The amygdala is a paired nuclear complex present in the cerebral hemispheres of vertebrates. It is considered part of the limbic system. In primates, it is located medially within the temporal lobes. It consists of many nuclei, each made up of further subnuclei. The subdivision most commonly made is into the basolateral, central, cortical, and medial nuclei together with the intercalated cell clusters. The amygdala has a primary role in the processing of memory, decision-making, and emotional responses. The amygdala was first identified and named by Karl Friedrich Burdach in 1822.
The limbic system, also known as the paleomammalian cortex, is a set of brain structures located on both sides of the thalamus, immediately beneath the medial temporal lobe of the cerebrum primarily in the forebrain.
The mesolimbic pathway, sometimes referred to as the reward pathway, is a dopaminergic pathway in the brain. The pathway connects the ventral tegmental area in the midbrain to the ventral striatum of the basal ganglia in the forebrain. The ventral striatum includes the nucleus accumbens and the olfactory tubercle.
The olfactory bulb is a neural structure of the vertebrate forebrain involved in olfaction, the sense of smell. It sends olfactory information to be further processed in the amygdala, the orbitofrontal cortex (OFC) and the hippocampus where it plays a role in emotion, memory and learning. The bulb is divided into two distinct structures: the main olfactory bulb and the accessory olfactory bulb. The main olfactory bulb connects to the amygdala via the piriform cortex of the primary olfactory cortex and directly projects from the main olfactory bulb to specific amygdala areas. The accessory olfactory bulb resides on the dorsal-posterior region of the main olfactory bulb and forms a parallel pathway. Destruction of the olfactory bulb results in ipsilateral anosmia, while irritative lesions of the uncus can result in olfactory and gustatory hallucinations.
Pavlovian fear conditioning is a behavioral paradigm in which organisms learn to predict aversive events. It is a form of learning in which an aversive stimulus is associated with a particular neutral context or neutral stimulus, resulting in the expression of fear responses to the originally neutral stimulus or context. This can be done by pairing the neutral stimulus with an aversive stimulus. Eventually, the neutral stimulus alone can elicit the state of fear. In the vocabulary of classical conditioning, the neutral stimulus or context is the "conditional stimulus" (CS), the aversive stimulus is the "unconditional stimulus" (US), and the fear is the "conditional response" (CR).
The nucleus accumbens is a region in the basal forebrain rostral to the preoptic area of the hypothalamus. The nucleus accumbens and the olfactory tubercle collectively form the ventral striatum. The ventral striatum and dorsal striatum collectively form the striatum, which is the main component of the basal ganglia. The dopaminergic neurons of the mesolimbic pathway project onto the GABAergic medium spiny neurons of the nucleus accumbens and olfactory tubercle. Each cerebral hemisphere has its own nucleus accumbens, which can be divided into two structures: the nucleus accumbens core and the nucleus accumbens shell. These substructures have different morphology and functions.
The locus coeruleus (LC), also spelled locus caeruleus or locus ceruleus, is a nucleus in the pons of the brainstem involved with physiological responses to stress and panic. It is a part of the reticular activating system.
Explicit memory is one of the two main types of long-term human memory, the other of which is implicit memory. Explicit memory is the conscious, intentional recollection of factual information, previous experiences, and concepts. This type of memory is dependent upon three processes: acquisition, consolidation, and retrieval.
Dominique de Quervain is a Swiss neuroscientist. He is professor of neuroscience and director of the Division of Cognitive Neuroscience at the University of Basel, Switzerland. He is known for his pioneering research into the use of glucocorticoids (cortisol) in the treatment of PTSD and phobias. He is understood to have found a link between cortisol and forgetting, specifically that cortisol can inhibit memory retrieval. Furthermore, he is known for his contributions to the field of genetics of human memory.
The amygdalofugal pathway is one of the three major efferent pathways of the amygdala, meaning that it is one of the three principal pathways by which fibers leave the amygdala. It leads from the basolateral nucleus and central nucleus of the amygdala. The amygdala is a limbic structure in the medial temporal lobe of the brain. The other main efferent pathways from the amygdala are the stria terminalis and anterior commissure.
