A microelectrode study of amygdaloid afferents: temporal neocortical inputs

Acute experiments were performed on anesthetized cats using standard techniques of electrical stimulation and single unit recording in order to study the responses of amygdaloid neurons to neocortical inputs. Satisfactory records were obtained from 272 amygdaloid neurons. The majority of those fired spontaneously, at low rates, with single, randomly occurring spikes. The lateral neocortex, particularly the portion which is homologous to temporo-insular cortex in man, is capable of influencing the discharges of many amygdaloid neurons. The typical response pattern consisted of an excitatory-inhibitory sequence with the median onset latency of 12.0 msec, which is consistent with monosynaptic excitation of the output-type nerve cells in the affected regions of the amygdala (Al, Ac, Ab). There was an absence of clear topographical arrangement: all of the effective neocortical areas influenced the neuronal discharges in Al, Ac and Ab fairly equally. These results correlate well with neuroanatomical studies of amygdaloid structure and connectivity. Our finding of diffuse non-topographic excitatory influence upon the lateral, central and basal amygdaloid nuclei exerted by insular-temporal regions known to be involved with higher order sensory analysis and pattern recognition is quite consistent with a view of this system serving as a link between neocortical information stores and the fundamental motivational drive mechanisms of the hypothalamus.