Influência de parâmetros espaciais sobre potenciais corticais provocados visuais gerados por estimulação pseudoaleatória

Abstract

The contributions of contrast detection mechanisms to the visual cortical evoked potential (VECP) have been investigated studying the contrast-response and spatial frequency-response functions. Previously, the use of m-sequences for stimulus control has been almost restricted to multifocal electrophysiology stimulation and, in some aspects, it substantially differs from conventional VECP. Single stimulation with spatial contrast temporally controlled by msequences was not extensively tested or compared to multifocal techniques. Our purpose was to evaluate the influence of spatial frequency and contrast of sinusoidal gratings on the VECP elicited by pseudo-random stimulation. Nine normal subjects were stimulated by achromatic sinusoidal gratings driven by a pseudo-random binary m-sequence at seven spatial frequencies (0.4-10 cpd) and three stimulus sizes (4º, 8º, and 16º of visual angle). At 8º of visual angle, it was also used six contrasts levels (3.12-99%). First order kernel had not provided a consistent measurable signal across spatial frequencies and contrasts that were tested – signal was very small or absent – while the second order kernel first and second slices exhibited reliable responses for the stimulus range. The main differences between results obtained with the first and second slices of the second order kernel were the shape of the amplitude versus contrast and amplitude versus spatial frequency functions. The results indicated that the second order kernel first slice was dominated by M pathway, but for some stimulus condition some P pathway contribution could be found, while the second order kernel second slice reflected the P pathway contribution. The present work extended previous findings of the visual pathways contribution to VECP elicited by pseudo-random stimulation for a wider range of spatial frequencies.