Abstract
ObjectiveThe current investigation examined verbal memory in idiopathic non-dementia Parkinson’s disease and the significance of the left entorhinal cortex and left entorhinal-retrosplenial region connections (via temporal cingulum) on memory impairment in Parkinson’s disease.MethodsForty non-demented Parkinson’s disease patients and forty non-Parkinson’s disease controls completed two verbal memory tests – a wordlist measure (Philadelphia repeatable Verbal Memory Test) and a story measure (Logical Memory). All participants received T1-weighted and diffusion magnetic resonance imaging (3T; Siemens) sequences. Left entorhinal volume and left entorhinal-retrosplenial connectivity (temporal cingulum edge weight) were the primary imaging variables of interest with frontal lobe thickness and subcortical structure volumes as dissociating variables.ResultsIndividuals with Parkinson’s disease showed worse verbal memory, smaller entorhinal volumes, but did not differ in entorhinal-retrosplenial connectivity. For Parkinson’s disease entorhinal-retrosplenial edge weight had the strongest associations with verbal memory. A subset of Parkinson’s disease patients (23%) had deficits (z-scores < -1.5) across both memory measures. Relative to non-impaired Parkinson’s peers, this memory-impaired group had smaller entorhinal volumes.DiscussionAlthough entorhinal cortex volume was significantly reduced in Parkinson’s disease patients relative to non-Parkinson’s peers, only white matter connections associated with the entorhinal cortex were significantly associated with verbal memory performance in our sample. There was also no suggestion of contribution from frontal-subcortical gray or frontal white matter regions. These findings argue for additional investigation into medial temporal lobe gray and white matter connectivity for understanding memory in Parkinson’s disease.
Highlights
Individuals with Parkinson’s disease (PD) frequently self-report problems with memory
Entorhinal cortex volume was significantly reduced in Parkinson’s disease patients relative to non-Parkinson’s peers, only white matter connections associated with the entorhinal cortex were significantly associated with verbal memory performance in our sample
There was no suggestion of contribution from frontal-subcortical gray or frontal white matter regions. These findings argue for additional investigation into medial temporal lobe gray and white matter connectivity for understanding memory in Parkinson’s disease
Summary
Individuals with Parkinson’s disease (PD) frequently self-report problems with memory (e.g., most often reporting difficulty recalling names or words, etc.). The temporal lobe white matter connections between the ERC and retrosplenial cortex (RSC) are presumed to play a role in anterograde memory formation. In light of comments from the 2012 Movement Disorder Society task force on cognitive impairment in PD[24] and MCI classification for dementia[25] individuals were classified using a conservative definition as PD Memory Impaired (PD-MI) if the verbal memory composite score was z -1.5. Individuals scoring above this cutoff were classified as PD-Well (PD-Well) for group comparisons on anatomical metrics
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