamine levels
than
in
neutral
affect
control conditions. Unfortunately, this naive
hypothesis
is
surely wrong. Negative
affect
is not
simply
the
opposite
of
positive
affect
in
either
its
behavioral
or
cognitive
effects,
and
happiness
and
sadness apparently
are
also mediated
by
independent
neural pathways
(e.g.,
M. S.
George
et
al.,
1995).
Some researchers have suggested that negative
and
positive
affect
may
even
be
localized
in
different
cerebral hemispheres (e.g.,
Davidson, 1992;
Henriques
&
Davidson, 1991).
In
support
of
this
hypothesis,
for
example, there
is
evidence
for
hemispheric asym-
metry
in the
dopaminergic pathways (with
the
left
hemisphere
favored
over
the right
hemisphere; Tucker
&
Williamson, 1984).
Thus,
the
evidence that positive
and
negative
affect
are not
polar
opposites
in
process
and
function
is
strong,
and we
believe that
there
is no way to use the
theory
developed
in
this
article
to
make
predictions about
the
influence
of
negative
affect
on
cognition.
Instead,
for
that purpose,
a new
theory would
be
required that
focuses
specifically
on
negative
affect.
Such
a
theory
is
beyond
the
scope
of
this article.
The
remainder
of
this section
briefly
describes
a
few of the
problems associated with
the
assumption that negative
and
positive
affect
are
related
in any
simple manner.
First,
if
negative
and
positive
affect
were opposites
and if the
theory
developed here
is
correct, then reducing brain dopamine
levels below normal resting levels should induce negative
affect.
However,
the
best evidence
is
that
reductions
in
dopamine levels

POSITIVE
AFFECT
533
are
associated with anhedonia (flattened
affect
or
loss
of
pleasure)
rather than negative
affect.
For
example,
dopamine
antagonists
(i.e.,
neuroleptics), which block
the
effects
of
dopamine,
flatten
affect.
Neuroleptics (e.g.,
haloperidol)
are
commonly prescribed
drugs because
of
their antipsychotic properties
(e.g.,
Hyman
&
Nestler, 1993).
For
this reason, they
are
included
in the
routine
treatment
for
senile
dementia
and
schizophrenia. Their
effect
on
mood
is
well known.
For
example, Physicians' Desk
Reference
(Huff,
1988) prominently lists "flattened affect"
as a
common side
effect
associated with
use of the
popular neuroleptic
haloperidol.2
Anhedonia
is a
prominent diagnostic criterion
of
major depression
(American Psychiatric Association, 1994),
but it is not
typically
associated with
a
brief episode
of
mild negative
affect.
Second,
stressful
or
anxiety-provoking events, which presum-
ably
would produce
a
negative
affective
state
in
humans, actually
appear
to
increase
dopamine
levels
in
certain
brain
regions.
In
particular, animal studies indicate that stressful events (e.g., foot-
shock, tailpinch) cause increased dopamine
release
from
some
dopamine-producing
areas
(i.e.,
the
ventral tegmental area
[VTA])
but
have little
or no
effect
on
dopamine
release
from
other areas
(i.e.,
the
substantia nigra; Abercrombie, Keefe,
DiFrischia,
&
Zigmond, 1989; Cenci,
Kalen,
Mandel,
&
Bjorklund,
1992;
Im-
perato, Puglisi-Allegra, Casolini,
&
Angelucci, 1991; Sorg
&
Kalivas,
1993; Zacharko
&
Anisman, 1991). Thus, there
is no
evidence that brain dopamine levels
are
decreased
following
ex-
posure
to
stressful
or
anxiety-provoking events.
Figure
1.
Some dopamine projections
in the
human brain. Dopamine-
producing
areas
are
shaded
in
gray,
and
dopamine projections
are
illus-
trated
by the
dashed lines.
NAc =
nucleus
accumbens;
VTA =
ventral
tegmental
area;
SN =
substantia nigra;
LC =
locus
ceruleus.
Dopamine
and
Positive
Affect
Two
separate,
but
interacting, dopamine systems
are
especially
relevant
to
this
article.
The
nigrostriatal
system consists
of
dopamine-producing cells
in the
substantia nigra pars compacta
that
project into
the
striatum
(i.e.,
the
input region
of the
basal
ganglia that consists
of the
caudate nucleus
and the
putamen). This
system
is
primarily associated with motor activity, although
re-
cently
it has
been implicated
in
certain cognitive tasks
(e.g.,
Ashby,
Alfonso-Reese, Turken,
&
Waldron, 1998).
The
mesocor-
ticolimbic system consists
of
dopamine-producing cells
in the VTA
that
project
to a
number
of
limbic
and
cortical areas. This system
is
primarily associated with reward
and
motivation.
Some
of the
more important projections
are
shown
in
Figure
1.
There
is a
good deal
of
evidence that
the
dopamine pathways
shown
in
Figure
1 are
active during periods
of
positive
affect
and
that
dopamine
may
mediate some
of the
effects
positive
affect
has
on
cognition. First,
of
course,
is the
already mentioned
fact
that
dopamine
is
released
after
presentation
of
rewarding stimuli,
and
reward
is
closely associated with positive
affect,
at
least
in hu-
mans.
Second, drugs that mimic
the
effects
of
dopamine (i.e.,
dopamine agonists)
or
that enhance dopaminergic activity elevate
feelings
(e.g., Beatty, 1995).
These
drugs include morphine
and
apomorphine
(agonists), cocaine (which blocks
reuptake),
and
amphetamines (which increase dopamine
release).
Similar
effects
occur with naturally produced
endorphins,
because
endorphin
re-
lease stimulates
the
dopamine system
and
improves
affect
(e.g.,
Beatty, 1995;
Harte,
Eifert,
&
Smith, 1995). Third,
as
mentioned
in
the
previous section, dopamine antagonists (i.e., neuroleptics)
are
thought
to flatten
affect.
Fourth, both dopamine release
and
positive
affect
are
associated
with
increased motor activity.
The
well-documented increase
in
motor activity that occurs when brain dopamine levels increase
(e.g., Kelly,
Sevior,
&
Iversen, 1975;
Protais,
Bonnet,
&
Costentin,
1983)
is
associated
primarily
with
the
nigrostriatal
system.
There-
fore,
as one
might expect, damage
to the
nigrostriatal system tends
to
decrease
motor activity.
The
most widely known example
of
this
damage occurs
in
Parkinson's
disease,
in
which there
is a
progres-
sive death
of
dopamine-producing cells
in the
substantia nigra
(e.g., Strange, 1992).
The
classical symptoms
of the
disease
in-
clude
akinesia
(dramatic reduction
in
motor activity)
and
bradyki-
nesia
(difficulty
in
initiating
movement
and a
slowness
of
move-
ment, once initiated).
These
symptoms
are
alleviated
by the
drug
L-dopa,
a
precursor
to
dopamine. Although positive
affect
has
been
shown
to
increase motor activity
in
laboratory conditions (e.g.,
Hale
&
Strickland, 1976; Strickland, Hale,
&
Anderson, 1975),
much
of the
evidence that positive
affect
increases motor
activity
is
anecdotal,
as
represented
by
colloquial expressions such
as
"dancing"
or
"jumping"
with joy.
There
also
is
substantial evi-
dence that
flattened
affect
and
depression
are
associated with
reduced motor activity.
For
example,
the
Diagnostic
and
Statisti-
cal
Manual
of
Mental Disorders (4th ed.; American Psychiatric
Association,
1994)
lists decreased energy
and
psychomotor retar-
dation (e.g., slowed body movements, speech that
is
slowed
and
decreased
in
volume)
as
symptoms that commonly co-occur
with
2
However,
it is
difficult
to
rule
out the
possibility that
the flattened
affect
commonly ascribed
to
neuroleptic therapy
is not
due,
at
least
partially,
to a
reduced range
of
facial
expression caused
by
extrapyramidal
side
effects
of
these drugs.
In
this case, there would
be the
appearance
of
an
affect
reduction
but
little
or no
true change
in
affective state
(J. D.
Cohen, personal communication, January
15,
1998).

534
ASHBY,
ISBN,
AND
TURKEN
a
major depressive
episode.3
The
dopaminergic theory
of
positive
affect
argues that increased motor activity occurs with positive
affect
because
the
events precipitating
the
elevation
in
mood lead
to
stimulation
of the
VTA, which
in
turn stimulates
the
substantia
nigra
(probably
through
intermediate
stimulation
of the
nucleus
accumbens;
see
Figure
1).
This stimulation causes
the
substantia
nigra
to
increase dopamine
release
into
the
striatum,
which leads
to
increases
in
motor activity.
We
propose that dopamine mediates
the
cognitive
effects
(or
some
of the
cognitive effects)
of
pleasant feelings.
An
interesting
and
important question
is
whether dopamine also mediates
the
pleasant feelings that
are
associated with positive
affect.
Until
recently,
for the
following reasons,
it
appeared that such feelings
were
associated with
the
mesolimbic projection
from
the VTA
into
the
nucleus accumbens. First, severing these
fibers or
injecting
dopamine
antagonists into
the
nucleus accumbens blocks
the re-
warding properties
of
food, water,
and
other reinforcers (e.g.,
Lyness,
Friedle,
&
Moore, 1979). Second, injecting dopamine
agonists directly into
the
nucleus accumbens
is
rewarding (e.g.,
Monaco, Hernandez,
&
Hoebel,
1980).
More specifically, there
is
growing
evidence
of
increased dopamine
release
in the
nucleus
accumbens whenever
an
animal anticipates
or
prepares
for a re-
ward
(for
a
review, see, e.g., Robbins
&
Everitt,
1996), actions
that,
in
humans,
are
likely
to
elicit positive
affect.
In
addition,
the
nucleus
accumbens communicates directly with brain areas known
to be
closely associated
with
emotion.
In
particular,
the
(basolat-
eral)
amygdala
and the
anterior
cingulate
cortex
project
directly
to
the
nucleus accumbens.
The
nucleus accumbens,
in
turn,
can
affect
activity
in the
anterior cingulate
by way of a
known loop through
the
pallidum
and the
thalamus
(Alexander, DeLong,
&
Strick,
1986).
The
cingulate played
a key
role
in
Papez's (1937) original
circuit
for
emotions,
and
more recent work confirmed
the
associ-
ation
between emotion
and
anterior cingulate activation (e.g.,
Vogt, Finch,
&
Olson, 1992).
The
importance
of the
amygdala
in
emotional
response
is
well known (e.g., Shepherd, 1994).
In
par-
ticular,
there
is a
large literature showing that
the
amygdala
is
vital
for
learning
to
associate primary rewards with previously neutral
stimuli
(e.g., Robbins
&
Everitt, 1992; Rolls, 1995).
In
the
past
few
years, however, evidence
has
accumulated that
the
story
is not so
simple. First,
it was
discovered that
the
dopa-
mine
cells
in the VTA
that project
to the
nucleus accumbens
respond
most strongly
to
unanticipated reward (Mirenowicz
&
Schultz,
1994; Schultz, 1992).
After
a
reward
has
become routine
or
expected,
VTA
dopamine cell
firing
is
substantially reduced.
Thus,
if the firing of
dopamine cells
in the VTA is
correlated with
positive
affect,
then positive
affect
should follow
the
same rules.
Evidence
from
the
positive
affect
literature
is
compatible with this
prediction,
in
that many
of the
positive
affect
inductions involve
unexpected
events
(e.g.,
an
unexpected gift, humor,
or
report
of
success
on an
ambiguous task).
