[Show abstract][Hide abstract] ABSTRACT: The correlation between amplitude and latencies of the pattern-reversal VEP (1.7-3.6 50% contrast) and the serum glucose was studied in six healthy, male volunteers (21-26 yr.; mean: 23.2 +/- 1.6 yr.). Pattern-VEP and serum glucose were obtained at 2-h intervals during a 8-h experimental session. The effect of spatial frequency on VEP (increased latencies and amplitude with increasing spatial frequency) was removed statistically by computing the residuals from the nonlinear regression function vs. the spatial frequency. The residuals were then processed as stimulus-independent variables. At glucose serum concentrations within the physiological range of variability (55-103 mg/dl), the P100 latency increased (p < 0.04) with increasing serum glucose, with a 6.9% estimated latency difference between lower and higher glucose concentrations. This correlation depends mostly on the association of shorter and longer P100 latencies with glucose concentration values in the lower and upper portions of the normal concentration range respectively, but accounts for about 4% of the overall variance and may be accidental (therefore a potential bias in otherwise controlled VEP studies) or suggest functional relationships between glucose availability and vision.
No preview · Article · Nov 1995 · Physiology & Behavior
[Show abstract][Hide abstract] ABSTRACT: Human visual-evoked potentials (VEPs) from upper and lower hemifield stimulation are thought to reflect the anatomical and functional differences between the hemiretinas and corresponding visual pathways. Conflicting results have, however, been reported in topographic studies on the putative cortical generators. We have estimated by automatic perimetry (Octopus 2000R, Program 32) and compared the sensitivity thresholds of lower and upper hemifields of the retina in 12 healthy subjects with no history or evidence of visual or neurological diseases. A visual P3 that is linked to cognitive function was recorded in an odd-ball paradigm with presentation of high-contrast checkerboards at two different spatial frequencies at 20 degrees eccentricity in each hemifield. VEP and P3 were recorded at O1 and O2 and at Cz according to the 10/20 international system. Lower sensitivity thresholds were found, and higher VEP and event-related potential (ERP) amplitude values were obtained when stimulating the lower, compared with the upper, visual hemifield. The results are consistent with previous findings and anatomical and physiological evidence in animals and man. Interactions between perceptive process in the visual system and higher cognitive functions are a possible explanation for this finding.
No preview · Article · Jan 1995 · Journal of Medical Engineering & Technology