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

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Abstract
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 comparaisons 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. Before and after visual stimulation, changes occurred when compairing EC1 and EC2: after EC2, the alpha and alpha 1 frequencies were decreased when the alpha 2 frequency was increased and alpha 2 relative amplitude % was decreased. These results indicate more cortical EEG activation in the alpha 2 frequency band after EC2 following visual stimulation.

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