Short communicationCholinesterase inhibitor, donepezil, improves visual contrast detectability in freely behaving rats

- Effect of donepezil on contrast sensitivity (CS) was tested in behaving rats.
- Rats showed low-pass spatial frequency (SF) tuning of the CS.
- The stimulus size correlated with the CS in an SF-dependent manner.
- Donepezil improved the CS in a highly sensitive SF range only.
- Acetylcholine is suggested to improve contrast detectability in a sensitive SF range.

Acetylcholine (ACh) modulates neuronal activities in extensive brain regions to play an essential role in various brain functions including attention, learning and memory, and cognition. Although ACh is known to modulate information processing in the primary visual cortex (V1) in many species including rodent, its functional role in visual ability has remained unknown. We examined whether and how ACh influences behavioral contrast detectability in rat. The detectability was assessed as the contrast sensitivity (CS) to a grating stimulus. Measurements were performed in a two-alternative forced-choice task combined with a staircase method in freely behaving rats. The contrast sensitivity function of rats under the no drug condition showed a low-pass spatial frequency (SF) tuning peaking at 0.1 cycles/degree (cpd) of SF (SFpeak) that bottomed at 0.5 cpd (SFbottom), which was sensitive to the stimulus size, but to neither the temporal frequency nor orientation of the stimulus. The stimulus size was correlated with the CS only at the low SF range. The effect of donepezil on the size- and SF-dependency of the CS was examined using three stimulus conditions: an easy detectability condition with large grating at SFpeak, a difficult detectability condition with small grating at SFpeak, and an upper limit SF condition with large grating at SFbottom. Donepezil improved the CS at SFpeak, especially in the difficult detectability condition. Therefore, we conclude that ACh plays an important role in enhancing behavioral CS at sensitive SF ranges, but not in improving the upper limit of SF.