Origins of the short latency somatosensory evoked potentials in cat--with special reference to the sensory relay nuclei.
In order to identify the generators of short latency somatosensory evoked potential (SL-SEP) components, we studied, in cats, the relationship between the latencies of SL-SEP components and those of action potentials travelling along the somatosensory pathway. We also studied the changes of SL-SEPs after small lesions at various levels along the pathway. In the record with a noncephalic reference, four positive peaks (PI, PII, PIII, PIV) and three negative peaks (NI, NII, NIII) were identified. Two to three small negative waves (III-a, III-b, III-c) were superimposed on the waves from PIII to NIII. We concluded as follows: (i) NIII is a near-field component originating in the primary somatosensory cortex. (ii) III-a, III-b, and III-c originate between the decussation of the medial lemniscus and the thalamus. (iii) PIII probably originates from multiple structures rostral and caudal to the decussation of the medial lemniscus. PII, NII, and a part of PIII may originate in the region where C6 to T1 dorsal roots enter the spinal cord. (iv) The earliest components or PI and NI originate in the peripheral nerve at the axilla. (v) No components of SL-SEP originating at the dorsal root ganglia, dorsal column nuclei, thalamic VPL nucleus, or cerebellum were identified. (vi) Most of the SL-SEP components may originate where the volume conductor geometry or the impedance of the conducting medium changes suddenly.
Ryu
H
H
Department of Neurosurgery, Hamamatsu University, School of Medicine, Japan.
Uemura
K
K
D000200:Action Potentials; D000344:Afferent Pathways / Q000502:physiology; D000818:Animals; D001917:Brachial Plexus / Q000502:physiology; D002415:Cats; D004558:Electric Stimulation; D005073:Evoked Potentials, Somatosensory; D005727:Ganglia, Spinal / Q000502:physiology; D008475:Median Nerve / Q000502:physiology; D009424:Nervous System Physiological Phenomena; D011930:Reaction Time; D012677:Sensation / Q000502:physiology*; D013003:Somatosensory Cortex / Q000502:physiology; D013116:Spinal Cord / Q000502:physiology; D013787:Thalamic Nuclei / Q000502:physiology