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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).

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Summary The EEG of six subjects was recorded from two pairs of symmetrically positioned electrodes (O1-P3 and O2-P4). The interhemispheric synchrony of the filtered alpha rhythms was determined by an on-line compilation of Pearson's correlation coefficient r. The positive values of r were used to determine the loudness of a tone which was fed back to the subject. Maximum and minimum intensities corresponded respectively to r = + 1 and r = 0. For all subjects a sustained maximum loudness (corresponding to a well developed alpha rhythm on both sides) appeared when they succeeded to voluntarily maintain a stabilized field of awareness and to allow them-selves to be deeply absorbed in this cognitive act. On the contrary, the sound disappeared (blockage of alpha) when subjects mode an intense effort at focussing their attention on such activities as performing a mental arithmetical computation or clenching the fist. A tone of a medium and variable intensity corresponded to the usual fluctuations of the alpha rhythm of a subject with eyes closed and in a state of mental relaxation. The results suggest a distinction, from the EEG point of view as well as from the subjective one, between the effort of attention to an object and the effortless cognitive experience which results from it. One can hypothesize that to each mental content corresponds a pattern of neuronal excitation and inhibition. Selecting and stabilizing a mental representation would then result in favouring and stabilizing the corresponding functional pattern. Consequently the diminution of the functional noise determining synchronization phenomena and development of alpha rhythm would in turn favour the formation of the selected pattern of nervous activity.