How is electrical stimulation of the brain experienced, and how can we tell? Selected considerations on sensorimotor function and speech

ABSTRACT

Electrical stimulation of the nervous system is a powerful tool for localizing and examining the function of numerous brain regions. Delivered to certain regions of the cerebral cortex, electrical stimulation can evoke a variety of first-order effects, including observable movements or an urge to move, or somatosensory, visual, or auditory percepts. In still other regions the subject may be oblivious to the stimulation. Often overlooked, however, is whether the subject is aware of the stimulation, and if so, how the stimulation is experienced by the subject. In this review of how electrical stimulation has been used to study selected aspects of sensorimotor and language function, we raise questions that future studies might address concerning the subjects’ second-order experiences of intention and agency regarding evoked movements, of the naturalness of evoked sensory percepts, and of other qualia that might be evoked in the absence of an overt first-order experience.

KEYWORDS:

• Cerebral cortex
• electrical stimulation
• intracortical microstimulation
• perception
• sensation

Acknowledgements

The authors thank Marsha Hayles for editorial comments.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Kevin A. Mazurek http://orcid.org/0000-0002-9002-2339

Marc H. Schieber http://orcid.org/0000-0002-4315-8161

Notes

1. We have totalled the number of precentral points at which responses were reported of the tongue, mouth, jaw, eyelid, face, swallow, fingers, hand/arm/shoulder, and trunk/legs. This total may be an overestimate, however. For example, a movement recorded as “closure of the fingers and thumb, slight wrist flexion” might have been counted both under fingers and under hand/arm/shoulder.

2. Penfield stimulated relatively few points on the precentral gyrus because of the known tendency for stimulation there to evoke seizures. In his procedures, the Rolandic fissure typically was identified by stimulating multiple points along its posterior aspect in primary somatosensory cortex, and then stimulating only a few selected spots anteriorly to confirm that this was motor cortex (personal communication to MHS from William Feindel).

3. The association of ICMS at a given electrode with a particular movement may have been made through Hebbian learning, such that the monkeys eventually performed the correct movements subconsciously (Lebedev & Ossadtchi, 2018). Even in such case, however, the Hebbian process may have led to the formation of distinguishable qualia specifying which movement to perform.

4. A gas-filled electron tube that provides a high-power switch and controlled rectifier, able to handle larger currents than a vacuum tube.

5. Indeed, repetitive trains of transcranial magnetic stimulation (rTMS) now are used routinely to produce transient “virtual lesions” (Pascual-Leone, Walsh, & Rothwell, 2000; Ziemann, 2010).

Additional information

Funding

This work was supported by grants F32NS093709 to KAM and R01NS092626 and R01NS107271 to MHS from the National Institute of Neurological Disorders and Stroke (NINDS).