Amygdala-hippocampus dynamic interaction in relation to memory.
Explain the physiology of emotional response in terms of the structures and The amygdala, located in the left and right temporal lobes of the brain, has. Amygdala-Hippocampus Dynamic Interaction in Relation to Memory of stress on hippocampal functioning and about what factors define an. to fear, the hippocampus seems to hold all the fear memories in relation to contextual information about the Keywords: context, fear, memory, conditioning , amygdala, hippocampus .. Contextual fear conditioning could also be defined.
Some of these are subcortical structures, while many are portions of the cerebral cortex. Cortical regions that are involved in the limbic system include the hippocampus as well as areas of neocortex including the insular cortex, orbital frontal cortex, subcallosal gyrus, cingulate gyrus and parahippocampal gyrus.
This cortex has been termed the "limbic lobe" because it makes a rim surrounding the corpus callosum, following the lateral ventricle. Subcortical portions of the limbic system include the olfactory bulb, hypothalamus, amygdala, septal nuclei and some thalamic nuclei, including the anterior nucleus and possibly the dorsomedial nucleus.
One way in which the limbic system has been conceptualized is as the "feeling and reacting brain" that is interposed between the "thinking brain" and the output mechanisms of the nervous system. In this construct, the limbic system is usually under control of the "thinking brain" but obviously can react on its own.
Additionally, the limbic system has its input and processing side the limbic cortex, amygdala and hippocampus and an output side the septal nuclei and hypothalamus.
Most of these regions are connected by pathways that are shown in figure Hypothalmus The hypothalamus, the primary output node for the limbic system, has many important connections. It is connected with the frontal lobes, septal nuclei and the brain stem reticular formation via the medial forebrain bundle. It also receives inputs from the hippocampus via the fornix and the amygdala via two pathways ventral amygdalofugal pathway and stria terminalis.
The hypothalamus has centers involved in sexual function, endocrine function, behavioral function and autonomic control.
In order to perform its essential functions, the hypothalamus requires several types of inputs. There are inputs from most of the body as well as from olfaction, the viscera and the retina. It also has internal sensors for temperature, osmolarity, glucose and sodium concentration.
In addition, there are receptors for various internal signals, particularly hormones. These include steroid hormones, and other hormones as well as internal signals such as hormones involved in appetite control such as leptin and orexin. The hypothalamus strongly influences many functions including autonomics, endocrine functions and behaviors. Autonomic functions are controlled via projections to the brain stem and spinal cord.
There are localized areas in the hypothalamus that will activate the sympathetic nervous system and some that will increase parasympathetic activity. Endocrine functions are controlled either by direct axonal connections to the posterior pituitary gland vasopressin and oxytocin control or via release of releasing factors into the hypothalamic-hypophyseal portal system to influence anterior pituitary function.
There are also projections to the reticular formation that are involved in certain behaviors, particularly emotional reactions.
Some functions are intrinsic to the hypothalamus. These are functions that require a direct input to the hypothalamus and where the response is generated directly via hypothalamic outputs. Included are such things as temperature and osmolarity regulation. There are many functions where the hypothalamus monitors the internal melieu and produces a regulatory response. These include the regulation of endocrine functions and appetite.
For example, the ventromedial nucleus of the hypothalamus is considered a satiety area, while the lateral hypothalamic area is a feeding center. Additionally, there are many complex behaviors that are patterned by the hypothalamus, including sexual responses.
The preoptic area is one of the areas of greatest sexual dimorphism i. These sexual responses involve autonomic, endocrine and behavioral responses.
Finally, the suprachiasmatic nucleus receives direct retinal input.
This nucleus is responsible for entraining circadian rhythms to the day-night cycle. Amygdala The amygdala is an important structure located in the anterior temporal lobe within the uncus.
The amygdala makes reciprocal connections with many brain regions figure 32 including the thalamus, hypothalamus, septal nuclei, orbital frontal cortex, cingulate gyrus, hippocampus, parahippocampal gyrus, and brain stem. The olfactory bulb is the only area that makes input to the amygdala and does not receive reciprocal projections from the amygdala. The amygdala is a critical center for coordinating behavioral, autonomic and endocrine responses to environmental stimuli, especially those with emotional content.
It is important to the coordinated responses to stress and integrates many behavioral reactions involved in the survival of the individual or of the species, particularly to stress and anxiety. Lesions of the amygdala reduce responses to stress, particularly conditioned emotional responses.
Stimulation of the amygdala produces behavioral arousal and can produce directed rage reactions. Various stimuli produce responses mediated by the amygdala.
Amygdala - Wikipedia
The convergence of inputs is important since it allows the generation of learned emotional responses to a variety of situations. The amygdala responds to a variety of emotional stimuli, but mostly those related to fear and anxiety.
Hippocampus The hippocampus is an ancient area of cerebral cortex that has three layers. This is located in the medial aspect of the temporal lobe, forming the medial wall of the lateral ventricle in this area.
The hippocampus has several parts. The dentate gyrus contains densely packed granule cells. These are designated as CA1 to CA4. These contain prominent pyramidal cells. The CA fields blend into the adjacent subiculum, which, in turn, is connected to the entorhinal cortex on the parahippocampal gyrus of the temporal lobe.2-Minute Neuroscience: Amygdala
There are several sources of hippocampal afferents. These are primarily from the septum and hypothalamus via the fornix and from the adjacent entorhinal cortex. This cortical region receives input from diffuse areas of the neocortex, especially the limbic cortex, and from the amygdala. The entorhinal cortex projects to the dentate gyrus of the hippocampus via the perforant pathway, synapsing on granule cells.
