Neuroscience: Thalamus and Cerebral Cortex

Limbic System Overview

• The limbic system is a group of structures that are involved in emotions, motivations, and memory.
• It separates the medial surface of the cerebral cortex from the diencephalon.
• It includes several structures (cortical and subcortical) with loops connecting the hypothalamus.

Thalamus

• It is the largest nuclear mass in the body and part of the diencephalon.
• Formed from two oval masses of grey matter located as a gateway to the cortex
• It connects to the opposite side by the interthalamic connexus.

Thalamic Nuclei

• Thalamic nuclei are sub-divided into groups (lateral, medial, posterior, anterior).
• Each group is further divided into nuclei with different functions and connections. (e.g., Ventral Anterior, Ventral Lateral, Medial, Ventral Posterior etc)
• Specific examples of nuclei include : Anterior thalamic nuclei, Medial Nuclei, Ventral Anterior, Ventral Lateral, Ventral Posterior, Lateral geniculate body, medial geniculate body, and Pulvinar.

Thalamic Projections

• Each thalamic nucleus has a certain projection.
• Specific afferent and efferent pathways link each nucleus to different areas of the cerebral cortex.
  • Example: Anterior thalamic nuclei receive input from mammillary bodies & project to cingulate gyrus.

Limbic System Structures

• Limbic Lobe (cortical structure) - a C-shaped ring on the medial side of each hemisphere, including the cingulate gyrus, subcallosal area, isthmus, parahippocampal gyrus, uncus.
• Hippocampus - A horseshoe-shaped structure (one in each hemisphere) important for memory and learning. Its role is in forming, organizing, and storing memories by linking emotions and senses with memories.
• Amygdala - Almond-shaped structure near the temporal pole and the tail of the caudate nucleus, is involved in emotions such as fear, anger, aggression, and hormone secretions.
• Septal Nuclei- Located anterior to the interventricular septum, and the septal nuclei are involved in pleasure and some memory systems.

Hippocampus Structure & Function

• Site: (infolding structure found in the inferior medial portion of the temporal lobe.)
• Function: Memory consolidation, new memories are formed and filed, connecting emotions and senses & short-term memory to long-term storage.

Fornix

• It is a C-shaped group of fibres (connecting the hippocampus), involved in relating the hippocampus to the mammillary body and then anterior nuclei of the thalamus.
• Consists of : Fimbria, Crus, Body, and Columns.
• It plays an essential role for emotions control pathways.

Limbic System lesions & Disorders

• Lesions within the limbic lobe may result in memory problems, emotional disturbances, or even changes in personality.
• Specific diseases affecting the hippocampus include korsakoff syndrome, epilepsy, or Alzheimer's Disease.
• Other conditions to be aware of are temporal lobe epilepsy & Schizophrenia.

Connections Amygdala

• Inputs: Association areas of visual, auditory and somatosensory cortices
• Outputs: Hypothalamus and autonomic nuclei in the brain stem
• Lesions: can result in emotional responses to be affected

Function of the Limbic System

• Emotions: Emotional response involves many cortical and subcortical structures.
• Memory: Memory involves the cerebral cortex and hippocampus, the hippocampus forming and storing memories with sense and emotions.
• Motivation: A complex issue with many factors and areas involved.
• Pleasure: A complex issue with many factors and areas involved.
• Olfaction: Involved in memory and emotion.