Evoked Potential Exam Preparation 2026 – Complete Practice Test

Somatosensory evoked potentials show how the brain processes a touch stimulus along a standard pathway. The earliest cortical volley, N20–P25, comes from the contralateral primary somatosensory cortex, where initial processing of somatosensory information occurs as it decussates to the opposite hemisphere. The P37 component appears later and reflects processing in the contralateral parietal cortex, a higher-order area involved in integrating somatosensory input. Because the pathways cross to the opposite side, the recorded activity is typically over the hemisphere opposite to the stimulated limb. That’s why the correct description is that N20–P25 arise in the contralateral primary somatosensory cortex and P37 in the contralateral parietal cortex. The other choices don’t fit because brainstem sources wouldn’t produce these specific late cortical peaks in the expected cortical regions, and ipsilateral or occipital locations aren’t consistent with the known somatosensory pathways.