Event-related potentials predict the outcome of the vegetative state.
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Cognition↗
Biomedical subjects
Boris Kotchoubey
Publications and source records attributed to Boris Kotchoubey.
The t-CWT: a new ERP detection and quantification method based on the continuous wavelet transform and Student's t-statistics.
OBJECTIVE: This study was aimed at developing a method for extraction and assessment of event-related brain potentials (ERP) from single-trials. This method should be applicable in the assessment of single persons' ERPs and should be able to handle both single ERP components and whole waveforms. METHODS: We adopted a recently developed ERP feature extraction method, the t-CWT, for the purposes of hypothesis testing in the statistical assessment of ERPs. The t-CWT is based on the continuous wavelet transform (CWT) and Student's t-statistics. The method was tested in two ERP paradigms, oddball and semantic priming, by assessing individual-participant data on a single-trial basis, and testing the significance of selected ERP components, P300 and N400, as well as of whole ERP waveforms. The t-CWT was also compared to other univariate and multivariate ERP assessment methods: peak picking, area computation, discrete wavelet transform (DWT) and principal component analysis (PCA). RESULTS: The t-CWT produced better results than all of the other assessment methods it was compared with. CONCLUSIONS: The t-CWT can be used as a reliable and powerful method for ERP-component detection and testing of statistical hypotheses concerning both single ERP components and whole waveforms extracted from either single persons' or group data. SIGNIFICANCE: The t-CWT is the first such method based explicitly on the criteria of maximal statistical difference between two average ERPs in the time-frequency domain and is particularly suitable for ERP assessment of individual data (e.g. in clinical settings), but also for the investigation of small and/or novel ERP effects from group data.
Acoustic Stimulation↗
Deactivation of brain areas during self-regulation of slow cortical potentials in seizure patients.
This study investigates the neurophysiological basis of EEG feedback for patients with epilepsy. Brain areas are identified that become hemodynamically deactivated when epilepsy patients, trained in EEG self-regulation, generate positive slow cortical potentials (SCPs). Five patients were trained in producing positive SCPs, using a training protocol previously established to reduce seizure frequency in patients with drug refractory epilepsy. Patients attempted to produce positive SCP shifts in a functional magnetic resonance imaging (fMRI) scanner. Two patients were able to reliably produce positive SCP shifts. When these successful regulators were prompted to produce positive SCPs, blood oxygen level-dependent (BOLD) response indicated deactivation, in comparison to a control state, around the recording electrode, frontal lobe, and thalamus. Unsuccessful regulators' BOLD response indicated no deactivation in cortical areas proximal to the active electrode. No thalamic deactivation was found in poor regulators. Decreased seizure frequency from SCP training may be the result of positively reinforced inhibition in cortical areas proximal to active electrode placement, the frontal cortex, and the thalamus.
Adult↗
Event-related potentials, cognition, and behavior: a biological approach.
The prevailing cognitive-psychological accounts of event-related brain potentials (ERPs) assume that ERP components manifest information processing operations leading from stimulus to response. Since this view encounters numerous difficulties already analyzed in previous studies, an alternative view is presented here that regards cortical control of behavior as a repetitive sensorimotor cycle consisting of two phases: (i) feedforward anticipation and (ii) feedback cortical performance. This view allows us to interpret in an integrative manner numerous data obtained from very different domains of ERP studies: from biophysics of ERP waves to their relationship to the processing of language, in which verbal behavior is viewed as likewise controlled by the same two basic control processes: feedforward (hypothesis building) and feedback (hypothesis checking). The proposed approach is intentionally simplified, explaining numerous effects on the basis of few assumptions and relating several levels of analysis: neurophysiology, macroelectrical processes (i.e. ERPs), cognition and behavior. It can, therefore, be regarded as a first approximation to a general theory of ERPs.
Animals↗
Predictors of seizure reduction after self-regulation of slow cortical potentials as a treatment of drug-resistant epilepsy.
