Qualitative Deficits in Verbal Fluency in Parkinson's Disease with Mild Cognitive Impairment: A Clinical and Neuroimaging Study

Exploring the utility of process scores in elucidating the role of cognitive and affective factors that influence verbal fluency performance in Parkinson's disease

OBJECTIVES

Cognitive and affective factors have been implicated in verbal fluency (VF) performance in Parkinson's disease (PD). This exploratory study aimed to investigate the relationships between cognitive and affective variables on traditional ("core") and "process" (error and interval) scores of VF and elucidate unique information these scores may provide regarding mechanisms underlying VF.

METHODS

Sixty-two PD patients without dementia completed clinical neuropsychological examinations consisting of attention, processing speed, language, executive functioning, visuospatial, memory, and mood measures. Hierarchical regression and negative binomial regression analyses were used to evaluate relationships between outcome and predictor variables.

RESULTS

Generativity results revealed that processing speed and working memory explained up to 34% of the variance of total letter fluency responses (p = <.001) and processing speed explained 24% of the variance for total semantic fluency (p = .003). For category switching generativity, only age predicted 20% of the variance (p = .01). Two executive functioning measures were negatively associated with error production over the duration (b = -.055, p = .028; b = -.062, p = .004) and final 45-second interval (b = -.072, p = .003; b = -.044, p = .033) of the category switching task. In the initial 15-second task interval, a positive predictive relationship between error production and indifference apathy (b = .616, p = .044) was demonstrated.

CONCLUSIONS

Findings demonstrate the potential utility of "process" scores in detecting subtle cognitive impairment in Parkinson's disease patients without dementia and tentatively evidence the role of indifference apathy in task initiation.

Neurocognitive correlates of semantic memory navigation in Parkinson's disease

Cognitive studies on Parkinson's disease (PD) reveal abnormal semantic processing. Most research, however, fails to indicate which conceptual properties are most affected and capture patients' neurocognitive profiles. Here, we asked persons with PD, healthy controls, and individuals with behavioral variant frontotemporal dementia (bvFTD, as a disease control group) to read concepts (e.g., 'sun') and list their features (e.g., hot). Responses were analyzed in terms of ten word properties (including concreteness, imageability, and semantic variability), used for group-level comparisons, subject-level classification, and brain-behavior correlations. PD (but not bvFTD) patients produced more concrete and imageable words than controls, both patterns being associated with overall cognitive status. PD and bvFTD patients showed reduced semantic variability, an anomaly which predicted semantic inhibition outcomes. Word-property patterns robustly classified PD (but not bvFTD) patients and correlated with disease-specific hypoconnectivity along the sensorimotor and salience networks. Fine-grained semantic assessments, then, can reveal distinct neurocognitive signatures of PD.

Analyses of correct responses and errors on measures of verbal fluency among Parkinson's disease and essential tremor patients

Objective: Parkinson's disease (PD) and essential tremor (ET) involve neuroanatomical circuitry that impact frontal lobe functioning, via the striatum and cerebellum, respectively. The aim of this exploratory study was to investigate quantitative and qualitative performance between and within these groups on measures of verbal fluency. Method: Sixty-three PD and 53 ET patients completed neuropsychological testing. Linear regression models with robust variance estimation compared verbal fluency performance between groups related to correct responses and errors. Paired t-tests investigated within group error rates. Results: PD patients gave more correct responses for phonological (β ̂   =5.3, p=.01) and category fluency (β ̂   =4.1, p=.01) than ET patients; however, when processing speed was added as a covariate, this attenuated performance on both measures and only phonological fluency remained significant (β ̂   =4.0, p=.04). There were no statistical differences in error scores between groups. Error rates within groups suggested that PD patients had higher error rates in total errors and perseveration errors on phonological fluency (M = 2.6, p=.00; M = 1.6, p=.00) and higher total errors and set-loss error rates on category switching (M = 5.1, p<.001; M = 4.1, p<.001). ET patients had higher error rate with relation to total errors and set-loss errors on phonological fluency (M = 2.5, p=.00; M = 1.5, p=.02) and category switching (M = 3.9, p=,00; M = 3.9, p<.001). Conclusions: PD patients performed better than ET patients on phonological fluency. PD patients appear to make more perseveration errors on phonological fluency, while ET patients made more set-loss errors. Implications for frontal lobe dysfunction and clinical impact are discussed.