John Gruzelier

Impaired Auditory Frequency Discrimination in Dyslexia Detected with Mismatch Evoked Potentials

Deficits in phonological skills appear to be at the heart of reading disability; however, the nature of this impairment is not yet known. The hypothesis that dyslexic subjects are impaired in auditory frequency discrimination was tested by using an attention‐independent auditory brain potential, termed mismatch negativity (MMN) while subjects performed a visual distractor task. In separate blocks, MMN responses to graded changes in tone frequency or tone duration were recorded in 10 dyslexic and matched control subjects. MMN potentials to changes in tone frequency but not to changes in tone duration were abnormal in dyslexic subjects. This physiological deficit was corroborated by a similarly specific impairment in discriminating tone frequency, but not tone duration, which was assessed separately. Furthermore, the pitch discrimination and MMN deficit was correlated with the degree of impairment in phonological skills, as reflected in reading errors of regular words and nonwords. It is possible that in dyslexia a persistent sensory deficit in monitoring the frequency of incoming sound may impair the feedback control necessary for the normal development of phonological skills. Ann Neurol 1999;45:495–503

The effect of training distinct neurofeedback protocols on aspects of cognitive performance

The use of neurofeedback as an operant conditioning paradigm has disclosed that participants are able to gain some control over particular aspects of their electroencephalogram (EEG). Based on the association between theta activity (4-7 Hz) and working memory performance, and sensorimotor rhythm (SMR) activity (12-15 Hz) and attentional processing, we investigated the possibility that training healthy individuals to enhance either of these frequencies would specifically influence a particular aspect of cognitive performance, relative to a non-neurofeedback control-group. The results revealed that after eight sessions of neurofeedback the SMR-group were able to selectively enhance their SMR activity, as indexed by increased SMR/theta and SMR/beta ratios. In contrast, those trained to selectively enhance theta activity failed to exhibit any changes in their EEG. Furthermore, the SMR-group exhibited a significant and clear improvement in cued recall performance, using a semantic working memory task, and to a lesser extent showed improved accuracy of focused attentional processing using a 2-sequence continuous performance task. This suggests that normal healthy individuals can learn to increase a specific component of their EEG activity, and that such enhanced activity may facilitate semantic processing in a working memory task and to a lesser extent focused attention. We discuss possible mechanisms that could mediate such effects and indicate a number of directions for future research.

Learned self-regulation of EEG frequency components affects attention and event-related brain potentials in humans

Learned enhancement of EEG frequency components in the lower beta range by means of biofeedback has been reported to alleviate attention deficit hyperactivity disorder (ADHD) symptoms. In order to elucidate frequency-specific behavioural effects and neurophysiological mediators, this study applied neurofeedback protocols to healthy volunteers, and assessed impact on behavioural and electrocortical attention measures. Operant enhancement of a 12–15 Hz component was associated with reduction in commission errors and improved perceptual sensitivity on a continuous performance task (CPT), while the opposite relation was found for 15–18 Hz enhancement. Both 12–15 Hz and 15–18 Hz enhancement were associated with significant increases in P300 event-related brain potential amplitudes in an auditory oddball task. These relations are interpreted as stemming from band-specific effects on perceptual and motor aspects of attention measures.

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.

EEG-neurofeedback for optimising performance. I: A review of cognitive and affective outcome in healthy participants

A re-emergence of research on EEG-neurofeedback followed controlled evidence of clinical benefits and validation of cognitive/affective gains in healthy participants including correlations in support of feedback learning mediating outcome. Controlled studies with healthy and elderly participants, which have increased exponentially, are reviewed including protocols from the clinic: sensory-motor rhythm, beta1 and alpha/theta ratios, down-training theta maxima, and from neuroscience: upper-alpha, theta, gamma, alpha desynchronisation. Outcome gains include sustained attention, orienting and executive attention, the P300b, memory, spatial rotation, RT, complex psychomotor skills, implicit procedural memory, recognition memory, perceptual binding, intelligence, mood and well-being. Twenty-three of the controlled studies report neurofeedback learning indices along with beneficial outcomes, of which eight report correlations in support of a meditation link, results which will be supplemented by further creativity and the performing arts evidence in Part II. Validity evidence from optimal performance studies represents an advance for the neurofeedback field demonstrating that cross fertilisation between clinical and optimal performance domains will be fruitful. Theoretical and methodological issues are outlined further in Part III.

