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Biomedical subjects

B Kotchoubey

Publications and source records attributed to B Kotchoubey.

At least 19 recordsLinked to original sources
PubMed2007

Predicting coma and other low responsive patients outcome using event-related brain potentials: a meta-analysis.

OBJECTIVE: A meta-analysis was performed to estimate the predictive power (odd ratio, OR) for awakening of auditory event-related potential (ERP) components in low responsive patients with stroke or hemorrhage, trauma, anoxic, post-operative, and metabolic encephalopathy etiologies. METHODS: We reviewed MEDLINE and analyzed citations for retrieved articles. Logistic regressions were applied on patient samples (Glasgow Coma Scale <12) across and for separate etiologies. RESULTS: For stroke and hemorrhage the ORs with 95% confidence intervals were: 2.05 [1.12-3.75] (N100), 4.47 [1.92-10.44] (MMN), 10.29 [2.00-52.79] (P300), for trauma: 1.63 [0.70-3.80] (N100), 4.72 [1.35-16.44] (MMN), 12.89 [4.82-34.43] (P300), anoxic: 8.03 [2.83-22.75] (N100), 15.50 [4.27-56.26] (MMN), 5.93 [2.38-14.77] (P300), post-operative: 10.66 [1.98-57.50] (N100), metabolic encephalopathy: 2.12 [0.34-13.13] (N100), 3.60 [0.28-46.36] (MMN), 7.71 [0.75-79.77] (P300), and all etiologies: 2.85 [1.91-4.27] (N100), 6.53 [3.55-12.01] (MMN), and 8.79 [4.88-15.83] (P300). Based on six N100 studies (N=548 patients), five MMN studies (N=470), and six P300 studies (N=313), the N100, MMN, or P300, when present, significantly predicted awakening, P300 and MMN being significantly better predictors than N100. CONCLUSIONS: The MMN and P300 appear to be reliable predictors of awakening. SIGNIFICANCE: The prognostic assessment of low responsive patients with auditory ERP should take into account both MMN and P300.

Coma↗
PubMed2005

Information processing in severe disorders of consciousness: vegetative state and minimally conscious state.

OBJECTIVE: To study the presence of electrophysiological indicators of remaining cortical functions in patients with persistent vegetative state (PVS) and minimally conscious state (MCS). Previous electrophysiological and PET data indicated that some PVS patients have partially intact cortical processing functions. However, it remains unclear whether the reported patients were representative for PVS population or just some exceptional cases. METHODS: Event-related brain responses to stimuli of different complexity levels, recorded in 98 patients with extremely severe diffuse brain injuries, 50 of which in PVS. Four main indicators of cortical functions were: (i) N1-P2 complex as an index of simple, undifferentiated cortical processing; (ii) mismatch negativity as an index of pre-attentive, probably unconscious, cortical orientation; (iii) P3 wave as an index of deep cortical analysis of physical stimuli, and (iv) brain responses to semantic stimuli. RESULTS: Cortical responses were found in all PVS patients with a background EEG activity > 4 Hz. All responses investigated, including those to semantic stimuli that indicated comprehension of meaning, occurred significantly above chance, though less frequently than in patients with severe brain injuries who were conscious. CONCLUSIONS: Cortical responses were lacking in most patients with severe EEG slowing (< 4 Hz). Follow-up data revealed that the presence of a mismatch negativity, a short disease duration, and the traumatic etiology were related to a better outcome. SIGNIFICANCE: The data show that in a subpopulation of PVS patients with preserved thalamocortical feedback connections, remaining cortical information processing is a consistent finding and may even involve semantic levels of processing.

Auditory Cortex↗
PubMed2003

Stimulus complexity enhances auditory discrimination in patients with extremely severe brain injuries.