In
addition,
at
least
one
influential
theoretical
account (Mandler, 1975, 1984), which proposes that
emotion results
from
interruption,
is
also compatible
with
this
prediction.
Although there
has not
been
a
direct comparison
of
expected
and
unexpected
gifts,
it
seems likely that giving
a
small
gift
will induce positive
affect
much more
effectively
when
it is
unexpected.
Second, there
is a
time-course problem. Dopamine cells
in the
VTA fire in the
presence
of
unanticipated reward
for
only
a few
seconds (Mirenowicz
&
Schultz, 1994; Schultz, 1992), whereas
the
change
in
affect
that
is
caused
by
giving
an
unexpected
gift
can
last
for 30
min
or
longer. Recent neurophysiological results sug-
gest
a
possible resolution
to
this apparent paradox.
Floresco,
Yang,
Phillips,
and
Blaha
(1998) electrically stimulated
the
basolateral
amygdala
of
rats
and
measured
dopamine
release
in the
nucleus
accumbens.
As
indicated
in
Figure
1,
there
is a
direct
(glutamate)
projection
from
the
amygdala
to the
nucleus accumbens,
and a
number
of
studies have
found
that
these
projections
may
directly
modulate dopamine
release
from
dopamine cells
in the VTA
that
project
to the
nucleus accumbens (e.g., Gracy
&
Pickel, 1996;
Imperato, Scrocco, Bacchi,
&
Angelucci, 1990;
L. R.
Johnson,
Aylward,
Hussain,
&
Totterdell,
1994).
Floresco
et
al.
found
that
stimulation
of the
basolateral amygdala
for 10 s
increased dopa-
mine release
in the
nucleus accumbens
for
about
30
min, even
under
conditions
in
which
the VTA
cells
were unable
to fire
(i.e.,
following
microinjections
of
lidocaine directly into
the
VTA).
Thus, dopamine
release
occurs long
after
dopamine
cells
have
stopped
firing, and the
time course
for
dopamine
release
reported
by
Floresco
et al. is
remarkably similar
to the
time course
for
standard affect-induction techniques.
Third, dopamine cells
in the VTA of
cats have been shown
to
fire
to
loud clicks
and
bright flashes
of
light that have never been
paired
with
a
reward
(Horvitz,
Stewart,
&
Jacobs,
1997).
Although
is
seems possible that
cats
confined
to
laboratory cages might
find
such
stimulation rewarding, such results
also
raise
the
possibility
that
VTA
dopamine
cells
fire not
only
to
stimuli that signal reward
but
to any
novel
or
startling stimulus
(e.g.,
Wickelgren,
1997).
Fourth,
as
mentioned earlier, stressful
or
anxiety-provoking
events, which presumably would produce
a
negative
affective
state
in
humans, actually appear
to
increase dopamine levels
in
certain
brain regions (i.e., prefrontal cortex).
In
particular, animal studies
indicate that mildly
stressful
events
(e.g.,
footshock, tailpinch)
cause increased dopamine
release
from
dopamine cells
in the VTA
that project
to the
prefrontal
cortex
but
have
little
or no
effect
on
dopamine levels
in the
nucleus accumbens
or on
dopamine release
from
the
substantia nigra (Abercrombie
et
al.,
1989; Cenci
et
al.,
1992; Imperato
et
al.,
1991; Sorg
&
Kalivas, 1993;
Zacharko
&
Anisman,
1991). However,
it is not
completely clear that
the
increased dopamine release
from
parts
of the VTA is
associated
with
negative
affect.
Because dopamine cells
in the VTA are
known
to
respond
in
anticipation
of
reward,
one
possibility,
which
cannot
be
ruled
out at the
present time,
is
that dopamine cells
in the
VTA
respond
to
stressful
events
in
anticipation
of the
relief that
occurs with
the
termination
of the
event
(e.g.,
through
the
animal's
escape; e.g., Wilkinson, 1997).
Of
course, even
if
this were true,
the
dopamine
release
would occur
in
anticipation
of
pleasure;
therefore,
it
could
not
mediate
the
pleasure
per se.
Finally,
many researchers have argued that
a
primary
function
of
dopamine
is to
serve
as the
reward signal
in
reward-mediated
learning
(e.g., Beninger, 1983; Miller, 1981; Montague, Dayan,
&
Sejnowski,
1996; White, 1989; Wickens, 1993). Thus,
one
possi-
bility
is
that
at
least some
of the
results that purportedly link
3
Psychomotor agitation also
is
possible
(e.g.,
inability
t o sit
still,
pacing,
hand-wringing),
and
major
depression
is
commonly thought
to
involve
a
variety
of
neurotransmitter systems
(e.g.,
norepinephrine
and
serotonin,
as
well
as
dopamine; see, e.g.,
Hyman
&
Nestler,
1993).
Consequently, results
from
patients
with
major depression must
be
interpreted
with
caution.

POSITIVE AFFECT
535
dopamine
and
reward
are
actually
due to a
failure
of
learning.
For
example, when animals
are
administered neuroleptics (i.e., dopa-
mine
antagonists),
the
animals behave
as if
primary
rewards,
such
as
food, have lost their rewarding properties (e.g., Wise, 1982).
However,
it is
also possible that such rewards
still
do
elicit
the
same hedonic response under neuroleptics
but
that
the
animals
have failed
to
leam
the
association between
the
reward
and the
predictive
stimulus.
Although
these results
do not
disconfirm
the
hypothesis that
dopamine release occurs during periods
of
positive
affect,
they
do
argue against
the
stronger hypothesis that dopamine
release
is
responsible
for
initiating
the
pleasant feelings associated with
positive
affect.
Berridge
(1996) argued that reward
is
associated
with
functionally
separate motivational
and
feeling components
(which
he
called "wanting"
and
"liking").
He
argued that dopa-
mine
mediates
the
motivational component
of
reward
and
that
the
pleasant
feelings induced
by
consuming
the
reward
are
mediated
by
forebrain opioid circuits. Endogenous opioid peptides
are a
promising
candidate because there
is a
large literature associating
opiates
and
reward (for reviews, see, e.g., Feldman, Meyer,
&
Quenzer, 1997; Wise,
1989).
In
addition, there also
are
reports that
opioid
antagonists decrease
the
pleasantness ratings
of
foods
(Drewnowski,
Krahn,
Demitrack, Nairn,
&
Gosnell, 1992;
Fantino, Hosotte,
&
Apfelbaum,
1986;
but see
Hetherington,
Ver-
baet,
Blass,
&
Rolls,
1991).
This
interesting
hypothesis
deserves
further
study. However,
for the
purposes
of
this article,
in
which
we
propose that dopamine mediates
the
cognitive
effects
of
posi-
tive
affect,
it is
important
that
dopamine release
or
uptake
in-
creases during conditions
of
positive
affect
but not
that dopamine
causes
the
pleasant feelings associated with positive
affect.
In
closing this section,
it is
important
to
note that
in
addition
to
dopamine, other neurotransmitters
and
neuromodulators
are
known
to
influence mood
and
emotion.
For
example, theories
of
depression have long focused
on
norepinephrine
and
serotonin
(e.g., Schildkraut, 1965).
As a
result,
a
complete theory
of
mood,
and
probably also
a
complete theory
of
positive
affect,
must
consider many neurochemicals. Even
so, we
believe that
to ac-
count
for the
influences
of
positive
affect
on
cognition,
the
most
important
place
to
begin
is
with
dopamine.
Dopaminergic Projections
and
Preliminary Tests
of
the
Theory
If
positive
affect
is
associated with increased dopamine
release
from
the
VTA, then
the VTA
projections illustrated
in
Figure
1
provide strong clues about
the
types
of
behaviors that should
and
should
not be
influenced
by
positive
affect.
Specifically,
two
separate
hypotheses seem reasonable. First, positive
affect
may
alter processing
in any
structure that receives
a
direct projection
from
the
VTA. Therefore,
we
should look
for
influences
of
posi-
tive
affect
on any
behavior
mediated
by
such
structures.
Second,
changes
due to
positive
affect
are
less likely
in
behaviors mediated
by
structures that
do not
receive
a
direct projection
from
the
VTA.
Locus
Ceruleus
The VTA
(and
to a
lesser extent
the
substania nigra) projects
to
the
locus
ceruleus
(Feldman
et
al.,
1997; McRae-Deguerce
&
Milton,
1983; Simon
&
Le
Moal,
1977)—a
brain stem
site
(i.e.,
in
the
pons) that
is the
largest producer
of
norepinephrine
in the
brain
(e.g., Heimer,
1995).
Although little
is
known about
the
function
of
dopamine
in the
locus ceruleus,
the
VTA-locus-ceruleus
projec-
tion
is
potentially quite important because norepinephrine
is the
neurotransmitter
most important
for
arousal.
In
fact,
a
prominent
theory
is
that arousal
is
largely mediated
by
norepinephrine release
from
the
locus ceruleus (other monoaminergic
and
cholinergic
systems
are
thought
to
also contribute; e.g., Robbins
&
Everitt,
1995). Although earlier
we
reviewed extensive evidence that pos-
itive
affect
and
arousal
are
mediated
by
separate systems,
we
also
noted
that they
are
nevertheless empirically correlated,
in the
sense
that
positive
affect
is
often
associated with increases
in
arousal.
The
dopaminergic theory
of
positive
affect
predicts that
a
possible
mediator
of
this empirical correlation
is the
VTA-locus-ceruleus
projection.
Olfactory
Cortex
Figure
1
illustrates
a
direct projection
from
the VTA
into pri-
mary olfactory
areas.
Actually, these
are
reciprocal connections
because there also
are
direct projections
from
the
primary olfactory
cortex (i.e., olfactory tubercle) into
the VTA
(Oades
&
Halliday,
1987)
and the
nucleus accumbens (Newman
&
Winans,
1983).
There also
is
evidence that these projections have important
be-
havioral effects. First, patients with
Parkinson's
disease
are im-
paired
in
olfactory
same-different
matching tasks, even when
the
two
odors
are
presented only
a few
seconds apart (Zucco, Zaglis,
&
Wambsganss, 1991). Although
the
most widely known
effect
of
Parkinson's
disease
is
damage
to the
nigrostriatal
system, there
also
is
concomitant damage
to the
mesocorticolimbic
system.
In
particular,
dopamine production
in the VTA is
substantially
di-
minished
as the
disease progresses (Javoy-Agid
&
Agid, 1980;
Scatton,
Rouquier, Javoy-Agid,
&
Agid,
1982).
Second,
presenting
odors
to
anesthetized rats changes
firing
rates
of
cells
in the
nucleus
accumbens,
and
these rates
are
altered
after
electrical
stimulation
of the VTA
(West
&
Michael,
1990).
Similarly, dopa-
mine
levels
in the
nucleus accumbens increase after male rats
are
exposed
to air
that
was
passed through
the
bedding
of
estrus
female
rats (Mitchell
&
Gratton,
1992).4
These results suggest
a
possible association between odor
and
positive
affect.
The VTA
does
not
project
to any
other primary
sensory
areas
(at
least
not to any
substantial
degree),
which sug-
gests that
of all the
senses,
odor
may be
most closely linked
to
affect
(for
a
review
of the
literature
on
olfaction
and
emotion,
see
Ehrlichman
&
Bastone, 1992). Thus,
the
dopaminergic theory
of
positive
affect
makes several strong predictions. First, positive
affect
could directly influence odor perception. Second,
the ab-
sence
of a
significant
projection
from
the VTA
into visual
or
auditory
areas suggests that,
in
contrast, positive
affect
might
be
unlikely
to
directly
affect
visual
or
auditory perception. Third,
of
all
stimuli,
odors
might
elicit
the
most direct
and
immediate
affective
response.
