Hybrid brain-computer interface and functional electrical stimulation for sensorimotor training in participants with tetraplegia: a proof-of-concept study

Background and Purpose: Impaired hand function decreases quality of life in persons with tetraplegia. We tested functional electrical stimulation (FES) controlled by a hybrid brain-computer interface (BCI) for improving hand function in participants with tetraplegia. Methods: Two participants with subacute tetraplegia (participant 1: C5 Brown-Sequard syndrome, participant 2: complete C5 lesion) took part in this proof-of-concept study. The goal was to determine whether the BCI system could drive the FES device by accurately classifying participants' intent (open or close the hand). Participants 1 and 2 received 10 sessions and 4 sessions of BCI-FES, respectively. A novel time-switch BCI strategy based on motor imagery was used to activate the FES. In one session, we tested a hybrid BCI-FES based on 2 spontaneously generated brain rhythms: a sensory-motor rhythm during motor imagery to activate a stimulator and occipital alpha rhythms to deactivate the stimulator. Participants received BCI-FES therapy 2 to 3 times a week in addition to conventional therapy. Imagery ability and muscle strength were measured before and after treatment. Results: Visual feedback was associated with a 4-fold increase of brain response during motor imagery in both participants. For participant 1, classification accuracy (open/closed) for motor imagery-based BCI was 83.5% (left hand) and 83.8% (right hand); participant 2 had a classification accuracy of 83.8% for the right hand. Participant 1 had moderate improvement in muscle strength, while there was no change for participant 2. Discussion and Conclusion: We demonstrated feasibility of BCI-FES, using 2 naturally generated brain rhythms. Studies on a larger number of participants are needed to separate the effects of BCI training from effects of conventional therapy

Rehabilitation of hand in subacute tetraplegic patients based on brain computer interface and functional electrical stimulation: a randomised pilot study

Objective. To compare neurological and functional outcomes between two groups of hospitalised patients with subacute tetraplegia. Approach. Seven patients received 20 sessions of brain computer interface (BCI) controlled functional electrical stimulation (FES) while five patients received the same number of sessions of passive FES for both hands. The neurological assessment measures were event related desynchronization (ERD) during movement attempt, Somatosensory evoked potential (SSEP) of the ulnar and median nerve; assessment of hand function involved the range of motion (ROM) of wrist and manual muscle test. Main results. Patients in both groups initially had intense ERD during movement attempt that was not restricted to the sensory-motor cortex. Following the treatment, ERD cortical activity restored towards the activity in able-bodied people in BCI-FES group only, remaining wide-spread in FES group. Likewise, SSEP returned in 3 patients in BCI-FES group, having no changes in FES group. The ROM of the wrist improved in both groups. Muscle strength significantly improved for both hands in BCI-FES group. For FES group, a significant improvement was noticed for right hand flexor muscles only. Significance. Combined BCI-FES therapy results in better neurological recovery and better improvement of muscle strength than FES alone. For spinal cord injured patients, BCI-FES should be considered as a therapeutic tool rather than solely a long-term assistive device for the restoration of a lost function

Brain rhythms of pain

Pain is an integrative phenomenon that results from dynamic interactions between sensory and contextual (i.e., cognitive, emotional, and motivational) processes. In the brain the experience of pain is associated with neuronal oscillations and synchrony at different frequencies. However, an overarching framework for the significance of oscillations for pain remains lacking. Recent concepts relate oscillations at different frequencies to the routing of information flow in the brain and the signaling of predictions and prediction errors. The application of these concepts to pain promises insights into how flexible routing of information flow coordinates diverse processes that merge into the experience of pain. Such insights might have implications for the understanding and treatment of chronic pain

Modulation of laser-evoked pain perception and event-related potentials with non-invasive stimulation of the motor cortex

In the last two decades new techniques of non-invasive brain stimulation have been introduced that enable relatively long-lasting and reversible facilitation or inhibition of distinct cortical areas by modulating the excitability of underlying neurons. Among these methods, repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) are the most widespread ones. To date, both have been successfully used to modulate various perceptual, cognitive and motor functions in healthy subjects and several diseases, including chronic pain. Their efficacy regarding acute pain perception in healthy subjects, however, is still not well-established. The aims of our studies were to investigate the effects of a novel rTMS paradigm, called continuous theta-burst stimulation (cTBS), and tDCS on laser-induced acute pain perception and laser-evoked potentials (LEPs) when applied to the motor cortex of healthy adult volunteers. In two psychophysical and two electrophysiological experiments, we have compared the effects of real cTBS and two tDCS protocols (anodal and cathodal) to those of sham stimulations. We have shown for the first time that cTBS over the motor cortex significantly alleviated laser-induced pain on both hands, accentuating on the con tralateral limb. The effect of cTBS was accompanied by reduced N2-P2 LEP amplitudes in the case of medium intensity pain. In the tDCS experiments, cathodal stimulation of the motor cortex reduced mild pain contralateral to the side of stimulation. Moreover, cathodal tDCS attenuated N2-P2 LEP components, without modulating thresholds of medium intensity pain. On the contrary, anodal tDCS facilitated laser-induced warm sensation contralateral to the side of tDCS, without affecting either pain sensation or LEPs. Our results indicate that non-invasive stimulation of the motor cortex causes antinociceptive effects that depend on the parameters of stimulation and are probably due to excitability changes in remote pain-related areas such as the operculoinsular region and the anterior cingulate cortex. These findings further strengthen the application of cTBS and tDCS in pain research, which might contribute to a more efficient manipulation of brain plasticity for therapeutic purposes

Prefrontal gamma oscillations encode tonic pain in humans

Under physiological conditions, momentary pain serves vital protective functions. Ongoing pain in chronic pain states, on the other hand, is a pathological condition that causes widespread suffering and whose treatment remains unsatisfactory. The brain mechanisms of ongoing pain are largely unknown. In this study, we applied tonic painful heat stimuli of varying degree to healthy human subjects, obtained continuous pain ratings, and recorded electroencephalograms to relate ongoing pain to brain activity. Our results reveal that the subjective perception of tonic pain is selectively encoded by gamma oscillations in the medial prefrontal cortex. We further observed that the encoding of subjective pain intensity experienced by the participants differs fundamentally from that of objective stimulus intensity and from that of brief pain stimuli. These observations point to a role for gamma oscillations in the medial prefrontal cortex in ongoing, tonic pain and thereby extend current concepts of the brain mechanisms of pain to the clinically relevant state of ongoing pain. Furthermore, our approach might help to identify a brain marker of ongoing pain, which may prove useful for the diagnosis and therapy of chronic pain