Interactions and Firing Patterns of Rabbit Amygdalar Neurons in Unconditioned Fear Manifested as Freezing
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The characteristics of the operation of the amygdalar neural network in unconditioned fear were identified by studying the interactions and nature of the spike activity of individual neurons in the basal and central nuclei of the amygdala in rabbits during freezing (fear), active unconditioned motor reactions (absence of fear), and in response to emotionally significant stimuli, as well as in calm waking. When rabbits froze, there were specific changes in the interactions of close-lying amygdalar neurons as compared with other states; these changes were not seen in the spike activity of individual neurons. Freezing increased the numbers of short-latency (up to 100 msec) excitatory connections and decreased the numbers of long-latency (250–450 msec) inhibitory connections. Neuron interactions were seen at frequencies in the delta2 range (2–4 Hz) more often in this state than in others. When the animals made active motor responses to the stimulus, there were decreases in the numbers of interacting neurons and increases in the numbers of longlatency (200–250 msec) excitatory and short-latency (50–200 msec) inhibitory connections, and a greater proportion of interactions occurred at frequencies of the theta1 range more frequently than in other states. Thus, the balance between the excitatory and inhibitory components of the amygdalar neural network is important for the occurrence of fear.
Key wordsamygdala neuron interaction freezing orientational-investigative reactions unconditioned shaking reflex
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