The basolateral complex (BLA) consists of the lateral, basal and accessory-basal nuclei of the amygdala. The lateral nuclei receives the majority of sensory information, which arrives directly from the temporal lobe structures, including the hippocampus and primary auditory cortex. The information is then processed by the basolateral complex and is sent as output to the centromedial nucleus of the amygdala. This is how most emotional arousal is formed in mammals.
The primary function of the basolateral complex is stimulating fear response. The fear system is intended to avoid pain or injury. For this reason the responses must be quick, and reflex-like. To achieve this, the “low-road” or a bottom-up process is used to generate a response to stimuli that are potentially hazardous. The stimulus reaches the thalamus, and information is passed to the lateral nucleus, then the basolateral system, and immediately to the central nucleus where a response is then formed. There is no conscious cognition involved in these responses. Other non-threatening stimuli are processed via the “high road” or a top-down form of processing. In this case, the stimulus input reaches the sensory cortex first, leading to more conscious involvement in the response. This is why in immediately threatening situations, such as your little brother jumping out at you, responses are reflexive, and conscious thought processing doesn’t occur until later.
An important process that occurs in basolateral amygdala is consolidation of cued fear memory. One proposed molecular mechanism for this process is collaboration of M1-Muscarinic receptors, D5 receptors and beta-2 adrenergic receptors to redundantly activate phospholipase C, which inhibits the activity of KCNQ channels that conduct inhibitory M current. The neuron then become more excitable and the consolidation of memory is enhanced.
The amygdala has several different nuclei and internal pathways; the basolateral complex (or basolateral amygdala), the centromedial nucleus, and the cortical nucleus are the most well-known. Each of these has a unique function and purpose within the amygdala.
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