The challenge of controlling an auditory BCI in the case of severe motor disability.

BACKGROUND: The locked-in syndrome (LIS), due to a lesion in the pons, impedes communication. This situation can also be met after some severe brain injury or in advanced Amyotrophic Lateral Sclerosis (ALS). In the most severe condition, the persons cannot communicate at all because of a complete oculomotor paralysis (Complete LIS or CLIS). This even prevents the detection of consciousness. Some studies suggest that auditory brain-computer interface (BCI) could restore a communication through a « yes-no¼ code. METHODS: We developed an auditory EEG-based interface which makes use of voluntary modulations of attention, to restore a yes-no communication code in non-responding persons. This binary BCI uses repeated speech sounds (alternating "yes" on the right ear and "no" on the left ear) corresponding to either frequent (short) or rare (long) stimuli. Users are instructed to pay attention to the relevant stimuli only. We tested this BCI with 18 healthy subjects, and 7 people with severe motor disability (3 "classical" persons with locked-in syndrome and 4 persons with ALS). RESULTS: We report online BCI performance and offline event-related potential analysis. On average in healthy subjects, online BCI accuracy reached 86% based on 50 questions. Only one out of 18 subjects could not perform above chance level. Ten subjects had an accuracy above 90%. However, most patients could not produce online performance above chance level, except for two people with ALS who obtained 100% accuracy. We report individual event-related potentials and their modulation by attention. In addition to the classical P3b, we observed a signature of sustained attention on responses to frequent sounds, but in healthy subjects and patients with good BCI control only. CONCLUSIONS: Auditory BCI can be very well controlled by healthy subjects, but it is not a guarantee that it can be readily used by the target population of persons in LIS or CLIS. A conclusion that is supported by a few previous findings in BCI and should now trigger research to assess the reasons of such a gap in order to propose new and efficient solutions. CLINICAL TRIAL REGISTRATIONS: No. NCT02567201 (2015) and NCT03233282 (2013).

Transient Locked-in Syndrome after Aneurysmal Subarachnoid Bleeding due to Spasm Hypoxemia?

How to cite this article: Finsterer J. Transient Locked-in Syndrome after Aneurysmal Subarachnoid Bleeding due to Spasm Hypoxemia? Indian J Crit Care Med 2024;28(1):86.

Who gets to decide?: Substitute decision making following severe brain injury with communication impairment.

Purpose: In our prior study (Malhi et al., 2021), we demonstrated that cognitive ability may be masked by communication impairments. We used binary choice (i.e., yes/no) neuropsychological tests to assess cognitive functioning in four patients with severe brain injury and communication impairments. In this study, we aimed to better understand the decision-making process of their substitute decision makers (SDMs). Methods: We interviewed SDMs - two SDMs were supporting patients in the minimally conscious state, one SDM was supporting a patient who had locked-in syndrome and was an augmentative communication user, and the last SDM was supporting a patient who was an alternative communication user. Results: SDMs were performing various roles ranging from making all decisions to simply being the vocal advocate (for the augmentative and alternative communication users). SDMs described heuristics they used to make decisions, and all identified auditory comprehension capabilities as being an important element for decision making. Conclusion: We argue that if mode of communication is established and utilized, and binary choice neuropsychological tests are used to ascertain cognitive functioning, SDMs may more confidently make low/medium stakes decisions based on the present condition and context, rather than solely on past wishes and values before capacity was in question.

Thinking without speaking: Neuropsychological testing with individuals who have communication impairments.

Cognitive ability may be masked by communication impairments. This study aimed to assess cognitive functioning using binary choice (i.e., yes/no) neuropsychological tests in patients with communication impairments. Four participants underwent neuropsychological testing. Two participants were in the minimally conscious state (MCS), one participant had locked-in syndrome and was an alternative communication user, and one participant was an augmentative communication user. There was better performance in all cognitive domains for the augmentative and alternative communication (AAC) users (who performed like the non-communication impaired normative data) compared to the MCS participants. However, using established yes/no communication methods, MCS participants performed above chance on a measure of memory and performance on measures of auditory comprehension was variable. Auditory comprehension appeared to be more influenced by working memory demands for the MCS participants than for the AAC users. For emotional functioning, the AAC users endorsed lower mood compared to the MCS participants. The results support the need to assess cognition, communication, as well as capacity in individuals with communication impairments with the consultation of a neuropsychologist and a speech-language pathologist.

The locked-in syndrome: The early French descriptions.

The classic 1966 description of locked-in syndrome was performed by Plum and Posner. Here, we revisit the world's first case report of this condition, which was presented in 1875 by Camille Darolles, an intern supervised by François Damaschino, at a monthly meeting of the Société Anatomique de Paris chaired by Jean-Martin Charcot. We also review the fascination of classic writers with this syndrome, including Alexandre Dumas, a genius of literature and known admirer of the medical sciences who, in the book "The Count of Monte Cristo" published in 1846, described a character with this condition.

