Lateral amygdala unit activity: II. Habituating and non-habituating neurons.

Abstract Unit activity was recorded from the lateral amygdala in immobilized cats. The units were recorded for prolonged periods during which habituation procedures were applied (somatic, auditory and visual stimuli were used); the inter-trial interval was randomized with a mean of 13 sec ∓ 7 sec; the ECoG and the arterial blood pressure were also recorded. 1. 1. The changes induced by the procedure were consistently similar for a large number of units: either the response parameters, particularly the duration, decreased progressively (habituating (H) units) or were unchanged (non-habituating (NH) units). 2. 2. The relationship between spontaneous and evoked activity described in the preceding paper (Ben-Ari et al. 1974) enables differentiation of H from NH units: H units most frequently have inhibitory responses, an initial long duration response (> 300 msec) and a low spontaneous frequency ( 6 spikes/sec). Moreover, the spontaneous frequency which is initially low in H units progressively increases (in parallel with the decrease of the response duration) whereas it is stable for NH units. 3. 3. The differences between somatic and auditory response decrements are examined in terms of dishabituation and transfer of habituation phenomena. 4. 4. The time course of neuronal habituation is different from that of any EEG changes which occur; the former is not a direct consequence of the latter. 5. 5. In relation to the results of similar studies some of the characteristics of habituation which are usually considered to be of importance are discussed.

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