Variables were identified that predict seizure reduction following self-regulation of slow cortical potentials (SCPs) as part of a behavioral self-management program. A sequence analysis across 52 weeks determined 14 patients to have greater than 50% seizure reduction, 8 patients with less than 50% reduction, and 12 patients without improvement. Three variables accounted for 70% of treatment success: (1) cortical excitability at the beginning of training, (2) epileptic focus, and (3) personality variables. Reduction of complex partial and secondary generalized seizures covaried with SCP control attained in the last training session. EEG spectral parameters and cognitive function appeared unrelated to treatment outcome. Successful patients may be those without large negative SCP amplitudes at the beginning of training, without a left temporal epileptic focus, and who score low on life satisfaction and are highly reactive to stress. Patients with complex partial and secondarily generalized seizures may be more likely to experience seizure reduction if they demonstrate good SCP control at the end of their training.
Adolescent↗
Event-related potential measures of consciousness: two equations with three unknowns.
This is a brief review of event-related brain potentials (ERPs) as indices of cortical information processing in conditions in which conscious perception of stimuli is supposed to be absent: sleep, coma, vegetative state, general anesthesia, neglect as well as presentation of subliminal or masked stimuli. Exogenous ERP components such as N1 and P2 are much more likely to remain in all these conditions than endogenous components. Further, all varieties of the late posterior positive ERP waves (e.g., P3b, P600, late positive complex) are most difficult to be elicited in such conditions, indicating that the cortical activity underlying the late posterior positivity may have a particularly close relationship to brain mechanisms of conscious perception. Contrary to what might be expected, reliable ERP effects indicating complex analysis of semantic stimulus features (i.e., meaning) can be recorded without conscious awareness, generally, as easy as (in some conditions, even easier than) ERP components related to rather simple physical stimulus features. It should be emphasized, however, that we never should overestimate our confidence about the degree of subjects' unawareness. Particularly in the conditions in which no behavioral response can be obtained (e.g., sleep, coma, anesthesia), residual conscious processing, at least in some subjects and on some trials, cannot be ruled out.
Anesthesia↗
Psychobiology of altered states of consciousness.
The article reviews the current knowledge regarding altered states of consciousness (ASC) (a) occurring spontaneously, (b) evoked by physical and physiological stimulation, (c) induced by psychological means, and (d) caused by diseases. The emphasis is laid on psychological and neurobiological approaches. The phenomenological analysis of the multiple ASC resulted in 4 dimensions by which they can be characterized: activation, awareness span, self-awareness, and sensory dynamics. The neurophysiological approach revealed that the different states of consciousness are mainly brought about by a compromised brain structure, transient changes in brain dynamics (disconnectivity), and neurochemical and metabolic processes. Besides these severe alterations, environmental stimuli, mental practices, and techniques of self-control can also temporarily alter brain functioning and conscious experience.
Arousal↗
A device for the detection of cognitive brain functions in completely paralyzed or unresponsive patients.
Unresponsive patients with remaining cognitive abilities may be able to communicate with a brain-computer interface (BCI) such as the Thought Translation Device (TTD). Before initiating TTD learning, which may imply considerable effort, it is important to classify the patients' state of awareness and their remaining cognitive abilities. A tool for detection of cognitive activity (DCA) in the completely paralyzed was developed and integrated into the TTD which is a psychophysiological system for direct brain communication. In the present version, DCA entails five event-related brain-potential (ERP) experiments and investigates the capability of a patient to discriminate, e.g., between semantically related and unrelated concepts and categories. ERPs serve as an indicator of the patients' cortical information processing. Data from five severely brain-injured patients in persistent vegetative state diagnosed as unresponsive and five healthy controls are presented to illustrate the methodology. Two patients showing the highest responsiveness were selected for TTD training. The DCA integrated in the TTD allows screening of cognitive abilities and direct brain communication in the patients' home.
Adult↗
Assessment of cognitive functions in severely paralysed and severely brain-damaged patients: neuropsychological and electrophysiological methods.
A systematic neuropsychological assessment technique is described for use with severely physically disabled individuals, possibly with combined motor and cognitive disorders. Target neurological conditions may be, e.g., an incomplete locked-in state, a minimally conscious state, or severe combinations of paralysis, agnosia, and apraxia. Neuropsychological assessment in these patients is difficult, because standard neuropsychological tests require fast motor responses, which can be manual, verbal, or both. To assess the cognitive status of patients with residual motor function, tests have been applied that can be answered by a binary (yes/no) signal and whose outcomes were not based on reaction times. Further, a battery of neurophysiological examination procedures based on event-related brain potentials has been developed. These procedures can be performed directly at a patient's bedside (at home or in a hospital) and applied for assessment of cognitive functions even in patients without residual motor function.
