Effects of galvanic mastoid stimulation in seated human subjects

Abstract

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.

Modulation of soleus H reflex by spinal DC stimulation in humans

“…First, the onset of tsDCS is accompanied by an initial itching sensation due to the activation of cutaneous afferents beneath the electrodes. Indeed, it has been shown that cranial (Delwaide and Crenna 1983;Ghanim et al 2009) and peripheral (Baldwin et al 2006;Klakowicz et al 2006;Lagerquist and Collins 2010) cutaneous stimulation may influence Sol H reflex (i.e., cutaneous effects might, by themselves, result in changes in spinal excitability). However, this possibility seems unlikely since 1) none of the subjects was able to differentiate active conditions from verum stimulation, and cutaneous perception has been shown to be similar between anodal and cathodal conditions (Ambrus et al 2011); 2) tsDCS-induced effects were specific to anodal polarity; and 3) spinal excitability was unchanged after both cathodal and sham stimulations.…”

Vestibular stimulation-induced facilitation of cervical premotoneuronal systems in humans

“…A pair of disposable surface electrodes (Vitrode F-150S, Nihon Kohden Corporation) was placed over the bilateral mastoid processes for bipolar stimulation [15, 16, 26, 27]. We used two electrode montages for GVS: anodal and cathodal GVS (e.g., anodal GVS indicated that the right electrode was the anode).…”

The Effects of Transcranial Direct Current Stimulation on Functional Movement Performance and Balance of the Lower Extremities

“…No previous research directly examined power among investigations on lower extremity motor function in accordance with tDCS application. In a study of a single muscle in the lower extremities, Ghanim et al 20) reported increased strength of the soleus muscle during sitting and standing motions. Tanaka et al 21) noted that stimulation of the lower extremity motor area led to increased muscle strength of a single joint, activation of dorsiflexor muscles, and increased toe strength to grab.…”

“…Jeffrey et al 17) noted that a current intensity of 2mA increased response time and muscle activity of the lower extremities more than a current intensity of 1mA level, and activation of the pre-motor area continued for some time after stimulation 7,[18][19] . Among research on lower extremity motor functions, Ghanim et al 20) reported improved activity of the soleus muscle during sitting and standing motions. Tanaka et a1.…”