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Background The neural correlates of anxiety associated with obsessive-compulsive symptomlike provocation in normal volunteers are unknown. Methods Ten healthy volunteers participated in four functional magnetic resonance experiments. Subjects were scanned while viewing alternating blocks of emotional (normally aversive, washing-relevant, checking-relevant, or hoarding-relevant pictures) and neutral pictures, and imagining scenarios related to the content of each picture type. Nonparametric brain mapping analyses were used. Results In response to the provocative pictures in all experiments, increases in subjective anxiety and activation in bilateral ventral prefrontal, limbic, dorsal prefrontal, and visual regions were demonstrated. Anxiety related to different symptom dimensions was associated with different patterns of activation: provocation of washing-relevant anxiety predominantly activated dorsal and ventral prefrontal regions; checking-relevant anxiety predominantly activated dorsal prefrontal regions; and hoarding-relevant anxiety predominantly activated ventral prefrontal regions and the left amygdala. Conclusions Our findings support a dimensional model of obsessive-compulsive disorder (OCD) whereby 1) the brain systems implicated in the mediation of anxiety in response to symptom-related material in normal subjects are similar to those identified in OCD patients during symptom provocation, and 2) anxiety associated with different symptom dimensions is associated with differential patterns of activation of these neural systems. Further investigation of the neural basis of OCD symptom dimensions is required.

Background The amygdala, hippocampus, ventral, and dorsal prefrontal cortices have been demonstrated to be involved in the response to fearful facial expressions. Little is known, however, about the effect of task instructions upon the intensity of responses within these regions to fear-inducing stimuli. Methods Using functional magnetic resonance imaging, we examined neural responses to alternating, 30-sec blocks of fearful and neutral expressions in nine right-handed male volunteers during three different 5-min conditions: 1) passive viewing; 2) performance of a gender-decision task, with no explicit judgment of facial emotion; 3) performance of an emotionality judgment task — an explicitly emotional task. Results There was a significant effect of task upon activation within the left hippocampus and the left inferior occipital gyrus, and upon the magnitude of response within the left hippocampus, with maximal activation in these regions occurring during passive viewing, and minimal during performance of the explicit task. Performance of the gender-decision and explicit tasks, but not passive viewing, was also associated with activation within ventral frontal cortex. Conclusions Neural responses to fearful facial expressions are modulated by task instructions.