To our
knowledge, Prediction
1 i s
untested.
We
know
of no
data that address this question.
As
with
any
null
hypothesis, Prediction
2 is
difficult
to
affirm.
Nevertheless, there
4
Mitchell
and
Gratton (1992) attributed this increase primarily
to
activ-
ity
in the
accessory
olfactory system, which responds
to
pheromones,
rather
than
to
activity
in the
olfactory system, which responds
to
odors.

536
ASHBY,
ISEN,
AND
TURKEN
are no
data indicating that positive
affect
directly changes visual
or
auditory
perception
(e.g.,
see
Niedenthal
&
Kitayama,
1994).
Indeed,
the
existing data indicate that even
the
interpretations
of
clear
visual stimuli
are not
altered
by
positive
affect,
although
those
of
ambiguous stimuli
are
(e.g.,
Isen
&
Shalker, 1982;
Schiffenbauer,
1977a, 1977b). Although these data
do not
directly
address
the
question
of the
impact
of
positive
affect
on
perceptions
themselves,
they
do
suggest that
the
perceptions
are not
directly
influenced.
The
third prediction
is the
most
difficult
to
test because
it
does
not
state that odors
are the
only stimuli that
are
able
to
elicit
an
affective
response,
but
only that they will tend
to
elicit
a
more
immediate affective response than visual
or
auditory stimuli. Nev-
ertheless, there
is a
wealth
of
data showing that odors
do
elicit
immediate
affective
responses.
For
example, much
of the
variance
in
multidimensional-scaling solutions
of
odors
is
accounted
for by
the
participant's
affective
response
(e.g.,
Wright
&
Michaels,
1964; Yoshida, 1979).
In
contrast, multidimensional-scaling solu-
tions
of
visual stimuli rarely load
on an
affective
dimension.
Even
so,
noticing that
an
odor
is
pleasant does
not
necessarily induce
positive
affect.
Therefore,
it is
also important that there
are
pre-
liminary
data showing that certain
odors
may
induce positive
affect.
For
example, Baron
and his
colleagues (Baron, 1990; Baron
&
Bronfen, 1994; Baron
&
Thomley, 1994)
found
that pleasant
odors increased helping behaviors
and
improved performance
on
an
anagrams task,
in
much
the
same
way as
other methods
for
inducing
positive
affect
(e.g., giving
a
small unexpected
gift).
Of
course, visual
and
auditory
stimuli
are
also sometimes used
to
induce
positive
affect,
so the
fact
that odors
can
induce positive
affect
is
necessary,
but not
sufficient,
to
verify
Prediction
3.
Hippocampus
and
Amygdala
Figure
1
indicates
a
dopamine projection into
the
hippocampus
(mostly into sector CA1; e.g.,
Gloor,
1997),
a
medial temporal lobe
structure
that
is
thought
to be
necessary
for the
consolidation
of
episodic memories (e.g.,
Gluck
&
Myers, 1997; McClelland,
Mc-
Naughton,
&
O'Reilly, 1995; Polster,
Nadel,
&
Schacter, 1991;
Squire
&
Alvarez, 1995). Normal
functioning
in the
hippocampus
depends critically
on the
neurotransmitter acetylcholine because
reductions
in
hippocampal
cholinergic
activity produce spatial
memory
deficits
in
rats (Kim
&
Levin,
1996).
Dopamine
has
been
shown
to
increase acetylcholine release
in the
hippocampus
(Im-
perato, Obinu,
&
Gessa,
1993)
and to
improve memory consoli-
dation
in a
brightness discrimination task
(Grecksch
&
Matthies,
1981).
Thus,
it is
plausible that positive
affect
could improve
episodic
memory.
In
fact, there
is
substantial evidence that positive
affect
facilitates
the
recall
of
neutral
and
positive material (Isen
et
al.,
1978; Nasby
&
Yando, 1982; Teasdale
&
Fogarty,
1979).
The
fact
that this type
of
memory facilitation
is
often
asymmetrical,
favoring
positive
affect
and
positive material,
may
simply reflect
the
fact
that
people
typically organize material
for
memory storage
in
terms
of
positive
but not
negative feelings. This
does
not
mean
that
material
is
never organized
in
terms
of a
negative
affective
tone,
especially
in
cases
of
extreme
affect,
but
rather that under
normal
circumstances, most
people
do not use
negative feelings
for
memory
organization
and
storage.
Another structure that could play
an
important role
in the
relation
between memory
and
affect
is the
amygdala, which
also
receives
a
dopamine projection
from
the
VTA5
(see Figure
1). The
amygdala
is
reciprocally connected
to the
hippocampus,
and as
mentioned above,
it
plays
a key
role
in
learning
to
associate stimuli
with
either
primary reward
or
punishment
(e.g.,
see
Rolls, 1995).
For
example, animals with bilateral removal
of the
anterior tem-
poral lobes (which include
the
amygdala;
the
so-called
Kliiver-
Bucy
syndrome;
Kliiver
&
Bucy, 1939) show deficits
in
learning
to
associate
neutral
stimuli
with primary reinforcement
(either
reward
or
punishment)
but not
with secondary reinforcement
(e.g.,
Gaffan,
1992). Even
so, the
amygdala appears
to
respond
differ-
ently
during happiness
and
sadness.
M. S.
George
et al.
(1995)
found
substantially more activation
in the
amygdala during tran-
sient sadness than during transient happiness.
There
is
also convincing evidence that
the
amygdala
is a key
component
in the
memory system
for
emotional events
and
stimuli
(e.g.,
see
Cahill
&
McGaugh,
1998; LeDoux, 1993).
For
example,
there
is a
well-known recall advantage
for
emotionally salient
material
relative
to
neutral
affect
control material (e.g.,
see
Blaney,
1986,
for a
review).
Patients
with
a
rare
hereditary
disorder
that
causes bilateral damage
to the
amygdala
(i.e.,
Urbach-Wiethe
disease)
lose
this recall advantage (Cahill, Babinsky,
Markowitsch,
&
McGaugh,
1995).
One
possibility
is
that during memory con-
solidation,
the
amygdala plays
an
important role
in
associating
an
affective
state with
a
memory trace. This association could involve
automatic
processes, attentive
processes,
or
both. This
is
essen-
tially
a
special
case
of
Damasio's
(1994;
Damasio, Tranel,
&
Damasio, 1991) somatic marker hypothesis, with
the
additional
provision
of a
possible attentive process that operates either during
recall
or
when material
is
organized
for
memory storage
(or at
both
times). Such tagging
or
marking could
affect
memory
in two
ways.
First, traces associated with extreme
affective
states might
be
easier
to
recall,
and
second,
the
person's
current
affective
state
might
serve
as a cue
that facilitates
the
recall
of
material tagged
with
that state. Although research indicates that positive
affect
more
effectively
cues
the
recall
of
positive material than negative
affect
cues
the
recall
of
negative material (e.g.,
see
Isen, 1987,
1999,
for
reviews), this
may be
more true when
the
negative
affect
is
sadness rather than other negative states such
as
anger (see Isen,
1990,
for a
discussion).
Prefrontal
Cortex
The
projections
from
the VTA
into
the
prefrontal cortex
and the
anterior cingulate
are
especially important because they provide
a
direct mechanism through which positive
affect
can
influence
cognition.
There
is
evidence
that
these
two
projections might
influence
separate cognitive
functions.
In
particular, there
is
evi-
dence that
the
dopamine projection into
the
prefrontal cortex
facilitates
working memory, whereas
the
projection into
the
ante-
rior
cingulate
facilitates
executive attention
and the
selection
of
cognitive perspective.
There
is
growing consensus that
the
prefrontal cortex
is the key
cortical substrate
of
working memory
(a
review
is
beyond
the
scope
of
this article; see, e.g., Fuster, 1989;
Goldman-Rakic,
1987,
1995). There also
is
strong evidence
that
dopamine
is
necessary
for
5
The
densest dopamine projections
are
into
the
central nucleus,
but the
basal nucleus also receives
a
prominent projection (e.g., Gloor, 1997).

POSITIVE
AFFECT
537
the
normal
functioning
of
this memory system. First,
loss
of
dopamine
input
to the
prefrontal cortex causes working memory
deficits
in
monkeys
(Brozoski,
Brown, Rosvold,
&
Goldman,
1979; Roberts
et
al.,
1994; Sawaguchi
&
Goldman-Rakic,
1991,
1994).
Second,
patients with
Parkinson's
disease,
who
have
re-
duced
dopamine levels
in the
prefrontal cortex, show working
memory deficits (e.g., Gotham, Brown,
&
Marsden, 1988; Levin,
Labre,
&
Weiner, 1989). Third,
in
vivo (iontophoretic) application
of
dopamine agonists
and
antagonists systematically
affects
firing
rates
of
cells that
are
thought
to
subserve working memory
in the
prefrontal
cortex
of
monkeys (Williams
&
Goldman-Rakic, 1995).
Thus,
the
evidence suggests that reductions
in
dopamine levels
in
the
prefrontal cortex cause working memory deficits.
There
is
less data, however, that allow
us to
predict
the
effects
on
working
memory
of
increases
in
dopamine levels. Some evidence suggests
an
overall facilitation. First, when patients with Parkinson's dis-
ease
are
given L-dopa
(a
precursor
to
dopamine that increases brain
dopamine levels), their working memory
is
improved (Lange
et
al.,
1992). Second, several studies have reported improvements
in the
working memory
of
healthy humans
who
were given
a
dopamine
agonist (Luciano, Depue, Arbisi,
&
Leon, 1992;
Miiller,
von
Cramon,
&
Pollmann, 1998).
In
contrast, Williams
and
Goldman-
Rakic
(1995)
found
that high levels
of a
dopamine antagonist
disrupted
the
memory properties
of
cells
in the
prefrontal
cortex
of
monkeys
but
that very
low
levels
of the
same antagonist were
facilitative.
On the
basis
of
this evidence, they concluded that
working
memory
performance
is
optimized
at
some
intermediate
dopamine
level.6
If
positive
affect
is
associated
with
increased
dopamine
release,
then working memory
may be
affected
in a
similar manner when
positive
feelings
are
induced.
A
plausible
hypothesis,
and one
supported
by the
behavioral
and
neuroscience
data,
is
that moderate levels
of
positive
affect
may
improve work-
ing
memory
but
extreme levels
may
disrupt
it
(e.g.,
Isen,
1999).
This suggestion
is
compatible with
the
findings
in the
affect
literature,
which
has
typically used mild, rather than strong,
affect
inductions,
but
thus
far, there have been
no
rigorous tests
of
this
prediction.
Anterior
Cingulate
and
Selection
of
Cognitive Perspective
As
mentioned
in the
previous
section,
there
is a
prominent
dopamine projection from
the VTA
into
the
anterior cingulate.
Although
it has
been
the
subject
of
much recent investigation,
the
function
of the
anterior cingulate
is
still
in
question.
In
addition
to
the
classical view
of the
cingulate cortex
as
part
of the
Papez
(1937) emotional circuit, many recent results also implicate
the
anterior cingulate
in a
variety
of
cognitive
functions.
It
could
be
that
many
of
these views
are
correct, with
different
areas
of the
anterior
cingulate
having different functions.
