Abstract #38: Transcranial Electric Stimulation with Multiple Electrodes Can Reach Deep Brain Areas

To reach a deep target in the brain with transcranial electric stimulation (TES), currents have to pass also through the cortical surface. Thus, it is generally thought that TES cannot achieve focal deep brain stimulation. Recent efforts with interfering waveforms and pulsed stimulation have argued that one can achieve deeper or more intense stimulation in the brain. Here we argue that conventional transcranial stimulation with multiple current sources is just as effective as these new approaches. The conventional multi-electrode approach can be numerically optimized to maximize intensity or focality at a desired target location. Using such optimal electrode configurations we find in a detailed and realistic head model that deep targets may in fact be strongly stimulated, with cerebrospinal fluid guiding currents deep into the brain.

Download Full-text

Electric Field Dynamics in the Brain During Multi-Electrode Transcranial Electric Stimulation

10.1101/340224 ◽

2018 ◽

Cited By ~ 4

Author(s):

Ivan Alekseichuk ◽

Arnaud Y. Falchier ◽

Gary Linn ◽

Ting Xu ◽

Michael P. Milham ◽

...

Keyword(s):

Electric Field ◽

Electric Stimulation ◽

Brain Regions ◽

Neural Oscillations ◽

Non Invasive ◽

Multiple Electrodes ◽

Transcranial Electric Stimulation ◽

Mechanistic Understanding ◽

Linear Manner ◽

The Brain

ABSTRACTNeural oscillations play a crucial role in communication between remote brain areas. Transcranial electric stimulation with alternating currents (TACS) can manipulate these brain oscillations in a non-invasive manner. Of particular interest, TACS protocols using multiple electrodes with phase shifted stimulation currents were developed to alter the connectivity between two or more brain regions. Typically, an increase in coordination between two sites is assumed when they experience an in-phase stimulation and a disorganization through an anti-phase stimulation. However, the underlying biophysics of multi-electrode TACS has not been studied in detail, thus limiting our ability to develop a mechanistic understanding. Here, we leverage direct invasive recordings from two non-human primates during multi-electrode TACS to show that the electric field magnitude and phase depend on the phase of the stimulation currents in a non-linear manner. Further, we report a novel phenomenon of a “traveling wave” stimulation where the location of the electric field maximum changes over the stimulation cycle. Our results provide a basis for a mechanistic understanding of multi-electrode TACS, necessitating the reevaluation of previously published studies, and enable future developments of novel stimulation protocols.

Download Full-text

Human Sensation of Transcranial Electric Stimulation

Scientific Reports ◽

10.1038/s41598-019-51792-8 ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 1

Author(s):

Fan-Gang Zeng ◽

Phillip Tran ◽

Matthew Richardson ◽

Shuping Sun ◽

Yuchen Xu

Keyword(s):

Auditory Nerve ◽

Electric Stimulation ◽

Stimulus Frequency ◽

Low Frequency ◽

Electrode Position ◽

Computer Interfaces ◽

Transcranial Alternating Current Stimulation ◽

Transcranial Electric Stimulation ◽

Somatic Sensation ◽

Deep Brain

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.

Download Full-text