These granule cells connect to pyramidal neurons in the CA3 region, which, in turn, project by Sheaffer collaterals to CA1 pyramidal cells. It is these latter cells that give rise primarily to the fornix. The physiology of these pathways has been studied extensively, particularly in terms of long-term physiological changes associated with memory.
Hippocampal neurons have been studied extensively in terms of long-term potentiation.
Amygdala-hippocampus dynamic interaction in relation to memory.
This requires activation of glutamate receptors and results in long-term changes in neuronal excitability by way of calcium mediated physiologic effects. Outputs from the hippocampus pass primarily via two pathways. The first of these outputs is through the fornix. These fibers project to the mamillary bodies via the post-commissural fornix, to the septal nuclei, to the preoptic nucleus of the hypothalamus, to the ventral striatum and to portions of the frontal lobe through the precommisural fornix.
There are large numbers of projections from the hippocampus back to the entorhinal cortex. Figure 31 demonstrates many of the important pathways within the limbic system. Buddhist monks who do compassion meditation have been shown to modulate their amygdala, along with their temporoparietal junction and insuladuring their practice. However, this correlation depends on the relative "emotionalness" of the information.
More emotionally arousing information increases amygdalar activity, and that activity correlates with retention. Amygdala neurons show various types of oscillation during emotional arousal, such as theta activity.
These synchronized neuronal events could promote synaptic plasticity which is involved in memory retention by increasing interactions between neocortical storage sites and temporal lobe structures involved in declarative memory. The researchers note, "Since previous reports have indicated that unique responses were observed at higher frequency in the artistic population than in the nonartistic normal population, this positive correlation suggests that amygdalar enlargement in the normal population might be related to creative mental activity.
As early asrhesus monkeys with a lesioned temporal cortex including the amygdala were observed to have significant social and emotional deficits.
Some monkeys also displayed an inability to recognize familiar objects and would approach animate and inanimate objects indiscriminately, exhibiting a loss of fear towards the experimenters.
Monkey mothers who had amygdala damage showed a reduction in maternal behaviors towards their infants, often physically abusing or neglecting them. A variety of data shows the amygdala has a substantial role in mental states, and is related to many psychological disorders. Some studies have shown children with anxiety disorders tend to have a smaller left amygdala. In the majority of the cases, there was an association between an increase in the size of the left amygdala with the use of SSRIs antidepressant medication or psychotherapy.
The left amygdala has been linked to social anxiety, obsessive and compulsive disordersand post traumatic stressas well as more broadly to separation and general anxiety. Some borderline patients even had difficulties classifying neutral faces or saw them as threatening. Patients with severe social phobia showed a correlation with increased response in the amygdala.
This hyperactivity was normalized when patients were administered antidepressant medication. A study found that adult and adolescent bipolar patients tended to have considerably smaller amygdala volumes and somewhat smaller hippocampal volumes. This may provide clues as to how specific parasites may contribute to the development of disorders, including paranoia.
Homosexual men tend to exhibit more feminine patterns in the amygdala than heterosexual males do, just as homosexual females tend to show more masculine patterns in the amygdala than heterosexual women do. It was observed that amygdala connections were more widespread from the left amygdala in homosexual males, as is also found in heterosexual females.
Amygdala connections were more widespread from the right amygdala in homosexual females, as in heterosexual males. They were also better able to make accurate social judgments about other persons' faces. It does not, however, process the direction of the gaze of the person being perceived. It is particularly hypothesized that larger amygdalae allow for greater emotional intelligence, enabling greater societal integration and cooperation with others.
These reactions are absent in persons in whom the amygdala is damaged bilaterally.
Chapter 9 - Limbic System
Likewise, studies using brain lesions have shown that harm to the amygdala may produce the opposite effect. Thus, it appears that this part of the brain may play a role in the display and modulation of aggression. This finding reinforces the conclusion that the amygdala "plays a pivotal role in triggering a state of fear".
The protein is involved in controlling the function of other proteins and plays a role in development of the ability to consume a large amount of ethanol. In an experiment, degu pups were removed from their mother but allowed to hear her call. In response, the males produced increased serotonin receptors in the amygdala but females lost them. This led to the males being less affected by the stressful situation.
The clusters of the amygdala are activated when an individual expresses feelings of fear or aggression. This occurs because the amygdala is the primary structure of the brain responsible for fight or flight response. Anxiety and panic attacks can occur when the amygdala senses environmental stressors that stimulate fight or flight response.
The amygdala is directly associated with conditioned fear. Conditioned fear is the framework used to explain the behavior produced when an originally neutral stimulus is consistently paired with a stimulus that evokes fear. The amygdala represents a core fear system in the human body, which is involved in the expression of conditioned fear. Fear is measured by changes in autonomic activity including increased heart rate, increased blood pressure, as well as in simple reflexes such as flinching or blinking.
The central nucleus of the amygdala has direct correlations to the hypothalamus and brainstem — areas directly related to fear and anxiety.
This connection is evident from studies of animals that have undergone amygdalae removal. Such studies suggest that animals lacking an amygdala have less fear expression and indulge in non-species-like behavior. Many projection areas of the amygdala are critically involved in specific signs that are used to measure fear and anxiety. Mammals have very similar ways of processing and responding to danger.
Scientists have observed similar areas in the brain — specifically in the amygdala — lighting up or becoming more active when a mammal is threatened or beginning to experience anxiety. Similar parts of the brain are activated when rodents and when humans observe a dangerous situation, the amygdala playing a crucial role in this assessment.