Abstracts

RATIONALE: In humans, startle eyeblinks are larger during negative emotional states such as fear and anxiety. This effect presumably reflects the amygdala's dual role in detecting danger and in modulating the subcortical startle circuitry. In a previous study, we reported that right, but not left, temporal resections involving the amygdala disrupted aversion-enhanced startle during picture viewing tasks. We now wished to learn whether this startle disruption was modality specific or whether a similar defect would occur when verbal -contextual stimuli were used to induce a motivational state. METHODS: Controls and patients with unilateral anterior temporal lobectomy (ATL)listened, via headphone, to standard sets of emotional sentences (fear, sad, happy, neutral) spoken in a neutral tone of voice. Emotion was conveyed solely by semantic content (e.g., As you swim, the sharks begin to circle you slowly). During the 5 sec period after each sentence, a binaural white noise burst (95db)was randomly presented to elicit startle eyeblinks, measured by sensors over the orbicularis oculi muscle. Sentence ratings of valence and arousal were obtained from each S. The two ATL groups (12 Right, 10 Left) were matched for age, seizure onset and duration. All were left language dominant and had nonlesional temporal lobe epilepsy prior to surgery. RESULTS: Controls and the Left ATL group had significantly greater startle reactivity when listening to sentences that conveyed fear vs the other emotions (Fear > Happy = Sad = Neutral). In contrast, the Right ATL group did not show aversion enhanced startle. This defect was not due to failure to understand the emotional meaning of the sentences, as verbal ratings of emotion were identical across groups. CONCLUSIONS: Right, but not left, temporal resections disrupted aversion-enhanced startle, even when verbal-contextual stimuli were used to induce an emotional state. We propose that the right temporal region plays a unique role in translating the results of cognitive appraisal of sensory emotional stimuli (visual or auditory) into somato-motor changes that are associated with an aversive motivational state.