The Limbic System Overview

The Limbic System

• The limbic system is a group of structures that control emotions, memory, and behaviours.
• It is located on the medial side of the cerebral hemispheres, encircling the diencephalon.
• This system is interconnected with the hypothalamus.

Limbic System Structures

• Limbic Lobe: Consists of a ring-shaped region of grey matter on the medial aspect of each cerebral hemisphere, encircling the corpus callosum.
  • Parts of the Limbic Lobe: Subcallosal area, cingulate gyrus, isthmus, parahippocampal gyrus, and uncus.
• Hippocampus: A horseshoe-shaped structure that is situated in each cerebral hemisphere.
  • Functions: Formation, organization, and storage of memories. It helps connect emotions and senses with memories, and acts as a memory indexer to the appropriate cerebral hemisphere.
• Amygdala: An almond-shaped mass of nuclei located near the temporal pole within the temporal lobes.
  • Function: Involves emotions like fear, anger, aggression, and hormonal secretions.
• Septal Nuclei: Located anterior to the interventricular septum.
  • Function: Plays a role in pleasurable sensations.

Thalamus

• The largest nuclear mass in the whole body, forming the largest part of the diencephalon.
• It's a gateway to the cortex; receives sensory input and relays it to the corresponding areas in the cerebral cortex. Sensory input from all parts of the body except the olfactory system passes through the thalamus.
• It is divided into two oval masses of grey matter, acting as a relay centre for sensory information.
• It is connected to the opposite thalamus by the interthalamic connexus, a narrow adhesion of tissue or Massa intermedia.

Thalamic Nuclei

• Anterior Thalamic Nuclei: Afferent connections from the mamillary body; efferent connections to the cingulate gyrus.
• Medial Nuclei:
  • Afferent connections to the hypothalamus;
  • Efferent connections to the prefrontal cortex and the frontal cortex.
• Ventral Anterior Nucleus:
  • Afferent connections to parts of the globus pallidus body;
  • Efferent connections to the premotor cortex.
• Ventral Lateral Nucleus:
  • Afferent connections from the dentate nucleus;
  • Efferent connections to the primary motor cortex.
• Ventral Posterior Lateral Nucleus:
  • Afferent connections from the medial and spinal lemnisci;
  • Efferent connections to the sensory cortex.
• Ventral Posterior Medial Nucleus:
  • Afferent connections from the trigeminal lemniscus;
  • Efferent connections to the sensory cortex.
• Lateral Geniculate Body:
  • Afferent connections from the optic tract;
  • Efferent connections to the visual cortex.
• Medial Geniculate Body:
  • Afferent connections from the lateral lemniscus;
  • Efferent connections to the auditory cortex.

White Matter of Thalamus

• External Medullary Lamina: Located on the lateral surface of the thalamus; consists of thalamocortical and corticothalamic fibers.
• Internal Medullary Lamina: A Y-shaped bundle of myelinated fibers (afferent and efferent). Divides the thalamus into anterior, medial, and lateral nuclear groups. Each group is further divided into named nuclei.

Lesions

• Lesions in the limbic lobe are associated with disorders, such as Korsakoff's psychosis, temporal lobe epilepsy, herpes encephalitis, Alzheimer's disease, and schizophrenia.