Brain Injuries↗
Recognition of affective prosody: continuous wavelet measures of event-related brain potentials to emotional exclamations.
The affective state of a speaker can be identified from the prosody of his or her speech. Voice quality is the most important prosodic cue for emotion recognition from short verbal utterances and nonverbal exclamations, the latter conveying pure emotion, void of all semantic meaning. We adopted two context violation paradigms-oddball and priming-to study the event-related brain potentials (ERP) reflecting this recognition process. We found a negative wave, the N300, in the ERPs to contextually incongruous exclamations, and interpreted this component as analogous to the well-known N400 response to semantically inappropriate words. The N300 appears to be a real-time psychophysiological measure of spontaneous emotion recognition from vocal cues, which could prove a useful tool for the examination of affective-prosody comprehension. In addition, we developed a new ERP component detection and estimation method that is based on the continuous wavelet transform (CWT), does not rely on visual inspection of the waveforms, and yields larger statistical difference effects than classical methods.
Adult↗
Brain areas activated in fMRI during self-regulation of slow cortical potentials (SCPs).
In humans, surface-negative slow cortical potentials (SCPs) originating in the apical dendritic layers of the neocortex reflect synchronized depolarization of large groups of neuronal assemblies. They are recorded during states of behavioural or cognitive preparation and during motivational states of apprehension and fear. Surface positive SCPs are thought to indicate reduction of cortical excitation of the underlying neural networks and appear during behavioural inhibition and motivational inertia (e.g. satiety). SCPs at the cortical surface constitute summated population activity of local field potentials (LFPs). SCPs and LFPs may share identical neural substrates. In this study the relationship between negative and positive SCPs and changes in the BOLD signal of the fMRI were examined in ten subjects who were trained to successfully self-regulate their SCPs. FMRI revealed that the generation of negativity (increased cortical excitation) was accompanied by widespread activation in central, pre-frontal, and parietal brain regions as well as the basal ganglia. Positivity (decreased cortical excitation) was associated with widespread deactivations in several cortical sites as well as some activation, primarily in frontal and parietal structures as well as insula and putamen. Regression analyses revealed that cortical positivity was predicted with high accuracy by pallidum and putamen activation and supplementary motor area (SMA) and motor cortex deactivation, while differentiation between cortical negativity and positivity was revealed primarily in parahippocampal regions. These data suggest that negative and positive electrocortical potential shifts in the EEG are related to distinct differences in cerebral activation detected by fMRI and support animal studies showing parallel activations in fMRI and neuroelectric recordings.
Adult↗
Cortical processing in Guillain-Barré syndrome after years of total immobility.
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Adult↗
Parallel processing of physical and lexical auditory information in humans.
We usually process auditory information at the physical level (e.g., pitch or side of presentation) and the formal level (e.g., semantic or syntax) simultaneously. However, most physiological studies investigate either the former or the latter level of processing. In this experiment, words belonging to three lexical categories (nouns, verbs, and adverbs) were randomly presented to the right or left ear. Participants were required to count all nouns presented on the relevant side. All side-relevant stimuli elicited two negativities between 100-250 and 450-650 ms post-stimulus. Nouns yielded more positive potential amplitudes between 200 and 700 ms than verbs and adverbs. This effect was observed for words presented in both relevant and irrelevant ear, i.e., it was independent of whether nouns were targets or not. After 600 ms post-stimulus, a P300-like wave was recorded to target nouns only. This component was maximal at left temporal sites. The data contradict the hierarchic processing hypothesis (first side selection, then target selection) and indicate parallel processing of physical and lexical information. Implications for the issue of language specificity of brain potentials are discussed.
Adult↗
Electrocortical and behavioral effects of chronic immobility on word processing.
