The basolateral amygdala, or basolateral complex, consists of the lateral, basal and accessory-basal nuclei of the

amygdala The amygdala (; plural: amygdalae or amygdalas; also '; Latin from Greek, , ', 'almond', 'tonsil') is one of two almond-shaped clusters of nuclei located deep and medially within the temporal lobes of the brain's cerebrum in complex ver ...

. The lateral nuclei receives the majority of sensory information, which arrives directly from the

temporal lobe The temporal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The temporal lobe is located beneath the lateral fissure on both cerebral hemispheres of the mammalian brain. The temporal lobe is involved i ...

structures, including the

hippocampus The hippocampus (via Latin from Greek , 'seahorse') is a major component of the brain of humans and other vertebrates. Humans and other mammals have two hippocampi, one in each side of the brain. The hippocampus is part of the limbic syste ...

and

primary auditory cortex The auditory cortex is the part of the temporal lobe that processes auditory information in humans and many other vertebrates. It is a part of the auditory system, performing basic and higher functions in hearing, such as possible relations ...

. The basolateral amygdala also receives dense neuromodulatory inputs from ventral tegmental area (VTA), locus coeruleus (LC), and basal forebrain, whose integrity are important for associative learning. The information is then processed by the basolateral complex and is sent as output to the

central nucleus of the amygdala The central nucleus of the amygdala (CeA or aCeN) is a nucleus within the amygdala. It "serves as the major output nucleus of the amygdala and participates in receiving and processing pain information." CeA "connects with brainstem areas that con ...

. This is how most emotional arousal is formed in mammals.

Function

The amygdala has several different nuclei and internal pathways; the basolateral complex (or basolateral amygdala), the central nucleus, and the cortical nucleus are the most well-known. Each of these has a unique function and purpose within the amygdala.

Fear response

The basolateral amygdala and

nucleus accumbens shell The nucleus accumbens (NAc or NAcc; also known as the accumbens nucleus, or formerly as the ''nucleus accumbens septi'', Latin for "nucleus adjacent to the septum") is a region in the basal forebrain rostral to the preoptic area of the hypo ...

together mediate specific Pavlovian-instrumental transfer, a phenomenon in which a

classically conditioned stimulus Classical conditioning (also known as Pavlovian or respondent conditioning) is a behavioral procedure in which a biologically potent stimulus (e.g. food) is paired with a previously neutral stimulus (e.g. a triangle). It also refers to the learn ...

modifies

operant behavior Operant conditioning, also called instrumental conditioning, is a learning process where behaviors are modified through the association of stimuli with reinforcement or punishment. In it, operants—behaviors that affect one's environment—are c ...

. One of the main functions of the basolateral complex is to stimulate the 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 The thalamus (from Greek θάλαμος, "chamber") is a large mass of gray matter located in the dorsal part of the diencephalon (a division of the forebrain). Nerve fibers project out of the thalamus to the cerebral cortex in all direct ...

, and information is passed to the lateral nucleus, then the basolateral system, and immediately to the

central nucleus The central nucleus of the amygdala (CeA or aCeN) is a nucleus within the amygdala. It "serves as the major output nucleus of the amygdala and participates in receiving and processing pain information." CeA "connects with brainstem areas that co ...

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. In immediately threatening situations, the

fight-or-flight response The fight-or-flight or the fight-flight-or-freeze response (also called hyperarousal or the acute stress response) is a physiological reaction that occurs in response to a perceived harmful event, attack, or threat to survival. It was first des ...

is 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 receptor The beta-2 adrenergic receptor (β2 adrenoreceptor), also known as ADRB2, is a cell membrane-spanning beta-adrenergic receptor that binds epinephrine (adrenaline), a hormone and neurotransmitter whose signaling, via adenylate cyclase stimulati ...

s to redundantly activate

phospholipase C Phospholipase C (PLC) is a class of membrane-associated enzymes that cleave phospholipids just before the phosphate group (see figure). It is most commonly taken to be synonymous with the human forms of this enzyme, which play an important role ...

, which inhibits the activity of

KCNQ channels KCQN genes encode family members of the Kv7 potassium channel family. These include Kv7.1 (KCNQ1) - KvLQT1, Kv7.2 ( KCNQ2), Kv7.3 ( KCNQ3), Kv7.4 ( KCNQ4), and Kv7.5 (KCNQ5). Four of these (KCNQ2-5) are expressed in the nervous system. They constitu ...

that conduct inhibitory

M current M current is a type of noninactivating potassium current first discovered in bullfrog sympathetic ganglion cells. The ''M-channel'' is a voltage-gated K+ channel ( Kv7/KCNQ family) that is named after the receptor it is influenced by. The M-channel ...

. The neuron then becomes more excitable and the consolidation of memory is enhanced.

Pain memory

Distinct ensembles of neurons within the basolateral amygdala play a role in encoding associative memories and the response to painful stimuli. The ensemble activated in response to noxious stimuli are of particular interest for targeting treatments of chronic pain and cold allodynia. When neurons within this ensemble are silenced in a rodent model the affective component of pain is essentially erased, while a robust reflex response is maintained. This is thought to implicate the basolateral amygdala in assigning a “pain tag” to valence information which may intrinsically encode that there is a priority to engage in pain-protective behaviors.

References

{{authority control Amygdala