The reward system is a group of neural structures responsible for incentive salience, associative learning, and positively-valenced emotions, particularly ones involving pleasure as a core component. Reward is the attractive and motivational property of a stimulus that induces appetitive behavior, also known as approach behavior, and consummatory behavior. A rewarding stimulus has been described as "any stimulus, object, event, activity, or situation that has the potential to make us approach and consume it is by definition a reward". In operant conditioning, rewarding stimuli function as positive reinforcers; however, the converse statement also holds true: positive reinforcers are rewarding.The reward system motivates animals to approach stimuli or engage in behaviour that increases fitness. Survival for most animal species depends upon maximizing contact with beneficial stimuli and minimizing contact with harmful stimuli. Reward cognition serves to increase the likelihood of survival and reproduction by causing associative learning, eliciting approach and consummatory behavior, and triggering positively-valenced emotions. Thus, reward is a mechanism that evolved to help increase the adaptive fitness of animals. In drug addiction, certain substances over-activate the reward circuit, leading to compulsive substance-seeking behavior resulting from synaptic plasticity in the circuit.
The basolateral amygdala, or basolateral complex, 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 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. This is how most emotional arousal is formed in mammals.
Memory consolidation is a category of processes that stabilize a memory trace after its initial acquisition. A memory trace is a change in the nervous system caused by memorizing something. Consolidation is distinguished into two specific processes. The first, synaptic consolidation, which is thought to correspond to late-phase long-term potentiation, occurs on a small scale in the synaptic connections and neural circuits within the first few hours after learning. The second process is systems consolidation, occurring on a much larger scale in the brain, rendering hippocampus-dependent memories independent of the hippocampus over a period of weeks to years. Recently, a third process has become the focus of research, reconsolidation, in which previously consolidated memories can be made labile again through reactivation of the memory trace.
The neuroanatomy of memory encompasses a wide variety of anatomical structures in the brain.
Emotion can have a powerful effect on humans and animals. Numerous studies have shown that the most vivid autobiographical memories tend to be of emotional events, which are likely to be recalled more often and with more clarity and detail than neutral events.
The cellular transcription factor CREB helps learning and the stabilization and retrieval of fear-based, long-term memories. This is done mainly through its expression in the hippocampus and the amygdala. Studies supporting the role of CREB in cognition include those that knock out the gene, reduce its expression, or overexpress it.
The management of traumatic memories is important when treating mental health disorders such as post traumatic stress disorder. Traumatic memories can cause life problems even to individuals who do not meet the diagnostic criteria for a mental health disorder. They result from traumatic experiences, including natural disasters such as earthquakes and tsunamis; violent events such as kidnapping, terrorist attacks, war, domestic abuse and rape. Traumatic memories are naturally stressful in nature and emotionally overwhelm people's existing coping mechanisms.
The effects of stress on memory include interference with a person's capacity to encode memory and the ability to retrieve information. Stimuli, like stress, improved memory when it was related to learning the subject. During times of stress, the body reacts by secreting stress hormones into the bloodstream. Stress can cause acute and chronic changes in certain brain areas which can cause long-term damage. Over-secretion of stress hormones most frequently impairs long-term delayed recall memory, but can enhance short-term, immediate recall memory. This enhancement is particularly relative in emotional memory. In particular, the hippocampus, prefrontal cortex and the amygdala are affected. One class of stress hormone responsible for negatively affecting long-term, delayed recall memory is the glucocorticoids (GCs), the most notable of which is cortisol. Glucocorticoids facilitate and impair the actions of stress in the brain memory process. Cortisol is a known biomarker for stress. Under normal circumstances, the hippocampus regulates the production of cortisol through negative feedback because it has many receptors that are sensitive to these stress hormones. However, an excess of cortisol can impair the ability of the hippocampus to both encode and recall memories. These stress hormones are also hindering the hippocampus from receiving enough energy by diverting glucose levels to surrounding muscles.
Parental experience, as well as changing hormone levels during pregnancy and postpartum, cause changes in the parental brain. Displaying maternal sensitivity towards infant cues, processing those cues and being motivated to engage socially with her infant and attend to the infant's needs in any context could be described as mothering behavior and is regulated by many systems in the maternal brain. Research has shown that hormones such as oxytocin, prolactin, estradiol and progesterone are essential for the onset and the maintenance of maternal behavior in rats, and other mammals as well. Mothering behavior has also been classified within the basic drives.
Stephen Andrew Maren is an American behavioral neuroscientist investigating the brain mechanisms of emotional memory, particularly the role context plays in the behavioral expression of fear. He has discovered brain circuits regulating context-dependent memory, including mapping functional connections between the hippocampus, prefrontal cortex, and amygdala that are involved in the expression and extinction of learned fear responses.