There is controversy as to what extent the processing of spectrally rich sounds in the human auditory cortex is related to the processing of singular frequencies. An informative index of the function of the auditory cortex, particularly important in neurological patients, is the mismatch negativity (MMN), a component of auditory event-related potentials. In the present study the MMN was recorded in 79 patients with extremely severe diffuse brain injuries, most of them in persistent vegetative state or minimal consciousness state. Both sinusoidal ('pure') and complex musical tones were used. Different statistical approaches converged in that musical tones elicited an MMN significantly more frequently, and of a larger amplitude, than simple sine tones. This implies that using simple stimuli in clinical populations may lead to a severe underestimation of the functional state of a patient's auditory system. The findings are also in line with behavioral and physiological data indicating independent processing of complex sounds in the auditory cortex.

Acoustic Stimulation↗
PubMed2003

Cognitive processing in completely paralyzed patients with amyotrophic lateral sclerosis.

Cognitive functions have never been studied before in completely paralyzed patients, probably due to the lack of the appropriate method. In this study, three male patients in the last stage of amyotrophic lateral sclerosis (ALS) are examined. They were totally locked-in, i.e., incapable of any voluntary response including eye movements. Given this complete lack of motor expression, the method of event-related brain potentials (ERPs) was used. The ERP recording was carried out at the patients' bedside. In one patient indications of preserved cognitive abilities including adequate language comprehension were obtained. The data of the second patient also demonstrate a high degree of intactness of complex cognitive functions, but some ERP phenomena were consistently abnormal, which may be interpreted as a consequence of disease-related degenerative processes. In the third patient no electrocortical response which might indicate higher cortical processing was found. This first ERP study of totally paralyzed patients shows that some of them can possess high, perhaps even normal, information processing capacity after a long period of severe immobility and artificial ventilation.

Amyotrophic Lateral Sclerosis↗
PubMed2001

Event-related potentials in an auditory semantic oddball task in humans.

Whenever rare target stimuli are presented interspersed by frequent irrelevant stimuli (standards), the targets elicit a late parieto-central positive wave called P3. Usually standards and targets differ by a simple physical feature (e.g. tone pitch). Less consistent are the data obtained in semantic tasks, in which standards and targets are represented by different word classes. Given an equal number of words in the target and standard categories, each individual standard is more frequent than each target, that is, the frequency of the category is confounded with that of individual stimuli. In the present study participants were presented five semantic classes each being represented by 15 words. Words belonging to one particular class should be counted. Thus targets were rare (20%), although the frequencies of each word and of each semantic class were equal. A highly significant P3 was recorded. Its latency was longer, and the amplitude was smaller, than when standards and targets were two tones. These data indicate that brain waves recorded in semantic tasks are not necessarily manifestations of specific semantic processing.

Adult↗
PubMed2001

Brain potentials in human patients with extremely severe diffuse brain damage.

To test higher cortical functions of neurological patients, oddball tasks are often used in which a frequent and a rare stimulus are randomly presented and a P3 brain wave is recorded to the rare stimulus. We examined 33 patients with extremely severe brain injury. Three oddball conditions were used: with two sine tones (ST), with two complex tones (CT) and with vowels 'o' and 'i'. Across all patients, CT elicited P3 more often than ST, and the occurrence of the P3 after vowels was intermediate. However, among patients who showed a distinct P3 wave, its amplitude in the subgroup with traumatic brain injury was larger to vowels than to CT. In patients with non-traumatic etiology, CT and vowels elicited a P3 of a nearly equal amplitude. Stimuli of sufficient complexity should be used when the P3 technique is applied for assessment of cortical functions in severely impaired patients.

Adolescent↗
PubMed2001

Self-initiation of EEG-based communication in paralyzed patients.

OBJECTIVES: Severely paralyzed patients could learn to voluntarily generate slow cortical potential (SCP) shifts in their electroencephalogram and to use these signals to operate a communication device. To enhance the patients' autonomy, the present study describes the development of a permanently available communication system that can be turned on and off by locked-in patients without external assistance. A skill necessary for turning the system on is the ability to regulate one's slow potentials in the absence of continuous feedback. METHODS: A stepwise learning approach was employed to train two paralyzed patients to regulate their SCPs without continuous feedback. Elements of the original communication system were gradually removed and elements of the new stand-by mode were introduced. RESULTS: At the end of the learning procedure, both patients achieved correct response rates of above 84% in training sessions without continuous feedback. This skill enabled them to turn the communication device on and off without assistance from others. CONCLUSIONS: These findings suggest that severely paralyzed individuals can learn to operate an EEG-based communication device autonomously.

