FUNCTIONAL PERIMETRY BY TOPOGRAPHICAL ANALYSIS OF VISUAL EVOKED BRAIN ACTIVITY

97th DOG Annual Meeting 1999

V677
FUNCTIONAL PERIMETRY BY TOPOGRAPHICAL ANALYSIS OF VISUAL EVOKED BRAIN ACTIVITY

N. Kristin¹, A. Jedynak², W. Skrandies²

Introduction: The topographical analysis of evoked brain activity by visual stimulation of various visual fields produces a differentiated image of cortical stimulus processing. Due to the low signal-to-noise ratio, electrophysiological recordings commonly require stimuli of large area and, therefore, yield poor spatial resolution. The quasi-simultaneous local luminance stimulation, called binary m-sequence, allows us to reconstruct and assess the potential maps of many small (1,5º x 1,5º) visual field elements elicited independently at each of 54 visual field locations.

Methods: Twenty-two normal subjects participated in the experiment and observed monocularly the center of the stimulation field (13,5º x 9º) filled with 54 squares. Mean luminance was 6.5 cd/m² and contrast was 95%. The EEG was recorded in 30 channels over the occipital brain areas. The individual noise level of the data from the subjects was estimated by the plusminus reference and only significant signals were considered and analyzed.

Results: For every stimulated visual field location we obtained a series of potential maps of the electrical brain activity. Assessing the electric field strength (GFP) of the 54 map series we determined three components between 50 and 200 ms latency. Both the GFP and the topography of the components were affected by retinal stimulus location. The GFP showed a decline with retinal eccentricity, whereas scalp field topography, depending on the exact stimulus location in the central visual field, was affected by the stimulus lateralisation already within the parafoveal retinal areas.

Conclusion: The m-sequence technique allows to evaluate evoked brain activity of simultaneously stimulated very small visual field elements.

Supported by DFG-SK 26/5-2

¹University Eye Hospital, Ludwig-Maximilians-University, Munich, Germany
²Institut of Physiology, Justus-Liebig-University, Gießen, Germany

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