Electrophysiological correlates of the visual after effect by means of visual evoked potentials.

An attempt was made to determine whether changes of electrical activity could be seen in the posterior cortex during an after image of high frequency luminance gratings. Steady state visual evoked potentials were recorded (midoccipital, right and left temporo-occipital sites) immediately after a period of visual adaptation (15 min) to the stimulus, while the subjects experienced the after image. During this illusion, frequencies of the fast Fourier transform spectra linked to the stimulation differed from the noise and were larger at temporo-occipital sites than at the midoccipital one.

Spatial frequency and right hemisphere: an electrophysiological investigation.

The influence of the spatial frequency of visual stimuli on hemispheric asymmetry has been studied with visual evoked potentials (VEP). Nineteen different sinusoidal gratings (19 SF from 1 to 10 cpd) were presented in an ON-OFF mode to five right-handed subjects. The amplitude of the VEPs and the latency of the first positive component (C1) were analyzed.

The Stroop's test evokes a negative brain potential, the N400.

The Event Related Potential (ERP) of 8 french right handed subjects were recorded with 5 active electrodes located in frontal (Fz), central (Cz), occipital (Oz) and right/left parietal (RH, LH) sites while they were performing a modified version of the test of Stroop. They had either to read the names of basic colors (yellow, green, blue, red) written in the same colors (red written in red: concordant stimuli) or in a different color (red written in blue: discordant stimuli) or to name mentally the color in which was written the name of a color, both colors being concordant or discordant. The ERPs for reading were similar for concordant and discordant stimuli and showed no sign of a N400 wave, this was also the case for the mental naming of a color associated to the written name of the same color.

Hemispheric asymmetries of visual evoked potentials in relation to spatial frequency, handedness and familial left-handedness.

The effects of handedness and of familial left-handedness on the asymmetry of the cerebral hemispheres were investigated by means of visual evoked potentials. Square gratings of different spatial frequencies were presented, at 1 Hz in ON-OFF mode to 60 subjects: 30 right-handers and 30 left-handers, 15 with familial handedness and 15 without in each group. The results show that the patterns of hemispheric asymmetry differ in right- and left-handers.

Role of the cerebellum in spatial orientation in the rat.

Adult DA/HAN strain rats were submitted to a spatial orientation task consisting of finding a reward in an open field. They were first submitted to an initial learning session and 10 days later to a retrieval test. The animals were divided into four groups of five rats each: animals that were cerebellectomized before the initial learning session or after the initial learning session, sham-operated rats, and control (intact) animals.