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In a simple blind study to evaluate electroencephalographic criteria objectively, and to continue characterization of psychotropic compounds, 5 mg of nitrazepam, a hypnotic derivative, was given to seven subjects the night before the recording. We noted that in most subjects there was a reduction in the spectral intensity of the alpha rhythm, associated with a greater frequency instability, several hours after the absorption of nitrazepam. This corresponds to the tardive hypnotic action of the psychotrope, the importance of which is wellknown at the present time. In the same way as the increase in rapid rhythms, the slipping of 0.5 c/s of the dominant alpha frequency to the top could be characteristic of the action of nitrazepam.

10 male volunteers, right-handers, mean age 30.4 years, were recorded in four successive sequences: under 'eyes closed' conditions, right and then left hemisphere, followed by an 'eyes open' situation with visual attention fixed on a cartoon, right and then left hemisphere recordings. Each EEG recording was made simultaneously over 16 EEG channels for each hemisphere, according to a protocol previously described as well as Fourier analysis and EEG mapping on a minicomputer (HP 5451 C, HP 1000). Each EEG recording was stored on a cartography data base, and 90 maps could be drawn from 10 spectral parameters applied to the raw EEG and 5 frequency bands. Permutation paired Fisher tests were applied to three main EEG parameters: mean centroid frequencies, RMS amplitudes in microvolts and relative (%) amplitudes. Activation of EEG in the 'eyes open' situation during visual fixation was found compared to the 'eyes closed' situation: decreasing dominant EEG frequency and low delta and theta mean frequencies, no change in a mean alpha frequency; increasing fast mean beta frequencies, together with a major decrease in theta, alpha, beta 1 amplitudes, and a concomitant increase in raw EEG, delta and beta 2 amplitudes. Finally, the percent alpha amplitude was decreased when other percent amplitudes were increased in delta, theta, beta 1 and beta 2 frequency bands. A symmetry between hemispheres was observed in the 'eyes closed' situation. Averaged EEG maps between subjects illustrate these findings, especially relative (%) alpha amplitude maps and also maps of coefficients of resonance of the alpha rhythm.

A method is described which has been developed to topographically display the values of spectral EEG analysis from 11 electrodes on each hemisphere and 5 electrodes on the midline. The EEG from 16 channels at a time is multiplexed and sampled at 3.2 kHz. From power spectra averaged every 10 sec for 5 min a few spectral parameters are computed among which are the spectral intensities within the delta, theta, alpha and beta bands. The whole values are then displayed on maps representing lateral views of cerebral hemispheres by means of spectral iso-intensity surfaces with extrapolation of the intermediate points. Different spectral intensities are coded by means of different gray levels. These maps clearly illustrate the topographical distribution of EEG rhythms and their peculiarities related to the side of the head recorded.

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.