SEPs to finger joint input lack the N20-P20 response that is evoked by tactile inputs: contrast between cortical generators in areas 3b and 2 in humans

Abstract

A method using a DC servo motor is described to produce brisk angular movements at finger interphalangeal joints in humans. Small passive flexions of 2 degrees elicited sizable somatosensory evoked potentials (SEPs) starting with a contralateral positive P34 parietal response thought to reflect activation of a radial equivalent dipole generator in area 2 which receives joint inputs. By contrast, electric stimulation of tactile (non-joint) inputs from the distal phalanx evoked the usual contralateral negative N20 reflecting a tangential equivalent dipole generator in area 3b. Finger joint inputs also evoked a precentral positivity equivalent to the P22 of motor area 4, and a large frontal negativity equivalent to N30. It is suggested that natural stimulation allows human SEP components to be differentiated in conjunction with distinct cortical somatotopic projections.

Different contribution of joint and cutaneous inputs to early scalp somatosensory evoked potentials

“…1), which could be considered as resulting from a pure joint stimulation, do not show both N20/P20 and N24/P24 components. When compared with our study, earlier reports on scalp responses evoked by natural proprioceptive stimulation (brisk passive movement of finger joint) showed a definite parietal positivity ("P34" 9 or "P1" 34 ), which was absent in our traces. However, the contribution of muscle afferents to the scalp potential evoked by this type of natural stimulation is still a matter of debate.…”

“…10,11 Last, the selective activation of the finger proprioceptive inputs generates well-identifiable frontal responses. 9,34 However, a comparative analysis of frontal SEPs in response to stimulation of fibers subserving different sensory modalities has been performed only rarely. 9,37,46 To elucidate whether frontal responses depend on the type of peripheral input, we compared scalp SEPs in response to finger electric stimuli applied either to the proximal phalanx of the thumb, thus involving both deep and cutaneous afferents, or to the distal phalanx of the thumb, thus excluding tendinous inputs and joint inputs coming from the interphalangeal articulation.…”

“…9,34 However, a comparative analysis of frontal SEPs in response to stimulation of fibers subserving different sensory modalities has been performed only rarely. 9,37,46 To elucidate whether frontal responses depend on the type of peripheral input, we compared scalp SEPs in response to finger electric stimuli applied either to the proximal phalanx of the thumb, thus involving both deep and cutaneous afferents, or to the distal phalanx of the thumb, thus excluding tendinous inputs and joint inputs coming from the interphalangeal articulation. Moreover, because the mere visual inspection of traces can entail some ambiguity in the EP analysis, we analyzed our SEPs by means of spatiotemporal dipole modeling (BESA).…”

Neural connectivity in hand sensorimotor brain areas: An evaluation by evoked field morphology

“…Selected wiring and neuronal pools recruited in series or in parallel by the stimulated system result in a typical activation pattern of neuronal firing that shapes up the brain responses as detected by depth-implanted electrodes [Godey et al, 2001] as well as by scalp recordings [Creutzfeldt, 1977;Desmedt and Ozaki, 1991;Mauguiere et al, 1997;Rossini et al, 1981Rossini et al, , 1987 either by electroencephalography (EEG) [Dustman and Beck, 1965;Lewis et al, 1972] or via magnetoencephalography (MEG) [Kawamura et al, 1996;Tecchio et al, 2000].…”

Dipole Source Analyses of Early Median Nerve SEP Components Obtained From Subdural Grid Recordings

“…Scalp mapping studies and recordings from patients with cerebral lesions like Huntington's disease and from focal infarctions suggested area 4 as generator (Abbruzzese et al 1990;Desmedt and Ozaki 1991;Desmedt et al 1987;Mauguiere and Desmedt 1991;Rossini et al 1989;Töpper et al 1993). In a recent study using electroencephalographic (EEG) dipole source analysis, Jung et al (2008) localized the P22 dipole source in area 4 but could not rule out area 1, which also contributed to the signal.…”