Anticholinesterase agents affect contrast gain of the cat cortical visual evoked potential

The effects of the anticholinesterase agents physostigmine, pyridostigmine, diisopropylfluorophosphate and soman on the cortical visual evoked potential (VEP) were examined using phase reversed sine wave gratings of varying contrasts. All 4 agents decreased the slope (gain) of the response vs log contrast function while the intercept with the noise level (threshold, an indicator of contrast sensitivity) was unaffected. These results suggest that anticholinesterases modify the VEP by changing a contrast gain control mechanism.