Unexpected latency shifts of the stationary P9 somatosensory evoked potential far field with changes in shoulder position.

Early somatosensory evoked potential (SEP) components to median nerve stimulation were recorded with non-cephalic reference from scalp, neck and oesophagus in normal young adults. The nerve volley was recorded from the arm and Erb's point. The latencies of the stationary P9 far field were increased significantly by supporting the shoulder in a high position. This manoeuvre was shown in X-rays to change the axis of the nerve at levels between lateral and middle parts of the clavicle. This suggests that the far field is not related to inhomogeneities of the medium surrounding the nerve whereby abrupt changes in extracellular current flow might be produced as the volley arrives at a certain level. Rather, the axial orientation of the propagated dipole appears as a major factor determining the features of the stationary P9 far field. The reversible effect described does not significantly influence the conduction of the volley itself nor the latencies of the subsequent SEP components.

[1]  R. Cracco,et al.  Somatosensory evoked potential in man: far field potentials. , 1976, Electroencephalography and clinical neurophysiology.

[2]  W C Wiederholt,et al.  Short-latency somatosensory evoked potentials. , 1978, Archives of neurology.

[3]  F Mauguière,et al.  Neural generators of N18 and P14 far-field somatosensory evoked potentials studied in patients with lesion of thalamus or thalamo-cortical radiations. , 1983, Electroencephalography and clinical neurophysiology.

[4]  R. Cracco,et al.  Short latency SEPs to median nerve stimulation: comparison of recording methods and origin of components. , 1981, Electroencephalography and clinical neurophysiology.

[5]  R. L. Nó,et al.  A Study Of Nerve Physiology , 1947 .

[6]  T. Nakanishi.  Action potentials recorded by fluid electrodes. , 1982, Electroencephalography and clinical neurophysiology.

[7]  J E Desmedt,et al.  The cognitive P40, N60 and P100 components of somatosensory evoked potentials and the earliest electrical signs of sensory processing in man. , 1983, Electroencephalography and clinical neurophysiology.

[8]  G. Klem,et al.  Early somatosensory potentials evoked by median nerve stimulation , 1981, Neurology.

[9]  I. Tasaki,et al.  A NEW MEASUREMENT OF ACTION CURRENTS DEVELOPED BY SINGLE NODES OF RANVIER. , 1964, Journal of neurophysiology.

[10]  T. Yamada,et al.  Central latencies of somatosensory cerebral evoked potentials. , 1978, Archives of neurology.

[11]  J Arezzo,et al.  Topography and intracranial sources of somatosensory evoked potentials in the monkey. I. Early components. , 1979, Electroencephalography and clinical neurophysiology.

[12]  G Cheron,et al.  Prevertebral (oesophageal) recording of subcortical somatosensory evoked potentials in man: the spinal P13 component and the dual nature of the spinal generators. , 1981, Electroencephalography and clinical neurophysiology.

[13]  Gert Pfurtscheller,et al.  Progress in clinical neurophysiology. Vol. 1. Attention, voluntary contraction and event-related cerebral potentials: J.E. Desmedt (Ed.) (Karger, Basel, 256 p., 95 figs., 6 tab., 1977, DM 98.—) , 1979 .

[14]  G Cheron,et al.  Central somatosensory conduction in man: neural generators and interpeak latencies of the far-field components recorded from neck and right or left scalp and earlobes. , 1980, Electroencephalography and clinical neurophysiology.

[15]  J. Desmedt.  Non-invasive analysis of the spinal cord generators activated by somatosensory input in man: near field and far field potentials , 1984 .

[16]  G. Cheron,et al.  Non-cephalic reference recording of early somatosensory potentials to finger stimulation in adult or aging normal man: differentiation of widespread N18 and contralateral N20 from the prerolandic P22 and N30 components. , 1981, Electroencephalography and clinical neurophysiology.

[17]  J. B. Ranck,et al.  THE SPECIFIC IMPEDANCE OF THE DORSAL COLUMNS OF CAT: AN INISOTROPIC MEDIUM. , 1965, Experimental neurology.

[18]  A. Eisen.  The Somatosensory Evoked Potential , 1982, Canadian Journal of Neurological Sciences / Journal Canadien des Sciences Neurologiques.