Anatomy of the Limbic System

A limbic system is a group of mechanisms or the parts of the limbic system included in emotion and memory formation, such as the amygdala, and hypothalamus. The limbic system is placed in the cerebrum of your brain, underneath the temporal lobes, and hidden deep in the cerebral cortex (the cortex is the outermost portion of the brain).

The parts of the limbic system were formerly referred to as the rhinencephalon (roughly “scent brain”) since it was assumed to be primarily concerned with the ability to smell. The limbic lobe, located on the inferomedial side of the cerebral hemispheres, is made up of two concentric gyri that encircle the corpus callosum. Broca advocated naming the bigger outer gyrus “limbic gyrus” and the narrower inner gyrus “intralimbic gyrus.”

The cingulate gyrus (Latin for “Belt ridge”), which is dorsal to the corpus callosum, is intricately linked to the cerebral cortex’s association regions. The medial temporal lobe’s parahippocampal gyrus comprises multiple separate sections, the most significant of which is the entorhinal cortex (ERC). The ERC is the primary output conduit of the hippocampus formation, funnelling heavily processed cortical data there.

Psychologists now understand that the function of the limbic system is much more than previously thought. These components are found to be involved in emotion processing and regulation, memory development and storage, sexual desire, and learning. 

The limbic system, which is closely linked to the endocrine and autonomic nervous systems, is considered to play a significant role in your body’s reaction to a stressor. The limbic system is composed of two universally recognized structures: the hippocampus and the amygdala. Different people have different ideas on which of the other structures should be included in this system and which should merely connect with it intimately.

The limbic system’s nerve cells or neurons are organised differently than those from the cerebral cortex. The cells in the cerebral cortex are predominantly neocortical, which means they are organised into 6 sections. The cells in the limbic system are either organised in fewer layers or have been more disordered. Because the cells of the limbic system are less complicated, it has been assumed that such a system is biologically older than that of your cerebral cortex.

Hippocampus

The hippocampus, along with many other neural structures, is found in pairs, one on either half. It has the form of a curved seahorse (and is called only after biological genus) and serves as our brain’s recollection centre. Our sequential memories are produced and documented here before being stored away in extended storage in different areas of your cerebral cortex. 

The interconnections formed in your hippocampus also play a key role in the function of the limbic system and assist you in associating memories with other sensations. The hippocampus also happens to be vital for spatial configuration and navigation in the environment. 

The hippocampus is one of the brain regions where new neurons are formed from adult stem cells. This process is known as neurogenesis, and it’s at the root of one form of brain plasticity. As a result, it’s not unexpected that this is an important brain region for discovering new skills. 

The hippocampus is a brain area that is mostly connected with memory. The hippocampus, which is located in the inner (medial) area of the temporal lobe, is a component of the limbic system, which is crucial in regulating emotional reactions. 

Though this is debatable, the hippocampus is assumed to be primarily involved in storing long-term memories and making those memories resistant to forgetting. It is also considered to be crucial in spatial processing and navigation.

The structure of the hippocampus in the parts of the limbic system is crucial to its functionality. The entorhinal cortex, which is positioned underneath the anterior part of the hippocampus, accepts data from and delivers output to the remainder of your brain via the hippocampus. The hippocampal formation is divided into multiple subregions, including the cornu ammonis (CA1–4), subiculum, and dentate gyrus. 

Modulatory neurotransmitter systems, such as serotonin, norepinephrine, and dopamine, provide input to your hippocampus. It also gets cholinergic input from the medial septum, which modulates the physiological state of the hippocampus. The medial septum is important in the establishment of theta rhythm, among the key oscillatory oscillations in the hippocampus. Eliminating that area or the related theta rhythm disrupts hippocampus function.

The 2 most prominent hippocampus functions of limbic system ideas are linked to memory and space. The spatial concept was backed by the key 1971 finding of hippocampal cells that generated bursts of action potentials whenever a rat passed particular areas in space, or “place fields.” That implied that the hippocampus is a mechanism utilised by your brain to sketch out the pattern of the world. 

Data from following virtual-navigation research in humans supported that theory, indicating a substantial link between your hippocampus and spatial navigation. The memory theory was proposed in 1957 and was backed by experiments and observations showing that hippocampus ablation led to the inability to generate new recollections, particularly fact- and declarative memories.

Amygdala

The amygdala, in the parts of the limbic system, is an almond-shaped region deep inside the temporal lobe discovered by Burdach in the early nineteenth century and happens to be a cluster of nuclei situated under the uncus. It joins with the periamygdaloid cortex, which comprises a portion of the outer part of the uncus, near the anterior end of the hippocampal formation and the anterior tip of the inferior horn of the lateral ventricle. The amygdaloid complex is composed of around 13 nuclei and has a variable structural makeup. 

These are subdivided further into subgroups as is seen in the limbic system diagram with substantial inter-and intra-nuclear linkages. The word “amygdala” relates to its almond-like form. The left and right amygdalae, which are located immediately adjacent to the hippocampus, contribute to human emotional reactions, including sensations such as enjoyment, fear, panic, and rage.

The amygdala not only modifies the intensity and emotional content of recollections; it also serves an important part in the development of new memories, particularly those associated with fear. Fearful memories can be generated with just a few repeats. As a result, ‘fear learning’ has become a common method for studying the mechanics of memory forming, integration, and retrieval. 

Scary memories could form after only a few repeats, resulting in avoidance of particular fearful stimuli. As a result, because activating activity in the amygdala could alter the body’s natural anxiety symptoms, the amygdala is also related to the fight-or-flight rebuttal. Disruption to the amygdala could lead to increased aggressiveness, irritability, lack of emotional control, and difficulties recognizing emotions, particularly fear.

Irritative temporal lobe epilepsy lesions have the effect of activating the amygdala. Irritative temporal lobe epilepsy can produce a panic episode in its most severe form. Panic attacks are short, recurring experiences of dread that convey a sensation of imminent doom but have no discernible reason. During anxiety episodes, blood flow increases similarly although at a lower rate. 

Destructive lesions, such as amygdala ablation, have the opposite impact as irritative temporal lobe epilepsy lesions. Destructive amygdala lesions produce tameness in animals and placid tranquillity in people, which is characterised by the flatness of affect. 

Amygdala lesions, as shown in the limbic system diagram can arise as a result of Urbach-Wiethe disease, in which calcium deposits in the amygdala. If this condition develops early in childhood, these people with bilateral amygdala lesions will be unable to distinguish emotion in facial expressions, but their capacity to recognize faces will be preserved.

Clinical Disorders

The parts of the limbic system are implicated in some of the most difficult neurobehavioral illnesses known to medicine, including mood and anxiety disorders like depression and posttraumatic stress disorder (PTSD), drug misuse and dependency, and cognitive and memory problems like Alzheimer’s disease. Limbic ADD might potentially be caused by Limbic system injury. Limbic ADD patients are assumed to have an overactive limbic system and an underactive prefrontal cortex, resulting in brain dysregulation and the disorder’s undesirable symptoms.

Conclusion

The parts of the limbic system are crucial to behaviour. Some forms of neuropsychiatric illnesses may be explained by the complicated functional neuroanatomy of the limbic system with its varied pathways. An extensive study of the limbic system has revealed the amygdala’s function in anxiety disorders and emotional memory. 

The surveillance role of the anterior cingulate, the trisynaptic hippocampal circuitry underlying cognitive performance in the limbic system, and the importance of the hypothalamus in numerous neurovegetative features all point to the limbic system playing an important role in psychology and its aberrations.