Anterior white commissure
The anterior white commissure is a bundle of nerve fibers which cross the midline of the spinal cord just anterior to the gray commissure. A delta fibers and C fibers carrying pain sensation in the spinothalamic tract contribute to this commissure, as do fibers of the anterior corticospinal tract, which carry motor signals from the primary motor cortex.
Two of the five sensory modalities, pain and temperature, cross sides at the anterior white commissure, reaching the contralateral side about two vertebral levels rostral to their origin. The spinothalamic tract thus decussates very soon after entering the spinal cord, ascending in the spinal cord, contralateral to the side from where it provides sensory information. Therefore, a lesion that is caudal to the sensory decussation where the remaining 3/5 modalities decussate will result in contralateral pain and temperature loss, whereas loss of crude touch, pressure, and proprioception will be ipsilateral as these have not yet crossed over.