Event-Related Brain Potential Correlates of Human Auditory Sensory Memory-Trace Formation

The event-related potential (ERP) component mismatch negativity (MMN) is a neural marker of human echoic memory. MMN is elicited by deviant sounds embedded in a stream of frequent standards, reflecting the deviation from an inferred memory trace of the standard stimulus. The strength of this memory trace is thought to be proportional to the number of repetitions of the standard tone, visible as the progressive enhancement of MMN with number of repetitions (MMN memory-trace effect). However, no direct ERP correlates of the formation of echoic memory traces are currently known. This study set out to investigate changes in ERPs to different numbers of repetitions of standards, delivered in a roving-stimulus paradigm in which the frequency of the standard stimulus changed randomly between stimulus trains. Normal healthy volunteers (n = 40) were engaged in two experimental conditions: during passive listening and while actively discriminating changes in tone frequency. As predicted, MMN increased with increasing number of standards. However, this MMN memory-trace effect was caused mainly by enhancement with stimulus repetition of a slow positive wave from 50 to 250 ms poststimulus in the standard ERP, which is termed here “repetition positivity” (RP). This RP was recorded from frontocentral electrodes when participants were passively listening to or actively discriminating changes in tone frequency. RP may represent a human ERP correlate of rapid and stimulus-specific adaptation, a candidate neuronal mechanism underlying sensory memory formation in the auditory cortex.

15O POSITRON EMISSION TOMOGRAPHIC SCANNING IN PREDOMINANTLY NEVER-TREATED ACUTE SCHIZOPHRENIC PATIENTS

Positron emission tomography with oxygen-15 was used to compare regional cerebral blood flow and the regional cerebral metabolic rate of oxygen in a group of predominantly never-treated, acute schizophrenic patients and in matched controls. The results of this study did not support the hypothesis that schizophrenics have reduced frontal blood flow and/or metabolism; and only equivocal support was obtained for the hypothesis that metabolism within the basal ganglia is reduced in schizophrenics. However, support was obtained for the hypothesis that an abnormality in hemisphere laterality may underlie schizophrenic illness.

Is the P300 wave an endophenotype for schizophrenia? A meta-analysis and a family study

INTRODUCTION We assessed the usefulness of the P300 wave as endophenotype for schizophrenia by means of a meta-analysis of the literature as well as our own family study. METHOD Meta-analysis: We conducted a systematic search for articles published between 1983 and 2003 that reported P300 measures in non-psychotic relatives of schizophrenic patients and in healthy controls. Meta-regression analyses were performed using a random effects procedure. The pooled standardized effect size (PSES) was calculated as the difference between the means of the two groups divided by the common standard deviation. Local study: We examined the P300 wave with a standard two-tone oddball paradigm in 30 patients with schizophrenia, 40 non-psychotic relatives, and 40 controls using linear mixed models. RESULTS Meta-analysis: We pooled 472 relatives and 513 controls. The P300 amplitude was significantly reduced in relatives (PSES = 0.61; 95% CI: 0.30 to 0.91; P < 0.001). The P300 latency was significantly delayed in relatives (PSES of -0.50; 95% CI: -0.88 to -0.13; P = 0.009]. Local study: The patients showed a trend for amplitude reductions (P = 0.06) and significant latency delays (P < 0.01). The relatives displayed normal amplitude but had significant latency delays (P = 0.01). The P300 amplitude and especially the P300 latency are promising alternative phenotypes for genetic research into schizophrenia.

Hypnosis decouples cognitive control from conflict monitoring processes of the frontal lobe.

Hypnosis can profoundly alter sensory awareness and cognitive processing. While the cognitive and behavioral phenomena associated with hypnosis have long been thought to relate to attentional processes, the neural mechanisms underlying susceptibility to hypnotic induction and the hypnotic condition are poorly understood. Here, we tested the proposal that highly hypnotizable individuals are particularly adept at focusing attention at baseline, but that their attentional control is compromised following hypnosis due to a decoupling between conflict monitoring and cognitive control processes of the frontal lobe. Employing event-related fMRI and EEG coherence measures, we compared conflict-related neural activity in the anterior cingulate cortex (ACC) and control-related activity in the lateral frontal cortex (LFC) during Stroop task performance between participants of low and high hypnotic susceptibility, at baseline and after hypnotic induction. The fMRI data revealed that conflict-related ACC activity interacted with hypnosis and hypnotic susceptibility, in that highly susceptible participants displayed increased conflict-related neural activity in the hypnosis condition compared to baseline, as well as with respect to subjects with low susceptibility. Cognitive-control-related LFC activity, on the other hand, did not differ between groups and conditions. These data were complemented by a decrease in functional connectivity (EEG gamma band coherence) between frontal midline and left lateral scalp sites in highly susceptible subjects after hypnosis. These results suggest that individual differences in hypnotic susceptibility are linked with the efficiency of the frontal attention system, and that the hypnotized condition is characterized by a functional dissociation of conflict monitoring and cognitive control processes.

Short duration synchronization of human theta rhythm during recognition memory.

STRUCTURES within the medial temporal lobe, particularly the hippocampus, have long been implicated in human episodic memory. The same structures are known to generate EEG in the theta frequency range in animals. The aim of this experiment was to investigate the time course of changes in the human theta rhythm during a word recognition memory task. In the period 125–250 ms after the visual presentation of a word, theta power increased by an average of 13% compared with the prestimulus baseline period and this increase was more than twice as great for repeated words (18%) as for new ones (8%). These results show that there are short duration changes in the human theta rhythm associated with recognition memory.