There
is
substantial
evidence
that rostral areas
of the
anterior
cingulate
(i.e.,
the
pregenual portions) play
a
direct
role
in
medi-
ating
a
number
of
affective
processes, including
the
regulation
of
autonomic
and
endocrine
function,
conditioned emotional learn-
ing,
assessment
of
motivational content, assignment
of
emotional
valence
to
internal
and
external stimuli,
and
social
interaction (for
a
review,
see
Devinsky,
Morrell,
&
Vogt, 1995).
First,
this region
is
densely interconnected with
the
amygdala,
the
nucleus accum-
bens,
and the
orbitofrontal cortex, structures that
are
crucial
for
affective
processes. Second, electrical stimulation
of
various sites
in
the
rostral anterior cingulate elicits emotional responses such
as
fear,
sadness, anguish,
and
euphoria (Meyer, McElhaney, Martin,
&
McGraw, 1973; Talairach
et
al.,
1973). Third, tumors
in the
anterior cingulate
are
often
associated
with
a
variety
of
emotional
changes
(e.g.,
see
Devinsky
et
al.,
1995).
Fourth,
neuroimaging
studies
indicate increased activation
in the
anterior cingulate
in
healthy
women during
transient
periods
of
happiness
or
sadness
(M.
S.
George
et
al.,
1995).
Similarly,
Drevets
and
Raichle (1995)
reported high levels
of
activation
in the
dorsal
and
rostral anterior
cingulate
in
participants
who
were asked
to
think
sad
thoughts.
In
contrast, when participants were required
to
generate
a
verb
se-
mantically
related
to a
stimulus noun, high levels
of
activation
were observed
only
in the
dorsal anterior cingulate. Thus,
a
com-
plete theory
of
positive
affect
is
likely
to
assign
an
important role
to
rostral regions
of the
anterior cingulate.
The
regions
of the
anterior cingulate implicated
in
cognitive
processing
are
dorsal
and
posterior
to the
affective
region.
Differ-
ent
researchers have attributed
a
number
of
different
cognitive
functions
to
these regions, including executive attention (Posner
&
Petersen, 1990), selection among alternative motor programs
(Paus, Petrides, Evans,
&
Meyer, 1993), error monitoring (De-
haene, Posner,
&
Tucker, 1994;
Gehring,
Goss,
Coles,
Meyer,
&
Donchin, 1993), anticipatory
and
preparatory processing
(Murtha,
Chertkow,
Beauregard, Dixon,
&
Evans,
1996),
and the
general
monitoring
of
internal events (Frith,
1992).
Although
each
of
these
functions
could dramatically
affect
cognitive performance, perhaps
the
most
profound effects
on
cognition
would
be due to
manipu-
lations
of
executive attention.
Posner
and
Petersen
(1990;
see
also Posner
&
Raichle, 1994)
proposed
that
there
are a
number
of
separate
but
interacting atten-
tion
systems
in the
human brain.
For our
purposes,
two of
these
systems
are
especially important. Roughly speaking,
the
posterior
system
mediates perceptual attention, whereas
the
anterior system
mediates cognitive
or
executive attention.
The
anterior cingulate
cortex
is
assumed
to be a key
structural component
of the
anterior
attentional
system. Posner
and his
colleagues (Posner
&
Petersen,
1990; Posner
&
Raichle, 1994) hypothesized
that
the
(dorsal)
anterior cingulate
is
involved
in the
selection
of
cognitive perspec-
tive
and in the
conscious directing
of
executive attention. Their
arguments
were based partly
on
neuroimaging studies, which
indicated
that
the
anterior cingulate
is
activated
in
tasks
in
which
a
person must select
or
switch among various interpretations
or
aspects
of the
stimulus.
In
conditions
in
which such selection
or
switching
is not
required,
the
cingulate
is not
activated.
For ex-
ample, Corbetta, Miezin, Dobmeyer, Shulman,
and
Petersen
(1991)
found
cingulate activation
in a
same-different
task
in
which
two
visual stimuli could
differ
in any one of
three compo-
nents
but not
when
the
stimuli could
differ
in
only
one
component.
6
There
are two
classes
of
dopamine
receptors.
The
D,
class includes
the
D, and
D5
receptors,
and the
D2
class includes
the
D2,
D3,
and
D4
receptors
(e.g.,
Seeman
& Van
Tol,
1994; Sibley, Monsma,
&
Shen,
1993).
Of
these,
the
D,
and
D2
receptors
are,
by
far,
the
most common,
and in the
prefrontal
cortex
and the
anterior cingluate, there
are
approximately
10
times
as
many
D,
receptors
as
there
are
D2
receptors (Lidow, Goldman-Rakic, Gallagher,
&
Rakic,
1991).
As one
migh t expect
from
this numerical discrepancy,
most studies reporting
an
effect
of
dopamine
on
working memory have
used either general dopamine agonists
or
antagonists,
or
drugs
that
act
selectively
on D,
receptors.

538
ASHBY,
ISBN,
AND
TURKEN
The
former
condition
requires
selection
of the
appropriate
dimen-
sion,
whereas
the
latter condition does not. Similarly,
the
cingulate
is
not
activated when
people
are
simply required
to
read
a
stimulus
word,
but it is
activated when they
are
required
to
name
a
verb
related
to the
stimulus word (Petersen, Fox, Posner, Mintun,
&
Raichle,
1988)
or
when
the
word
is a
color
name printed
in the ink
of
a
different
color (i.e.,
the
classic
Stroop
task; Bench
et
al.,
1993).
Reading
a
word does
not
require
people
to
select
a
meaning,
but
naming
a
related verb does,
and
Stroop tasks require people
to
select between conflicting semantic
and
perceptual cues.
One
difficulty
with interpreting neuroimaging results such
as
these
is
that, because
of
massive reciprocal
innervation,
the
dor-
solateral prefrontal cortex tends also
to be
activated when there
is
anterior cingulate
activation.7
Thus, neuroimaging results alone
make
it
difficult
to
decide
whether
the
selection
of
cognitive
perspective
and the
directing
of
executive attention
are
mediated
by
the
anterior cingulate
or by the
dorsolateral prefrontal cortex.
However,
Turken
and
Swick
(1998) recently reported results
from
a
patient with
a
lesion restricted
to the right
anterior cingulate
who
participated
in a
task similar
to the
same-different
task used
by
Corbetta
et al.
(1991).
As
predicted
by the
hypothesis that
the
anterior cingulate
is an
important executive-attention structure,
the
patient showed deficits
in
performing
the
task, especially
in the
divided-attention
condition (i.e.,
on
trials
in
which
the
stimuli
could
differ
in any one of
several components).
Oades
(1985)
argued that
dopamine
facilitates switching among
a
broad variety
of
signals
in the
central nervous system.
We
propose, more specifically, that dopamine
and
also positive
affect
facilitate
the
selection
of, or the
switching among,
alternative
cognitive
perspectives.8
In
fact, there
is
considerable behavioral
evidence
that dopamine enhances this ability. First, dopamine
antagonists impair cognitive
set
shifting
(Berger
et
al.,
1989).
Berger
et al.
administered
haloperidol,
a
common dopamine
an-
tagonist,
to
patients with
idiopathic
spasmodic
torticollis—a
dis-
order without known
neuropsychological
dysfunction
in
which
the
symptoms
are
sometimes alleviated
by
treatments with either
dopamine agonists
or
antagonists. Before haloperidol administra-
tion,
the
group
with
torticollis performed
as
well
as a
control group
on
a
simplified version
of the
Wisconsin Card Sorting
Test.
In
this
task, participants sort cards according
to
some perceptual attribute
(e.g.,
color).
After
reaching
a
criterion level
of
accuracy,
the
relevant attribute
is
changed without warning
(e.g.,
from
color
to
shape).
After
the
group with
torticollis
was
administered
haloper-
idol, however,
they
made
significantly
more perseverative errors
than
the
control group. Similarly, several studies have
found
that
administering
a
dopamine antagonist
(i.e.,
chlorpromazine)
to
healthy adults impairs their ability
to see
alternative interpretations
of
ambiguous
(i.e.,
reversible)
figures
(Harris
&
Phillipson,
1981;
Phillipson
&
Harris, 1984).
Second, patients
with
Parkinson's
disease, which reduces brain
dopamine levels,
are
impaired
in
performing tasks that require
selection
or set
shifting.
For
example, these patients show more
perseverative errors than age-matched controls
on the
Wisconsin
Card Sorting Test (e.g., Brown
&
Marsden,
1988; Cools,
van den
Bercken,
Horstink,
van
Spaendonck,
&
Berger, 1984).
Following Posner
and
Petersen (1990),
we
hypothesized that
the
structure most important
for the
selection
of
cognitive
perspective
is
the
(dorsal) anterior cingulate.
The
results reviewed
in
this
section support this hypothesis. However,
it is
important
to
realize
Table
1
The
Logical Structure
of the Two
Tasks
Designed
by
Owen
et al.
(1993)
Perseveration
task Selection task
Relevant Irrelevant Relevant Irrelevant
Condition
component component component component
Training
Transfer
A
C
B
A
A
B
B
C
that many patients
with
neuropsychological disorders besides
those with Parkinson's disease perseverate
on the
Wisconsin Card
Sorting
Test,
including
several
populations
with
no
known cingu-
late
dysfunction.
For
example, patients with lesions
of the
prefron-
tal
cortex perseverate
on
this task.
In
fact,
the
Wisconsin Card
Sorting Test
is
used primarily
as an
instrument
for
detecting
frontal
dysfunction
(e.g.,
Kolb
&
Whishaw, 1990).
Owen
et al.
(1993) argued that perseverative errors
on the
Wisconsin Card Sorting Test could occur
for two
different
reasons.
One is a
failure
to
select
the
appropriate stimulus aspect,
and the
second
is a
failure
to
switch attention
from
an
inappropriate
to an
appropriate aspect.
To
test this hypothesis, Owen
et al.
designed
two
new
tasks
in
which
the
different
errors would
be
observable.
Let A, B, and C
represent
different
aspects, components,
or
dimen-
sions
of the
stimulus display.
For
example,
A
might represent
rectangles that vary
in
shape,
B
might represent circles that vary
in
size,
and C
might
represent
lines
that vary
in
orientation. Next,
let
AB, for
example, represent
an
experimental condition
in
which
the
stimuli
vary
in
aspects
A and B, and
aspect
C is not
present,
and in
which
participants must learn
to
sort
the
stimuli according
to the
value
of
each stimulus
on
aspect
A.
Thus,
the first
aspect listed
is
critical,
and the
second aspect
is
irrelevant.
In our
earlier example,
the
stimulus displays
in the AB
condition would contain
a
rectangle
and
a
circle,
and the
participants' task would
be to
sort
the
stimuli
according
to the
shape
of the
rectangle.
Owen
et al.
(1993) created
two
different
tasks with
the
logical
structure
illustrated
in
Table
1.
The
perseveration task consists
of
condition
AB
followed
by
condition
CA. A
perseverative error
occurs
if the
participant continues
to
respond
on the
basis
of
aspect
A in the
transfer condition.
In
contrast,
the
selection task consists
of
condition
AB
followed
by
condition
BC.
Here,
an
error
in the
transfer
condition cannot
be
attributed
to
perseveration because
aspect
A is not
present
on
transfer trials. Thus, attention
must
naturally
switch
from
A to
something else.
