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Behavioural Neurology
Volume 2017 (2017), Article ID 7348101, 10 pages
Research Article

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

1National Hospital for Neurology and Neurosurgery, Queen Square, London, UK
2UCL Institute of Neurology, Queen Square, London, UK
3Dipartimento di Scienze Psicologiche, Pedagogiche e della Formazione, Università degli Studi di Palermo, Palermo, Italy

Correspondence should be addressed to Lisa Cipolotti

Received 14 November 2016; Accepted 8 February 2017; Published 20 March 2017

Academic Editor: Luigi Trojano

Copyright © 2017 Jennifer A. Foley et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Objective. Reduced verbal fluency is a strikingly uniform finding following deep brain stimulation (DBS) for Parkinson’s disease (PD). The precise cognitive mechanism underlying this reduction remains unclear, but theories have suggested reduced motivation, linguistic skill, and/or executive function. It is of note, however, that previous reports have failed to consider the potential role of any changes in speed of processing. Thus, the aim of this study was to examine verbal fluency changes with a particular focus on the role of cognitive speed. Method. In this study, 28 patients with PD completed measures of verbal fluency, motivation, language, executive functioning, and speed of processing, before and after DBS. Results. As expected, there was a marked decline in verbal fluency but also in a timed test of executive functions and two measures of speed of processing. Verbal fluency decline was associated with markers of linguistic and executive functioning, but not after speed of processing was statistically controlled for. In contrast, greater decline in verbal fluency was associated with higher levels of apathy at baseline, which was not associated with changes in cognitive speed. Discussion. Reduced generativity and processing speed may account for the marked reduction in verbal fluency commonly observed following DBS.