The speed of lexical activation is altered in Parkinson's disease

Abstract

Disturbed comprehension of complex noncanonical sentences in Parkinson's disease (PD) has been linked to dopamine depletion and delayed lexical retrieval. The aim of the present study was to replicate findings of delayed lexical activation in PD patients with noncanonical sentence processing difficulties, and investigate the influence of dopamine depletion on these changes to lexical access. In the first experiment, 20 patients with PD (tested whilst ‘on’ dopaminergic medication) and 23 controls participated in a list priming experiment. In this paradigm, stimuli are presented as a continuous list of words/nonwords, and semantic priming effects were measured across inter-stimulus intervals (ISIs) of 500 ms, 1000 ms and 1500 ms, with data analyzed using multivariate analyses of variance. The results revealed longer delays in lexical activation for PD patients with poor comprehension of noncanonical sentences, suggesting that the speed of lexical access may be compromised in PD, and that this feature may contribute to certain sentencecomprehension difficulties. In the second experiment, 7 patients with PD who participated in the first experiment, performed the same lexical decision task while ‘off’ their dopaminergic medication. Semantic priming effects were measured across ISIs of 500 ms and 1500 ms. Within group comparisons revealed a different pattern of semantic priming for the PD patients when ‘on’ compared to ‘off’ medication, providing further support for a dopaminergic influence on the speed of information processing and lexical activation.

Acknowledgments

Preliminary results of this study were presented at the 42nd Annual Meeting of Academy of Aphasia, 2004. This research was supported by participants from the 50+ Registry of the Australasian Centre on Ageing, The University of Queensland.