Cerebral Asymmetry
Although EEG data can be used to assess activity level in many different re-
gions of the brain, research on alpha wave levels in the anterior (front) regions
of the cerebral hemisphere has proven particularly useful in understanding in-
dividual differences in emotion. This region has considerable connections with
the parts of the brain that regulate emotions. More important, researchers
find the anterior region of a person’ s right cerebral hemisphere often shows a
different activity level than the anterior region of that same person’ s left cere-
bral hemisphere. Researchers refer to this difference in right and left hemi-sphere activity as cerebral asymmetry .
Investigators find that different patt erns of cerebral asymmetry are associ-
ated with differences in emotional experi ence. Originally researchers noticed
that higher activation in the left hemisphere was associated with positive moods,
whereas higher activation in the right hemisphere was indicative of negativemoods (Wheeler, Davidson, & Tomarken, 1993). In one study, researchers
showed emotion-arousing films to participants while taking EEG measures of
right and left hemisphere activity (Davidson, Ekman, Saron, Senulis, & Friesen,
1990). When participants experienced happiness, as determined by their facial
expressions, the activity in their left cerebral hemisphere increased. When partici-
pants experienced disgust, there was more activity in the right hemisphere.
Researchers measure brain activity levels with an instrument known as an EEG. This
information may tell us about the person ’s tendency to experience different emotions.244 CHAPTER 9 The Biological Approach