Direct Electrical Stimulation in Electrocorticographic Brain–Computer Interfaces: Enabling Technologies for Input to Cortex

Abstract

Electrocorticographic brain computer interfaces (ECoG-BCIs) offer tremendous opportunities for restoring function in individuals suffering from neurological damage and for advancing basic neuroscience knowledge. ECoG electrodes are already commonly used clinically for monitoring epilepsy and have greater spatial specificity in recording neuronal activity than techniques such as electroencephalography (EEG). Much work to date in the field has focused on using ECoG signals recorded from cortex as control outputs for driving end effectors. An equally important but less explored application of an ECoG-BCI is directing input into cortex using ECoG electrodes for direct electrical stimulation (DES). Combining DES with ECoG recording enables a truly bidirectional BCI, where information is both read from and written to the brain. We discuss the advantages and opportunities, as well as the barriers and challenges presented by using DES in an ECoG-BCI. In this article, we review ECoG electrodes, the physics and physiology of DES, and the use of electrical stimulation of the brain for the clinical treatment of disorders such as epilepsy and Parkinson’s disease. We briefly discuss some of the translational, regulatory, financial, and ethical concerns regarding ECoG-BCIs. Next, we describe the use of ECoG-based DES for providing sensory feedback and for probing and modifying cortical connectivity. We explore future directions, which may draw on invasive animal studies with penetrating and surface electrodes as well as non-invasive stimulation methods such as transcranial magnetic stimulation (TMS). We conclude by describing enabling technologies, such as smaller ECoG electrodes for more precise targeting of cortical areas, signal processing strategies for simultaneous stimulation and recording, and computational modeling and algorithms for tailoring stimulation to each individual brain.

Biomarkers and neuromodulation techniques in substance use disorders

“…ECoG applications are mainly used in patients suffering from medically intractable epilepsy to localize seizure foci prior to surgical intervention (Fernández and Loddenkemper 2013) and for real-time functional brain mapping to assess language, motor performance and sensory function through application of DES via EcoG electrodes (Boyer et al 2018;Caldwell et al 2019;Mouthaan et al 2016).…”

“…To our knowledge, ECoG and/or DES have neither been used for therapeutic applications nor for research purposes related to addictive disorders so far but have long been discussed in the context of brain computer interfaces (Caldwell et al 2019;Kapeller et al 2014;Leuthardt et al 2006;Rembado et al 2017;Schalk and Leuthardt 2011) and therefore provide a basis for medical closed-loop neuroprosthetics with a great potential also in treatment of addictive disorders.…”

Evoking highly focal percepts in the fingertips through targeted stimulation of sulcal regions of the brain for sensory restoration

“…In this study, all stimulation was done using a bipolar configuration involving adjacent electrodes. In case of HD-ECoG grids, with the electrodes arranged on the cortical surface, bipolar stimulation can potentially activate a wide area of the cortex evoking diffuse sensory percepts (55). Since SEEG electrodes can be inserted parallel to the orientation of the cortical columns and a contact diameter of only 0.8 mm, a bipolar stimulation configuration can potentially restrict stimulation to a couple of columns.…”

The Short-Term Repeatability of Subdermal Electrical Stimulation for Sensory Feedback

“…Placing electrodes under the skin may overcome some of these disadvantages, as the electrodes are placed permanently, bypassing the skin impedance. This can be achieved by using implanted interfaces to directly stimulate peripheral nerves via circumferential electrodes [18], [19] or intraneural electrodes [20]- [24], or through the application of cortical surface stimulation [25], [26] and intracortical microstimulation [27], [28]. These methods have led to promising results [9], [29], [30]; however, a surgical procedure is required which may not be accepted by all amputees.…”