Aversive learning in patients with unilateral lesions of the amygdala and hippocampus

The present study applied a visual half field paradigm with emotional facia l expressions in patients with selective unilateral amygdalo-hippocampectom y (AHE) to elucidate the contributions of the left and right medial tempora l lobe and amygdala to emotional learning. Electrodermal indicators of aver sive learning were studied in 14 left AHE and 12 right AHE patients, as wel l as 13 controls matched in sex and age. In a differential conditioning par adigm with negative (CS+) and positive (CS-) facial expressions, CS+ were a ssociated with an aversive vocalization (US, 95 dB, 3 s). During extinction , stimuli were presented laterally and preattentively using backward maskin g. Appropriate CS durations yielding preattentive presentation were individ ually determined prior to conditioning. In contrast to controls, both left and right AHE patients failed to show an autonomic conditioning effect foll owing left visual field presentations of masked negative CS+ during extinct ion. AHE patients also showed no clear differential acquisition. Moreover, right AHE patients poorly recognised that negative valence was an affiliati ng dimension of the CS-US compound. (C) 2001 Elsevier Science B.V. All righ ts reserved.