An
error occurs
in the
transfer
condition
of the
selection task
if the
participants select
the
7
The
projections into
the
prefrontal
cortex tend
to
originate
from
regions
of
the
cingulate that
are
more anterior
than
the
cingulate regions that
receive projections
from
the
prefrontal cortex. This allows
the
possibility
that anterior
and
dorsal regions
of the
anterior cingulate participate
in
Posner
and
Petersen's (1990) anterior
attentional
system, whereas more
posterior regions
of the
anterior cingulate mediate
the
selection
of
alter-
native
responses (Paus
et
al.,
1993).
8
There
are
obvious adaptive benefits
of
such facilitation. When
an
animal
receives
an
unexpected reward,
an
increased cognitive flexibility
should
improve
the
animal's ability
to
explore
and
exploit
the
environment
in
which
the
reward
was
received.

POSITIVE
AFFECT
539
wrong aspect
for
switching. Using this clever design, Owen
et
al.
found
that patients with frontal damage were impaired
on the
perseveration task
but not on the
selection task, whereas (unmedi-
cated) patients with
Parkinson's
disease
were impaired
on
both
tasks.
These
results support
the
hypothesis that
the
anterior cingu-
late
mediates
the
selection operation
and
that
the
prefrontal cortex
participates
in the
switching operation. This
is
because
(a)
there
are
dopamine
projections from
the VTA
into both
the
prefrontal cortex
and the
anterior cingulate,
(b)
Parkinson's
disease causes
the
death
of
dopamine-producing
cells
in the VTA (as
well
as in the
sub-
stantia nigra),
and (c)
people
with frontal impairment have pre-
frontal
cortex lesions
but not
anterior cingulate lesions.
Although
the
evidence
is
strong that
the
prefrontal cortex par-
ticipates
in the
switching operation,
the
hypothesis that
it
plays
the
main
role
is
controversial (e.g.,
Curran,
1995). Another possibility
is
that
the
basal ganglia perform
the
switching. There
are
known
loops from
the
prefrontal cortex that project into
the
striatum,
then
to the
globus pallidus, then
to the
thalamus,
and
finally, back
to the
prefrontal
cortex (Alexander
et
al.,
1986). Separate loops could
be
established
for
each
of the
critical alternatives, which would allow
the
basal ganglia
to
perform
the
switching. There
are
several lines
of
evidence
supporting this hypothesis.
We
mention two. First,
injection
of a
glutamate agonist directly into
the
striatum increases
the
frequency with which cats switch from
one
motor activity
to
another
in a
task
in
which food rewards
are
delivered
for
such
switching
behaviors9
(Jaspers,
De
Vries,
&
Cools,
1990a, 1990b).
Second, lesioning
the
dopamine fibers that project from
the VTA
into
the
prefrontal cortex improves
the
performance
of
monkeys
on
an
analogue
of the
Wisconsin Card Sorting Test (Roberts
et
al.,
1994).
If
switching occurs
in the
prefrontal cortex, then such
lesions should impair switching performance
(as
seen, e.g.,
in
patients
with Parkinson's disease).
If the
switching occurs
in the
basal ganglia, then lesioning dopamine fibers
in the
prefrontal
cortex should have
no
direct
effect
on
switching.
How
then
can one
explain
that lesioning dopamine fibers
in the
prefrontal cortex
actually
improves performance
on the
Wisconsin Card Sorting
Test?
An
important clue
to
this apparent paradox comes
from
reports that such lesions tend
to
increase dopamine levels
in the
basal
ganglia10
(Roberts
et
al.,
1994).
If the
basal ganglia
are
responsible
for
switching,
if
switching
is
enhanced
by
dopamine,
and
if
lesioning
the
dopamine fibers that enter
the
prefrontal cortex
increases dopamine levels
in the
basal ganglia, then lesioning
the
dopamine fibers
in the
prefrontal cortex should improve switching.
On
the
basis
of
these
data,
therefore,
we
hypothesized that switch-
ing
among cognitive perspectives
is
mediated primarily
by the
basal
ganglia whereas
the
selection
of
cognitive perspective
is
mediated primarily
by the
anterior cingulate.
This hypothesis
may
also explain
why
people
with schizophre-
nia
who
have positive symptoms (e.g., delusions, hallucinations;
also called Type
I
schizophrenia) have
difficulty
maintaining cog-
nitive
set
(e.g., American Psychiatric Association, 1994), despite
good evidence
of
reduced activity
in
frontal
cortical areas
of
people
with
schizophrenia11
(e.g.,
Farkas
et
al.,
1984;
Ingvar
&
Franzen,
1974; Weinberger,
Berman,
&
Zee,
1986).
If
both selec-
tion
and
switching were mediated
by
frontal structures, then
hy-
pofrontality
should lead
to
reduced switching
and
perseveration,
rather than
to the
frequent
and
inappropriate switching (e.g., "de-
railment,"
"word
salad")
actually exhibited
by
people with schizo-
phrenia.
In
contrast,
the
hypothesis that selection
is
mediated
by
the
anterior cingulate
and
switching
by the
basal ganglia predicts
that
the
derailment
and
word salad
of
schizophrenia could co-occur
with
hypofrontality
if
people with schizophrenia show increased
activity
in the
basal ganglia.
In
fact, there
is
substantial evidence
of
increased dopaminergic activity
in the
basal ganglia
of
people with
schizophrenia (mediated
by
D
2
receptors;
for
reviews, see, e.g.,
Feldman
et
al.,
1997; Grace, 1991).
It is
important
to
note, how-
ever, that
we are not
proposing
a
connection between positive
affect
and
schizophrenia.
The
increased dopaminergic activity
postulated
to
occur
in the
basal
ganglia
of
individuals with schizo-
phrenia should
far
exceed
the
relatively modest increases that
we
hypothesized might occur under normal positive
affect.
Presum-
ably,
this
is why the
speech
of
people
who are
feeling happy does
not
typically resemble
a
word salad. People
in
positive
affect
are
flexible,
not
psychotic. Also,
the
hypofrontality
thought
to
occur
in
schizophrenia
differs
dramatically
from
the
enhanced
frontal
func-
tioning
that
we
predicted
for
positive
affect.
Clearly, positive
affect
and
schizophrenia
are
qualitatively
different,
and we
cer-
tainly
do not
expect positive
affect
to
induce symptoms that
are
even approximately schizophrenia-like.
For
example,
in
striking
9
Alternatively, switching between motor behaviors
and
switching
be-
tween cognitive sets
may be
mediated
differently.
The
striatum consists
of
two
structures:
the
caudate nucleus
and the
putamen. Generally speaking,
the
putamen
is
more involved
in
motor activity,
and the
caudate
is
more
involved
in
cognitive activity. There
are two
separate, parallel projections
from
the
putamen
to the
internal segment
of the
globus pallidus.
One is a
direct projection,
and the
other
is an
indirect projection through
the
external
segment
of the
globus pallidus
and the
subthalamic
nucleus (e.g., Heimer,
1995).
Berns
and
Sejnowski (1996) proposed that both these direct
and
indirect pathways
are
necessary
for
selection
or
switching
to
occur
in the
basal ganglia. This hypothesis works well
for
motor swi tching
but
less
so
for
cognitive switching. This
is
because cortical projections
to the
subtha-
lamic
nucleus
are
exclusively
from
motor areas,
and the
fibers that project
from
the
caudate through
the
subthalamic nucleus (i.e., through
the
globus
pallidus)
are
apparently less dense than those projecting
from
the
putamen
through
the
subthalamic nucleus (e.g., Heimer, 1995).
10
Dopamine levels
in the
basal ganglia apparently increase because
the
prefrontal
cortex tonically inhibits
the
VTA. Lesioning
the
dopamine fibers
into
the
prefrontal cortex releases this
inhibition,
which
effectively
stim-
ulates
the
VTA. There
are a
number
of
scenarios
in
which increased
VTA
activation could lead
to
increased dopamine levels
in the
striatum. Perhaps
the
most
likely
is the
VTA-nucleus
accumbens-substantia
nigra-striatum
pathway.
1'
In
contrast, some researchers have argued that (positive) schizophre-
nia
is
associated
with
elevated cortical dopamine levels (e.g., Crow, 1980,
1982; Swerdlow
&
Koob,
1987), largely because
of the
success
of
dopa-
mine
antagonist (neuroleptic) therapy
in
treating schizophrenia.
In
support
of
this assumption, recent evidence suggests that
the
therapeutic action
of
neuroleptics
is
primarily
on
cortical dopamine
D2
receptors (Lidow, Wil-
liams,
&
Goldman-Rakic,
1998).
However,
in
contrast
to
this
view,
neu-
roleptic treatment
is not
immediately effective. Partly
for
this reason,
a
number
of
current theories argue that although
subcortical
dopamine
ac-
tivity
is
increased
in
schizophrenia, cortical dopamine activity
is
act ually
decreased
(Cohen
&
Servan-Schreiber, 1992; Goldman-Rakic, 1991;
Karoum,
Karson,
Bigelow, Lawson,
&
Wyatt,
1987;
Weinberger, Berman,
&
Illowsy, 1988). This latter view
is
supported
by
recent results indicating
that chronic neuroleptic treatment
is
efficacious because
it
leads
to
upregu-
lation
of
cortical
D
2
receptors (although apparently
at the
cost
of
down-
regulation
of D|
receptors; Lidow
et
al.,
1998).

540
ASHBY,
ISBN,
AND
TURKEN
contrast
to
schizophrenia,
we
expect positive
affect
to
have
a
general facilitative
effect
on
cognitive processing
and
speech.
If
positive
affect
is
associated with increased
dopamine
release
from
the
VTA,
and if
dopamine facilitates selection
in the
anterior
cingulate, then
we
would expect positive
affect
to
improve cogni-
tive
flexibility
and the
selection
of
cognitive perspective. There
is
preliminary
support
for
this
hypothesis.
Estrada
et
al.
(1997)
reported that positive
affect
reduced "anchoring"
or
rigidity
in
thinking
on a
medical decision-making task. Specifically, Estrada
et al.
induced positive
affect
in a
group
of
physicians
and
asked
them
to
read
a
medical chart
and
make
a
diagnosis. Compared
with
a
control group
of
neutral
affect
physicians,
the
positive
affect
physicians
were more open
to new
information, even when
it
contradicted
an
early diagnostic hypothesis they were holding.
It
is
possible that much
of the
improvement
in
creative problem
solving that
is
observed
under
conditions
of
positive
affect
is due
to
the
facilitation
of
executive attention that occurs with increased
dopamine release into
the
anterior cingulate cortex.
For
example,
consider Duncker's (1945) candle problem,
in
which participants
are
given
a box of
tacks,
a
book
of
matches,
and a
candle
and are
asked
to
attach
the
candle
to the
wall
and
light
it in
such
a way
that
no
wax
drips
on the
floor.
Isen
et al.
(1987)
found
that
people
in
the
positive
affect
group were significantly more accurate (58%
correct)
on the
candle problem than were neutral
affect
controls
(13% correct). Success
on
this task
is
more likely
for
participants
who
overcome
the
dominant cognitive
set
(viewing
the box as a
container)
and
select
a set
that
is
less typical (viewing
the box as
a
platform).
If
dopamine enhances
the
ability
of the
executive-
attention
system
to
select more
flexibly,
then
it
seems reasonable
to
expect positive
affect
to
improve performance
on the
candle
task.
Positive
affect
may
facilitate performance
on
other creative
problem-solving tasks
in a
similar way.
For
example, consider
the
word-association
and
remote-associates tasks discussed earlier.
