Septal nuclei

At a glance

English

Septal nuclei

Latin (TA2)

Nuclei septales

System

Brain and spinal cord

Region

Head

Side

Single, on the midline

About the septal nuclei

The septal nuclei lie in the septal area, a small region of the medial forebrain under the rostrum and genu of the corpus callosum, ahead of the lamina terminalis and anterior commissure. The region continues upward into the thin septum pellucidum between the lateral ventricles, and much of the nuclear tissue lies in the base of that septum. Below and in front it blends with the subcallosal area and the paraterminal gyrus. The area was once called the medial olfactory area, although it plays little part in smell.

The nuclei are made of medium-sized neurons and are grouped into a lateral septum and a medial septum. The medial group continues into the nucleus of Broca's diagonal band. The lateral group is the largest and receives much of the input from the hippocampus. Related cell groups include the bed nucleus of the stria terminalis and a small bed nucleus belonging to the anterior commissure.

Their connections are widespread and mostly two-way. They exchange fibres with the hippocampal formation through the fornix and fimbria, with the amygdala through the stria terminalis, and with the hypothalamus, midbrain tegmentum and habenula through the medial forebrain bundle and the stria medullaris thalami. Cholinergic and GABA neurons of the medial septum and diagonal band project to every field of the hippocampus and pace its theta rhythm, an oscillation tied to memory and spatial navigation. The lateral septum relays hippocampal signals to the hypothalamus and ventral tegmental area and is thought to link reward and drive to place and context.

Experiments in rats in the 1950s showed that animals would press a lever repeatedly to stimulate this region, which made it one of the first known reward sites. In humans the septal area is linked with pleasure, motivation and emotional calm, and lesions in animals can make them markedly irritable. Loss of the cholinergic septal and basal forebrain neurons contributes to memory decline in Alzheimer's disease.

Function and supply

Function

Paces the hippocampal theta rhythm and links hippocampal memory and context signals with hypothalamic and midbrain systems for reward, motivation and emotional behaviour.

Blood supply

Small branches of the anterior cerebral and anterior communicating arteries, including the subcallosal and medial striate branches.