Hyperhomocysteinemia induced locked-in syndrome in a young adult due to folic acid deficiency.

'Locked-in syndrome (LIS)' is a neurological disorder, often missed initially and can have grave consequences. A rare case of LIS caused due to folic acid deficiency-induced hyperhomocysteinemia is being described here. A 16-year-old boy presented with complaints of sudden onset weakness of all the four limbs with loss of voice for one day. All the tendon reflexes were increased, bilateral planters were extensor and sensory system was intact. Patient was conscious and responded to verbal commands by ocular movements in vertical direction. Hence, a diagnosis of LIS was made. Magnetic resonance imaging of the head revealed an acute infarct in ventral pons. Serum homocysteine level was elevated (20.65 µmol/l) and folic acid level was severely low (1.7 nmol/ml). Cause of LIS was found to be hyperhomocysteinemia induced stroke in the pons, related to folic acid deficiency. The patient was managed with antiplatelet agents and folic acid supplementation and was discharged subsequently. Recognition of LIS is important as casual remarks at bedside can severely traumatize an already paralyzed but conscious and awake patient. Folic acid deficiency can lead to hyperhomocysteinemia, which can cause strokes and even LIS. Prevention of hyperhomocysteinemia may possibly prevent such neurological disasters.

The current state of electrocorticography-based brain-computer interfaces.

Brain-computer interfaces (BCIs) provide a way for the brain to interface directly with a computer. Many different brain signals can be used to control a device, varying in ease of recording, reliability, stability, temporal and spatial resolution, and noise. Electrocorticography (ECoG) electrodes provide a highly reliable signal from the human brain surface, and these signals have been used to decode movements, vision, and speech. ECoG-based BCIs are being developed to provide increased options for treatment and assistive devices for patients who have functional limitations. Decoding ECoG signals in real time provides direct feedback to the patient and can be used to control a cursor on a computer or an exoskeleton. In this review, the authors describe the current state of ECoG-based BCIs that are approaching clinical viability for restoring lost communication and motor function in patients with amyotrophic lateral sclerosis or tetraplegia. These studies provide a proof of principle and the possibility that ECoG-based BCI technology may also be useful in the future for assisting in the cortical rehabilitation of patients who have suffered a stroke.

Disorders of consciousness terminology: history, evolution and future directions.

There has been a significant evolution of nomenclature with regards to classification of persons with disorders of consciousness (DoC) over the last 100 years. This paper provides a review of the evolution of this terminology with discussion of the advantages and disadvantages of historical and current terms. Recommendations for how this evolution should continue moving forward in the best interest of patients, their families, society, clinical care, and research will also be addressed. The taxonomy we choose, hopefully by international consensus, has multifaceted implications that go well beyond just a debate on nomenclature.

'Without A Key': A Classroom Case Study.

This case study uses a narrative focused on locked-in syndrome to engage upper-level undergraduate students with functional neuroanatomy, clinical neuroscience, and brain computer interface technology. Students 'diagnose' the etiology of a composite patient's symptoms using behavioral, neurological, neuroimaging, and electrophysiological test results. Students work both in small groups and as a class to develop analytical and communication skills by exploring the underpinnings, symptoms, and outcomes of locked-in syndrome and how behavioral and brain computer interface techniques could be used to improve quality of life in patients. A complete, detailed description of classroom implementation and the case narratives are available from the corresponding author or from cases.at.june@gmail.com.

Stable long-term BCI-enabled communication in ALS and locked-in syndrome using LFP signals.

Restoring communication for people with locked-in syndrome remains a challenging clinical problem without a reliable solution. Recent studies have shown that people with paralysis can use brain-computer interfaces (BCIs) based on intracortical spiking activity to efficiently type messages. However, due to neuronal signal instability, most intracortical BCIs have required frequent calibration and continuous assistance of skilled engineers to maintain performance. Here, an individual with locked-in syndrome due to brain stem stroke and an individual with tetraplegia secondary to amyotrophic lateral sclerosis (ALS) used a simple communication BCI based on intracortical local field potentials (LFPs) for 76 and 138 days, respectively, without recalibration and without significant loss of performance. BCI spelling rates of 3.07 and 6.88 correct characters/minute allowed the participants to type messages and write emails. Our results indicate that people with locked-in syndrome could soon use a slow but reliable LFP-based BCI for everyday communication without ongoing intervention from a technician or caregiver. NEW & NOTEWORTHY This study demonstrates, for the first time, stable repeated use of an intracortical brain-computer interface by people with tetraplegia over up to four and a half months. The approach uses local field potentials (LFPs), signals that may be more stable than neuronal action potentials, to decode participants' commands. Throughout the several months of evaluation, the decoder remained unchanged; thus no technical interventions were required to maintain consistent brain-computer interface operation.