Sensorimotor ECoG Signal Features for BCI Control: A Comparison Between People With Locked-In Syndrome and Able-Bodied Controls

Abstract

The sensorimotor cortex is a frequently targeted brain area for the development of Brain-Computer Interfaces (BCIs) for communication in people with severe paralysis and communication problems (locked-in syndrome; LIS). It is widely acknowledged that this area displays an increase in high-frequency band (HFB) power and a decrease in the power of the low frequency band (LFB) during movement of, for example, the hand. Upon termination of hand movement, activity in the LFB band typically shows a short increase (rebound). The ability to modulate the neural signal in the sensorimotor cortex by imagining or attempting to move is crucial for the implementation of sensorimotor BCI in people who are unable to execute movements. This may not always be self-evident, since the most common causes of LIS, amyotrophic lateral sclerosis (ALS) and brain stem stroke, are associated with significant damage to the brain, potentially affecting the generation of baseline neural activity in the sensorimotor cortex and the modulation thereof by imagined or attempted hand movement. In the Utrecht NeuroProsthesis (UNP) study, a participant with LIS caused by ALS and a participant with LIS due to brain stem stroke were implanted with a fully implantable BCI, including subdural electrocorticography (ECoG) electrodes over the sensorimotor area, with the purpose of achieving ECoG-BCI-based communication. We noted differences between these participants in the spectral power changes generated by attempted movement of the hand. To better understand the nature and origin of these differences, we compared the baseline spectral features and task-induced modulation of the neural signal of the LIS participants, with those of a group of able-bodied people with epilepsy who received a subchronic implant with ECoG electrodes for diagnostic purposes. Our data show that baseline LFB oscillatory components and changes generated in the LFB power of the sensorimotor cortex by (attempted) hand movement differ between participants, despite consistent HFB responses in this area. We conclude that the etiology of LIS may have significant effects on the LFB spectral components in the sensorimotor cortex, which is relevant for the development of communication-BCIs for this population.

Brain-Computer Interfaces for Communication: Preferences of Individuals With Locked-in Syndrome

“…Of these, 2 participants were implanted with a cBCI at the time of the interview. 9,24 The revised Amyotrophic Lateral Sclerosis Functional Rating Scale (ALSFRS-r 25 ) score was used to assess the level of paralysis and communication impairment of each participant. Responses to each item of the ALSFRS-r were described by the participant and caregiver and scored by both researchers independently.…”

MEG Sensor Selection for Neural Speech Decoding

“…Additionally, it may be challenging to establish long-term biocompatibility between the ECoG electrode grid and the brain. Although some recent ECoG BCI studies have shown promising results for ALS patients with relatively longer-term motor applications via a few (2 – 4) electrodes those were placed around the motor cortex [ 31 ]–[ 33 ], it is unknown how many electrodes are needed for speech production decoding. Moreover, prior ECoG studies have analyzed only part of the brain, as ECoG electrodes are typically implanted only into the areas prone to epileptic seizures.…”

Typical somatomotor physiology of the hand is preserved in a patient with an amputated arm

“…In these patients, a robust HFB response was retained (Freudenburg et al 2019). Whether and/or how the LFB response was affected varied between studies.…”

“…Some studies observed robust low frequency power decreases in patients with ALS and/or PLS (Bai et al 2010;Riva et al 2012;Proudfoot et al 2017). Other studies reported reduced power decreases in ALS (Kasahara et al 2012), or more variability between patients with ALS, tetraplegia and brainstem stroke, with only some patients showing robust low frequency power decreases (Höhne et al 2014;Freudenburg et al 2019). These studies suggest that whether low frequency power decreases are retained depends on the disease (progression) and the influence of closed-loop feedback training.…”