The paleocortex is part of the cerebrum. Together with the archicortex, it forms the allocortex. It is responsible for olfactory processing in the brain.
What is the paleocortex?
The paleocortex or paleocortex is part of the cerebral cortex, the cortex cerebri. The word “paleo” translates to “primeval.” Developmentally, the cerebrum consists of the striatum, paleocortex, archicortex, and neocortex. From a phylogenetic point of view, the paleocortex is, according to its name, the oldest part of the cerebral cortex. Together with the archicortex it forms the allocortex. With its structures it forms the olfactory brain. In addition, it occupies a small part of the frontobasally located cerebrum. The paleocortex is divided into three layers. Its functions include the reception and transmission of all olfactory impulses from the olfactory nerves. Olfactory cues are processed and discriminated via the olfactory brain. The olfactory bulb belongs to the paleocortex. This is visually reminiscent of a butterfly antenna. From an evolutionary point of view, the sense of smell represents an important source of information. Other sensory impressions such as tasting are strongly connected to it. In addition, this system warns very insistently of dangerous situations. Anatomically, the peculiarity is shown in the form that the information of the smell, unlike the other sensory impressions, is conducted from the nose directly to the cerebral cortex. The otherwise existing switching in the thalamus is completely omitted here.
Anatomy and structure
The cerebral cortex or cortex cerebri is a part of the terminal brain. This is called the telencephalon and histologically consists of the isocortex and the allocortex. Together with the archicortex, the paleocortex forms the allocortex. Both represent over 50% of the cortical volume. In the course of evolution, it has continuously decreased in volume and importance. The allocortex consists of three layers. Specifically, these are called the lamina molecularis or stratum moleculare. It denatures the apical dendrites of the pyramidal cells. The second layer is the lamina pyramidalis or stratum pyramidale. It contains the cell bodies of the pyramidal cells. The last layer is the lamina multiformis or stratum oriens. It contains the basal dendrites of the pyramidal cells. The paleocortex is also called the olfactory cortex. It includes the olfactory pathway and the olfactory cortex. In detail, the paleocortex consists of the bulbus olfactorius as well as the tractus olfaktorius. Furthermore, the tuberculum olfactorium, the septum with the stria diagonalis and the prepiriform cortex belong to it. Likewise, cortical parts of the corpus amygdaloideum are assigned to the paleocortex. A portion of the olfactory cortex is included in the amygdala.
Function and tasks
From the paleocortex, olfactory information is transmitted to various autonomic centers as well as the thalamus. The thalamus then relays the signals to frontobasal neocortex areas. These form the so-called secondary olfactory cortex. There, the perceived information is analyzed, interpreted and recognized. The olfactory system regulates an important function in the recognition of dangerous situations. These include situations such as fire, but also poisonous food. Thus, the paleocortex controls life-sustaining appetence and aversion movements in dangerous situations. The paleocortex is responsible for behaviors such as nausea in the presence of nauseating odors. Likewise, pleasant odors are interpreted by it and trigger vegetative reactions. Positive stimuli such as the smell of tasty food cause processes such as salivation through its activity. In reproduction, the paleocortex performs a kind of mate selection function. The odor of the partner is crucial in mating behavior and elements such as family planning. Via body odor, the organism automatically and thus unconsciously checks whether the potential partner is sufficiently suitable for species maintenance in terms of its immunogenetic makeup. For evolutionary reasons, couples find each other with the aim that the potential offspring should have the optimal genetic makeup. Only with a stable immune system and strong physique can the defense against diseases and thus the preservation of the species be guaranteed. The corpus amygdaloideum is located in the anterior third of the temporal lobe and has fiber connections to important centers of the limbic system. Here they play an essential role in the emotional modulation of vegetative parameters.These are significant in controlling behavior triggered by fear and anger.
Diseases
Impairments and lesions in the paleocortex lead to loss of important social as well as emotional functions. Even a cold suggests the effects that lesions in the paleocortex can have. Smell is picked up by receptor cells in the nasal mucosa. If these are not fully functional due to swelling, this affects the processing of odors. They can lead to the fact that no smell can be perceived and interpreted any more. In addition, it has an impact on the sense of taste. The senses of smell and taste are directly related to each other. Food and beverages lose flavor as soon as the sense of smell is impaired. The functional activity of the paleocortex can be affected by the intake of drugs. For example, the sense of smell changes when contraceptives such as the birth control pill are taken. This has implications in mate choice and thus in reproduction. The paleocortex assumes an important function in the learning of emotional memory content. Memories are stored in memory in greater detail and for longer periods of time when they are tied to odors. As a result, positive odors are recognized more quickly and a greater distance is kept from dangerous odors. In disease, this process can no longer take place sufficiently.
