THE INTERACTION OF THE SOMATOSENSORY-EVOKED POTENTIALS TO SIMULTANEOUS FINGER STIMULI IN THE HUMAN CENTRAL-NERVOUS-SYSTEM - A STUDY USING DIRECT RECORDINGS
Cl. Hsieh et al., THE INTERACTION OF THE SOMATOSENSORY-EVOKED POTENTIALS TO SIMULTANEOUS FINGER STIMULI IN THE HUMAN CENTRAL-NERVOUS-SYSTEM - A STUDY USING DIRECT RECORDINGS, Electroencephalography and clinical neurophysiology. Evoked potentials, 96(2), 1995, pp. 135-142
In order to investigate the interaction of sensory electrophysiologic
fields arising from the adjacent second (II) and third (III) fingers a
nd the distant second and fifth (V) fingers, direct recordings of soma
tosensory evoked potentials (SEPs) were performed from the sensory and
motor cortices, the sensory thalamic nucleus (nucleus ventralis cauda
lis, VC) and the cuneate nucleus in humans during neurosurgical operat
ions. Electrical stimulation was given to the II, III or V fingers ind
ividually, and also to pairs of either the II and III fingers or the I
I and V fingers simultaneously. The interaction ratio (IR) was devised
as the ratio of amplitude attenuation caused by the simultaneous stim
ulation to two fingers compared with the amplitude of the arithmetical
ly summed SEPs to the individual stimulation of two fingers. The IRs w
ere calculated on N20 and P25 from the sensory cortex, P22 from the mo
tor cortex, P17(thal) from the VC, and N16(cune) and P35(cune) from th
e cuneate nucleus. With both stimulations to the II and III fingers an
d the II and V fingers, P25 showed the greatest IR, followed by P22, t
hen by P17(thal) while N16(cune) exhibited the smallest IR. N20 and P3
5(cune) showed similar IRs and significantly greater IRs with II and I
II finger stimulation compared with II and V finger stimulation. These
results thus indicate that the interaction of somatosensory impulses
occurs in several structures along the sensory pathway in CNS, includi
ng the cuneate nucleus, the sensory thalamic nucleus, as well as senso
ry and motor cortices, with the greatest IRs in the cerebral cortices
and the weakest ones in the brain-stem. They also suggest that the rec
eptive fields of the fingers in the cortical area generating N20 are a
rranged according to the order of the fingers while those in the gener
ating sites for cortical P25 and P22, thalamic P17(thal) and cuneate N
16(cune) tend to be arranged in clusters, while P35(cune) is possibly
modulated by the somatosensory cortex through a long-loop feedback pat
hway.