In
word association, participants
are
presented with
a
stimulus word
and
then asked
to
respond with
the first
word that comes
to
mind.
As
described above, Isen
et al.
(1985)
found
that people
in the
positive
affect
group were more likely
to
respond with
unusual
first
associates (54%
of
total responses) compared with neutral
affect
controls (39%
of
total responses), where unusualness
was
defined
by
Palermo
and
Jenkins's (1964) word-association norms.
In
addition, participants
in the
positive
affect
condition showed
greater diversity
in
their responses than
did
those
in the
control
group.
It is
easy
to
imagine situations
in
which
the
selection
of
unusual
or
nondominant
cognitive sets would lead
to
unusual
responses
in the
word-association task.
For
example, consider
a
trial
in
which
the
stimulus
word
is
pen.
To
respond, participants
must
select among
the
various meanings
of
this word.
The
dom-
inant
interpretation
(or
set)
is
of
pen as a
writing implement.
In
this
case,
participants
are
likely
to
respond with
a
high-frequency
associate,
such
us
pencil
or
paper.
A
more unusual
interpretation
is
of
pen as a
fenced
enclosure. Participants
who
select this interpre-
tation
are
likely
to
respond
with
a
low-frequency associate, such
as
bam or
pig.
In
the
Remote Associates Test
(M. T.
Mednick
et
al.,
1964),
participants
are
presented with three
cue
words
and are
asked
to
find a
fourth
word that
is
related
in
some
way to
each
of the
three
cue
words.
For
example,
one set of cue
words
is
gown, club,
and
mare.
In
this case,
the
correct response
is
night (i.e., nightgown,
nightclub,
and
nightmare).
As
mentioned previously, Isen
et al.
(1987)
found
that people
in a
positive
affect
group were signifi-
cantly
more accurate
on a
subset
of
moderately
difficult
items
from
the
Remote Associates Test than were neutral
affect
controls
(71%
correct
vs. 43%
correct, respectively). Note that
in
this example,
to
produce
the
word night when presented with
the cue
words club,
gown,
and
mare, participants must overcome
the
dominant cogni-
tive
set
that
the
correct
response
is
semantically
related
to the cue
words. Instead, participants must consider alternative ways
in
which
the
words
may be
related, such
as by
being part
of a
compound
word. Thus,
it is
possible that
the
effects
of
positive
feelings
on the
candle, word-association,
and
remote-associates
tasks
are all due to a
common phenomenon, namely, that positive
affect
is
associated with increased dopamine release into
the an-
terior cingulate, which increases
the flexibility of the
executive-
attention
system.
A
rough sketch
of one
possible
model that instantiates these
ideas
is
shown
in
Figure
2, for a
trial
of the
word-association task
in
which
the
stimulus word
is
pen.
The
alternative cognitive sets
are
represented
in the
prefrontal cortex (i.e.,
pen as a
writing
implement
and pen as a
fenced enclosure).
On the
basis
of
appro-
priate context,
one of the
cognitive sets
is
activated (pen
as a
writing
implement
in
Figure
2), and the
anterior cingulate
is
involved
in
this selection. Presumably, this cognitive
set is
loaded
into
working memory.
If an
alternative
set is to be
noted
or
selected, then
the
switching
is
accomplished
in the
striatum
(i.e.,
in
Anterior Cingulate
Figure
2.
Proposed architecture
of a
neural network that mediates cre-
ative
problem solving.
Dopamine-producing
areas
are
shaded
in
gray,
and
dopamine projections
are
illustrated
by the
dashed lines.
VTA =
ventral
tegmental
area;
SN =
substantia
nigra.

POSITIVE
AFFECT
541
the
caudate nucleus
in the
case
of
word association).
A
simple
way
this might work
is
through lateral inhibition. Although competition
within
the
striatum
is
often
thought
to be
resolved
in
this manner
(e.g.,
Wickens,
1993),
direct recording studies have
so far
failed
to
find
evidence
of
strong inhibition within
the
striatum (e.g., Jaeger,
Kita,
&
Wilson, 1994).
For
now,
we
tentatively assume that
switching
is
accomplished through lateral inhibition within
the
striatum,
but we
leave
open
the
possibility that
the
switching
is due
to
some other process within
the
basal ganglia
(e.g.,
an
alternative
was
proposed
by
Berns
&
Sejnowski,
1996;
see
Footnote
9).
In
the
model
shown
in
Figure
2,
each
of the
cognitive
set
units
projects back
to a
different semantic network
in
some cortical
language area (presumably
in the
temporal lobe).
For
example,
pen
as
a
writing implement
is
shown projecting
to a
network that might
include
the
words paper
and
pencil,
and pen as a
fenced enclosure
is
shown projecting
to a
network that might include barn
and
pig.
For the
present purposes, there
is no
need
to
make assumptions
about
the
details
of
these semantic networks.
In
Duncker's
(1945)
candle task,
we
assume
the
relevant
cortico-cortical
projections
are
from
the
cognitive
set
units
in the
prefrontal cortex
to
specific
motor units
in the
premotor
or
motor cortex, rather than
to
tem-
poral language areas,
as in
Figure
2. In the
model shown
in
Figure
2, the
dopamine
projection
from
the VTA
into
the
anterior
cingulate facilitates
the
selection
process,
and the
dopamine pro-
jection
from
the
substantia nigra into
the
striatum facilitates
switching.12
Of
course, dopamine
is
present even
in
neutral
affect
conditions,
so we
assume that
the
effect
of
positive mood
is to
alter
existing activation patterns, rather than
to
initiate
any new
pro-
cessing.
The
model
in
Figure
2 is
greatly oversimplified.
In
prac-
tice, positive
affect
has
also been found
to
allow more flexible
consideration
of
complex bodies
of
material, such
as
goals (e.g.,
Carnevale
&
Isen,
1986),
and
component sets
of
relevant problem-
solving
material (e.g., Estrada
et
al.,
1997).
In
such cases,
a
much
more elaborate conceptualization would
be
needed.
Neuroimaging data support
a
general model
of
this type.
For
example, Frith, Friston, Liddle,
and
Frackowiak
(199la)
used
positron emission tomography scanning
to
examine cortical activ-
ity
in
normal adults during word fluency
and
lexical-decision
tasks,
as
well
as a
number
of
control tasks. Relative
to the
control
tasks, they
found
increased activation
in the
anterior cingulate
and
the
(dorsal lateral) prefrontal cortex
in the
semantic tasks
and
either increased
or
decreased
activation
in the
temporal language
areas,
depending
on the
type
of
semantic task.
On the
basis
of
these
results, Friston, Frith,
Liddle,
and
Frackowiak (1991) postulated
that
in
semantic tasks involving selection
or
generation,
the
pre-
frontal
cortex modulates activity
in the
temporal language areas
through (glutaminergic) cortico-cortical projections. Frith, Friston,
Liddle,
and
Frackowiak
(1991b)
generalized this hypothesis
to
nonsemantic tasks. Specifically, they
proposed
that
in
many tasks
requiring
"willed
action,"
the
prefrontal cortex modulates activity
in
remote,
but
task-relevant, cortical areas.
One
way to
test
a
neuropsychological theory
is to
evaluate
the
ability
of a
mathematical model derived
from
that theory
to ac-
count
for
behavioral data. Unfortunately,
to
derive quantitative
predictions
from
the
model
in
Figure
2,
many more assumptions
must
be
made. Following this approach, Ashby, Turken,
and
Isen
(1996)
developed
a
formal connectionist network
based
on the
model
in
Figure
2.
Standard pharmacological techniques were used
to
derive
the
theoretical effects
of
dopamine
on the
activation
function
of
uni ts
in the
portion
of the
network
that
corresponds
to
the
anterior
cingulate.13
The
network successfully accounted
for
the
effects
of
amphetamines
on
two-choice guessing data (Ridley,
Baker, Frith, Dowdy,
&
Crow, 1988; i.e., amphetamines increased
the
number
of
alternation responses),
and it
accounted
for the
effects
of
positive feelings
on the
three creative problem-solving
tasks
discussed above (Duncker's [1945] candle task, word asso-
ciation,
and the
Remote Associates
Test).
Despite these successes,
Ashby
et
al.'s
modeling approach
is
limited because
the
data
on the
effects
of
feelings
on
cognition
do not
sufficiently
constrain
the
model. When
the
creative problem-solving data discussed
in
this
section were collected, there were
no
theories that made specific
quantitative
predictions about
how
positive
affect
would
influence
performance
on
these tasks. Instead,
the
major interest
was on
whether there would
be
effects.
It is
possible
that
a
number
of
different
models could account
for the
word-association, remote-
associates,
and
candle task data just
as
well
as the
network tested
by
Ashby
et al.
Thus,
the
success
of the
tested model should
be
considered more
a
demonstration
of the
potential
of the
dopami-
nergic theory
of
positive
affect
rather than
a
rigorous test
of
that
theory.
Also,
because
there
now is a
theory that
makes
rigorous
predictions,
future
experiments
can
collect
and
report data
in
such
a way
that allows more rigorous testing.
Another creative problem-solving task
in
which positive
affect
might
influence performance
is
word
fluency.
In
this task, partic-
ipants
are
asked
to
produce, within some time limit,
as
many words
as
possible that begin
(or
end) with some specified letter. This task
seems
closely related
to
word association,
so it is
natural
to ask
whether word
fluency is
also influenced
by
affect.
There
is
evi-
dence that word
fluency
is
affected
by
brain dopamine levels. First,
administration
of
haloperidol,
a
powerful
dopamine antagonist,
impairs
performance
on
word
fluency
tests
(Berger
et
al.,
1989),
and
second, patients
with
Parkinson's disease
are
impaired
in
word
fluency
compared with age-matched controls (Stuss
et
al.,
1983;
Wallesch,
Kornhuber,
Kollner,
Haas,
&
Hufnagl,
1983).
For
these
reasons, positive
affect
might improve word
fluency,
with
the
improvement largely coming
from
enhanced
flexibility in the
selection
of
cognitive perspective. More specifically,
we
predicted
that
positive
affect
might
lead
not
only
to
increased word produc-
12
This model
is
computationally similar
to a
model
of
cognitive pro-
cessing
in
individuals
with
schizophrenia
that
was
proposed
by
Cohen
and
Servan-Schreiber
(1992). Both models assume
that
alternative
cognitive
sets
are
represented
in the
prefrontal cortex
and
that these sets
are
used
to
support
task-relevant representations
in
more posterior systems. Both mod-
els
also assume that dopamine makes
it
easier
to
overcome dominant
response tendencies.
The
main difference
is
that
in
Cohen
and
Servan-
Schreiber's model,
the
prefrontal cortex representations
are
assumed
to
have equal strength,
and
selection
and
switching
are
performed
by
posterior
components (and Cohen
and
Servan-Schreiber
did not
link
dopamine
release
to
positive
affect).
13
This model assumed that dopamine, acting through
the
D[
receptor,
modulates
the
effects
of
glutamate. Specifically,
it was
assumed that
dopamine
increases
the
efficacy
of
glutamate
by
prolonging
the
action
of
the
Ca2+
second messenger
that
is
activated when glutamate binds
to the
N-methyl-D-aspartate
(NMDA)
receptor
(Hemmings,
Walaas, Ouimet,
&
Greengard, 1987; Pessin
et
al.,
1994; Wickens, 1990, 1993)
and
that
dopamine
decreases
the
affinity
of
glutamate
for
non-NMDA receptors
(Cepeda, Radisavljevic, Peacock, Levine,
&
Buchwald,
1992).