Neuroelectrical and subjective effects of chronic motor deficits (severe immobility) on word processing were explored. A total of ten artificially ventilated patients with end-stage amyotrophic lateral sclerosis (ALS), seven patients with tetraplegia due to a high spinal cord injury (SCI), and nine matched controls were examined. Both ALS and SCI patients were almost completely paralyzed; eye, head, and face movements were intact in SCI but not in ALS patients. Event-related brain potentials (ERPs) were recorded during presentation of verbs with strong motor-action associations and nouns with strong visual associations. Subjects estimated the subjective strength of motor and visual associations for each word using a scale from 0 to 5. No between-group difference was found for subjectively rated motor associations. All patients reported much stronger visual associations for both nouns and verbs than healthy subjects. ERPs to both word classes revealed a left occipital negativity in SCI patients at a latency of 200-300 ms, and a marked decrease of the slow positive wave in the interval of 300-800 ms in the two patient groups. Both psychophysical and electrophysiological data suggest compensatory activation of visual information processing areas in severely paralyzed patients. The more pronounced effects in the SCI group as compared with the ALS group may be attributed to somatosensory deafferentation in SCI patients, while the sensory inflow in ALS remains relatively intact.
Adult↗
Event-related brain potentials in a patient with akinetic mutism.
The clinical pattern of complete akinetic mutism (AM) was observed in a patient with a bilateral infarction of the anterior cerebral arteries extending to the rostral cingulate cortex and the supplementary motor areas. Since the patient was unable to produce any overt response, event-related brain potentials (ERPs) were used to obtain information about cortical processing of stimuli. Oddball tasks with simple acoustical stimuli and semantic categories were used. Verbal processing was further assessed by comparing event-related potentials to words compatible versus incompatible to the semantic context. Although the pattern of cortical responses was abnormal, differential responses were clearly obtained to semantically different word classes. Thus, the hypothesis about cortical non-responsivity of AM patients, drawn from several previous reports, was not supported. An ERP examination in AM patients can deliver information about their mental state, provided that the stimuli and tasks possess a wide range of informational complexity and motivational value.
Akinetic Mutism↗
Can humans perceive their brain states?
Although the brain enables us to perceive the external world and our body, it remains unknown whether brain processes themselves can be perceived. Brain tissue does not have receptors for its own activity. However, the ability of humans to acquire self-control of brain processes indicates that the perception of these processes may also be achieved by learning. In this study patients learned to control low-frequency components of their EEG: the so-called slow cortical potentials (SCPs). In particular "probe" sessions, the patients estimated the quality of the SCP shift they had produced in the preceding trial. The correspondence between the recorded SCP amplitudes and the subjective estimates increased with training. The ability to perceive the SCPs was related to the ability to control them; this perception was not mediated by peripheral variables such as changes in muscle tonus and cannot be reduced to simple vigilance monitoring. These data provide evidence that humans can learn to perceive the neural activity of their brain. Alternative interpretations are discussed.
Adult↗
Brain responses to number sequences with and without active task requirement.
OBJECTIVE: To examine the effect of the active task involvement versus the passive knowledge of the structure of the stimulation on event-related potentials (ERPs) to violation in number sequences. This should contribute to future development of an ERP test for neurological patients. METHODS: ERPs were recorded in subjects who listened to 4-item sequences of numbers incrementing by one. Half of the sequences had an appropriate end item, whereas the other half ended inappropriately. The role of active versus passive condition was investigated in a between-subject design. RESULTS: Incorrectly ending sequences yielded a large P300 wave in all groups. Subjects who were explicitly informed about the nature of the stimulation but did not have a motor task displayed a slow negativity which followed P300 and slightly suppressed it. In addition, incorrect sequence endings elicited an early (70-200 ms) negativity at frontal sites. This effect was inverted on mastoids. CONCLUSIONS: Auditory perception of 3 consecutive numbers constituting a simple incrementing row leads to building a strong expectancy concerning the subsequent number, and unexpected events are detected already after the initial phoneme.
Acoustic Stimulation↗
Is there a mind? Electrophysiology of unconscious patients.
Event related brain potentials (ERPs) provide information about cortical processing in severe neurological patients whose cognitive abilities cannot be expressed in their behavior. In coma, ERPs contribute to the prediction of the outcome. In a vegetative state, ERPs uncover the functional state of cortical processes. The significance of ERPs in the neurophysiological study of consciousness is discussed.
Cerebral Cortex↗