Worsening of Verbal Fluency After Deep Brain Stimulation in Parkinson's Disease: A Focused Review

Abstract

Worsening of verbal fluency after treatment with deep brain stimulation in Parkinson's disease patients is one of the most often reported cognitive adverse effect. The underlying mechanisms of this decline are not well understood. The present focused review assesses the evidence for the reliability of the often-reported decline of verbal fluency, as well as the evidence for the suggested mechanisms including disease progression, reduced medication levels, electrode positions, and stimulation effect vs. surgical effects. Finally, we highlight the need for more systematic investigations of the large degree of heterogeneity in the prevalence of verbal fluency worsening after DBS, as well as provide suggestions for future research.

Strategies for the Treatment of Parkinson’s Disease: Beyond Dopamine

“…Nonetheless, after DBS, both sexes show a similar functional improvement (Hariz et al, 2013). Although it is effective at motor symptom alleviation, DBS can also induce adverse side effects such as an aggravation of freezing of gait and worsening of verbal fluency (Carlson et al, 2014;Foley et al, 2017;Højlund et al, 2017). Yet another downside of DBS is that PD-induced speech disruption is much less responsive to DBS than any other motor dysfunctions (Limousin and Martinez-Torres, 2008;Moro et al, 2010).…”

Effect of Low versus High Frequency Subthalamic Deep Brain Stimulation on Speech Intelligibility and Verbal Fluency in Parkinson’s Disease: A Double-Blind Study

“…Neuropsychological studies [12][13][14][15] and meta-analyses have established that semantic verbal fluency (SVF) and phonemic verbal fluency (PVF) [16,17] deteriorate following STN-DBS. Neither disease progression [18] nor reduction in dopaminergic medication are thought to be responsible, thus implicating surgery [12][13][14][15][19][20][21], location of electrodes [21], high frequency stimulation (HFS) [22] or their combination [18] to be responsible for the fluency deterioration in these patients. There is also evidence that STN-DBS alters switching (the ability to disengage from a prior subcategory to a new one) [23], but not cluster size (the generation of words falling within subcategories) [23][24][25].…”

Sensorimotor subthalamic stimulation restores risk‐reward trade‐off in Parkinson's disease

“…One reason for the mixed results of previous studies could be that neither of them took electrode placement within the STN into account, although the effective site of stimulation determines the modulatory effect of STN‐DBS on cognition . The STN encompasses a motor territory and two nonmotor (i.e., associative and limbic) territories receiving projections from distinct functional cortical areas .…”