The Septum
The septal region is not large, but it contains a wide variety of chemical messengers. It is located at the interface between the hippocampus and the hypothalamus and is thought to be involved in emotional, vegetative, and memory functions.
Scientific support: Prof. Dr. Jochen F. Staiger
Published: 09.10.2025
Difficulty: serious
The septal region contains two important, highly interconnected nuclei that represent a central interface between emotion, memory, and behavior in the current context.
Not all septa are the same – above the “verum” is the “pellucidum,” the “translucent partition.” This septum is located exactly in the middle of the brain, between the two hemispheres. Like a triangular sail, it is stretched vertically between the corpus callosum and the fornix, and borders the two lateral ventricles at the anterior horn towards the center.
The septum pellucidum consists of two membranes, the laminae septi pellucidi. Between them, there is a slit-shaped cavity measuring only a few millimeters, the cavum septi pellucidi, which is particularly easy to see in cross-sectional images of the brain. This slit forms during development and is initially connected to the cavity between the two hemispheres until the corpus callosum grows into it and closes off the cavum at the top. It is still well developed in all newborns but usually disappears during childhood.
The area septalis, the septum region – also known as the septum verum, or “true” septum – is a relatively small area of the anterior inner cerebrum. The Latin word septum often refers to a partition in the body – for example, in the nose – but although this septum is the actual, true septum (see box), it does not separate, but rather connects: the hippocampus, hypothalamus, and amygdala.
Location and interconnection
In addition to a medial (i.e., inward) and a lateral (side) core area, the septum also consists of Broca's diagonal band, the stria diagonalis. This extends to the anterior substantia perforata of the olfactory brain. The septum region is bounded at the top by the anterior part of the corpus callosum, its beak. To the side lies the nucleus accumbens.
One of the most important connections of the septum is to the hippocampus. It runs via the fornix (the “vault”), which forms an impressive arch along the corpus callosum, connecting, among other things, the septum and the hippocampus. Despite this detour, the connection is very close: the fibers of the cornu ammonis and, above all, of the subiculum in the hippocampus end via the fornix – either in the contralateral, opposite hippocampus, or in the septum. The fact that this central structure of memory formation has such close connections to the septum says a lot about its importance. In the case of the medial septal nucleus, it is even central; more on that in a moment.
The septum has further connections to the olfactory cortex areas in the immediate vicinity and – also via the fornix – to other structures of the limbic system. Dopaminergic pathways from the midbrain also terminate in the septum. Conversely, the lateral nucleus also influences central structures of the reward system: the ventral tegmental area – the origin of dopaminergic fibers –and the nucleus accumbens. And thus, motivation. At the same time, this nucleus also maintains connections to the amygdala, thereby influencing fear and aggression. Last but not least, the septal region has extensive reciprocal connections with the hypothalamus. These connections make it an important factor in stress processing.
Functions
If we wanted to span the entire arc of life, three aspects are crucial from an evolutionary perspective: nutrition, reproduction, and survival. The septum is a good example of the extensive networking required for this: the amygdala evaluates a situation as helpful or threatening – we could also say: emotional. The reward system specifies helpful situations, i.e., reproduction and food, with a dopaminergic exclamation mark. The hypothalamus, as part of the stress axis as well as the homeostasis of the internal environment, ensures that the body is prepared accordingly. The lateral septum is a central part of this complex processing in search for the right response. In addition, some studies show that it is also involved in the mothering (or “fathering”) of offspring.
But we are still missing the player that ensures that a current situation becomes an experience, that the location of a food source or the habitat of a predator can still be recalled tomorrow: memory, and thus the hippocampus. This is where the medial core of the septum comes into play – also in a central role. Its neurons send their fibers to the hippocampus, where they release two neurotransmitters: the inhibitory GABA and the often excitatory acetylcholine. GABAergic projections seem to provide a basic rhythm for the neural timing of the hippocampus, the so-called theta waves. These waves are important for exploration and memory retrieval – which includes not only important phone numbers and irregular verbs, but also orientation and navigation in the terrain. The hippocampus needs cholinergic inputs to encode new memory content, i.e., for learning. This is particularly evident in cases of damage to the septum, which causes memory loss.
Given the multitude of tasks, it is no wonder that up to 35 different chemical messengers have been found in the various neuron groups of the septum.
First published on September 9, 2011
Updated on October 9, 2025
