Lateral amygdala unit activity: I. Relationship between spontaneous and evoked activity

Abstract

Unit activity was recorded from the lateral amygdala in cats locally anesthetized and paralyzed with Flaxedil. The units were recorded from between 0.5 to 8 h and both the spontaneous and evoked discharges characterized in detail. The EEG, hippocampal activity and arterial blood pressure were also recorded. Spontaneous activity. (1) A high percentage of low firing rate units was found. (2) Low rate units were particularly frequent in the central core of the nucleus. (3) Four types of pattern of discharge were described. Evoked activity. (1) Somatic stimuli were more effective in evoking a response than auditory or visual stimuli. (2) Inhibitory type responses were more frequent than excitatory or complex ones ( i.e., excitation followed by inhibition or vice versa). (3) The responses evoked by the different stimuli were of the same type, but other parameters (latency, duration, magnitude) differed. Relationship between spontaneous and evoked activity. (1) The spontaneous rate of responsive units was higher than that of non-responsive ones. (2) The spontaneous rate of inhibited units was lower than that of excited ones. (3) The spontaneous rate was inversely proportional to the response duration. During long term recording, the type of response was not changed even though the firing rate may have been modified in relation to sleep-waking changes. In contrast, the relationship between firing rate and response duration was maintained.