The archicortex is a part of the cerebrum. The largest part of it is formed by the hippocampus. It consists of a very characteristic cortical structure.
What is the archicortex?
Archicortex is the name given to a part of the cerebral cortex. It is delineated as the medial border of the neocortex. The archicortex has a developmental background. The cerebrum is phylogenetically differentiated into paleocortex, striatum, archicortex, and neocortex. The archicortex is considered a stage between the paleocortex and the neocortex. The archicortex is largely composed of the hippocampus. In addition, some structures lying around it are counted as part of it. These are parts of the parahippocampal gyrus and the cingulate gyrus. The archicortex consists of a curled cortical structure. This is three-layered and consists of the dentate gyrus, the cornu ammonis (Ammon’s horn), and the subiculum. All three layers have the functions of learning and memory formation. In particular, long-term potentiation takes place here. This forms the basis for storing long-term memories and learning courses of action, for example. The archicortex, together with the paleocortex, is called the allocortex. This is contrasted with the six-layer neocortex. As a result, with appropriate detection techniques, additional layers than those mentioned become delineable in most allocortex areas.
Anatomy and structure
The archicortex consists of a microscopic structure and is formed primarily by the hippocampus, portions of the prahippocomapales gyrus, and the cingulate gyrus. The hippocampus consists of a convoluted archicortex structure, also known as the cortical structure. It lies beneath the temporal lobes. These are located on the medial side of the inferior horn of the lateral ventricle. The efferent fibers of the fornix are the vault that spans from posterior to anterior as the roof of the III ventricle. The cingulate gyrus is located above the bar. This connects the right and left hemispheres. Together with the hippocampus, it forms the limbic system. The archicortex consists of three layers. In them are the dentate gyrus, the cornu ammonis and the subiculum. They consist of pyramidal cells of different sizes. The three layers are divided into lamina molecularis (stratum moleculare), lamina pyramidalis (stratum pyramidale) and lamina multiformis (stratum oriens). In the first layer both are apical dendrites of the pyramidal cells, followed by the cell bodies of the pyramidal cells in the second layer. In the last layer are the basal dendrites of the pyramidal cells.
Function and tasks
The tasks of the archicortex include important functions of learning, thinking, and emotional processing. Essential processes of memory consolidation take place in the three layers of the archicortex. Learning and all associated learning processes are associated with this. The process by which information is transferred from short-term memory to long-term memory takes place here. For memories to be permanently stored in memory, what is known as long-term potentiation must occur. This process takes several days to months and only occurs if the potentiating impulses are passed on at a sufficiently high speed. Long-term potentiation serves as the basis for all learning and memory processes. The archicortex is responsible for knowledge formation. This includes spatial facts, factual knowledge, memories or conditioning processes. Knowledge about actions, habits or motor learning is formed here. The contents of declarative memory as well as those of implicit memory are formed in the archicortex. Emotion processing takes place in the limbic system. This includes the understanding of emotions and the associated emotion experience. Processes that allow emotional expression and empathy to take place are controlled from this brain region. All learning processes around positive as well as negative emotions take place in the archicortex. This includes the recognition of danger as well as the sensation of pleasure. Need satisfaction is regulated in this part of the brain. Mood, affect, emotion, and feeling originate in the archicortex. This means that long-term as well as short-term emotional episodes occur through the processing of stimuli in the limbic system.
Diseases
Lesions and impairments of functional activity in the archicortex lead to far-reaching consequences in all learning processes as well as emotion processing. Various diseases, circulatory disorders, tumors, or damage due to accidents or as a result of surgical procedures can induce lesions. Inflammations in the archicortex can lead to a loss of memory. In addition, affected persons suffer from temporal as well as local disorientation. Amnesia is one of the best known memory disorders. Anterograde amnesia must be distinguished from retrograde amnesia. Anterograde amnesia does not allow for new memory formation. Retrograde amnesia results in the existing memory contents no longer being available. They are partially or completely erased. The pyramidal cells in the hippocampus are particularly susceptible to damage from alcohol abuse. Diseases such as Wernicke’s encephalopathy or Korsakow’s syndrome are consequences of alcohol disorders. They are accompanied by confabulation. Patients replace missing memories with false statements and narratives. Even answers to easy questions can no longer be given by patients with damage to the pyramidal cells. Lesions of the hippocampus have relevance beyond the formation of long-term memory in diseases such as epilepsy. Damage to the temporal lobe can lead to Klüver-Bucy syndrome. This disorder leads to hyperoral as well as hypersexual behavior. Lesions of the amygdala lead to problems with emotion processing. In particular, fear and anxiety stimuli can no longer be processed. These are important for self-protection and survival.
