This study begins at Week 1 with a baseline assessment. Participants are then randomly assigned to either donepezil HCl or placebo. Participants will start with either a 5mg/day dose of donepezil HCl or placebo followed by a cognitive assessment after 4 weeks on this dose. Participants will then have their dose increased to 10mg/day. Another cognitive assessment will be given after 4 weeks on this dose.