LIMBIC SYSTEM

 

In the Fourteenth Century, Broca[1] described the limbic[2] lobe as the gray matter belonging to the medial and basal portions of the cerebral hemispheres that surround the diencephalon. At present, the limbic lobe and the structures that are connected to it are considered to be the limbic system, which serves an important role in visceral functions like behavior, emotions and memory.

 

The limbic system is made up of the following structures. At the cerebral level it consists of the septal portion of the paleocortex, the archicortex (hippocampal formation), the amygdaloid body or amygdala (basal nucleus), the medial portion of the prefrontal cortex (neocortex) and the cingulate gyrus. At the level of the diencephalon, it consists of the rostral nuclei of the thalamus, the habenula (epithalamus) and the mamillary bodies (hypothalamus). At the level of the mesencephalon, the intercrural nucleus and the reticular formation.

 

The structures which form the limbic system are connected to one another by: the habenular stria (connects the telencephalic septum with the habenula), the stria terminalis (connects the amygdaloid body with the telencephalic septum and the mamillary bodies), the fornix (connects the hippocampus, the septum and the mamillary bodies), the fasciculus uncinatus (connects the prefrontal cortex and the amygdaloid body), the diagonal band (connects the amygdaloid body with the telencephalic septum), the mamillothalamic tract (connects the mamillary body with the rostral thalamic nuclei), the mamillary peduncle (connects the intercrural nucleus of the mesencephalon with the mamillary bodies) and the habenulointerpeduncular[3] tract (connects the habenula with the interpeduncular nucleus. The rostral nuclei of the thalamus project to the medial prefrontal cortex and the cingulated gyrus.

 

[1] Pierre Paul Broca (1824-1880), a French pathologist and anthropologist, localized the cortical motor area of the limbic system and described the diagonal band of Broca in the rostral perforated substance.

[2] From the Latin, limbus, “limit, margin.”

[3] Also known as the fasciculus retroflexus.