Special issue: Original article Semantic activation in Parkinson’s disease patients on and off levodopa Anthony J. Angwin a, *, Wendy L. Arnott a , David A. Copland a , Miriam P.L. Haire a , Bruce E. Murdoch a , Peter A. Silburn a,b and Helen J. Chenery a a Centre for Research in Language Processing and Linguistics, The University of Queensland, Brisbane, Australia b School of Medicine, The University of Queensland, Brisbane, Australia article info Article history: Received 14 April 2008 Reviewed 1 August 2008 Revised 6 November 2008 Accepted 16 February 2009 Published online 11 March 2009 Keywords: Dopamine Language Parkinson’s disease Semantic priming Spreading activation abstract Research suggests that dopamine may exert a neuromodulatory influence on automatic spreading activation within semantic networks. In order to investigate the influence of dopamine depletion on semantic activation in Parkinson’s disease (PD), nine patients with PD performed a lexical decision task when on and off levodopa medication. Eleven healthy controls matched to the PD patients in terms of sex, age and education also participated in the study. Both directly related word pairs (e.g., tiger – stripe) and indirectly related word pairs (word pairs related via a mediating word, e.g., chalk – black) were used to measure semantic activation across stimulus onset asynchronies (SOAs) of 270 msec, 520 msec and 1020 msec. Analysis of variance statistics revealed that the activation of directly related and indirectly related targets was slower for the PD group relative to the control group. Within group comparisons revealed further changes to semantic activation in PD patients off medication, with no activation of directly or indirectly related target words evident in PD patients off medication. These results further clarify the nature of dopamine’s neuro- modulatory influence on semantic activation, and suggest that the nature of altered semantic activation in PD may depend on the magnitude of dopamine depletion. ª 2009 Elsevier Srl. All rights reserved. 1. Introduction Parkinson’s disease (PD) is characterized by degeneration of the nigrostriatal dopaminergic system (Mink, 1996) and in addition to movement disorders, subtle language processing deficits are a frequently reported feature of the disease. There is currently substantial evidence to suggest that even in the absence of overt dementia, many patients with PD exhibit deficits in lexical-semantic processing (Bayles et al., 1993; Gurd, 1996, 2000; Lewis et al., 1998; Portin et al., 2000; Randolph et al., 1993). While the results of emerging research have indicated that semantic processing deficits in PD may be related to alterations in dopaminergic transmission (Gross- man et al., 2002; Watters and Patel, 1999, 2002), the precise nature of dopamine’s influence on semantic processing currently remains unclear. The objective of the present study was to use online semantic priming tasks to delineate the impact of dopamine depletion in PD on semantic activation. Semantic priming refers to the faster recognition of a target word when it is preceded by a related prime word (tiger – stripe) * Corresponding author. Centre for Research in Language Processing and Linguistics, Division of Speech Pathology, The University of Queensland, Brisbane, QLD 4072, Australia. E-mail address: a.angwin@uq.edu.au (A.J. Angwin). available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/cortex 0010-9452/$ – see front matter ª 2009 Elsevier Srl. All rights reserved. doi:10.1016/j.cortex.2009.02.012 cortex 45 (2009) 950–959