The septum lucidum — also known as the septum pellucidum — is a thin, sheet-like membrane near the midbrain that is shaped like a teardrop. It lies beneath the corpus callosum — a band of nerve strands connecting the left and right hemispheres of the brain — and above the fornix — an arch-shaped band connecting the left and right cerebral hemispheres — or conscious mental centers of the brain. The lower right and left sides of this membrane are fused together near the center of the brain to form the middle wall of the lateral ventricles, which are triangular-shaped spaces with projections called “horns” and are filled with the cerebrospinal fluid that circulates around the brain’s nerve-processing centers.
The area of the brain known as the septum lucidum has not been recognized by neuroscience — the study of the workings of the brain — as serving any specific anatomic purpose other than as a separation membrane between the septal nuclei and the corpus callosum. As such, the membrane consists mainly of glial cells — one of the two main types of cells in the brain. Glial cells are the most abundant type of brain tissue, outnumbering neurons, the other type of brain cells, by 9:1, as well as making up over 50 percent of the volume of the brain. While neurons are called the “thinking” cells that transmit signals around the brain’s neural network, it has been speculated that glial cells actually do more than simply support the informational processing function of the neurons.
Some modern studies have shown that the glial cells — especially those contained in such crucially located midbrain structures as the septum lucidum — may have functions that were previously unknown, such as the ability to propagate calcium waves. It is further theorized that calcium waves represent a form of low-intensity signaling within the brain that is separate from the high-speed electrical activity conducted by neurons, which have been traditionally accepted as being the sole initiators of thinking activities within the brain. Study of these waves demonstrates the subtle ways of functioning of the brain become apparent, adding additional layers of complexity to the commonly perceived operations of the brain.