Predictors of successful self control during brain-computer communication

OBJECTIVES: Direct brain-computer communication uses self regulation of brain potentials to select letters, words, or symbols from a computer menu to re-establish communication in severely paralysed patients. However, not all healthy subjects, or all paralysed patients acquire the skill to self regulate their brain potentials, and predictors of successful learning have not been found yet. Predictors are particularly important, because only successful self regulation will in the end lead to efficient brain-computer communication. This study investigates the question whether initial performance in the self regulation of slow cortical potentials of the brain (SCPs) may be positively correlated to later performance and could thus be used as a predictor. METHODS: Five severely paralysed patients diagnosed with amyotrophic lateral sclerosis were trained to produce SCP amplitudes of negative and positive polarity by means of visual feedback and operant conditioning strategies. Performance was measured as percentage of correct SCP amplitude shifts. To determine the relation between initial and later performance in SCP self regulation, Spearman's rank correlations were calculated between maximum and mean performance at the beginning of training (runs 1-30) and mean performance at two later time points (runs 64-93 and 162-191). RESULTS: Spearman's rank correlations revealed a significant relation between maximum and mean performance in runs 1-30 and mean performance in runs 64-93 (r= 0.9 and 1.0) and maximum and mean performance in runs 1-30 and mean performance in runs 162-191 (r=1.0 and 1.0). CONCLUSIONS: Initial performance in the self regulation of SCP is positively correlated with later performance in severely paralysed patients, and thus represents a useful predictor for efficient brain-computer communication.     

Quality of life in fatal disease: the flawed judgement of the social environment

Decisions to prolong or shorten life in fatal diseases like amyotrophic lateral sclerosis are strongly influenced by healthy individuals, such as caregivers and physicians. Furthermore, many believe that amyotrophic lateral sclerosis (ALS) patients should decide ahead of time on advanced directives to circumvent confounding effects of subsequent cognitive impairments. The ability of healthy persons (caregivers and age-matched healthy subjects) to anticipate patients’ quality of life (QoL), depression and vital decisions was determined in a cross-sectional approach. Eighty-nine ALS patients, 86 caregivers and 102 age-matched healthy subjects were asked to judge ALS patients’ QoL and depression and the patients' wish for hastened death. Patients judged their own, the caregivers judged that of the patient under their care, healthy subjects were asked to judge that of a virtual patient. Additionally, healthy persons were asked to judge their own QoL and depression. Patients reported a satisfactory well-being and a low wish for hastened death. Healthy persons rated the patients’ QoL significantly lower and the rate of depression significantly higher. The wish for hastened death was significantly lower in the patient group compared to what healthy subjects thought the patient would wish. The assessment by others was closely related to the persons’ own well-being. Significant differences were identified between caregiver’s perspectives and the patient’s own perception of their psychological well-being. Our data suggest that caregivers and the general public significantly underestimate the QoL of ALS patients. A positive affective state can indeed be preserved in a progressive, fatal disease.     

A portable auditory P300 brain–computer interface with directional cues

ObjectivesThe main objective of the current study was to implement and evaluate a P300 based brain–computer interface (BCI) speller that uses directional cues of auditory stimuli, which are presented over headphones. The interstimulus interval (ISI) was successively reduced to determine the optimal combination of speed and accuracy. The study further aimed at quantifying the differences in subjective workload between the auditory and the visual P300 spelling application. The influence of workload, mood and motivation on BCI performance and P300 amplitude was investigated.MethodsTwenty healthy participants performed auditory and visual spelling tasks in an EEG experiment with online feedback.ResultsSixteen of twenty participants performed at or above a level necessary for satisfactory communication (?70% spelling accuracy) with the auditory BCI. Average bit rates of up to 2.76 bits/min (best subject 7.43 bits/min) were achieved. A significantly higher workload was reported for the auditory speller compared to the visual paradigm. Motivation significantly influenced P300 amplitude at Pz in the auditory condition.ConclusionsThe results of the online study suggest that the proposed paradigm offers a means of communication for most healthy users.SignificanceThe described auditory BCI can serve as a communication channel for completely paralyzed patients.     

Abnormal Reactivity of the Primary Somatosensory Cortex During the Experience of Pain in Complex Regional Pain Syndrome: A Magnetoencephalograhic Case Study

A 49-year-old male worker developed persistent pain in his left wrist after work strain injuries. Clinical symptoms met with criteria for Complex Regional Pain Syndrome (CRPS) type I. In the present study, the effect of the experience of pain on the somatotopy of the primary cortical hand representation was investigated. Somatosensory evoked magnetic fields (SEF) elicited by non-painful tactile stimulation at the index finger of the affected and the unaffected hand were recorded when experiencing pain elicited by a moderate physical load condition (holding a 1.6 kg object in the hand). It was shown that MEG and subjective responses to innocuous tactile stimuli were reduced when simultaneous nociceptive stimulation was applied. These findings suggest a gating effect in the central nervous system elicited by concurrent simultaneous information from two different somatosensory modalities (pain and tactile). The results revealed the existence of nociceptive-induced plastic changes in the central nervous system associated with CRPS type I.     

