Biological Psychology 67 (2004) 219–233
What does the prefrontal cortex “do” in affect:
perspectives on frontal EEG asymmetry research
Richard J. Davidson∗
Laboratory for Affective Neuroscience, W.M. Keck Laboratory for Functional Neuroimaging and Behavior,
University of Wisconsin-Madison, 1202 West Johnson Street, Madison, WI 53706, USA
This commentary provides reflections on the current state of affairs in research on EEG frontal
on this topic 25 years ago, research on frontal EEG asymmetries associated with affect has largely
evolved in the absence of any serious connection with neuroscience research on the structure and
function of the primate prefrontal cortex (PFC). Such integration is important as this work progresses
since the neuroscience literature can help to understand what the prefrontal cortex is “doing” in
affective processing. Data from the neuroscience literature on the heterogeneity of different sectors
of the PFC are introduced and more specific hypotheses are offered about what different sectors of
the PFC might be doing in affect. A number of methodological issues associated with EEG measures
of functional prefrontal asymmetries are also considered.
© 2004 Elsevier B.V. All rights reserved.
Keywords: Frontal EEG asymmetry; Emotion; Prefrontal cortex; Neuroimaging
It is very gratifying for me personally to be writing this commentary since the publi-
cation of this Special Issue marks the fact that there now exists a substantial corpus of
scientific literature investigating methodological and conceptual issues surrounding the use
of measures of asymmetric prefrontal electrical signals recorded from the scalp surface
to make inferences about emotional processes. With my colleagues and students at the
time, I first reported 25 years ago on the use of asymmetries in scalp-recorded frontal brain
∗Tel.: +1-608-262-8972; fax: +1-608-265-2875.
E-mail address: email@example.com (R.J. Davidson).
0301-0511/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
R.J. Davidson/Biological Psychology 67 (2004) 219–233
electrical activity to make inferences about emotional processes (Davidson et al., 1979).
At the time, it was a lonely field though there were investigators from other domains of
neuroscience who underscored the important role played by the prefrontal cortex in dif-
ferent aspects of emotional processes (e.g., Nauta, 1971). This Special Issue has brought
together the best of current research using these non-invasive measures to investigate dif-
ferent aspects of the methodology and construct validity of these measures. When I be-
gan to work in this area, research on the central nervous system substrates of emotional
processes was largely restricted to studies in non-human species that focused on the role
of subcortical structures in emotional and motivational processes, leading to a view, still
championed by some (e.g., Panksepp, 2003; but see Davidson, 2003a for a rebuttal), that
the fundamental circuitry for emotion and motivation lies in subcortical zones and that
cortical tissue has little if anything directly to do with emotion. The only exceptions to this
view at the time came from observations of patients with localized cortical brain damage
(e.g., Gainotti, 1972) and from early studies on the role of prefrontal lesions on the socioe-
motional behavior of monkeys (e.g., Myers, 1972). The research featured in this Special
Issue is part of a larger body of work (see e.g., Rolls, 1999 for a modern example) that
forcefully underscores the importance of prefrontal cortex for emotional and motivational
However, the work represented in this Special Issue has, for the most part, evolved with
little connection to the core neuroscience research on the structure and function of the
prefrontal cortex. I will argue that this state of affairs must change if this work is to become
an accepted part of the influential body of neuroscientific research on the prefrontal cortex.
Just what specific role the primate prefrontal cortex (PFC) might be playing in emotion still
substantive portions of this commentary will be divided into two parts. The first part will
address some of the fundamental conceptual issues that lie at the core of this work, most of
which were not addressed in the articles in this Special Issue. I will focus on what the PFC
is “doing” in emotion and will draw on other neuroscience literature on PFC from which
insights about its role in emotion might be gleaned. In this section, I will also emphasize
the fact that the PFC is heterogeneous, both anatomically and functionally and any serious
discussion of PFC function must make distinctions among the sub-territories of the PFC.
Also to be emphasized is the fact that the PFC is part of a larger overall circuit and that
other components of the circuitry are crucial for understanding how the brain implements
emotional and motivation processes. It cannot be solely through the prefrontal cortex that
the brain implements emotional and motivational processes. One unwitting consequence
of the work my laboratory began on prefrontal asymmetries and affect is the view that the
and/or motivational processes in question. It is essential that we remind ourselves that the
prefrontal cortex is part of a larger and more complex circuit and that other components
of this circuitry will undoubtedly be important for many of psychological phenomena of
with which we are dealing. It has been easy for those who study EEG frontal asymmetry
to ignore other components of the circuitry because the measure in question here does not
reflect many of the other features of the circuit. In particular, scalp-recorded brain electrical
signals reflect activity primarily from cortex and without more complex source localization
R.J. Davidson/Biological Psychology 67 (2004) 219–233
methods which have not been used in any of the articles in this Special Issue, one cannot
make inferences about subcortical signals.
2. Conceptual issues that underlie research on EEG asymmetries associated
2.1. Heterogeneity of prefrontal cortex
within the prefrontal cortex (e.g., Rolls, 1999). For the purposes of the present discussion,
it is important to simply call attention to this fact and to indicate that the majority of the
neuroscience literature indicates that the prefrontal sector most directly associated with
emotion is the sector that is least likely to be reflected in scalp-recorded brain electrical
signals—namely, orbital frontal cortex (e.g., Hornak et al., 2003). Both the lateral orbital
sectors and the ventromedial sectors have been directly implicated in various aspects of
emotion, with the orbital sectors in particular thought to play an important role in the as-
signment of affective value to stimuli (e.g., Rolls et al., 2003). It is true that there are major
interconnections among the different sectors of the PFC and that the dorsolateral sector
receives input from the orbital sector (Rolls, 1999). However, according to most investi-
gators, the dorsolateral sector of the PFC is primarily associated with various cognitive
processes, particularly with cognitive control (see Miller and Cohen, 2001 for review). It
is the dorsolateral sector which is likely most directly reflected in the scalp signals from
which metrics of functional prefrontal asymmetry are constructed.
Recent neurophysiological data from awake behaving rhesus macaques in whom single
cell recordings were simultaneously acquired from multiple neurons in both dorsolateral
and orbitofrontal sectors of PFC (Wallis and Miller, 2003) provide a new understanding of
what these different regions of PFC may be doing and how they interact. These investiga-
tors recorded single cell activity as well as behavior during a reward preference task. The
monkeys had to choose between pictures associated with different amounts of juice reward.
Neuronal activity in both regions of PFC reflected the reward amount. However, neurons
in the dorsolateral sector encoded both the reward amount and the monkey’s forthcoming
response while neurons in the orbital sector primarily encoded the reward amount alone.
The authors propose that their data are consistent with a model where reward information
enters the PFC via the orbital sector where it is then passed on to the dorsolateral sector and
used to guide behavior. Unfortunately since neurophysiological studies of this kind are so
difficult to perform and since there were only two animals tested, it was not possible for the
draw from this work is that tasks that include a response component will be more likely to
show affect-related PFC activation asymmetry in the dorsolateral regions and it is activity
Recent studies have also identified a ventrolateral region of prefrontal cortex that shows
robust asymmetries during response inhibition tasks. In response to cues that signal the
requirement to inhibit a dominant response, activation of right inferior and middle frontal
gyrus has been found (e.g., Garavan et al., 1999; Konishi et al., 1999). Moreover, patients
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