Onset and offset of brain events as indices of mental chronometry.

Analysis of single-trial electroencephalogram waveforms in a reaction time task demonstrated that the onset and offset values of event-related potentials can be used as indices of the duration of information processing. Two negative waves have been identified which peak at different times in different regions of the scalp, with the second overlapping the last part of the first. These waves are related in different ways to the duration of perceptual processing.

Effect of task and stimulus probability on evoked potentials.

Some experimental data demonstrate the existence of at least two different P300s distinguished by latency, topography and functional significance. These positive waves are preceded by a negative component which has been labelled N200. The purpose of this study was to analyze the modifications of these negative and positive components according to probability and task (GO vs. NOGO) in order to better understand the significance of each of them in terms of stages of information processing. Six normal subjects were tested twice on separate days, in a GO-NOGO paradigm. Auditory stimuli - high pitch (GO) and low pitch (NOGO) - were presented in three different occurrence probability combinations: 0.2/0.8; 0.5/0.5; 0.8/0.2, in successive blocks. In both GO and NOGO responses, a vertex N200 component was followed by two positive waves - the first peaking at 300 msec at Cz (Cz : P300), the other one Ca 400 msec at Pz (Pz : P400). An inverse relation between amplitude and probability was seen for the three components but it was twice as large for P400 as for P300. A task effect was only seen for N200, the amplitude and latency of which increased in the GO condition. From the first session to the second, the amplitude of N200 decreased whereas that of P300 increased.

Ideomotor apraxia and P300: a preliminary study.

Event-related cerebral potentials and reaction time were studied in two patients with life parietal lesions inducing ideomotor apraxia and in seven control subjects. Results showed no marked increase of P300 latency in the patients with respect to the control group, whereas the RT was largely lengthened. This suggests that the decision-making processes are left intact in IMA and that only the motor execution stage is impaired.

Electrophysiological changes elicited by auditory stimuli given a positive or negative value: a study comparing anhedonic with hedonic subjects.

The present experiment investigates in 'normal' subjects the relationship between personality characteristics (anhedonia versus hedonia) and the influence of the affective value of acoustic stimuli (positive, negative, neutral) on various electrophysiological indices reflecting either tonic activation or phasic arousal (EEG power spectra, contingent negative variation: CNV, heart rate, skin potential responses: SPR) as well as on behavioural indices (reaction time: RT). Eighteen subjects were divided into two groups according to their scores at two self-rating questionnaires, the Chapman's Physical Anhedonia Scale (PAS) and the Beck-Weissman's Dysfunctional Attitude Scale (DAS) that quantifies cognitive distortions presumed to constitute high risk for depression: 9 with high scores at both scales formed the A group (Anhedonic-dysfunctional), 9 with low scores at both scales, the H group (Hedonic-adapted) The electrophysiological indices were recorded during 3 situations: the first one was a classical CNV paradigm with a motor reaction time task in which one of 3 tones of different pitch represented the warning stimulus S1; during the second, conditioning phase, two of these tones were associated with either a success (and reward) or a failure (and punishment) during a memory task in order to make them acquire either a positive or a negative affective value; the third situation consisted in the repeating of the first CNV paradigm in order to test the effect of the positive and the negative stimuli versus the neutral one on RTs and electrophysiological data. Significant between-group differences were found regarding tonic activation as well as phasic arousal indices from the very beginning of the experiment when all stimuli were neutral ones, the anhedonics exhibiting higher activation and arousal than the hedonics at the cortical (increased CNV amplitude, increased power in the beta frequency band), cardiovascular (higher heart rate habituating more slowly) and behavioural (faster RTs) levels. Significant between-group differences were also found concerning reactivity to affective stimuli during the third situation: both the orienting response (but only at the cortical level: early CNV) and the motor preparation processes (late CNV) were in the A group significantly less reactive to affective stimuli (especially to the positive one) than in the H group, in particular concerning the frontal (Fz) data.

Hemisphere asymmetry of alpha burst sequential organization in depression.

A new quantitative EEG index based on the sequential variability of the frequency of occurrence of alpha bursts (alpha-BVI) was utilized for investigating the respective role of the two hemispheres in depression and their relationship with two clinical dimensions of this illness: psychomotor retardation and blunted affect. The EEG (at P3 and P4 referred to Fz) was recorded during rest periods in two groups of patients selected according to their scores on various clinical scales: one consisted of 12 patients characterized by psychomotor retardation (PMR group), the other of 9 patients characterized by blunted affect (BA group). A control group of 12 normal subjects was recorded in the same conditions. All subjects were dextral. The following main results were obtained: (1) in both groups of patients the right and the left alpha-BVI were, before treatment, significantly lower than those of the controls. (2) In controls, the sequential alpha burst variability was identical on both hemispheres. (3) In patients, before treatment, the right hemisphere alpha-BVI was significantly lower than the left. (4) Electro-clinical correlations were also observed: (A) in the BA group, before treatment, (a) between the degree of blunted affect and the decrease of the right alpha-BVI, (b) between ideoverbal retardation and the decrease of the left alpha-BVI (these correlations disappeared after treatment); (B) in the PMR group, ideoverbal retardation was, on the contrary, correlated to a right alpha-BVI decrease, this correlation persisting after treatment. These results are discussed according to the role of each hemisphere in depression.

[Concepts underlying the analysis of late evoked potentials applied to the study of information processing and its disturbances in psychopathology]. / Concepts sous-jacents à l'analyse des potentiels évoqués tardifs appliquée à l'étude du traitement de l'information et de ses perturbations en psychopathologie.

