Brown-Séquard syndrome, first described by the physiologist Charles-Édouard Brown-Séquard, is a condition associated with hemisection or damage to one half of the spinal cord. The hemisection damages neural tracts in the spinal cord that carry information to and from the brain. This results in a loss of sensations like pain, temperature, touch, as well as paralysis or loss of muscle function in some parts of the body.
Now, if you look at the cross-section of the spinal cord, the white matter is on the outside and the gray matter is on the inside, and overall it looks like a butterfly. If we draw a horizontal line through the spinal cord, the front half is the anterior or ventral half, and the back half is the posterior or dorsal half. And the butterfly wings are sometimes referred to as horns; so we have two dorsal horns that contain cell bodies of sensory neurons and two ventral horns that contain cell bodies of motor neurons. The white matter consists of myelinated axons which are separated into tracts that carry information to and from the brain. Think of them like highways for neural signals, where some highways carry sensory information to the brain and some carry motor information from the brain to the muscles.
There are a few main tracts to remember. First, there’s the spinothalamic tract which is an ascending pathway and it’s divided into two parts. The lateral tract carries sensory information for pain and temperature, while the anterior tract carries information for pressure and crude touch--or the sense one has been touched, without being able to localize where they were touched. Second, there are two ascending dorsal column tracts- the fasciculus gracilis which carries sensory information from the lower trunk and legs, and the fasciculus cuneatus which carries sensory information from the upper trunk and arms. These tracts both carry sensations like vibration; fine touch, which is where you can localize where you were touched; and proprioception, which is an awareness of your body position in space. Finally, there’s the corticospinal tract which is a descending pathway that carries motor information from the brain to different muscles in the body and it controls voluntary muscle movement.