Neuronal correlates of fear in the lateral amygdala: Multiple extracellular recordings in conscious cats

Much data implicates the amygdala in the expression and learning of fear. Y et, few studies have examined the neuronal correlates of fear in the amygda la. This study aimed to determine whether fear is correlated to particular activity patterns in the lateral amygdaloid (LA) nucleus. Cats, chronically implanted with multiple microelectrodes in the LA and a catheter in the fe moral artery, learned that a series of tones interrupted by a period of sil ence (5 sec) preceded the administration of a footshock. During the silent period, their blood pressure increased, indicating that they anticipated th e noxious stimulus. In parallel, the firing rate of LA neurons doubled, and the discharges of simultaneously recorded cells became more synchronized. Moreover, cross-correlation of focal LA waves revealed a significant increa se in synchrony restricted to the theta band. In keeping with this, perieve nt histograms of neuronal discharges revealed rhythmic changes in the firin g probability of LA neurons in relation to focal theta waves. Finally, the responsiveness of LA cells to the stimuli predicting the footshock (the ton es) increased during the trials, whereas responses to unrelated stimuli (pe rirhinal shocks) remained stable. Thus, during the anticipation of noxious stimuli, a state here defined anthropomorphically as fear, the firing rate of LA neurons increases, and their discharges become more synchronized thro ugh a modulation at the theta frequency. The presence of theta oscillations in the LA might facilitate cooperative interactions between the amygdala a nd cortical areas involved in memory.