Reciprocal changes in the firing probability of lateral and central medialamygdala neurons

The amygdala is essential for classical fear conditioning. According to the current model of auditory fear conditioning, the lateral nucleus is the in put station of the amygdala for conditioned auditory stimuli, whereas the c entral nucleus is the output station for conditioned fear responses. Yet, t he lateral nucleus does not project to the central medial nucleus, where mo st brainstem projections of the amygdala originate. The available evidence suggests that the basal nuclei could transmit information from the lateral to the central medial nucleus. However, interposed between the basolateral complex and the central nucleus are clusters of GABAergic cells, the interc alated neurons, which receive inputs from the lateral and basal nuclei and contribute a massive projection to the central medial nucleus. Because it i s impossible to predict the consequences of these connections, we correlate d the spontaneous and auditory-evoked activity of multiple simultaneously r ecorded neurons of the lateral, basal, and central nuclei. The spontaneous activity of lateral and basolateral neurons was positively correlated to th at of central lateral cells but negatively correlated to that of central me dial neurons. In response to auditory stimuli, the firing probability of la teral and central medial neurons oscillated in phase opposition, initially being excited and inhibited, respectively. In light of previous anatomical findings, we propose that the lateral nucleus exerts two indirect actions o n central medial neurons: an excitation via the basal nuclei and an inhibit ion via intercalated neurons.