Neuronal connection between the posterior insular cortex and the amygdara in rats : an elelctrophysiological study

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In this project we examined the neuronal connections in the posterior insular cortex. We recorded the extracellular neural responses from the posterior insular cortex following electrical stimulation of the amygdala or the thalamic reticular nucleus, using a tungsten electrode. Sixteen neurons were identified to respond to electrical stimulation of the amygdala. Of the 16 stimulation sites in the amygdala, 9 were found in the basolateral nucleus, 4 in the basomedial nucleus, 2 in the central nucleus, and 1 in the lateral nucleus. Electrical stimulation of the amygdala evoked synaptic potentials and/or action potentials in the posterior insular cortex neurons with a mean latency of 15.3 ms (n = 16, range, 2.9-88.5). Most of the neurons recorded in the present study were also responsive to electrical stimulation of the superior laryngeal nerve (SLN). Interactions between amygdala and SLN inputs were observed. Following electrical stimulation of the various brain sites including the thalamic reticular nucleus, 43 cases in the posterior insular cortex responded with action potential and/or compound action potential. Of the 43 stimulation sites, 16 were found in the internal capsule, 13 in the thalamic reticular nucleus, 4 in the amygdaloid complex, 4 in the caudate putamen, 3 in the ipsilateral posterior-most portion of the insular cortex, 2 in the mediodorsal thalamic nucleus, and 1 in the ventral posterolateral thalamic nucleus. The average latency was 5.8 ms (n = 43), ranging from 0.8 to 42.3 ms. In the present study, 15 cases were examined the types of connection ; 7 showed an antidromic response, mainly from the internal capsule (6/7) and 8 showed an orthodromic response, mainly from the thalamic reticular nucleus (5/8). These data suggest that connection between insular cortex and the thalamic reticular nucleus (and the amygdara) may have an important role in information processing in the posterior insular cortex.