In the past several years, a few functional imaging techniques focusing on the central nervous system have been utilized to study the neurophysiology of sexual arousal (8
). Stoleru (8
) and Redoute (16
) have used PET to investigate changes in regional cerebral blood flow (rCBF) in male subjects presented with visual sexual stimuli. They reported that the right orbitofrontal cortex activation was correlated with both the cognitive and motivational components of their proposed model. They also suggested that the rostral portion of the anterior cingulate cortex (Brodmann area: BA 24) and the posterior portion of the hypothalamus activations were correlated with the autonomic component of sexual arousal, whereas activations in superior and middle frontal gyrus (BA 9) and anterior cingulate gyrus (BA 32) were related to the level of perceived emotion. Park (12
) and Karama (11
) have recently used the BOLD fMRI technique to evaluate the cerebral center associated with the sexual arousal response in both males and females during viewing of erotic films. The significant activation patterns of the brain in male and female volunteers were similar to those of the PET studies (8
) mentioned before. However, there is no clinical report using fMRI in evaluating the functional neuroanatomy associated with sexual arousal for the depressed patients with sexual dysfunction. In this study, we have shown significant differences of brain activation between depressed patients and healthy volunteers during visually evoked sexual arousal. During sexual stimulation, the depressed patients experienced one half less sexual arousal than did healthy volunteers: the mean scores of sexual arousal on the 10-point scale were 7.8±1.6 and 3.7±1.1 in healthy volunteer and depressive subjects, respectively. The finding is consistent with the previous reports (1
). Also, the level of activation was significantly less in depressed subjects than in healthy volunteers in the cortical areas: hypothalamus, thalamus, caudate nucleus, and inferior & superior temporal gyri. These areas are involved in the regulation of sexual behavior both in animals and humans. However, the depressed patients had greater activation in comparison with the healthy volunteer in the middle and superior frontal regions.
In animals, the hypothalamus has, perhaps, the most frequently claimed pivotal role in the regulation of sexual behavior and physiological arousal (17
). In this study, activation of the hypothalamus in response to visually presented erotic stimuli is in agreement with other well-known findings (17
), and this is also consistent with the result of a recent PET study (14
) that demonstrated a correlation between activation in the hypothalamus and objective measures of penile tumescence. More specifically, the greater hypothalamic activation found in healthy volunteers could be viewed as suggesting that healthy volunteers were physiologically more aroused than were depressed subjects in response to the erotic video film.
The thalamus represents a hub that is capable of communicating with many important cortical areas for the integration of somatic and visceral function. The extensive thalamocortical interconnectivity has been theorized to constitute a neuronal basis for conscious awareness (21
). In light of such a view, the greater sexual arousal experienced by healthy volunteers might be related to the fact that depressed subjects had significantly less thalamic activation. If this hypothesis were accurate, then the thalamus would be implicated in the cognitive dimension of sexual arousal.
Activation of the caudate nucleus is correlated with the urge to perform handwashing rituals in patients suffering from obsessive-compulsive disorder (22
). McGuire (22
) noted that during viewing of an erotic film, subjects were simultaneously confronted with the urge to act and with the impossibility to do so, hence suggesting a role for the ventral striatum in the control of the motor expression of sexual arousal, that is, in withholding the motor output of sexual arousal. Such a role could be implemented through the anatomic projections that the striatum receives from the cognitive subdivision of the anterior cingulate cortex (23
Activation of the occipitotemporal area is in accord with the results of recent functional neuroimaging studies showing that, when compared to neutral visual stimuli, emotionally laden visual stimuli elicit increased activation in this cortical region (24
). Assuming that viewing emotionally laden stimuli automatically elicits increased attentional tapping, the occipitotemporal activation noted in this study would be consistent with the hypothesis that attention to visual stimuli can modulate neural activity in the extrastriate visual cortex (27
). On the contrary, activation during the neutral condition showed a similar pattern between two groups. Especially, the temporal and occipital lobes were highly activated. The visual association cortices are involved in the perception of visual stimulation. Various areas of the cerebral cortex are functionally related to the thalamic nuclei. The occipital and temporal lobes have extensive connections with the pulvinar nucleus of the thalamus and are involved in the processing of visual and auditory information (33
In the region of middle and superior frontal gyri, the level of activation during the sexual arousal condition was significantly greater for depressed subjects than for the healthy volunteers. It is interesting to note that these areas are well-known cerebral cortices associated with major depressive disorders. The medial prefrontal cortex has previously been shown to be activated during the recall of happy, sad or disgusting moments in one's life or when viewing stimuli known to elicit these three emotional states (25
). These findings led Lane et al. (25
) to suggest that this region participates in aspects of emotional processing that is independent of valence, type or method of induction. Although the exact function of this cortical area remains to be elucidated, there is some evidence that the medial prefrontal cortex is involved in the conscious experience of emotion (34
). Here, we must concur with Redoute et al. (16
), that the activation seen in the medial prefrontal cortical region may be related to the level of perceived emotion and not to the sexual quality of emotion.
In this study, we have identified by using FMRI, for the first time, the functional neuroanatomy of the brain associated with sexual dysfunction in depressed patients. From this neuroanatomical and neurobiological perspective, we can presume that sexual dysfunction may be closely related to the pathogenesis of depressive symptoms; in addition the sexual dysfunction may have an important role in the neurobiology of major depressive disorders. However, additional correlative studies that would include depressed patients without sexual dysfunction and aftertreatment response are needed to clarify our findings of the functional neuroanatomy on sexual dysfunction in depressed patients. Also, objective measures of sexual arousal such as index of penile tumescence and a larger sample of subjects are needed to gain more informative results as well.