542
ASHBY,
ISEN,
AND
TURKEN
tion
but
also
to
more words coming
from
different categories
or
word types.
For
example, when producing words that begin with
the
letter
c, a
person might initially focus
on
nouns
(or
some subset
of
nouns, such
as
words
of a
certain category
or
from
a
certain
context).
When
the
response rate decreases,
an
effective
strategy
is
to
shift
attention
to
some other word group
or
context (e.g., verbs
or
nouns
in
another category). Such
shifting
should
be
enhanced
by
positive
affect.
Some preliminary data support this prediction.
In
particular,
Greene
and
Noice (1988) reported that positive
affect
increased word
fluency
in
adolescents
(eighth
graders).14
In
this section,
we
postulated that, because
of
increased dopa-
mine
release
in the
anterior cingulate
and
possibly
the
striatum,
positive
affect
is
likely
to
facilitate cognitive
set
switching
and
selection,
and we
argued that such facilitation might underlie
the
well-documented improvements
in
creative problem solving that
occur with
positive
affect. However, improvements
in
cognitive
set
switching
and
selection could facilitate performance
on a
wide
variety
of
tasks, besides those traditionally associated with creative
problem
solving.
For
example,
earlier
we
presented evidence that
success
on the
Wisconsin Card Sorting Test
and on
Owen
et
al.'s
(1993) selection task (condition
AS
followed
by
condition
BC;
see
Table
1)
is
facilitated
by
flexibility
in
cognitive
set
switching
and
selection.
As a
consequence, positive
affect
might improve per-
formance
on
both
of
these classification tasks.
The
predictions
for
the
perseveration task (condition
AB
followed
by
condition
CA;
see
Table
1) are
less
clear.
There
is
evidence that increased
dopamine
in the
striatum should facilitate performance
on
this task
(Roberts
et
al.,
1994),
and as
discussed above, behavioral evidence
suggests
that positive
affect
is
associated
with
increased
dopamine
in
the
striatum (e.g., because
of the
increased motor activity that
occurs under positive
affect
conditions). Thus,
the
theory devel-
oped
in
this article predicts that both selection
and
switching could
be
facilitated. However, Roberts
et al.
found
that lesioning
the
dopamine fibers that project into
the
prefrontal cortex (i.e.,
from
the
VTA)
increased
striatal
dopamine
levels.
We
assumed that
positive
affect
increases dopamine levels
in the
prefrontal cortex,
so one
might
infer
from
Roberts
et
al.'s results that positive
affect
could
lead
to
decreases
in
striatal dopamine
levels.
Unfortunately,
there
is not
much data
in the
current literature that addresses this
question. Most tasks that
putatively
study
cognitive switching
actually
require
facility
in
switching
and
selection.
As
such, evi-
dence that positive
affect
facilitates performance
on
these tasks
does
not
allow
us to
determine where
the
facilitation
is in
switch-
ing
alone, selection alone,
or
both processes. Further research
on
this question
is
needed.
A
recent neuropsychological theory
of
category learning sug-
gests that
the
influence
of
positive
affect
on
classification might
extend
considerably beyond
the
Wisconsin Card Sorting Test.
Ashby
et al.
(1998) proposed that category learning
is a
competi-
tion
between separate explicit
(i.e.,
hypothesis
or
theory testing)
and
implicit (i.e., procedural learning) categorization systems.
Explicit
categorization rules were defined operationally
as
those
rules
that
are
easy
to
describe verbally.
The
resulting model
was
called
Competition
between Verbal
and
Implicit
Systems
(COVIS).
Each system
in
COVIS
is
mediated
by
separate
cortical-
striatal-pallidal-thalamic
loops.
The
anterior cingulate
is
assumed
to
select
the
type
of
explicit rule
to be
used
on the
coming trial,
so
COVIS assigns essentially
the
same
functions
to the
anterior
cingulate
as we
propose
in
this article. Together,
the
dopaminergic
theory
of
positive
affect
and
COVIS predict that positive
affect
might facilitate learning
in any
categorization task
in
which per-
formance
is
maximized
by an
explicit rule (e.g.,
one
that
is
easily
verbalized).15
The
facilitation
is
predicted because
the
anterior
cingulate should
be
more adept
at
selecting
the
correct explicit rule
type under positive
affect
conditions.
By
this logic, positive
affect
might improve performance
on the
Wisconsin Card Sorting Test
because
all of the
classification rules that succeed
in
this task
are
explicit (e.g., they
all are
easily verbalized because category mem-
bership
is
determined
by the
number
of
geometric symbols
on a
card,
by the
shape
of the
symbols,
or by the
color
of the
symbols).
COVIS
is
helpful,
however,
in
identifying
the
verbalizability
of the
correct classification rule
as the key
feature
of the
task that renders
it
susceptible
to
manipulations
of
affect.
In
particular, COVIS
predicts that many other surface features
of the
Wisconsin Card
Sorting
Test
are of
relatively
little
importance
to the
affect
predic-
tions. These include
the
nature
of the
stimuli used, whether
the
stimulus
dimensions
are
continuous-
or
discrete-valued, whether
participants
are
shown specific category exemplars,
and
whether
the
task requires participants
to
learn
a
single rule
or a
series
of
different
rules.
In
addition
to the
tasks
discussed
in
this
section,
there
are
many
other tasks that seem
to
involve cognitive
or
perceptual
set
switch-
ing.
It is
natural
to ask
whether positive
affect
might influence
performance
on all
such tasks. Although
it is
tempting
to
adopt
a
strong
position with respect
to
this question, there
are a
number
of
reasons
to be
cautious.
For
example, dopamine antagonists impair
the
ability
to see
alternative
interpretations
of
ambiguous
(i.e.,
reversible) figures (Harris
&
Phillipson,
1981;
Phillipson
&
Harris,
1984),
so one
might hastily conclude that positive
affect
would
improve this spontaneous ability. However, positive
affect
might
not
produce this result, because
the
rather tedious reversible-
figures
task could destroy
the
participant's
positive
affect
or
lead
the
participant
to
prefer
engaging
in
other
tasks
or
thought pro-
cesses available
at the
time. Accumulating evidence shows that
this would
not be
likely
if the
task were presented
as
being
important (e.g.,
Bodenhausen,
Kramer,
&
Susser, 1994),
but it
could
be a
factor
if the
task
is
tedious
or
aversive
and is not
14
In a
related study, Baker, Frith,
and
Dolan
(1997)
had
normal adults
perform
the
verbal
fluency
task under neutral, negative,
and
positive
affect
conditions while undergoing positron emission tomography scanning.
No
behavioral data were reported,
so our
main prediction
was not
tested
in
their
study. However, overall,
the
verbal
fluency
task
was
associated with
greater anterior cingulate activation than
a
control task
in
both
the
neutral
and
positive
affect
conditions.
In the
negative
affect
condition, anterior
cingulate
activation
was
attenuated during verbal
fluency. In
contrast,
anterior cingulate activation during verbal
fluency was not
greater
in the
positive
affect
condition than
in the
neutral condition. Baker
et al.
required
participants
to
produce only
one
word every
5 s, so it is
possible that this
latter
null
result
was due to a
ceiling
effect.
15
This
is not to say
that
we
predicted
no
effect
in
tasks
in
which
the
optimal rule
is not
explicit
(i.e.,
not
easily
verbalized).
According
to
COVIS,
the
striatum
is a
critical structure
in
such implicit tasks (although
the
anterior cingulate
is
not). Because there
is a
prominent dopamine
projection
from
the
substantia nigra into
the
striatum (see Figure
1),
which
is
thought
to
facilitate learning (Ashby
et
al.,
1998), there
is a
possibility
that
positive
affect
might also improve performance
in
implicit category-
learning tasks.

POSITIVE
AFFECT
543
perceived
as
being important
or
necessary. Staring
at the
same
figure
for
an
extended time might
be
considered tedious
by
many
people,
and if the
task
is not
perceived
as
being important, then
an
influence
of
positive
affect
might
not be
apparent.
Finally,
it is
important
to
note
that
some predictions might
fail
because performance
on the
task might
not
steadily improve with
increasing
dopamine
levels.
For
example, some
of the
predictions
derived
in
this article
are
based solely
on
data showing that
performance
is
impaired when brain dopamine levels
are de-
creased (either because
of
administration
of
dopamine antagonists
or
because
of
some neurological disorder).
It is not
necessarily
the
case
that such results imply that increases
in
dopamine, above
normal levels,
will
enhance performance
on
this same task.
The
relation between dopamine level
and
performance
may be an
inverted
U, so
that either increases
or
decreases
in
dopamine
from
some
optimal
level
impair
performance
(as
predicted,
e.g.,
by
Lidow
et
al.,
1998). Another possibility
is
that
even
if the
neutral
affect
control group performs well below ceiling, increasing
do-
pamine levels above this normal level
may
have
no
more
effect
on
performance.
Other Tasks Influenced
by
Positive
Affect
The
theory developed
in
this article provides
an
account
of the
influence
of
positive
affect
on
creative
problem-solving
tasks;
it
predicts
potential effects
of
positive feelings
on
many cognitive
tasks
that have
not
been investigated
in the
affect
literature;
and
equally
important,
it
specifies some types
of
tasks
in
which per-
formance
should
be
unaffected
by an
elevation
in
mood (e.g.,
visual
and
auditory perception tasks). Even
so,
positive
affect
has
been
found
to
influence many tasks that
we
have
not yet
discussed.
These
include decision-making
and
risk-preference tasks (e.g.,
Carnevale
&
Isen,
1986;
Isen
&
Means, 1983;
Isen
et
al.,
1988,
1991)
and
some tasks related
to
social situations, such
as
stereo-
typing
of
members
of
groups (Bodenhausen
et
al.,
1994)
and
reactions
to
persuasive communications (e.g., Bless, Bohner,
Schwarz,
&
Strack, 1990;
Mackie
&
Worth, 1989; Petty, Schu-
mann,
Richman,
&
Strathman, 1993; Smith
&
Shaffer,
1991).
In
addition, positive
affect
is
sometimes assumed
to
lead
to a
global
or
nonsystematic
style
of
processing,
or to
foster
the use of
"heuristics,"
in
contrast
to
effortful
or
systematic processing.
In
most cases, evidence presented
in
support
of
this latter idea came
from
studies that used certain specific kinds
of
materials
or
tasks.
More recent
findings
suggest,
in
contrast, that when
the
task
is at
least
either minimally interesting
or
important, positive
affect
promotes careful, thorough, open-minded,
and
systematic process-
ing
(e.g., Aspinwall, 1998; Bodenhausen
et
al.,
1994; Estrada
et
al.,
1997; Isen
et
al.,
1991; Mano, 1997; Martin, Ward, Achee,
&
Wyer,
1993;
see
also Isen, 1993, 1999,
for
discussions
of
this
issue).
Although
the
increased dopamine
release
that
we
postulated
to
co-occur with positive
affect
may
contribute
to
some
of
these
effects,
in
general, these phenomena seem more complex than
the
tasks considered
earlier
in
this article.
In
particular, many
of
these
tasks involve complex strategies
and
goals.
For
example,
in the
attitude-change
paradigms, many goals besides pure processing
of
the
persuasive message
may be in
operation.
In
particular,
a
desire
to
be
accommodating
or to go
along
with
the
attitude-change
attempt
may
play
a
role
in the
findings
obtained
in
those studies,
especially because positive
affect
is
known
to
promote sociability
and
helpfulness, among
its
other
effects
(see Isen, 1993,
for
further
discussion).
