Kent C. Berridge and Terry E. Robinson
Department of Psychology (Biopsychology Program), University of Michigan, Ann Arbor, MI 48109-1109 USA
Advances in neurobiology permit neuroscientists to
manipulate specific brain molecules, neurons and sys-
tems. This has lead to major advances in the neuro-
science of reward. Here, it is argued that further
advances will require equal sophistication in parsing
reward into its specific psychological components:
(1) learning (including explicit and implicit knowledge
produced by associative conditioning and cognitive
processes); (2) affect or emotion (implicit ‘liking’ and
conscious pleasure) and (3) motivation (implicit incen-
tive salience ‘wanting’ and cognitive incentive goals).
The challenge is to identify how different brain circuits
mediate different psychological components of reward,
and how these components interact.
Studies of the neurobiology of reward are important to
advance affective neuroscience, and they provide insights
into a variety of psychopathologies, including drug addic-
tion, eating disorders, obsession and depression. Progress
has been helped by the ability of neuroscientists to mani-
pulate an ever-expanding number of brain components.
Future studies will be most useful for elucidating the roles
of brain components if they can similarly parse behavioral
reward into its actual psychological components.
For example, imagine a new inducible knockout mouse
that shows abnormally slow (or fast) acquisition of cocaine
self-administration behavior. The gene manipulation appa-
rently alters cocaine reward – but which part of reward?
Reward contains multiple
(Fig. 1). The mutation might have changed any of them,
and their implications for function are very different. To
say simply that a brain manipulation alters reward,
without specification, is akin to saying it alters a
‘neurotransmitter receptor’ – without specifying which
be more precise.
What are the psychological components of reward?
First, it is necessary to learn about relationships among
stimuli and about the consequences of actions. Second,
reward consumption can produce hedonic consequences.
Third, the individual has to be motivated to learn and act.
Further, each of these three explanatory classes contains
multiple component psychological processes, any of which
could be affected by a neurobiological manipulation.
Neuroscientists will find it useful to distinguish these
psychological components of reward because understand-
ing the role of brain molecules, neurons and circuits
requiresunderstandingwhatbrainsreallydo – whichisto
mediate specific behavioral and psychological functions.
The following summarizes some important psychological
components of reward, many of which have been revealed
by neurobiological manipulations.
Multiple forms of learning are mediated by different brain
systems, and a change in any one of them might change
rewarded responses [1–7]. Learned responses require
knowledge – of some type – about the relationships
between stimuli and actions. Knowledge is required for
reward prediction, for making anticipatory responses, for
guidance by cues, and for goal-directed action. Learning
processes can be either associative or cognitive. The
products of learning can be declarative (conscious mem-
ories) or procedural (habits). And the elements of learning
can involve just stimuli [stimulus–stimulus (S–S) associ-
ations and predictive reward expectation] or involve
responses too [stimulus–response (S–R) associations
and act–outcome representations].
Associative learning usually refers to either Pavlovian
conditioning (S–S and S–R associations) or instrumental
conditioning (response–contingent reinforcement). In
Pavlovian conditioning, which is a procedural form of
reward prediction, conditioned stimuli (CSs) elicit con-
ditioned responses (CRs). The CRs can be anticipatory
responses, behavioral habits or even conditioned motiv-
ations and emotions appropriate to the unconditioned
reward stimulus (UCS). In instrumental conditioning,
specific instrumental responses are strengthened by
response–contingent reinforcement. Neural substrates
for Pavlovian and instrumental associations are distrib-
uted relatively widely across both subcortical and cortical
brain structures [4,8–10].
Cognitive forms of knowing are more elaborate [11,12].
They encode multiple relationships among stimuli and
actions, including declarative representations oftemporal,
spatial, predictive and causal relationships that guide
goal-directed plans of action. Brain mechanisms of cogni-
tive reward representation are more heavily cortical and
include orbitofrontal, insular and other regions of cortex,
plus particular subcortical structures that interact with
cortical regions [2,11,13,14].
Thus, neural manipulations could influence rewarded
behavior because they alter any one of many forms of
precisely which form is altered.
Reward: more than learning
Alternatively, neural manipulations can alter an affec-
tive (emotional) or motivational process. Components of
Corresponding authors: Kent C. Berridge (email@example.com),
Terry E. Robinson (firstname.lastname@example.org).
TRENDS in NeurosciencesVol.26 No.9 September 2003
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