<P> 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 . </P> <P> 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: </P> <Ul> <Li> Cortical areas: <Ul> <Li> Limbic lobe </Li> <Li> Orbitofrontal cortex, a region in the frontal lobe involved in the process of decision - making . </Li> <Li> Piriform cortex, part of the olfactory system . </Li> <Li> Entorhinal cortex, related with memory and associative components . </Li> <Li> Hippocampus and associated structures, which play a central role in the consolidation of new memories . </Li> <Li> Fornix, a white matter structure connecting the hippocampus with other brain structures, particularly the mammillary bodies and septal nuclei </Li> </Ul> </Li> <Li> Subcortical areas: <Ul> <Li> Septal nuclei, a set of structures that lie in front of the lamina terminalis, considered a pleasure zone . </Li> <Li> Amygdala, located deep within the temporal lobes and related with a number of emotional processes . </Li> <Li> Nucleus accumbens: involved in reward, pleasure, and addiction . </Li> </Ul> </Li> <Li> Diencephalic structures: <Ul> <Li> Hypothalamus: a center for the limbic system, connected with the frontal lobes, septal nuclei and the brain stem reticular formation via the medial forebrain bundle, with the hippocampus via the fornix, and with the thalamus via the mammillothalamic fasciculus . It regulates a great number of autonomic processes . </Li> <Li> Mammillary bodies, part of the hypothalamus that receives signals from the hippocampus via the fornix and projects them to the thalamus . </Li> <Li> Anterior nuclei of thalamus receive input from the mammillary bodies . Involved in memory processing . </Li> </Ul> </Li> </Ul> <Li> Cortical areas: <Ul> <Li> Limbic lobe </Li> <Li> Orbitofrontal cortex, a region in the frontal lobe involved in the process of decision - making . </Li> <Li> Piriform cortex, part of the olfactory system . </Li> <Li> Entorhinal cortex, related with memory and associative components . </Li> <Li> Hippocampus and associated structures, which play a central role in the consolidation of new memories . </Li> <Li> Fornix, a white matter structure connecting the hippocampus with other brain structures, particularly the mammillary bodies and septal nuclei </Li> </Ul> </Li>

What are the four parts of the limbic system