What is the Septum Pellucidum?

The septum pellucidum is a small membrane wall in the brain of humans and some animals. Its main job is to separate the lateral ventricles, important passageways within the brain tissue, and the membrane forms what’s basically a barrier between these sections. In terms of location, it extends from the corpus collosum, a collection of neural fibers under the cortex, to the fornix, a group of fibers above the thalmus. Aside from this divisionary role, it isn’t thought to have any particular function unto itself; just the same, an absence or serious malformation here can cause a number of potentially serious developmental concerns.

The human brain is a complex organ, and though it often looks somewhat homogeneous in scans or photos, its tissues perform a number of both very different and highly specific functions. Hidden from sight beneath the grey mass of tissue folds and creases is an entire universe of chemical signaling and synaptic commands. The different lobes and partitions each have their own specific tasks, and all the parts necessarily work together to allow the body to function optimally. Looking at things from a more universal view, the membrane isn’t necessarily noteworthy. Compared to more centralized nerve centers, it’s just a membrane; its role is functional more than it is intrinsically useful. That it is part of the brain makes it important, though, and brain functioning isn’t usually the same without it.

This membrane has a thin, triangular shape and is located in the center of the brain near the midline, pretty much exactly between the right and left hemispheres. It is surrounded on three sides — above, below, and in front — and is connected to the corpus collosum, the bundle of neural fibers that connects the cerebral hemispheres. On either side are the lateral ventricles, which are filled with cerebrospinal fluid. In back, it is connected to the fornix, fibers that carry signals from the hippocampus.

It doesn’t carry signals or conduct energy on its own, and no processing happens here. Most scholars agree that its primary function is to serve as a soft and somewhat malleable division between other, more critical brain parts. The membrane’s flexible and thin nature means that it can act as a partition without hindering any processes, and in fact may serve as something of a buffer, keeping signals contained and where they need to be.

The membrane is composed of two layers called laminae septi pellucidi, each of which is made up of both gray and white matter. Before birth, there are cavities or divisions between the layers of the septum pellucidum. These layers usually fuse within the first six months of life as the brain grows and develops and as the skull hardens. This fusion doesn’t always happen, though; scholars estimate that about 10% of people have membranes that are open or improperly sealed. Although most people with this condition do not appear to have any symptoms, it has been loosely connected to mental disturbances and problems with speech.

There are several variations in formation that are usually considered “normal.” A cavum vergae, for example, is a separation in the layers of the membrane in the rear of the membane, usually extending to the to the splenium of the corpus callosum. As a point of reference, the splenium is the rear-most portion of the corpus callosum. The cavum septum pellucidum, similarly, is a space near the front of the membrane. In most cases, these variations don’t cause any difficulties, and in many cases those affected have no idea unless there is occasion for a formal brain scan at some point.

If the septum pellucidum does not form at all, though, there can be some more serious problems. Most of the time, a total absence is caused by a genetic mutation. For example, a missing membrane is one of the major symptoms of a condition called septo-optic dysplasia, in which the patient also has an underdeveloped optic nerve and often some amount of pituitary deficiency. Other problems can include seizures, problems with coordination, and dysfunction of the hypothalmus.