Parkinson’s disease (PD) is associated with characteristic neuropsychological features that broadly fall under the umbrella of executive dysfunction.  In PD, these executive deficits have been linked to dopaminergic depletion of fronto-subcortical systems.  Neuropsychologists are trained to look for certain patterns beyond single test performance.  Three common test patterns that have been interpreted as reflecting fronto-executive difficulties in PD include:  1) letter fluency performance worse than category fluency (Vonk et al., 2018); 2) worse performance on list learning than story memory tasks (Zahodne et al., 2011); and 3) low initial learning, but normal retention of information that was initially learned (i.e., normal rate of forgetting).  These findings are consistently reported across numerous studies, though with relatively small PD sample sizes.  The goal of this study was to examine whether these three patterns were observed in a large group of non-demented individuals with idiopathic PD.

Participants included a clinical convenience sample of 787 individuals with idiopathic PD seen for neuropsychological evaluation at the UF Fixel Institute for Neurological Diseases (mean age=65±9, mean education=15±2yrs, 72% male; 93% white). Most participants were tremor-predominant (76%) and in the middle-stage of their disease (54% Hoehn-Yahr Stage 2; on-medication mean motor scores (26+11) from the Unified Parkinson Disease Rating Scale; UPDRS).  Participants scored above the dementia cutoff on a cognitive screener (DRS > 125), had no history of brain surgery, and no other clinically significant neurological/psychiatric diagnoses. Neuropsychological tests included: Controlled Oral Word Association Test (COWA; FAS), category (animals) fluency, Wechsler Memory Scale-III Logical Memory (WMS-III LM), and Hopkins Verbal Learning Test-Revised (HVLT-R). Raw scores were demographically normed based on test-specific manuals or previously published norms and converted to z-scores for analyses.  Data were analyzed using paired sample t-tests and correlation analyses.

Letter fluency performance (COWA z=-0.45±1.1) was significantly worse than category fluency (Animals z=-0.31±1.2; t(780)= -3.32, p=0.001), though with small effect size (Cohen’s d:-0.12). Similarly, delayed recall of the HVLT-R word list (z=-0.93±1.3) was significantly worse than WMS-III story recall (z=0.14±1.1; t(765)= -23.85, p<0.000), with large effect size (Cohen’s d:-0.86). Lastly, initial learning on HVLT-R word list (z=-0.88±1.0) was significantly worse than retention (z=-0.67±1.4; t(736)= -3.76, p<0.000,), though the effect size was small (Cohen’s d:-0.14). Performance on these tests did not correlate with PD motor subtype, UPDRS motor scores, or disease duration.

These findings support previous research on the contribution of fronto-subcortical dysfunction to performance on verbal fluency and memory tasks. Neurocognitive processing literature reports that letter fluency performance relies primarily on frontal systems compared to category fluency, which also requires temporally based semantic retrieval. Similarly, worse performance on learning likely reflects frontal deficits in strategic encoding and retrieval within the memory framework (Siquier & Adres, 2021). These patterns are not limited to PD, but are associated with fronto-subcortical dysfunction regardless of etiology (e.g., tumor, white matter burden). This study emphasizes the importance of considering cognitive processing models while looking at neuropsychological performance, to identify specific patterns that extend beyond individual test performance.