Automatic processing of self-regulation of slow cortical potentials: evidence from brain-computer communication in paralysed patients.

OBJECTIVE: Direct brain-computer communication utilizes self-regulation of brain potentials to select letters, words or symbols from a computer menu. Selection of letters or words with brain potentials requires simultaneous processing of several tasks such as production of certain brain potentials at predefined time points simultaneously with processing of presented letter strings. This study addresses the question of whether the self-regulation of slow cortical potentials (SCP) automatizes with practice and can thus be considered as a skill comparable to motor or cognitive skills. METHODS: Two nearly completely paralysed patients learned over several months to produce electrocortically negative and positive SCP by means of visual feedback. Improved performance and a reduction in performance variability were regarded as behavioural indicators for automaticity, while the topographic focalization of cortical activation was considered as a neurophysiological indicator for automaticity. Different indicators of automaticity were expected to covary along with practice. RESULTS: In patient 1, performance measured as the percentage of correct SCP shifts increased simultaneously with the topographic focalization of cortical activation. His performance became more stable with practice. For this patient the criteria for automaticity were all met. In patient 2, performance also improved, but his cortical activity became topographically less focal. His performance was less stable than that of patient 1. CONCLUSIONS: The present findings, albeit on only two subjects, provide preliminary evidence that SCP self-regulation may automatize with long-term practice and can therefore be considered a skill.     

Central effects of baroreceptor activation in humans: attenuation of skeletal reflexes and pain perception.

Activating the arterial baroreceptors blunts pain sensation and produces other forms of central nervous system inhibition in animals. These effects may be important to blood pressure regulation but have not been rigorously verified in humans. We describe (i) a noninvasive behaviorally unbiased method for baroreceptor stimulation and (ii) the application of this method to measurement of baroreceptor-mediated attenuation of pain perception and of the Achilles tendon reflex. The findings are relevant to basic mechanisms of blood pressure stabilization and cardiovascular reactivity and may also have implications for noncompliance with antihypertensive medications and for the pathophysiology of essential hypertension.     

Biofeedback-produced hemispheric asymmetry of slow cortical potentials and its behavioural effects

Two studies served to examine behavioural effects of slow cortical potentials (SPs). SPs were manipulated by means of a biofeedback procedure. The ability of human subjects to alter SPs differentially between the two hemispheres--specifically over the lateral aspects of the central sulcus--was tested by providing feedback of the SP difference between C3 and C4. In Expt. I, 21 of the 45 subjects produced hemispheric asymmetries of more than 2 microV between C3 and C4 on an average after 80 trials of analogue, continuous and immediate feedback. In Expt. II, SP changes were fed back digitally at the end of each trial. Within 120 trials, 20 of the 48 subjects reached the criterion of a minimum 2-microV difference in SPs between C3 and C4 on the average. Average differentiation remained significantly below the SP differentiations achieved for continuous feedback. Trials with feedback were followed by 'task' trials without feedback, during which subjects were still requested to produce SP changes but also had to complete a task: Either sensorimotor tasks (Expt. I) or forced choice handedness tasks (Expt. II) were presented to evaluate behavioural consequences of hemispheric SP differences. In subjects achieving the required SP differentiation it affected the behavioural output in agreement with the known functions of the respective cortical area.     

A non-invasive communication device for the paralyzed.

An EEG-based communication system has been developed to re-establish communication in severely paralyzed patients who operate the device by generating shifts of their slow cortical potentials. Training to gain control over slow cortical potentials was based on visual feedback and operant conditioning strategies. The vertical movement of a graphic signal on a computer screen informs the patients about the course of their slow cortical potential amplitude. Positive slow cortical potential shifts move the cursor up, negative shifts move it down. These shifts are then translated into binary responses. When a patient has achieved reliable control over his/her slow cortical potential shifts, these responses can be used to select or reject items presented at the bottom of the screen. As learning processes and applications differ considerably between patients, the present paper describes the data from one patient with amyotrophic lateral sclerosis. After about three months of training, this patient gained stable, near-perfect control over his slow cortical potentials. This skill enabled him to operate a specially designed program to communicate messages to his caregivers.