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The topographical aspects of fast rhythms induced by different psychotropic drugs have been studied in patients by means of a previously described method. This method is based on the spectral analysis of 28 EEG channels over both cerebral hemispheres. The spectral parameters, computed over 2 min 40 sec, are put into a data base. The clinician can then decide which of these parameters will be extracted from the data base and then displayed by means of maps on a graphic terminal. Those maps are useful for immediate comparison not only of the fast rhythms' characteristic values but also of those from other spectral bands. As quantitative EEG analysis is more and more frequently used in psychotropic drug studies, a good knowledge of the topography of the rhythms induced by these drugs will help in the selection of the most useful derivations.

In this work we have studied comparatively the relationships between alpha intensity, alpha frequency, root-mean-square amplitude and their standard deviations, versus the location of the four recorded EEG channels: left and right rolando-parietal, left and right parieto-occipital. Twenty-four spectral parameters were computed for each 5-min EEG recording, in the eyes closed situation. The hebephrenic group (36 EEGs from six patients) presented higher values of alpha intensity and RMS amplitudes with low coefficient of variation when compared with the other groups. The left/right rolando-parietal amplitude ratio was 0.73 versus 1.52 for the parieto-occipital ratio. An amplitude hypovariability in the central regions, probably associated with hyperarousal, especially in the left hemisphere, can then be observed in hebephrenics, together with high alpha intensity on the left parieto-occipital area. The two groups of schizophrenics differ from the control group (27 EEGs from 12 subjects) in terms of spectral parameters, the hebephrenic group presenting a possible interhemispheric dysfunction.

Eighty-seven EEG recordings were obtained from 9 healthy volunteers, medical students who were part of a controlled, double-blind, randomized study. After a first control recording, they received orally, at 1 week interval, either 3 placebos or 3 compounds: yohimbine chlorhydrate (4 mg), propranolol (40 mg), a psychotropic compound in experimentation. The polygraphic recordings were obtained 2 or 6 h after placebos or active compounds. Four EEG channels were recorded simultaneously (T4-C4, T3-C3, P4-O2, P3-O1). The EEGs were sampled at 200 Hz, for 120 successive epochs, free of artifacts. The recordings of 5 min were then submitted to spectral analysis followed by data reduction providing characteristic spectral parameters. A descriptive questionnaire of EEG made of 100 items was filled out by two electroencephalographists for each of 87 recordings. The items, with dichotomic choices, described 4 EEG frequency bands: delta, theta, alpha, and fast frequencies (beta). For each frequency band the following was evaluated: frequency, amplitude, asymmetry, morphology, relative abundance, irregularity, lability of frequency, diffusion, dominant localization, EMG activity and superposition of rhythms. The number of periods of drowsiness in 5 min and fluctuations of rhythms were also ascertained in the same way. The items were coded on punch cards and submitted to a first analysis of correspondences. The 3 factorial planes were plotted with the projections of each item together with the centers of gravity of placebos and treatments. The first factor can be interpreted as a bipolar axis 'mental activation-diffused vigilance', the first pole being characterized by a 'beta cluster' and the second by alpha and theta superimposed clusters. The second factor can be also considered as a bipolar axis 'drowsiness -quiet wakefulness', the first pole being characterized by a 'theta cluster' and a larger 'delta cluster' containing a smaller 'alpha cluster' of labile alpha rhythm intermingled with slower rhythms. In respect to the barycentric centers of gravity, yohimbine and propranolol are opposed to the placebo center along the factor-two axis. This may be considered as an 'anti-sedation effect'. However, along the first factor axis, the propranolol center can be associated with a greater diffusion of vigilance than the yohimbine center.