Memory Similarities Between Essential Tremor and Parkinson’s Disease: A Final Common Pathway?

Abstract

Objective-A growing body of literature supports the view that essential tremor (ET) involves alteration of cerebellar-thalamo-cortical networks which can result in working memory and executive deficits. In this study we tested the hypothesis that individuals with ET would exhibit worse performance on memory tasks requiring more intrinsic organization and structuring (i.e., word lists) relative to those with fewer 'executive' demands (i.e., stories), similar to that previously observed in individuals with Parkinson's disease (PD).Method-Participants included a convenience sample of 68 ET patients and 68 idiopathic PD patients, retrospectively matched based on age, education, and sex. All patients underwent routine neuropsychological evaluation assessing recent memory, auditory attention/working memory, language, and executive function. Memory measures included the Hopkins Verbal Learning Test-R and WMS-III Logical Memory.Results-Both ET and PD patients performed significantly worse on word list than story memory recall tasks. The magnitude of the difference between these two memory tasks was similar for ET and PD patients. In both patient groups, performance on measures of executive function and auditory attention/working memory was not distinctly correlated with word list vs. story recall.Conclusions-These findings suggest that frontal-executive dysfunction in both ET and PD may negatively influence performance on memory tests that are not inherently organized. Although the pathophysiology of these two 'movement disorders' are quite distinct, both have downstream effects on thalamo-frontal circuitry which may provide a common pathway for a similar memory phenotype. Findings are discussed in terms of neuroimaging evidence, conceptual models, and best practice.

Symptom Dimensions of Depression and Apathy and Their Relationship With Cognition in Parkinson’s Disease

“…Similar dissociations between word-list and story memory performance in PD have been reported in the literature (Lafo et al, 2015; Zahodne et al, 2011), with worse performance noted for word-lists. This discrepancy may be due to the executive demands of list-learning versus story memory tasks, such that word lists depend on self-generation in order to reorganize words into semantically-related categories, while story tasks are intrinsically organized into semantically meaningful prose.…”

Mild Cognitive Impairment Subtypes in a Cohort of Elderly Essential Tremor Cases

“…As amnestic MCI is typically defined based on recall memory, and was operationalized as such in the current study, it is possible that the prevalence of memory deficits in this sample reflects an underlying executive dysfunction that compromises memory retrieval (Lafo et al, 2015). To determine the extent to which amnestic MCI was characterized by memory storage deficits and not solely memory retrieval deficits, we compared a composite recognition memory score between a-MCI and na-MCI groups, finding that the amnestic groups had significantly lower scores (with the qualification that raw recognition scores were not normally distributed, thereby likely inflating the absolute level of impairment).…”

Mind the gaps: What we don't know about cognitive impairment in essential tremor

“…For example, individuals with ET have been shown to perform more poorly on tasks assessing theory of mind [25], verbal fluency [26], mental set shifting, inhibition, and problem solving [5], among others. With regard to the severity of the executive dysfunction, and its similarity to that seen in PD, at least two studies [6,27] have shown comparable levels of executive dysfunction in the two groups, as well as similarly impaired cognitive profiles more broadly in comparison to controls. However, a recent population based study did highlight subtle differences in the two groups; while both groups performed more poorly than controls, the PD group had differentially worse performance on an executive measure (i.e., verbal fluency) than the ET group, and the latter evidenced slower processing speed [26] than the PD group.…”