[Ascending limb of the N20 component of somatosensory evoked potential--an analysis on direct recording from the human midbrain].
Somatosensory evoked potential elicited by median nerve stimulation at the wrist was recorded from five loci on the trajectory of stereotactic rostral mensencephalic reticulotomy. Four distinct positive waves followed by one negative wave, the peak latency being 16.3 msec, were recorded from the rostral midbrain reticular formation near the medial lemniscus. The four positive waves were named as I, II, III, and IV respectively. Peak latency of these positive waves was 12.6, 13.7, 14.7 and 15.8 msec respectively. The first two positive waves (I, II) corresponded to P13 and P15 recorded over the scalp. The other two positive waves (III, IV) changed their polarity to negative at the level of the ventral thalamus and formed the ascending limb of N20 recorded over the scalp. N16 was most prominent at the level of nucleus ventrocaudalis externus. These findings suggest that the ascending limb of N20 is composed of at least three components, wave III, IV, and N16. The present report is compatible with the investigations by Abbruzzese et al.2) and Eisen et al.11) that there are several distinct dipoles between P15 and N20 of somatosensory evoked potential in man.
Taira
T
T
Amano
K
K
Kawamura
H
H
Tanikawa
T
T
Kawabatake
H
H
Notani
M
M
Iseki
H
H
Shiwaku
T
T
Nagao
T
T
Iwata
Y
Y
D000344:Afferent Pathways / Q000502:physiology; D004558:Electric Stimulation; D005073:Evoked Potentials, Somatosensory; D008475:Median Nerve / Q000502:physiology; D008636:Mesencephalon / Q000502:physiology*