As
another example,
in
risk-taking paradigms, posi-
tive
affect
is
associated with greater expectation
of
positive out-
comes
(E.
Johnson
&
Tversky, 1983). However,
in the
same
context, positive
affect
is
associated with greater disutility
of
negative outcomes (Isen
et
al.,
1988). Typically,
the
result
of
these
opposing
effects
is
that people
who are
feeling
happy
are
less
likely
to
take
a
real,
meaningful
risk than
are
neutral
affect
controls
(Isen
&
Geva, 1987; Isen
&
Simmonds,
1978).
For the
present
purposes,
however,
the
important point
is
that multiple processes
and
effects
are in
operation. Therefore, although brain dopamine
levels should
be
increased
in
these studies, their
effects
may not be
apparent
in
these tasks,
or if
other
affective
states
are
induced
inadvertently
along with positive
affect
(e.g., Mano, 1997), then
dopamine
may
contribute
to
these
effects
along
with
other
neuro-
transmitters
and
neurological pathways.
As
such, although
the
dopaminergic theory
of
positive
affect
may
provide
an
alternative
way
to
conceptualize these complex situations,
and may
eventually
help
to
address
an
even broader range
of
findings,
at
present these
tasks
are
beyond
the
scope
of
this article.
Neuropsychological Implications
The
dopaminergic
theory
of
positive
affect
has a
number
of
practical implications that
may be
quite important
for
several
neuropsychological patient populations. First,
the
theory proposed
in
this article might
be
used
to
improve
the
understanding
of
some
of
the
cognitive changes that occur with natural aging. During
the
course
of
normal aging, dopamine levels
in the
human brain
decrease
by 7% or 8%
during each decade
of
life
(e.g., Gabrieli,
1995;
van
Domburg
& ten
Donkelaar,
1991).
As a
consequence,
the
dopaminergic theory
of
positive
affect
suggests that
a
natural
question
to ask is
whether cognitive flexibility
and
creative
problem-solving
ability also decrease with age.
We are not
aware
of
any
studies that specifically have examined
the
effects
of age on
performance
in
word association,
the
Remote Associates Test,
or
Duncker's
(1945) candle task. Even
so, it is
generally assumed
that
people become less
flexible and
more rigid
and set in
their ways
as
they
age,
and a
large literature exists purporting
to
show that
cognitive
flexibility
does decrease during normal aging (e.g., Col-
lins
&
Tellier, 1994; Stankov, 1988).
It is
important
to
note,
however, that
life
experience
and
experience with solving fre-
quently
encountered problems
may
often
compensate
for
losses
in
problem-solving
ability caused
by
natural aging, especially
on
common tasks. Nevertheless,
the
theory
proposed
here appears
to
be
consistent with
the
available data
on the
effects
of
aging
on
mental
flexibility and
creative problem solving.
Second,
the
theory predicts that events
and
conditions that
induce
positive
affect
elevate brain dopamine levels. Therefore,
any
pathological
condition that
is
associated with reductions
in
brain
dopamine levels might
be
relieved temporarily
by
positive
affect.
For
example,
in
Parkinson's
disease,
there
is
reduced
do-
pamine production
in the
substantia nigra and,
to a
lesser extent,
in
the
VTA.
The
most widely known
and
obvious symptom
of
Parkinson's disease
is
motor
dysfunction
(akinesia
and
bradykine-
sia),
but as
discussed throughout this article, there
are
also well-
documented cognitive deficits. Treatment with L-dopa,
a
dopamine
precursor, alleviates
the
motor problems (one cannot
be
treated

544
ASHBY,
ISBN,
AND
TURKEN
with
dopamine itself because
it
does
not
cross
the
blood-brain
barrier). However, long-term treatment with
L-dopa
is
problematic
(e.g., Strange, 1992).
An
intriguing
and
potentially very exciting
prediction
of the
theory described
in
this article
is
that positive
affect
might stimulate increased production
or
release
of
dopa-
mine, which might contribute
to
alleviating (temporarily) some
of
the
motor
and
cognitive dysfunction that characterizes Parkinson's
disease.
Of
course, this requires that
the
disease
is not so
pro-
gressed that
the
induction
of
positive
affect
is
impossible
and
that
the
amount
of
dopamine
released
during
positive
affect
is not
negligible.16
Third,
the
dopaminergic
theory
of
positive
affect
sharpens
the
available predictions
as to the
cognitive
effects
that might
be
expected
from
administering dopamine antagonists.
This
is
impor-
tant
because dopamine antagonists
are
routinely prescribed
for a
variety
of
pathological
conditions.
The
principal
known benefit
of
these drugs
is
that they reduce hallucinations
and
other symptoms
of
psychosis, which
is why
they
are
classified
as
antipsychotics
and
why
they
are
routinely prescribed
as
treatment
for
schizophre-
nia
and
senile dementia.
As
mentioned above,
a
well-known side
effect
of
antipsychotic medication
is
flattened
affect.
The
theory
proposed here suggests that pronounced cognitive deficits also
might occur.
In
particular, patients taking dopamine antagonists
might
have reduced olfactory acuity, impaired working memory,
reduced cognitive flexibility,
and
impaired creative problem-
solving
ability.
In
some cases, however, reduced cognitive flexi-
bility
actually might
be an
advantage.
A
good example occurs with
(positive)
schizophrenia, because
a
hallmark
of
this disorder
is
loose
associations,
or an
inability
to
maintain set.
In
many cases,
however,
dopamine antagonists
are
routinely prescribed
to
patients
lacking
such symptoms (e.g., patients with Alzheimer's disease).
It
is
important that physicians
are
aware
of the
cognitive
and
affec-
tive
costs
of
dopamine antagonist therapy when they
are
consid-
ering
alternative treatments.
Conclusion
In
this article,
we
discussed many studies showing that positive
affect
systematically influences performance
on a
variety
of
cog-
nitive
tasks.
In
almost
all of
these studies, participants were
as-
signed randomly
to
either
a
neutral
affect
control condition
or a
positive
affect
condition,
and
positive
affect
was
induced
by
using
mild
and
innocuous methods (e.g.,
by
giving
a
small unanticipated
gift;
by
reporting success
on an
ambiguous task;
or by
using mild,
nonsexual
and
nonaggressive humor). Control conditions
for
arousal, surprise, negative
affect,
social contact,
and a
host
of
other
variables were included
in
many
of
these studies. Thus, there
is a
substantial
literature showing that mild positive
affect,
of the
sort
that
people
can
experience every day, systematically
affects
cog-
nitive
processing.
The
dopaminergic theory
of
positive
affect
that
was
proposed
and
developed
in
this article assumes that during periods
of
mild
positive
affect,
there
is a
concomitant increased dopamine release
in
the
mesocorticolimbic
system
and
perhaps
also
in the
nigrostri-
atal
system.
The
theory
further
assumes that
the
resulting elevated
dopamine levels influence performance
on a
variety
of
cognitive
tasks (e.g., olfactory, episodic memory, working memory,
and
creative
problem solving).
It
should
be
stressed, however, that
we
did
not
assume that positive
affect
simply turns dopamine
on or
off.
Instead,
we
assumed moderate levels
of
dopamine
are
present
even under neutral
affect
conditions.
The
induction
of
mild posi-
tive
affect
is
assumed
to
increase only slightly these normal
dopamine
levels. Similarly, although this article discusses
the
effects
of
several drugs
and
pathological conditions that
affect
brain dopamine levels
and
influence cognitive processes
in
ways
compatible with
the
dopaminergic theory
of
positive
affect,
it is
important
to
note that
the
fluctuations
i n
dopamine associated with
these conditions
are
more extreme than
we
anticipated
for
positive
affect.
Therefore,
the
pathological conditions discussed
in
this
article should
not be
interpreted
as
models
for
positive
affect.
We
do not
suggest that positive
affect
is
equivalent
to any
pathological
or
drugged state.
The
data that show facilitating
effects
of
positive
affect
on
problem solving, improved social interaction,
and a
host
of
other tasks argue convincingly
on
this point.
Posing
a
neurological
mechanism
or
mediator
of
processes
like
creativity,
problem solving,
and
emotional reaction
may
seem,
at
first,
to
suggest that
the
behavioral,
or
even experiential
or
cogni-
tive,
level
of
analysis
is
unnecessary
for
understanding these
processes.
To the
contrary,
we
believe that even
if a
solid under-
standing
of the
neurological mechanisms that mediate positive
affect
were
available,
research
at the
behavioral
and
experiential
levels
is
still needed
to
fully
understand
the
form
and
function
of
positive
affect
systems.
For
example,
for a
complete theory
of
positive
affect,
it is
necessary
to
understand
why
certain things
make people happy, even
if it
were known that dopamine
is
released
when
people
are
happy,
and why
dopamine release
has the
particular consequences
it
does
on
cognition. Moreover, purposive
and
constructive
processes
in the
generation
and
influence
of
affect
still
can
play
a
role
in the
effects
observed.
In
other words,
finding
a
neurological mechanism associated with
affective
processes
does
not
rule
out the
important role that thinking
and
planning play
in
these same processes.
The
many studies reporting
effects
of
vari-
ables such
as
task importance support this conclusion.
Furthermore,
it is
sometimes assumed that
finding
a
neurolog-
ical
mechanism
for
such processes means that
the
processes
are
genetically
based
or
innate. This
is not
necessarily
the
case. Learn-
ing
is
known
to
alter brain
functioning.
Moreover, even
if
some
aspects
of
affective
functioning
turn
out to be
genetically based,
this would
not
diminish
the
importance
of
experience, learning,
and
life
events
in
determining
the
specific
effects
and
processes
associated with
affect.
The
data
from
dozens
of
studies
on the
impact
of
induced
affect
attest
to
this point.
Throughout
the
course
of
this article,
we
made many assump-
tions.
In
some cases, these assumptions were based
on a
substantial
body
of
supporting evidence,
but a
number
of
assumptions must
be
considered
speculative.
As a
consequence,
at
least
some
details
of
the
theory proposed here
are
surely wrong. Nevertheless,
we
believe that
the
dopaminergic theory
of
positive
affect
makes
a
substantial
contribution. First,
it
provides
the
first
description
of
the
neuropsychological mechanisms that underlie
the
influence
of
positive
affect
on
cognition. Second,
it
provides bridges between
a
16
Another group that might
benefit
temporarily
from
positive
affect
is
substance
abusers, especially long-term users
of
heroin
or
cocaine. This
prediction
follows because prolonged exposure
to
these drugs
is
thought
t o
cause downregulation
of
dopamine receptors (e.g., Feldman
et
al.,
1997)
and
cognitive
inflexibility
(e.g., Beck, Wright, Newman,
&
Liese,
1993).

POSITIVE
AFFECT
545
number
of
huge
and
disparate
literatures,
including
the
social
psychological literature
on
positive
affect,
the
cognitive literature
on
creative problem solving,
the
emotions literature,
the
neuro-
science literature
on
reward,
and the
literature
on a
variety
of
neuropsychological patient groups.
Third,
the
theory presented
here predicts influences
of
positive
affect
on
many tasks that
previously have
not
been
investigated
in the
positive
affect
liter-
ature.
Fourth,
the
theory encourages several lines
of new
research,
which
we
believe
can
further
increase understanding
of
positive
affect
and its
influence
on
cognition. This last contribution
is the
most important that
the
theory
can
make,
and we
hope
it
will serve
this
function.
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