The allocortex is a part of the human brain. It is assigned to the cerebral cortex and is a part of the central nervous system.
What is the allocortex?
The allocortex comprises the regions in the human brain that form three to five layers. It forms about 10% of the cerebral cortex, referred to as the cortex cerebri. Opposite it is the six-layered neocortex or isocortex, which occupies 90% of the cerebral cortex. The allocortex is formed by the archicortex and the paleocortex. The archicortex consists of the limbic system. The hippocampus is assigned to this. To the paleocortex belongs the olfactory organ of the human organism. Thus, the allocortex performs important functions in emotional processing, learning and the processing of odors. In addition, the mesocortex is included in the allocortex as a transition between the isocortex and the archicortex. In adulthood, the mesocortex consists of the para-hippocompal cortex as well as the cingulate gyrus. While the para-hippocompal cortex is classified as part of the allocortex, the cingulate gyrus is part of the isocortex. The allocortex consists largely of pyramidal cells. These serve to transmit recorded stimuli from a sensory organ to the cortex. Phylogenetically, the allocortex belongs to the older region in the human brain.
Anatomy and structure
The archicortex describes the limbic system. It includes the hippocampus, the parahippocompalis gyrus, the amygdala, and the corpus mammillare. Even though the cingulate gyrus is part of the archicortex, it is not classified as part of the allocortex. The paleocortex combines various centers of the human brain. They include the bulbus and tractus olfactorius, the tuberculum olfactorium, the septum, the prepiriform cortex, and portions of the corpus amygdaloideum, the amygdala. The paleocortex with its structures forms the olfactory brain with the olfactory bulb. This has the shape of a butterfly antenna. The stimuli received are transmitted directly to the cerebral cortex via the olfactory epithelium without switching in the thalamus. The olfactory brain is called the olfactory cortex. This is where the processing of odors takes place. The allocortex consists of three layers. These are the lamina molecularis, the lamina pyramidales, and the lamina multifromis. The first layer is called the stratum molecularis and contains the upper dendrites of the pyramidal cells. The middle layer is formed by the stratum pyramidale and consists of the cell bodies of the pyramidal cells. The third layer contains the lower dendrites of the pyramidal cells and is called stratum oriens.
Function and tasks
Essentially, the allocortex is formed by the hippocampus and the olfactory system. The paleocortex, also known as the olfactory cortex, evaluates all the information that is received by the olfactory epithelium and travels to it via the olfactory pathway. Humans can distinguish 5,000 odors. In over 10 million olfactory cells, these are recorded and passed on for processing. Olfactory cells have a life span of a few weeks. They then die and are replaced by new ones. This in a task performed by the allocortex. Olfactory cells are the only neurons in the adult nervous system that divide mitotically. In mitosis, a nucleus divides producing two daughter nuclei that share the same genetic information. The functions of emotional processing, learning, and memory formation occur in the archicortex. Long-term potentiation, and thus memory consolidation, takes place in the layers of the archicortex. Long-term potentiation transfers recorded information from short-term memory to long-term memory. This includes memories, knowledge about action sequences or conditioning processes. Human habits as well as unconscious processes are taken over in the archicortex. In addition, the experience of emotions takes place in the limbic system and above all in the amygdala. Fear, pleasure, joy or sadness originate there. Emotions can take place for a short period of time or they can turn into long-lasting emotional phases. Positive as well as negative emotions, moods and the regulation of affect originate here. Thus, the allocortex assumes an important social function as well as the regulation of emotions. The awareness of an emotion that has arisen is defined as a feeling. This process includes parts of learning as well as evolutionary elements such as the fear reaction.
Diseases
Lesions in the allocortex result in impairments in odor processing as well as memory and emotion formation. Smell occupies an important role in partnered search. The partner attraction or sympathy is connected with the histocompatibility antigens of the human organism. Partners whose genetic structure is too similar are perceived as repulsive. Behind this is the evolutionary goal of preventing genetic dispositions of offspring and producing offspring that have a strong immune system. The process of odor processing is altered when lesions or impairments are caused by drugs. In addition, an impaired sense of smell affects the sense of taste. Alexithymia is a condition called emotional blindness. This disorder includes symptoms that describe an inability or limitation in recognizing feelings. One’s own feelings can be perceived only inadequately or not at all. Empathy is also not felt. A special feature of this disease is that those close to the patient suffer more than the person affected. Alcoholism affects the functioning of the pyramidal cells. Thus, memories are lost and cannot be replaced. If alcohol abuse leads to Korsakow’s syndrome, existing memory gaps are replaced by confabulation. Memory deficits are replaced by fictional narratives.
