In Brown-Sequard syndrome below the level of injury, contralateral loss of pain and temperature is due to disruption of which tract?

• A. Spinothalamic tract.
• B. Dorsal column.
• C. Corticospinal tract.
• D. Spinocerebellar tract.

Answer: (A)

Pain and temperature signals cross to the opposite side early in the spinal cord. When a hemisection (Brown-Sequard) interrupts one side, the fibers that carry pain and temperature have already crossed to the contralateral side and then ascend in the spinothalamic tract. Therefore, below the level of injury you lose pain and temperature on the opposite side. In contrast, motor control and position sense travel in the corticospinal and dorsal column pathways on the same side, so those functions are typically spared on the opposite side but impaired on the injured side. The spinocerebellar tract isn’t responsible for conscious pain or temperature, so it doesn’t explain contralateral loss of those modalities.