In the last century, knowledge about the anatomy and functions of the different regions of the brain has increased considerably. Scientific research has allowed us today to at least have some clues about how our brain works and, consequently, our cognitive and physiological processes.
In this article we will talk about the functions and nervous connections of the septal nuclei a part of the brain that is essential for memory, emotional expression, pleasure and other processes characteristic of humans and many different animals.
The septal nuclei are a set of subcortical structures that are located between the hypothalamus, the corpus callosum and the septum pellucidum, a membrane that separates the left and right lateral ventricles of the brain. It is also possible to find references to this brain region with the terms “septal area” and “medial olfactory area”.
This concept is not only used to refer to the nuclei themselves, but also to a series of closely interconnected regions at a morphological and functional level: the nucleus accumbens (which has a key role in the activity of the neurotransmitter dopamine), the nucleus of the stria terminalis and Broca’s diagonal band.
The septal nuclei connect the limbic system with subcortical structures of the diencephalon region, thereby They allow an exchange of nervous impulses to occur between these Specifically, the subcortical areas we are referring to are the hippocampus, the amygdala and the hypothalamus.
When lesions occur in the septal nuclei, symptoms related to excessive reactivity to food and sexual stimuli appear. This is associated with the connections of this structure with the hypothalamus, which we will talk about in the following sections.
Connections with other brain regions
The septal nuclei receive input from many different areas of the brain One of the most important connections is the one with the prefrontal cortex; Higher cognitive functions depend on this region, such as working memory, inhibition of inappropriate behavior, moral thinking, planning, and creating expectations.
The arch-shaped structure known as the fornix connects the septal nuclei with the hippocampus, a nucleus of gray matter essential for the consolidation and retrieval of memories, as well as the perception of space.
The medial olfactory stria, a set of nerve fibers, acts as a link between the septal nuclei and the olfactory bulb, which receives olfactory information from sensory receptors located in the olfactory mucosa.
The septal nuclei are also connected to the amygdala, a structure of the limbic system on which emotional learning and memory depend. In this case, the group of axons that links both regions is called the “stria terminalis.”
On the other hand, this structure is Also linked to the hypothalamus, which controls the release of hormones, and to the epithalamus or pineal gland, which produces melatonin. Unlike other pathways that the septal nuclei are part of, in this one the connection is bidirectional, since there are afferents and efferents in both directions.
Outputs from the septal nuclei
The pathways that start from the septal nuclei and project to the hypothalamus and epithalamus have different characteristics, despite the anatomical proximity of both structures.
Outputs to the hypothalamus occur through the medial telencephalic tract, a set of fibers with a low degree of myelination that reaches the tegmentum of the brain stem. Myelin is a substance that covers the axons of many neurons, protecting them from the extracellular environment and promoting the transmission of electrochemical impulses.
In contrast, projections to the epithalamus are made through the stria medullaris of the thalamus. When they reach the nucleus of the habenula, a relay occurs in neuronal transmission; From here the efferents travel through the habenointerpeduncular tract until they reach the interpeduncular nucleus and the brain stem.
Functions of this structure
Research suggests that the septal nuclei serve very diverse functions. Two of the main ones seem to be the expression of pleasure responses, including those related to sexuality and the inhibition of fear sensations, which depend on the amygdala.
The septal nuclei are believed to be involved in regulating the activity of the limbic system, as well as in that of brain alertness. In this sense, its function would allow mental preparation for the expectation that a specific significant event will occur, favoring the execution of responses to its appearance.
On the other hand, this set of nuclei is very important for the encoding of new information, and therefore for long-term learning and memory. This function is associated with the connections that the septal nuclei maintain with the hippocampus.
In general, it has been stated that the septal nuclei act by fulfilling a integration role of different physiological and cognitive processes, such as emotion, memory, pleasure, alertness, attention and reactivity to external stimuli. This is due to the multiple inputs that this structure receives from other regions of the brain.
