Episodic Memory Impairment in Parkinson's Disease: Disentangling the Role of Encoding and Retrieval

The source of episodic memory (EM) impairment in Parkinson's disease (PD) is still unclear. In the present study, we sought to quantify specifically encoding, consolidation, and retrieval process deficits in a list-learning paradigm by a novel method, the item-specific deficit approach (ISDA).

We applied the ISDA method to the Free and Cued Selective Reminding Test (FCSRT) in a sample of 15 PD patients and 15 healthy participants.

The results revealed differences in free recall performance between PD patients and controls. These patients, however, benefited from cues as much as controls did, and total recall did not differ between groups. When analyzing the ISDA indices for encoding, consolidation, and retrieval deficits, the results showed a general memory deficit, but with a clear focus on encoding and retrieval, as revealed by the sensitivity values. Moreover, controlling for initial learning did not eliminate group effects in retrieval.

Our findings reveal a mixed pattern in PD patients, with deficits in both encoding and retrieval processes in memory. Also, despite the fact that an encoding dysfunction may explain some of the deficits observed at retrieval, it cannot fully account for the differences, highlighting that both encoding and retrieval factors are necessary to understand memory deficits in PD.