Amygdaloid unit activity during classical conditioning of the nictitating membrane response in rabbit

Single and multiple unit activity was recorded from the amygdaloid nuclei in awake unanesthestized rabbits during classical conditioning of the nictitating membrane (NM) response. Over half o the unit recordings from the amygdaloid complex demonstrated changes in firing rate following the presentation of the tone conditioned stimulus (CS) or corneal air-puff unconditioned stimulus (US). Of the unit records that were responsive to the training stimuli, 58% showed responses to the CS and 73% showed responses to the US. Amygdaloid responses to either the CS or the US tended to be a long latency (greater than 70 msec), long duration (greater than 250 msec), modest increase (less than 2 fold) in unit firing. There were no statistically significant differences between the spontaneous firing rates, response latencies, response magnitudes, or response type distributions seen during unpaired (control) and paired stimulus presentations. However, four of 18 single and multiple unit groups that were tested during both unpaired and paired training developed new or enhanced responses following the onset of paired training. All four of these records were from the basolateral or lateral amygdaloid nuclei. Although these few records did develop response alterations after CS-US pairing, the majority of the records indicated that essentially the same amygdaloid response patterns occur during unpaired training as during paired training. it is therefore unlikely that the critical neuronal changes that underlying NM conditioning occur within the amygdaloid complex. Other possible roles for the amygdaloid complex during conditioning are considered.