EEG cartography before and after visual stimulation: a group study with descriptive non-parametric analysis of EEG data.

Ten right-handed students were submitted to a protocol of cognitive visual stimulations based on six successive sequences: EC1, EO, B1, B2, B3, EC2. Following a first "eyes closed" (EC1) multiple EEG recording (16 EEG leads, plus polygraphy), and an "eyes-open" recording (EO) with central visual fixation, 60 computer-controlled slides were presented successively for each of three successive recordings (B1, B2, B3) before the last "eyes-closed" recording (EC2). In B1, the subjects were asked to look at the meaningful black and white drawings presented without comment. In B2, a second set of similar pictures was presented, with the advice to try to remember later on the visually projected slides. In B3, a memory recognition task was introduced with 20 slides coming from the B1 set, 20 from the B2 set, completed by 20 new slides. Each slide was presented for 10.24s. followed by a beep audio-signal indicating that the subjects should press electronic mouse knobs alternatively in B1, B2, and for indicating their answers in B3. After artifact rejection, EEG spectral analysis was followed by parametrization and group studies applying Fisher non-parametric paired exact probability tests. Nine comparisons were computed: EC1-EC2, EC1-EO, EC2-EO, EO-B1, EO-B2, EO-B3, B1-B2, B1-B3, B2-B3. A statistical strategy of descriptive inter-individual non-parametric. Fisher tests was undertaken, together with computation and mapping of averaged spectral parameter differences (mean amplitudes and frequencies, mean amplitudes %, resonance coefficients) for raw EEG, delta, theta, alpha, alpha 1, alpha 2, beta 1 and beta 2 frequency bands and probability maps.(ABSTRACT TRUNCATED AT 250 WORDS)

Inter- and intra-individual probability maps in EEG cartography by use of nonparametric Fisher tests.

The three types of non-parametric permutation Fisher tests have been applied to inter-individual group studies and further to intra-individual multiple EEG recording sequences, providing computations of EEG probability maps testing two ordinal hypotheses. Two examples of previous group studies with "EEG local cerebral activation" are given: mental computation in a group of 20 controls and caffeine effects versus placebo in a group of 10 controls. For the intra-individual study, two successive recordings of 2.3 min eyes closed (EC1 and EC2), obtained at 50 min intervals, were compared by paired exact permutation Fisher tests (over 15 or 42 synchronous EEG sequences). These tests were applied to descriptive spectral parameters: RMS and % amplitudes, mean frequencies, resonance coefficient, for raw unfiltered EEG and delta, theta, alpha, alpha 1, alpha 2, beta 1, beta 2 frequency bands. Two hypotheses were tested for each of the computed 31 parameters, providing two probability maps indicating if the parameter was greater or lower in the first EEG recording or in the second. The second EEG sequence, EC2, was "EEG activated" compared to the first sequence EC1 if the following were present: decreased amplitudes mainly in raw EEG, low activity and alpha bands; increased frequencies mainly, in raw EEG, delta and beta 1 fast activities; increased fast activity percentages; decreased coefficient of resonance. The effect of choice of reference was also evaluated: probability maps for a frontal reference were different than other probability maps obtained after computation of average reference or source derivation.(ABSTRACT TRUNCATED AT 250 WORDS)