Adult↗
PubMed2001

Brain-computer communication: unlocking the locked in.

With the increasing efficiency of life-support systems and better intensive care, more patients survive severe injuries of the brain and spinal cord. Many of these patients experience locked-in syndrome: The active mind is locked in a paralyzed body. Consequently, communication is extremely restricted or impossible. A muscle-independent communication channel overcomes this problem and is realized through a brain-computer interface, a direct connection between brain and computer. The number of technically elaborated brain-computer interfaces is in contrast with the number of systems used in the daily life of locked-in patients. It is hypothesized that a profound knowledge and consideration of psychological principles are necessary to make brain-computer interfaces feasible for locked-in patients.

Brain↗
PubMed2001

Modification of slow cortical potentials in patients with refractory epilepsy: a controlled outcome study.

PURPOSE: To compare self-regulation of low-frequency EEG components (slow cortical potentials, SCPs) with other methods of seizure control for patients with drug-refractory partial epilepsy and to separate the real anticonvulsive effect from placebo effects. METHODS: Results of a treatment program of SCP self-regulation (experimental group) are compared with two groups of patients, one of which learned self-control of respiratory parameters (end-tidal CO2 and respiration rate: RES group); the other received medication with new anticonvulsive drugs (AEDs) in combination with psychosocial counseling (MED group). Clinical, cognitive, behavioral, and personality measures were assessed before and after treatment. In addition, to control for placebo responses, patients repeatedly estimated their beliefs in the efficiency of the respective treatment, their satisfaction and expectations, and the quality of the relationship with their therapists. RESULTS: SCP and MED groups showed a significant decrease of seizure frequency, but the RES group did not. Clear positive changes in the sociopsychological adjustment were obtained in all three groups, with the maximal improvement being attained in the RES group. CONCLUSIONS: All kinds of therapy result in considerable improvement of patients' emotional state, which may in part be due to potential placebo effects: however, this improvement is not related to the quality of the therapeutic effect proper (i.e., seizure reduction). Traditional double-blind control group designs are inappropriate for behavioral interventions or treatments with psychoactive pharmacologic drugs. Rather, specific tests can be developed to control the placebo effect and to separate it from the genuine therapeutic effects.

Adolescent↗
PubMed2001

Brain-computer communication: self-regulation of slow cortical potentials for verbal communication.

OBJECTIVE: To test a training procedure designed to enable severely paralyzed patients to communicate by means of self-regulation of slow cortical potentials. DESIGN: Application of the Thought Translation Device to evaluate the procedure in patients with late-stage amyotrophic lateral sclerosis (ALS). SETTING: Training sessions in the patients' homes. PARTICIPANTS: Two male patients with late-stage ALS. INTERVENTIONS: Patients learned voluntary control of their slow cortical potentials by means of an interface between the brain and a computer. Training was based on visual feedback of slow cortical potentials shifts and operant learning principles. The learning process was divided into small steps of increasing difficulty. MAIN OUTCOME MEASURES: Accuracy of self-control of slow cortical potentials (percentage of correct responses). Learning progress calculated as a function of training session. RESULTS: Within 3 to 8 weeks, both patients learned to self-regulate their slow cortical potentials and to use this skill to select letters or words in the Language Support Program. CONCLUSIONS: This training schedule is the first to enable severely paralyzed patients to communicate without any voluntary muscle control by using self-regulation of an electroencephalogram potential only. The protocol could be a model for training patients in other brain-computer interface techniques.

Adult↗
PubMed2000

Learning effects on event-related brain potentials.

