Feeling-of-knowing in episodic memory in patients with Parkinson's disease with various motor symptoms

The aim of this study was to examine metamemory in patients with Parkinson's disease (PD) with different dominant motor symptoms. This is a prospective case-control study. Fifty-five PD patients [25 patients with tremor-dominant (TD) motor symptoms and 30 patients with akinetic and rigidity-dominant (ARD) motor symptoms] and 30 normal controls were studied. The two patient groups were similar in terms of age, level of education, disease duration, and disease severity. Metamemory was measured using the experimental metamemory task [feeling-of-knowing (FOK) paradigm]. In addition, memory and executive functions were determined using detailed cognitive tests. In comparison with normal subjects and TD patients, ARD patients exhibited impaired FOK accuracy (P = 0.007). Furthermore, correlation analysis revealed an intergroup differential pattern, which indicated that FOK accuracy was primarily related to memory ability in ARD patients and executive function in TD patients. Our results provide evidence of impaired metamemory in the early stages of PD with ARD rather than TD motor symptoms. These findings might be useful for designing specific medical care strategies for ARD patients. Further studies are needed to determine whether impaired metamemory is an early predictor for brain alteration in PD patients.