Human Sensation of Transcranial Electric Stimulation

Abstract

Noninvasive transcranial electric stimulation is increasingly being used as an advantageous therapy alternative that may activate deep tissues while avoiding drug side-effects. However, not only is there limited evidence for activation of deep tissues by transcranial electric stimulation, its evoked human sensation is understudied and often dismissed as a placebo or secondary effect. By systematically characterizing the human sensation evoked by transcranial alternating-current stimulation, we observed not only stimulus frequency and electrode position dependencies specific for auditory and visual sensation but also a broader presence of somatic sensation ranging from touch and vibration to pain and pressure. We found generally monotonic input-output functions at suprathreshold levels, and often multiple types of sensation occurring simultaneously in response to the same electric stimulation. We further used a recording circuit embedded in a cochlear implant to directly and objectively measure the amount of transcranial electric stimulation reaching the auditory nerve, a deep intercranial target located in the densest bone of the skull. We found an optimal configuration using an ear canal electrode and low-frequency (<300 Hz) sinusoids that delivered maximally ~1% of the transcranial current to the auditory nerve, which was sufficient to produce sound sensation even in deafened ears. Our results suggest that frequency resonance due to neuronal intrinsic electric properties need to be explored for targeted deep brain stimulation and novel brain-computer interfaces.

Cutaneous sensation of electrical stimulation waveforms

“…tRNS and low-frequency tACS have lower perceived sensation levels than tDCS [17,22]. Sensations with tACS are non-monotonic with frequency in the range of 5 Hze10 kHz with a maximum at 50 Hz [23], similar to the pattern from transcutaneous stimulation studies (discussed above). Recent experimental work argued that DC or AC stimulation, when applied with a pulsed carrier at high frequencies (>1 kHz) may reduce sensation [24,25].…”

Tinnitus Treatment Using Noninvasive and Minimally Invasive Electric Stimulation: Experimental Design and Feasibility

“…In the present study, electric stimulation evoked tactile sensation ranging from tingling and vibration to prick or even pain in all 10 subjects tested here. In some subjects, electric stimulation also evoked visual sensation, such as white flickers, and vestibular responses, and muscle activation (Zeng et al, 2018). In one particular case, T8 who had otosclerosis and received a stapes prosthesis, electric stimulation not only produced tingling and stinging sensations on the dermal electrode sites (i.e., ear canal and forehead), but also similar sensations on nonelectrode sites including the back of the head, back of the throat, and the ipsilateral side of the tongue, plus muscular contraction of the mid-and upper face.…”

Input–Output Functions in Human Heads Obtained With Cochlear Implant and Transcranial Electric Stimulation

“…Thus, electrical stimulation is most effective when delivered directly to neural targets through nearby electrodes. Increasing the distance of the electrodes from the target not only decreases the efficiency, it also increases the likelihood of side effects because electric current unavoidably spreads through intermediate tissues including untargeted neurons and receptors [11][12][13] .…”