VISUAL-EVOKED POTENTIALS TO FLASH AND PATTERN-REVERSAL STIMULATION AFTER ADMINISTRATION OF SYSTEMIC OR TOPICAL SCOPOLAMINE

It has previously been shown that 0.6 mg of scopolamine produces a del ay in the flash visual evoked potential of young normal volunteers, wh ile the pattern-reversal response does not change in latency. Recent w ork has shown that this drug differentially affects parvocellular and magnocellular systems. To investigate this effect, two studies were pe rformed. In the first study, 0.4 mg of scopolamine was injected intram uscularly into 11 young, healthy male volunteers who had fasted overni ght. The visual evoked potential was recorded to both binocular flash stimulation and monocular pattern-reversal stimulation by means of a c heckerboard consisting of 56' checks in a 28 degrees field. Responses were recorded before administration of the drug and then 1, 2, 4 and 6 hours after administration. The scopolamine produced a slowing of the flash P2 latency of approximately 6 ms (p < 0.05) two hours after dru g administration. There was no effect on the latency of the flash N2 o r pattern-reversal N75 or P100. There was an increase in amplitude of the flash N2-P2 component 6 hours after drug administration and an inc rease in the amplitude of the N75 and P100 2, 4 and 6 hours after the drug. Further subjects were investigated with the use of topical admin istration of 0.125% scopolamine applied monocularly. In all studies th e other eye acted as a control. The subjects were again young healthy volunteers. The visual evoked potential was recorded to both flash and pattern-reversal stimulation with a checkerboard consisting of 60' ch ecks counterphasing at 2 Hz within a 5 degrees field. Results suggest that systemic scopolamine affects the tectal pathway but has no periph eral effect.