HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 106/3/893    most recent 90594.2008v1 Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Ghanim, Z. Articles by Katz, R. Search for Related Content PubMed PubMed Citation Articles by Ghanim, Z. Articles by Katz, R.

Effects of galvanic mastoid stimulation in seated human subjects

¹Université Pierre et Marie Curie-Paris 6, Unité Mixte de Recherche, Paris; ²Institut National de la Santé et de la Recherche Médicale, U 731, Paris; ³Service de Médecine Physique et Réadaptation, Assistance Publique-Hôpitaux de Paris, Pitié-Salpêtrière, Paris; ⁴Service de Médecine Physique et Réadaptation, Assistance Publique-Hôpitaux de Paris, Raymond Poincaré Hospital, Garches; ⁵National Hospital, Saint Maurice France; and ⁶Department of Functional Investigation Assistance Publique-Hôpitaux de Paris, Tenon Hospital, Paris France

Submitted 30 April 2008 ; accepted in final form 13 December 2008

The vestibular responses evoked by transmastoid galvanic stimulation (GS) in the rectified soleus electromyogram (EMG) in freely standing human subjects disappear when seated. However, a GS-induced facilitation of the soleus monosynaptic (H and tendon jerk) reflex has been described in few experiments in subjects lying prone or seated. This study addresses the issue of whether this reflex facilitation while seated is of vestibulospinal origin. GS-induced responses in the soleus (modulation of the rectified ongoing EMG and of the monosynaptic reflexes) were compared in the same normal subjects while freely standing and sitting with back and head support. The polarity-dependent biphasic responses in the free-standing position were replaced by a non-polarity-dependent twofold facilitation while seated. The effects of GS were hardly detectable in the rectified ongoing voluntary EMG activity, weak for the H reflex, but large and constant for the tendon jerk. They were subject to habituation. Anesthesia of the skin beneath the GS electrodes markedly reduced the reflex facilitation, while a similar, although weaker, facilitation of the tendon jerk was observed when GS was replaced with purely cutaneous stimulation, a tap to the tendon of the sternomastoid muscle, or an auditory click. The stimulation polarity independence of the GS-induced reflex facilitation argues strongly against a vestibular response. However, the vestibular afferent volley, insufficient to produce a vestibular reflex response while seated, could summate with the GS-induced tactile or proprioceptive volley to produce a startle-like response responsible for the reflex facilitation.

vestibular afferents; sensory afferents; H and T reflexes; startle pattern; galvanic stimulation; humans