 an axial section through the brain. When we take an axial section through the brain we see first a thin rim of gray matter which is referred to as the cortex, the cerebral cortex but let's focus on this white matter here. This is referred to as the subcautical white matter which becomes confluent with the central white matter and which merges with the periventricular white matter. This whole thing is composed of nerve fibers which are malenated and that's why this referred to as the white matter. For the ease of understanding this white matter has been divided into three broad groups. The so called commissural fibers, the projection fibers and association fibers. Let's take a look at how these fibers are disposed. This is a very special type of investigation which is referred to as diffusion tensor imaging with white matter tractography. It's a very sophisticated investigation which gives a three dimensional representation of the white matter inside the brain. So this is a coronal view of the brain and you can see that this is one hemisphere here this is another hemisphere. This is the longitudinal fissure. This is a commissural fiber here. These colors have been coated by the computer. This band of fibers that are running down here on either side this is an example of a projection fiber and these fibers that you see here these are some association fibers. The thrust of our discussion today will be on the projection fibers. Let's take a look at