Intact Lexicon Running Slowly – Prolonged Response Latencies in Patients with Subthalamic DBS and Verbal Fluency Deficits

Abstract

BackgroundVerbal Fluency is reduced in patients with Parkinson’s disease, particularly if treated with deep brain stimulation. This deficit could arise from general factors, such as reduced working speed or from dysfunctions in specific lexical domains.ObjectiveTo test whether DBS-associated Verbal Fluency deficits are accompanied by changed dynamics of word processing.Methods21 Parkinson’s disease patients with and 26 without deep brain stimulation of the subthalamic nucleus as well as 19 healthy controls participated in the study. They engaged in Verbal Fluency and (primed) Lexical Decision Tasks, testing phonemic and semantic word production and processing time. Most patients performed the experiments twice, ON and OFF stimulation or, respectively, dopaminergic drugs.ResultsPatients generally produced abnormally few words in the Verbal Fluency Task. This deficit was more severe in patients with deep brain stimulation who additionally showed prolonged response latencies in the Lexical Decision Task. Slowing was independent of semantic and phonemic word priming. No significant changes of performance accuracy were obtained. The results were independent from the treatment ON or OFF conditions.ConclusionLow word production in patients with deep brain stimulation was accompanied by prolonged latencies for lexical decisions. No indication was found that the latter slowing was due to specific lexical dysfunctions, so that it probably reflects a general reduction of cognitive working speed, also evident on the level of Verbal Fluency. The described abnormalities seem to reflect subtle sequelae of the surgical procedure for deep brain stimulation rather than of the proper neurostimulation.

Different outcomes of phonemic verbal fluency in Parkinson’s disease patients with subthalamic nucleus deep brain stimulation

“…The comparison between on-and off-conditions of DBS may be more indicative of the effect of the stimulation. Some previous studies using this approach found no differences in phonemic verbal fluency 12,13,14,23 , corroborating our analysis with the full sample, in which we did not find any effect of DBS on the phonemic fluency, despite finding a positive effect of the stimulation on the motor function.…”

“…Among the adverse effects of STN-DBS in patients with PD, the postoperative decline in verbal fluency is well documented 4,5,6,7,8,9,10,11 . However, there are fewer studies about the effect of the stimulation per se, comparing on-and off-stimulation conditions 12,13,14 . Longitudinal studies verified a worsening of verbal fluency in the first months after surgery, but an improvement in the later studied months 9 .…”

Apathy and Reduced Speed of Processing Underlie Decline in Verbal Fluency following DBS

“…Therefore, the pattern of findings could also be explained by a general pattern of postoperative slowing. A recent study by Ehlen et al [39] also suggested that any postoperative linguistic deficits, including reduced verbal fluency, may simply reflect reduced speed of processing.…”

Deep Brain Stimulation Frequency of the Subthalamic Nucleus Affects Phonemic and Action Fluency in Parkinson’s Disease

“…Studies have hypothesized that this impairment is due to a possible lesion effect from surgery and/or an effect of the neurostimulator parameters, for instance, the frequency of stimulation [1, 2, 4, 6, 8, 9]. Thus, studies assessing the impact of neurostimulation parameters, such as stimulation frequency, on VF are needed.…”