Limbic system

The limbic system, also known as the paleomammalian cortex, is a set of brain structures located on both sides of the thalamus, immediately beneath the medial temporal lobe of the cerebrum primarily in the midbrain. The limbic system, also known as the paleomammalian cortex, is a set of brain structures located on both sides of the thalamus, immediately beneath the medial temporal lobe of the cerebrum primarily in the midbrain. It supports a variety of functions including emotion, behavior, motivation, long-term memory, and olfaction. Emotional life is largely housed in the limbic system, and it critically aids the formation of memories. With a primordial structure, the limbic system is involved in lower order emotional processing of input from sensory systems and consists of the amygdaloid nuclear complex (amygdala), mammillary bodies, stria medullaris, central gray and dorsal and ventral nuclei of Gudden. This processed information is often relayed to a collection of structures from the telencephalon, diencephalon, and mesencephalon, including the prefrontal cortex, cingulate gyrus, limbic thalamus, hippocampus including the parahippocampal gyrus and subiculum, nucleus accumbens (limbic striatum), anterior hypothalamus, ventral tegmental area, midbrain raphe nuclei, habenular commissure, entorhinal cortex, and olfactory bulbs. The interacting components of the limbic system are often incorrectly considered part of the limbic system itself. Currently, these functional units, including the limbic system, together, comprise multiple higher order emotional processing systems including the Yakovlev and Papez circuits. Paul D. Maclean coined the term limbic system, referring to the Papez circuit, but the term has since evolved due to the advancement in the understanding of emotional processing. Hence, the 'system' part of the limbic system is no longer technically correct, but is still used to refer to the lower-order emotional processing areas in the mesencephalic region. The limbic system was originally defined by Paul D. MacLean as a series of cortical structures surrounding the limit between the cerebral hemispheres and the brainstem: the border, or limbus, of the brain. These structures were known together as the limbic lobe. Further studies began to associate these areas with emotional and motivational processes and linked them to subcortical components that were grouped into the limbic system. The existence of such a system as an isolated entity responsible for the neurological regulation of emotion has gone into disuse and currently it is considered as one of the many parts of the brain that regulate visceral autonomic processes. Therefore, the definition of anatomical structures considered part of the limbic system is a controversial subject. The following structures are, or have been considered, part of the limbic system: The structures and interacting areas of the limbic system are involved in motivation, emotion, learning, and memory. The limbic system is where the subcortical structures meet the cerebral cortex. The limbic system operates by influencing the endocrine system and the autonomic nervous system. It is highly interconnected with the nucleus accumbens, which plays a role in sexual arousal and the 'high' derived from certain recreational drugs. These responses are heavily modulated by dopaminergic projections from the limbic system. In 1954, Olds and Milner found that rats with metal electrodes implanted into their nucleus accumbens, as well as their septal nuclei, repeatedly pressed a lever activating this region, and did so in preference to eating and drinking, eventually dying of exhaustion. The limbic system also interacts with the basal ganglia. The basal ganglia are a set of subcortical structures that direct intentional movements. The basal ganglia are located near the thalamus and hypothalamus. They receive input from the cerebral cortex, which sends outputs to the motor centers in the brain stem. A part of the basal ganglia called the striatum controls posture and movement. Recent studies indicate that, if there is an inadequate supply of dopamine, the striatum is affected, which can lead to visible behavioral symptoms of Parkinson's disease. The limbic system is also tightly connected to the prefrontal cortex. Some scientists contend that this connection is related to the pleasure obtained from solving problems. To cure severe emotional disorders, this connection was sometimes surgically severed, a procedure of psychosurgery, called a prefrontal lobotomy (this is actually a misnomer). Patients having undergone this procedure often became passive and lacked all motivation.