E. Roy John

Millisecond by millisecond, year by year: normative EEG microstates and developmental stages.

Most studies of continuous EEG data have used frequency transformation, which allows the quantification of brain states that vary over seconds. For the analysis of shorter, transient EEG events, it is possible to identify and quantify brain electric microstates as subsecond time epochs with stable field topography. These microstates may correspond to basic building blocks of human information processing. Microstate analysis yields a compact and comprehensive repertoire of short lasting classes of brain topographic maps, which may be considered to reflect global functional states. Each microstate class is described by topography, mean duration, frequency of occurrence and percentage analysis time occupied. This paper presents normative microstate data for resting EEG obtained from a database of 496 subjects between the age of 6 and 80 years. The extracted microstate variables showed a lawful, complex evolution with age. The pattern of changes with age is compatible with the existence of developmental stages as claimed by developmental psychologists. The results are discussed in the framework of state dependent information processing and suggest the existence of biologically predetermined top-down processes that bias brain electric activity to functional states appropriate for age-specific learning and behavior.

The anesthetic cascade: A theory of how anesthesia suppresses consciousness

ADEQUATE surgical anesthesia must achieve three goals: immobility, amnesia, and absence of awareness. After the evidence of anesthetic lipophilicity was presented by Meyer and Overton, it was widely assumed that all these actions were accomplished at some unitary site. A body of evidence has now accumulated demonstrating that for many anesthetic agents, the dose required to suppress consciousness exceeds the amnestic dose but is substantially less then that required for surgical immobility during noxious stimuli. This suggests that these three dimensions may be mediated by different regions of the central nervous system. As has been pointed out by Rampil, the variability among anesthetics of the ratios of concentrations needed to suppress consciousness, to block memory, and to achieve surgical immobility further invalidate the unitary hypothesis. A comprehensive explanation of the mechanism by which anesthetics cause loss of consciousness (LOC) has not yet been developed. Abundant in vitro and in vivo evidence has been provided of effects of anesthetics on a wide variety of molecular and cellular processes. Campagna et al. have recently provided a review of current understanding of the molecular mechanisms of anesthesia, summarizing evidence showing that inhaled anesthetics achieve immobilization by depressing the spinal cord, whereas amnesic actions are mediated within the brain. They document research indicating that subtle differences in the clinical actions of inhaled anesthetics may be attributed to distinct actions on a number of critical molecular targets. Although this evidence makes it clear that neuronal actions and interactions at many different levels and in many different brain tissues are altered or disrupted by anesthetic drugs, it does not explain why these different more or less discrete effects have the common global effect of causing LOC, which we define as suppression of awareness. This article attempts to provide such an explanation in terms of the alteration of neurophysiologic processes that are essential for the mediation of consciousness. Before undertaking that effort, it is appropriate to provide a brief overview of the results of research in related fields.

3D Statistical Parametric Mapping of EEG Source Spectra by Means of Variable Resolution Electromagnetic Tomography (VARETA)

This article describes a new method for 3D QEEG tomography in the frequency domain. A variant of Statistical Parametric Mapping is presented for source log spectra. Sources are estimated by means of a Discrete Spline EEG inverse solution known as Variable Resolution Electromagnetic Tomography (VARETA). Anatomical constraints are incorporated by the use of the Montreal Neurological Institute (MNI) probabilistic brain atlas. Efficient methods are developed for frequency domain VARETA in order to estimate the source spectra for the set of 103–105 voxels that comprise an EEG/MEG inverse solution. High resolution source Z spectra are then defined with respect to the age dependent mean and standard deviations of each voxel, which are summarized as regression equations calculated from the Cuban EEG normative database. The statistical issues involved are addressed by the use of extreme value statistics. Examples are shown that illustrate the potential clinical utility of the methods herein developed.

Perceptual framing and cortical alpha rhythm

Abstract Apparent motion was used as a probe to test the hypothesis that perceptual framing is correlated to the phase of the alpha rhythm. Stimuli were presented phasically with respect to the occipital and parietal alpha cycle, and subjects were asked to judge whether the stimuli appeared simultaneous or sequential. The probability of perceived simultaneity was maximal for the positive phase of the occipital alpha cycle. Visual evoked potentials recorded during stimulus presentation were significantly different, in the late components, for the cases of perceived simultaneity or sequential motion. A brief review of previous experimental and theoretical studies of the relationship of perceptual framing to alpha rhythm is presented.

