Startle reflex and emotion modulation impairment after a right amygdala lesion

In the present study, startle responses during resting states as well as during the presentation of a set of emotive slides were recorded from a 32-year-old male patient with a rare localized lesion of the right amygdala. The startle reflex is a response modulated by affective states: it has been reliably used in the literature to measure the aversiveness of emotive stimuli. The animal literature has shown that the circuit of this reflex is directly influenced by amygdala projections. The startle responses of the patient were compared with those of eight age-matched normal subjects. The patient's startle amplitudes showed an overall impaired response and an inhibited reflex contralateral to the lesion. In addition, he failed to show the typical startle potentiation induced by an aversive emotive background. The data confirm, in the human, previous results from the literature in other species on amygdala involvement in startle and emotional responses. Furthermore, the observation of the importance of the right amygdala in the modulation of emotion is consistent with the hypothesis of right hemisphere specialization for aversive emotions. The results are discussed in the context of the literature on human amygdala lesions.