This paper gives a rapid overview of the information processing approach taken when recording and analysing endogenous event-related potentials (ERPs) with psychiatric patients, and its theoretical framework, born from information theory and cognitive psychology. The triarchic model of P 300 amplitude recently proposed by Johnson (1986) is given as an example of a particularly coherent framework that should help determine the various sources of the P 300 amplitude reduction usually observed in psychiatric patients, probably related to the impairment of a number of different processes. The concept of "functional component" is underlined and some examples are given concerning different ERP components reflecting normal and abnormal attention processes of either automatic or controlled mode of processing. The difference between this information processing approach of the cognitive electro-physiologist, aiming at shedding some light on the strategies utilized by patients in order to cope with the experimental situation, and the electro-clinical approach seeking chiefly for a diagnostic, is emphasized.

[Electrophysiological study of attention mechanisms in depressed patients with characteristics of psychomotor retardation]. / Etude électrophysiologique des mécanismes attentionnels chez des patients déprimés caractérisés par un ralentissement psychomoteur.

The ERPs and RTs of 8 drug-free depressed in-patients (mean age 58, with marked psycho-motor retardation) were recorded during a dichotic listening RT task and compared to those of 9 healthy, age-matched controls. The depressed showed significantly longer, more variable RTs than the controls and made more mistakes. Their ERPs for targets in the attended ear differed significantly from those of the controls by the small amplitude (or absence) of the N2 vertex component elicited by the controls in such a situation and by the presence in the same situation of a late frontal slow negativity (LFN) that did not show up in the grand average ERP of the control group. These results were discussed in terms of the two components of the processing negativity described by Näätänen (1982, 1985) and according to resource models: whereas the controls would perform quickly this easy task thanks to quasi-automatic matching processes (reflected by the vertex N2), the depressed would need further effortful, controlled processing (reflected by the LFN) in order to perform the same task. The ERPs of 6 of these depressed were recorded a second time, after anti-depressive treatment and clinical improvement. A tendency to improved RTs and ERPs (amplitude decrease of the LFN and increase of N2) was seen in most patients, but these improvements were far from being as marked as the clinical improvement.

[Changes in various activation indices as a function of the value given by a stimulus in anhedonic and deprossogenic subjects]. / Modifications d'indices d'activation variés en fonction de la valence acquise par un stimulus chez des sujets anhédoniques et dépressogenes.

The aim of this experiment was to investigate, in "normal" subjects, the relationship between personality characteristics (anhedonia and depressogenic attitudes) and various tonic and phasic activation indices (EEG power spectra, CNV (at Fz and Cz), heart rate and reaction time) recorded during auditory stimulations, and the influence of the affective value of stimuli on phasic activation indices. Eighteen subjects were divided into two opposite groups according to their scores on two self-rating questionnaires (the Chapman Physical Anhedonia Scale and the Beck-Weissman Dysfunctional Attitude Scale): the A group (anhedonic with depressogenic attitudes) and the H group (hedonic and non-depressogenic). The experiment was divided into three phases. The first and third phase utilised an identical classical CNV paradigm. During the second phase, two of the three neutral warning tones of the first phase were given, by conditioning, a positive or a negative value. The results showed that: 1) before conditioning, when all stimuli were neutral, all activation indices (tonic and phasic) were significantly higher in the A group than in the H group; 2) after conditioning, the two groups differed mainly by their cortical reactivity to the positively conditioned sound: the amplitude of the two CNV components increased in the H group whereas a tendency to a CNV decrease was seen in the A group; 3) all the between-group CNV differences were significant only at Fz. These results were discussed in terms of differences of optimal level of activation.

[Evoked potentials and the mode of cognitive development in boys 6 to 8 years of age presenting hyperactivity with attention deficit]. / Potentiels évoqués et mode de développement cognitif chez des garçons présentant entre 6 et 8 ans une hyperactivité avec déficit de l'attention.

Event-related potentials were recorded in 2 groups (attention deficit hyperactivity disorder--ADHD--and normal controls) of 12 male children aged between 6-8 years during 4 categorization tasks. Each task was performed with a different type of visual stimulus; pictures, words, geometrical figures or digits. The amplitudes and latencies of a fronto-central P250 and a parieto-occipital P350 were examined. The overall amplitude of the fronto-central P250 was larger in the ADHD group. However, the overall latency of the parieto-occipital P350 decreased with age; coincidentally, in the control group, the P350 latency measured in the left hemisphere became shorter with age for the words than for the pictures. This was not the case in the ADHD group. These results are discussed in relation to the level of the orienting reaction and the modes (general or differentiated) of cognitive development.

[Study of cognitive evoked potentials as a function of the affective value and significance of stimuli in anhedonic healthy subjects with dysfunctional attitudes]. / Etude de potentiels évoqués cognitifs en fonction de la valence affective et de la signification des stimulus chez des sujets sains anhédoniques avec attitudes dysfonctionnelles.

In depression studies, it is important to consider healthy subjects with characteristics which may be predictive of depression. Such are anhedonia and some "dysfunctional" attitudes. For this reason, subjects with or without these characteristics were submitted to an experimental paradigm allowing an analysis of their electroencephalographical (CNV and P300) reactivity according to affective value and meaning of stimuli, and according to the probability of occurrence of these stimuli. Subjects were divided into two groups according to their scores on two scales: the Physical Anhedonia Scale of Chapman et al. and the Dysfunctional Attitudes Scale of Weissman and Beck. Several results enabled to differentiate the two groups. Anhedonic and depressogenic subjects were characterized mainly by a particular type of processing for failure situations and for the stimulus which were associated with those situations.