Emotional cognition without awareness after unilateral temporal lobectomy in humans

To investigate the function of the amygdala in human emotional cognition, w e investigated the electrodermal activity (EDA) in response to masked (unse en) visual stimuli. Six epileptic subjects were investigated after unilater al temporal lobectomy. Emotionally valenced photographic slides (10 negativ e, 10 neutral) from the International Affective Picture System were present ed to their unilateral visual fields under either subliminal or supralimina l conditions. An interaction between hemispheres and emotional valences was found only under the subliminal conditions; greater EDA responses to negat ive stimuli compared with neutral ones were observed when stimuli were pres ented to the intact hemispheres. The findings suggest that nonconscious emo tional processing is reflected in EDA in a different manner from conscious emotional processing. Medial temporal structures, including the amygdala, t hus appear to play a critical role in the neural substrates for this automa tic processing.