Abstract
In searching for clinical biomarkers of the somatosensory function, we studied reproducibility of somatosensory potentials (SEP) evoked by finger stimulation in healthy subjects. SEPs induced by electrical stimulation and especially after median nerve stimulation is a method widely used in the literature. It is unclear, however, if the EEG recordings after finger stimulation are reproducible within the same subject. We tested in five healthy subjects the consistency and reproducibility of responses through bootstrapping as well as test–retest recordings. We further evaluated the possibility to discriminate activity of different fingers both at electrode and at source level. The lack of consistency and reproducibility suggest responses to finger stimulation to be unreliable, even with reasonably high signal-to-noise ratio and adequate number of trials. At sources level, somatotopic arrangement of the fingers representation was only found in one of the subjects. Although finding distinct locations of the different fingers activation was possible, our protocol did not allow for non-overlapping dipole representations of the fingers. We conclude that despite its theoretical advantages, we cannot recommend the use of somatosensory potentials evoked by finger stimulation to extract clinical biomarkers.
Highlights
Somatosensory impairment is highly associated with stroke severity (Connel et al 2008; Meyer et al 2016)
Somatosensory evoked potentials and fields (SEPs and SEFs, respectively) induced by electrical or mechanical stimulation on the median nerve is a well-established approach to investigate the electrophysiological phenomena linked to impaired somatosensation occurring, for example, while recovering from a stroke (Keren et al 1993; Péréon et al 1995; Timmerhuis et al 1996; Rossini et al 1998a, 2001; Wikström et al 1999, 2000; Hari and Forss 1999; Feys et al 2000; Tzvetanov and Rousseff 2003; Huang et al 2004; Oliviero et al 2004; Tecchio et al 2007a, b, 2006; Al-Rawi et al 2009)
In order to suggest somatosensory potentials (SEP) induced by electrical stimulation of the finger as a relevant patient-specific biomarker, reproducible SEP responses and discrimination of finger representations should be possible in all five healthy participants tested
Summary
Somatosensory impairment is highly associated with stroke severity (Connel et al 2008; Meyer et al 2016). Somatosensory evoked potentials and fields (SEPs and SEFs, respectively) induced by electrical or mechanical stimulation on the median nerve is a well-established approach to investigate the electrophysiological phenomena linked to impaired somatosensation occurring, for example, while recovering from a stroke (Keren et al 1993; Péréon et al 1995; Timmerhuis et al 1996; Rossini et al 1998a, 2001; Wikström et al 1999, 2000; Hari and Forss 1999; Feys et al 2000; Tzvetanov and Rousseff 2003; Huang et al 2004; Oliviero et al 2004; Tecchio et al 2007a, b, 2006; Al-Rawi et al 2009). By. Brain Topography (2018) 31:498–512 stimulating directly at the median nerve, both cutaneous muscle and joint afferents are stimulated and potentially efferent fibers intervening (muscles) (Dawson 1956; Mauguiere 1999; Kuiken et al 2007). In view of our interest on hand representation, we focused on activity induced by stimulation of the digits, as assuming this to elicit responses at a more specified area at the somatosensory cortex
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