Gastrodin, parishin and parishin C were purified from a water extract of GE (rhizome of Gastrodia elata, an herb medicine for treatment of neuronal disorders). In order to compare the pharmacological effects of gastrodin, parishin and parishin C on improving cognition deficits, we tested them in an animal model of cognition disorders induced by scopolamine and in a study of in vivo long-term potentiation (LTP) recordings. In the Morris water maze task, parishin C (15 and 50 mg·kg(-1), P<0.05) and parishin (150 mg·kg(-1), P<0.05), improved spatial learning and memory significantly. However, gastrodin showed no significant effects at the dose of 150 mg·kg(-1). In vivo LTP recordings showed that parishin C at 5,10 and 20 mg·kg(-1), parishin at 10, 30 and 100 mg·kg(-1) reversed the suppression of LTP by scopolamine in rats in a dose-dependent manner. However, gastrodin at 100 mg·kg(-1) showed only a modest effect. In summary, the action of parishin C in the improvement of dementia induced by scopolamine was more potent than parishin and gastrodin.