This study investigates whether learning can manifest itself in EEG changes without explicit awareness of the acquired knowledge and without any motor requirement (to rule out acquisition of motor skills). Subjects passively heard particular stimulus combinations interspersed with random combinations. Immediately after this, stimulus combinations were presented which contained violations of the previously learned regular sequences. These violations elicited two frontally distributed negative waves peaked at about 250 ms and 500 ms, respectively. None of the participants could detect any regularity of the stimulation. No significant difference between regular vs random stimulus combinations was found during acquisition. These findings indicate that learning without explicit knowledge does not require motor activity (i.e. is independent of learning response sequences) and does not depend on stimulus probabilities.

Adult↗
PubMed2000

The thought translation device (TTD) for completely paralyzed patients.

The thought translation device trains locked-in patients to self-regulate slow cortical potentials (SCP's) of their electroencephalogram (EEG). After operant learning of SCP self-control, patients select letters, words or pictograms in a computerized language support program. Results of five respirated, locked-in-patients are described, demonstrating the usefulness of the thought translation device as an alternative communication channel in motivated totally paralyzed patients with amyotrophic lateral sclerosis.

Biofeedback, Psychology↗
PubMed1999

The thought translation device: a neurophysiological approach to communication in total motor paralysis.

A thought translation device (TTD) for brain-computer communication is described. Three patients diagnosed with amyotrophic lateral sclerosis (ALS), with total motor paralysis, were trained for several months. In order to enable such patients to communicate without any motor activity, a technique was developed where subjects learn to control their slow cortical potentials (SCP) in a 2-s rhythm, producing either cortical negativity or positivity according to the task requirement. SCP differences between a baseline interval and an active control interval are transformed into vertical or horizontal cursor movements on a computer screen. Learning SCP self regulation followed an operant-conditioning paradigm with individualized shaping procedures. After prolonged training over more than 100 sessions, all patients achieved self-control, leading to a 70-80% accuracy for two patients. The learned cortical skill enabled the patients to select letters or words in a language-supporting program (LSP) developed for inter-personal communication. The results demonstrate that the fast and stable SCP self-control can be achieved with operant training and without mediation of any muscle activity. The acquired skill allows communication even in total locked-in states.

Adult↗
PubMed1999

Negative potential shifts and the prediction of the outcome of neurofeedback therapy in epilepsy.

About two-thirds of epilepsy patients who learn to control their slow cortical potential shifts (SCP) reduce their seizure rate, but the remaining third does not demonstrate clinical improvement. In the present study, this finding was replicated in a group of 27 patients with focal epilepsy. We found that patients who consistently produced larger negative SCP in all conditions during the first phase of treatment, showed no decrease in seizure frequency during the six-month follow-up, as compared with the three-month baseline phase. The large negative SCP explained about one-third of the variance of the clinical outcome. Age, medication, seizure history, or the localization of focus were found to be unrelated to clinical improvement.

Adult↗
PubMed1999

Changes in EEG power spectra during biofeedback of slow cortical potentials in epilepsy.

The goal of the study was to explore parallel changes in EEG spectral frequencies during biofeedback of slow cortical potentials (SCPs) in epilepsy patients. Thirty-four patients with intractable focal epilepsy participated in 35 sessions of SCP self-regulation training. The spectral analysis was carried out for the EEG recorded at the same electrode site (Cz) that was used for SCP feedback. The most prominent effect was the increase in the theta 2 power (6.0-7.9 Hz) and the relative power decrement in all other frequency bands (particularly delta 1, alpha 2 and beta 2) in transfer trials (i.e., where patients controlled their SCPs without continuous feedback) compared with feedback trials. In the second half of the training course (i.e., sessions 21-35) larger power values in the delta, theta, and alpha bands were found when patients were required to produce positive versus negative SCP shifts. Both across-subject and across-session (within-subject) correlations between spectral EEG parameters, on the one hand, and SCP data, on the other hand, were low and inconsistent, contrary to high and stable correlations between different spectral variables. This fact, as well as the lack of considerable task-dependent effects during the first part of training, indicates that learned SCP shifts did not directly lead to the specific dynamics of the EEG power spectra. Rather, these dynamics were related to nonspecific changes in patients' brain state.

Adult↗