Animal fluency in people with Parkinson's disease: Item-based performance before and after deep brain stimulation surgery.

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People with Parkinson disease (PD) after surgery for deep brain stimulation (DBS) of the subthalamic nucleus (STN-DBS) often decline in animal fluency due to impairments in executive functions and/or language. Item-based measures of animal fluency may shed light on the specific nature of this decline, and into the strategies used when performing this task. We aimed to investigate the mechanisms of decline in animal fluency by revealing impairments in language and/or executive functions in people with PD before and after STN-DBS by using item-based characteristics, the total number of correct words, average cluster size, number of switches and scores on tests for language and executive functions. People with PD (N = 61) produced fewer words and switches than healthy controls (N = 40) before and after STN-DBS surgery. After surgery they additionally produced smaller clusters and shorter words than healthy controls. Comparing pre- and post-surgery, people with PD produced fewer words, fewer switches, smaller clusters, more frequent and earlier-acquired words after surgery. Average cluster size predicted total number of words before surgery. No item-based measures predicted total number of words after surgery. Average cluster size before surgery correlated with object naming, not with executive functions. Item-based measures indicated difficulties in executive functions and language processing. New to the literature, the correlation of cluster size with object naming may stress difficulties in lexical retrieval before surgery. Finding no item-based measures predicting the total number of words after surgery may indicate a different type of impairment not accounted for in our analyses. Replication is needed.

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