Gender differences in regional cerebral activity during the perception of emotion: A functional MRI study
Introduction
While many of the differences between men and women in processing emotions may be attributable to social factors and learned patterns of behavior, it is likely that emotional differences also reflect genotypic differences in the sexual dimorphism of the nervous system. Correspondingly, in most functional imaging studies investigating emotional memory encoding and involving only male subjects, the amygdala effect was either exclusively (Cahill et al., 1996) or predominantly (Hamann et al., 1999) lateralized to the right, while in studies involving only female subjects, the amygdala effect was predominantly (Canli et al., 1999) or exclusively (Canli et al., 2000) on the left. In contrast, Wrase et al. (2003) used functional magnetic resonance imaging (fMRI) to investigate the neural correlates of emotional experience, and they observed no left but right amygdala activation in women confronted with affectively negative visual stimuli, with men also showing a trend to activate the right amygdala. On the other hand, during the presentation of positive stimuli, bilateral amygdala activation was only observed in men.
George et al. (1996) investigated gender-related cerebral activation patterns during transient self-induced sadness or happiness with Positron Emission Tomography (PET). Depending on the induced emotion, women showed significantly increased blood flow compared to men: these differences were located in left mid and inferior frontal regions, the right brainstem and globus pallidus/putamen when a neutral reference condition was subtracted from the sad condition, and in the left inferior frontal and precentral gyri and right cerebellum when a neutral reference condition was subtracted from the happy condition.
A standardized method to evoke and assess emotions with respect to arousal and valence is the International Affective Picture System (IAPS; Lang et al., 1988). Although this paradigm is frequently used in clinical studies, so far only a few brain imaging studies have used the IAPS to elicit emotions and to assess gender differences (e.g., Canli et al., 2002, Klein et al., 2003). We set out to assess brain activation in healthy men and women with fMRI during the presentation of aversive (negative) versus affectively positive visual stimuli taken from the IAPS, because knowledge about sex-related characteristics in the processing of emotional stimuli is essential to understand the mechanisms underlying the gender-related vulnerability of the prevalence and severity of certain neuropsychiatric disorders such as mood disorders (Risch et al., 1981).
Based on previous findings, we hypothesized that the perception of positive emotions would lead to an activation of the prefrontal cortex in both sexes, which would be greater in the left than in the right hemisphere, while the perception of negative emotions would lead to the opposite activation pattern. Furthermore, we hypothesized that the perception of negative emotions would be associated with an enhanced activity of the right amygdala in males and with an enhanced activity of the left amygdala in females, and, lastly, that the perception of emotions would lead to a greater activation of the basal ganglia in females.
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Subjects
The subjects were 19 male and 19 female right-handed healthy volunteers (20–48 years old) of comparable ages (mean [SD]: men = 34.1 [8.4], women = 31.8 [8.9]; P = 0.43) and education (mean [SD]: men = 14.5 [2.4], women = 13.6 [2.8]; P = 0.27). A brief medical screening interview was used to exclude subjects with any physical or neurological illness or any condition or medication affecting neural or cerebrovascular function. In this context, for both genders, urine drug screens were performed to
Subjective ratings
Mean scores and standard deviations for the PANAS subscales are presented in Table 1. During positive mood induction, men showed a trend to a reduction of the negative score of the PANAS, while the positive score remained unchanged. On the contrary, in women, there was a trend to higher scores of positive affect and a statistically significant reduction of negative affect. During negative mood induction, negative affect increased in both sexes (women > men), while positive affect remained
Discussion
The goal of the present study was to examine the neural bases, as measured by rapid event-related functional MRI, of putative sex differences in the perception of both positive and negative affect. Cerebral activity was directly compared in men and women in identical conditions, and clear sex differences were observed. However, when interpreting our data, one has to consider that neither personality traits nor smoking behavior, which are known factors influencing brain activation and differing
Acknowledgments
This study was supported by a Grant from the Austrian Science Fund (FWF), Grant Number P17225-B05.
The authors thank Dr. Georg Kemmler for his valuable statistical advice.
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