The pre–mild cognitive impairment, subjective cognitive impairment stage of Alzheimer’s disease

Subjective cognitive impairment (SCI) has been a common, but poorly understood condition, frequently occurring in older persons.

Quantitative electroencephalographic subtyping of obsessive-compulsive disorder

Current neuropsychological, electrophysiological, and other imaging data strongly suggest the existence of a neurobiological basis for obsessive-compulsive disorder (OCD), which was long considered to be exclusively of psychogenic origin. The positive response of some OCD patients to neurosurgery, as well as the efficacy of agents that selectively block serotonin reuptake, lends further support to a biological involvement. However, a survey of the treatment literature reveals that only 45-62% of OCD patients improve with these specific medications. In a pilot study using a quantitative electroencephalographic (QEEG) method known as neurometrics, in which QEEG data from OCD patients were compared statistically with those from an age-appropriate normative population, we previously reported the existence of two subtypes of OCD patients within a clinically homogeneous group of patients who met DSM-III-R criteria for OCD. Following pharmacological treatment, a clear relationship was found between treatment response and neurometric cluster membership. In this study, we have expanded the OCD population, adding patients from a second site, and have replicated the existence of two clusters of patients in an enlarged, statistically more robust population. Cluster 1 was characterized by excess relative power in theta, especially in the frontal and frontotemporal regions; cluster 2 was characterized by increased relative power in alpha. Further, 80.0% of the members of cluster 1 were found to be nonresponders to drug treatment, while 82.4% of the members of cluster 2 were found to be treatment responders.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative electrophysiological characteristics and subtyping of schizophrenia.

Quantitative descriptors of resting electroencephalogram (EEG) (QEEG) and event-related potentials (QERP) to visual and auditory stimuli were obtained from normal subjects and 94 chronic schizophrenic patients on medication, 25 chronic schizophrenics off medication, and 15 schizophrenics with no history of medication. These schizophrenic groups showed a high incidence of neurometric features that were significantly deviant from normative values. Multivariate discriminant analysis using these features successfully separated the schizophrenic patients from normals with high accuracy in independent replication. The data from the medicated group were subjected to cluster analysis. Newly developed algorithms were used for objective selection of the most effective set of variables for clustering and the optimum number of clusters to be sought. Five clusters were obtained, containing roughly equivalent proportions of the sample with markedly different QEEG profiles. The whole sample was then classified into these clusters. Each cluster contained patients both on and off medication, but patients who had never been medicated were classified into only three of these clusters. No significant clinical or demographic differences were found between members of the five clusters; however, clear differences in QERP profiles were seen. These results are described in detail and possible physiological and pharmacological implications are discussed.

Effects of Visual Form on the Evoked Response

The average visual evoked potentials elicited from relaxed human subjects are different for a blank visual field and one containing a geometric form, are different for different geometric forms of equal area, are similar for versions of the same geometric fortn of unequal area, and are different for two printed words equated for total letter area. These findings suggest that the waveform of evoked responses is not determined solely by the set of peripheral receptors which is stimulated, but it also reflects the perceptual content of the stimulus.

A Model of Consciousness

In the first textbook of physiological psychology, written by Wilhelm Wundt (1910) at the end of the 19th century, Wundt defined the task of physiological psychology as the analysis of the physiological bases of consciousness and subjective experience. In the textbook of physiological psychology which I used when a student, written by Morgan and Stellar (1950) in the middle of the 20th century, physiological psychology was defined as the study of the physiological bases of behavior. The word consciousness does not even appear in the index of the latter volume, nor have I encountered it anywhere in the text.

Quantitative EEG correlates of crack cocaine dependence

Evidence for a distinctive syndrome of neuroadaptation in cocaine dependence has accumulated from behavioral, neurophysiological, and preclinical and clinical pharmacological studies. The authors report on the results of a preliminary investigation of the quantitative electroencephalographic (QEEG) correlates of severe DSM-III-R crack cocaine dependence in seven patients abstinent from cocaine for 1 to 68 days. The major QEEG finding was increased absolute and relative alpha power. Increased alpha power has also been reported in multiple previous studies of depressed patients. This series of crack-dependent patients showed significant depressive morbidity; four patients attempted suicide subsequent to initiating their use of crack and the group mean (+/- SD) Beck Depression Scale score was 18.9 (+/- 6.5). These results complement other studies that support the concept of neuroadaptation to chronic cocaine exposure. Prospective studies correlating QEEG measures with subsequent response to pharmacological interventions for cocaine dependence should be considered.