Median nerve somatosensory evoked potentials recorded with cephalic and noncephalic references in central and peripheral nervous system lesions

Somatosensory evoked potentials (SSEP) to electrical stimulation of the med ian nerve by using cephalic and noncephalic references were studied to dete ct the generator sources of short latency evoked potentials in 29 patients with cerebral, brainstem, spinal and peripheral nerve lesions. Patients were divided into six groups according to the localization of thei r lesions: group 1: cortical and subcortical lesions, group 2: basal gangli on lesions, group 3: pons and mesencephalon lesions, group 4: diffuse cereb ral lesions, group 5: cervical cord lesions, group 6: brachial plexus lesio ns. Potentials were recorded using cephalic and noncephalic references afte r median nerve stimulation. Evidence obtained from patients suggested the following origins for these s hort latency SSEPs: P9 may arise in brachial plexus, P11 in dorsal basal ga nglions or dorsal column, P13 and P14 in the nucleus cuneatus and lemniscal pathways, N16 in subthalamic structures and most likely mid and lower pons , N18 from the thalamus and thalamocortical tract, and N20 from primary som atosensory cortex.