[Depression and functional EEG asymmetry]. / Dépression et asymétrie fonctionnelle EEG.

A new quantified EEG index (Alpha Burst Occurrence Variability Index: alpha BVI) has been devised in order to characterize sequential variations of alpha bursts in EEG. This index makes it possible to quantify slope variations of a cumulative graph (periodogram) where the rank of alpha bursts is traced as a function of their instant of arrival. Such quantitative analysis was applied to spontaneous EEG segments which were recorded in the parieto-occipital regions (P3-Fz and P4-Fz) during a rest period, in three groups of depressed patients, one being characterized by psychomotor retardation (PRM group), another one by an emotional blunting (EB group) and a group of impulsive depressed patients (I group). The patients were compared to a group of healthy control subjects. In the three patient groups, before treatment, it was observed that the right and left alpha BVI were significantly lower than those of the control subjects. The right hemisphere was involved in all cases, but the left hemisphere was involved only in severe cases. In the EB and I groups, two strong "electro-clinical" correlations were observed, each one being specific for each hemisphere, one relating the reduction of the right alpha BVI to the depressive mood, the other relating the reduction of the left alpha BVI to the degree of speech ("ideoverbal") retardation. These results emphasize the role of the right hemisphere in the probable pathogenesis of depression.

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.

Hemisphere asymmetry of alpha burst frequency of occurrence variations in depression.

A new EEG index (Alpha Burst Occurrence Variability Index: alpha BVI) has been designed for quantifying the sequential variability of the frequency of occurrence of alpha bursts, expressed on a cumulative graph (periodogram). EEG (P3-Fz and P4-Fz) was recorded during a rest situation: 1) in two groups of right handed depressed patients, characterized, one by psychomotor retardation (PMR group), the other by blunted affect (BA group); 2) in a group of right handed controls. In both groups of patients, before treatment, the mean right alpha BVI was always significantly lower than in controls (the left alpha BVI only in severe cases). In the BA group, two strong electroclinical correlations were found: 1) between blunted affect and the right alpha BVI decrease and 2) between ideoverbal retardation and the left alpha BVI decrease. These results are discussed regarding the role of the right hemisphere (and possibly of the right hippocampus).

[Voluntary synchronization and desynchronization of alpha rhythm by retroaction of EEG rhythms. Preliminary study (author's transl)]. / Synchronisation et désynchronisation volontaires du rythme alpha par rétroaction des rythmes EEG.

Research was carried out on twenty subjects on the volontary control of alpha rythm by retroaction. Retroaction was provided in real time as a sound indicating the presence of alpha bursts or the intervals between bursts when reaching a pre-selected amplitude threshold, in such a way as to ensure that the alpha Index of the control situation (LB) reached about 50% of its total length. There are five situations per session: the initial state or base line (LB), relaxation with eyes closed (DF) and eyes open (DO), concentration with eyes closed (CF)and eyes open (CO), each situation being subdivided into 4 one-minute sequences. Subjects are informed about the alpha Index achieved at the end of each sequence, thus creating a periodic reinforcement. From the outset, three subjects showed an evident ability to increase or decrease at will the alpha occurrence rate, which gradually improved as the sequences progressed. Three other subjects showed that the same ability but to a lesser extent. Subjects confirmed that the feedback signal helped them to determine the most effective strategy for voluntary control, thus indicating that training is possible and that it is greatly facilitated by feedback, at least in the early stages. A detailed analysis of the recordings has made it possible for us to formulate hypotheses about the most important aspects of this control.