[Show abstract][Hide abstract] ABSTRACT: Deep brain stimulation (DBS) of the subthalamic nucleus (STN) in individuals with Parkinson's disease (PD) has often been associated with reduced verbal fluency performance. This study aimed to directly assess semantic switching as a function of STN stimulation in PD participants with the Homophone Meaning Generation Test (HMGT). Seventeen participants with PD who had received STN DBS completed the HMGT in on and off stimulation conditions. Twenty-one non-neurologically impaired participants acted as controls. PD participants (in both on and off stimulation conditions) generated significantly fewer meanings than control participants and consistent with the previous reports of verbal fluency impairment, PD participants produced fewer definitions in the on stimulation condition. PD participants (in both on and off stimulation conditions) also had greater difficulty generating definitions for nonhomographic homophones compared with homographic homographs. The results of this study indicate that STN stimulation exacerbates impairment in semantic switching.
Journal of the International Neuropsychological Society 10/2008; 14(5):890-4. DOI:10.1017/S1355617708081046 · 2.96 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Impaired generation of verbs relative to nouns has been reported in Parkinson's disease (PD) and has been associated with the frontal pathophysiology of PD. The aim of the present study was to measure noun/verb generation abilities in PD and to determine whether noun/verb generation is affected by stimulation of the subthalamic nucleus (STN).
8 participants who had been diagnosed with PD and had received surgery for deep brain stimulation (DBS) of the STN as well as 15 control participants completed a noun/verb generation task with four probe-response conditions-namely, noun-noun, verb-noun, noun-verb and verb-verb conditions. Patients with PD were assessed while receiving STN stimulation and without stimulation.
During the off stimulation condition, patients with PD presented with a selective deficit in verb generation compared with control participants. However, when receiving STN stimulation, patients with PD produced significantly more errors than controls during the noun-noun and verb-verb conditions, supporting evidence from previous studies that STN stimulation modulates a frontotemporal network associated with word generation. Finally, errors during verb generation were significantly correlated with item selection constraint (ie, the degree to which a response competes with other response alternatives) in the on stimulation condition, but not the off stimulation condition.
Our results suggest that STN stimulation affects the ability to select from many competing lexical alternatives during verb generation.
Journal of neurology, neurosurgery, and psychiatry 07/2008; 79(6):700-5. DOI:10.1136/jnnp.2007.118729 · 6.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Inhibitory control may be affected by Parkinson's disease (PD) due to impairment within the non-motor basal ganglia-thalamocortical circuits. The present study aimed to identify the effects of chronic stimulation of the subthalamic nucleus (STN) on lexical-semantic inhibitory control. Eighteen participants with PD who had undergone surgery for deep brain stimulation (DBS) of the STN, completed a picture-word interference (PWI) task and the Hayling test in on and off stimulation conditions. The results of PD participants were compared with 21 non-neurologically impaired control participants. PD participants performed no differently from controls on the PWI task, and no significant differences between on and off stimulation conditions were revealed, therefore suggesting that PD participants are not impaired in lexical-semantic interference control. In contrast, in the off stimulation condition, PD participants had significantly delayed reaction times and increased errors on the inhibition section of the Hayling test compared with the STN stimulation condition and control participants. These results suggest that PD patients are impaired in aspects of inhibitory control that are dependent on behavioural inhibition (such as the suppression of prepotent responses) and selection from competing alternatives without the presence of external cues. Furthermore, STN stimulation acts to restore these behavioural inhibitory processes.
[Show abstract][Hide abstract] ABSTRACT: Lexical-semantic and emotional processing deficits have been associated with Parkinson's disease. This study investigated automatic and controlled lexical-semantic processing, the automatic activation of emotional evaluations, and the processing of words conveying negative and neutral emotional connotations in a combined affective and semantic priming paradigm. Eighteen participants with Parkinson's disease who had undergone surgery for deep brain stimulation (DBS) of the subthalamic nucleus (STN) completed a lexical decision task at short and long stimulus onset asynchronies (SOAs), during on and off stimulation conditions. Nineteen non-neurologically impaired participants acted as controls. The results indicated that automatic lexical-semantic and emotional evaluative processes are unimpaired in Parkinson's disease as reflected in the presence of comparable semantic and affective priming effects at the short SOA in on and off stimulation conditions compared with healthy controls. In contrast, participants with Parkinson's disease in the off stimulation condition showed a pattern of aberrant controlled lexical-semantic processing as evidenced by a lack of semantic priming effects at the long SOA condition. Controlled semantic priming was present, however, when the participants with Parkinson's disease were receiving stimulation of the STN, suggesting that STN stimulation modulates basal ganglia-thalamocortical circuits involved in such processes. Finally, delayed reaction times for negatively valenced targets compared with neutrally valenced targets was evident in participants with Parkinson's disease in the on stimulation condition and control participants, but not for participants with Parkinson's disease in the off stimulation condition, suggesting that the incidental evaluation of negatively versus neutrally valenced words in Parkinson's disease is modulated by basal ganglia-thalamocortical circuits.
[Show abstract][Hide abstract] ABSTRACT: Subthalamic nucleus (STN) deep brain stimulation (DBS) has become an established treatment strategy for patients with medically refractory Parkinson's disease (PD). There are however numerous strategies employed for STN lead placement. Variations include method of STN localisation, use of microelectrode recording, number of microelectrode recording passes and time taken for the procedure. We describe a relatively simple and rapid technique of STN lead placement utilising CT/ MRI image fusion, microelectrode recording and test stimulation. The first 58 consecutive patients undergoing STN DBS were assessed pre- and post-operatively. UPDRS scores, medication use and any surgical complication were assessed. Bilateral STN DBS was an efficacious treatment option for medically refractory PD. We have described a technique which can be performed with effect and low morbidity, and in a time which is well tolerated by patients.