Deficits in inhibitory control and conflict resolution on cognitive and motor tasks in Parkinson's disease

Recent imaging studies in healthy controls with a conditional stop signal reaction time (RT) task have implicated the subthalamic nucleus (STN) in response inhibition and the pre-supplementary motor area (pre-SMA) in conflict resolution. Parkinson's disease (PD) is characterized by striatal dopamine deficiency and overactivity of the STN and underactivation of the pre-SMA during movement. We used the conditional stop signal RT task to investigate whether PD produced similar or dissociable effects on response initiation, response inhibition and response initiation under conflict. In addition, we also examined inhibition of prepotent responses on three cognitive tasks: the Stroop, random number generation and Hayling sentence completion. PD patients were impaired on the conditional stop signal reaction time task, with response initiation both in situations with or without conflict and response inhibition all being significantly delayed, and had significantly greater difficulty in suppressing prepotent or habitual responses on the Stroop, Hayling and random number generation tasks relative to controls. These results demonstrate the existence of a generalized inhibitory deficit in PD, which suggest that PD is a disorder of inhibition as well as activation and that in situations of conflict, executive control over responses is compromised.This work was supported by a PhD studentship from Fundación Caja Madrid (IO), a Career Development Fellowship from the Parkinson’s disease Society (LW) and a Royal Society Travelling Fellowship.Peer reviewe

Semantic and phonemic verbal fluency in Parkinson's disease: Influence of clinical and demographic variables

Changes of cognitive function in PD have been extensively documented and defined as a 'frontal' type executive dysfunction. One of the main components of this executive dysfunction is the impairment of verbal fluency. The aim of the present study was to assess semantic and phonemic fluency in a large sample of PD patients and to investigate the effect of clinical and sociodemographic variables on verbal fluency in this patient group. Three hundred patients with idiopathic Parkinson's disease who were consecutive referrals to our clinic and 50 age and education matched healthy controls completed the phonemic and semantic verbal fluency tasks. Both phonemic and semantic verbal fluency were significantly impaired in PD patients relative to matched controls. Stage of illness, presence of depression, education and age influenced verbal fluency measures. Regression analyses established that global measures of cognitive ability (MMSE) and executive function (FAB) and side of onset of motor symptoms predicted 36-37% of variance of phonemic or semantic verbal fluency measures. Thus, future studies aimed at assessing cognitive functioning in PD patients treated by deep brain stimulation (DBS) should adequately take into account several factors (stage of illness, depression, executive functioning) which may potentially influence performance on verbal fluency tasks.This research was supported by a PhD studentship from Fundación Caja Madrid, Spain (IO), and a Royal Society Travelling Fellowship.Peer reviewe

La Neuropsicología en Cuba

Neuropsychology in Cuba is a welldeveloped specialty because of the high scientific level of Cuban neurosciences. It has the added distinction that clinical neuropsychological services are free and equally accessible to all Cubans according to medical need. The education of neuropsychologists is also free. Cuba�s neurological rehabilitation has attracted a significant volume of �medical tourism� from around the world, especially to the International Center for Neurological Restoration CIREN. Neuropsychology functions within comprehensive public health care and educational systems in a society with well-developed attention to disability rights. Massive population-based programs for helping the disabled are currently underway, many especially targeted towards better understanding and treatment of neurological and psychiatric diseases. These programs offer unique opportunities for research and international collaboration in neuropsychology.La Neuropsicología en Cuba se ha desarrollado de manera favorable como una especialidad en los últimos años, debida fundamentalmente al alto nivel científico que han alcanzado las neurociencias en el país. A esto se añade que los servicios de Neuropsicología clínica, al igual que los otros servicios de salud, se brindan de manera gratuita y son libres e igualmente accesibles a cualquier persona, sobre la base de las necesidades individuales del paciente. La educación de los psicólogos y la preparación de los neuropsicólogos son igualmente gratis de acuerdo a los sistemas de educación superior pre y postgraduada que existen en el país. Por otra parte, la restauración neurológica que se ofrece en Cuba ha atraído un volumen considerable de ¨turismo de salud¨ de muchos países del mundo, especialmente al Centro Internacional de Restauración Neurológica (CIREN). Además la Neuropsicología se inserta dentro de un sistema nacional de salud pública y programas educacionales en una sociedad con una atención bien desarrollada hacia los derechos de los discapacitados. Investigaciones poblacionales para estudiar y ayudar a los discapacitados están en marcha y muchos se diseñan hacia un mejor entendimiento y tratamiento de las enfermedades neurológicas y psiquiátricas. A su vez estos programas ofrecen oportunidades únicas para la investigación y colaboración en Neuropsicología con colegas de otros países

The subthalamic nucleus and inhibitory control: impact of subthalamotomy in Parkinson’s disease

The aim of our study was to investigate two inter-related hypotheses about the role of the subthalamic nucleus. First that the subthalamic nucleus plays a role in adjusting response thresholds and speed-accuracy trade-offs and second that it is involved in reactive and proactive inhibition and conflict resolution. These were addressed by comparing the performance of 10 patients with Parkinson's disease treated with right subthalamotomy and 12 patients with left subthalamotomy, to 14 unoperated patients with Parkinson's disease and 23 age-matched healthy control participants on a conditional stop signal task and applying the drift diffusion model. Unilateral subthalamotomy significantly improved Parkinson's disease motor signs. Patients with right subthalamotomy had significantly faster Go reaction times with their contra-lesional hand than the unoperated patients and did not differ from the control participants, indicating their speed of response initiation was 'normalized'. However, operated patients made significantly more discrimination errors than unoperated patients and controls, suggesting that subthalamotomy influenced speed-accuracy trade-offs. This was confirmed by the drift diffusion model, revealing that while the unoperated patients had significantly lower drift rate and higher response thresholds than the control participants, the response thresholds for the operated groups did not differ from the controls and the patients with right subthalamotomy had a significantly higher drift rate than unoperated patients and similar to that of controls. The drift diffusion model further established that unlike the control participants, operated patients failed to show context-dependent strategic modulation of response thresholds. The patients with right subthalamotomy could not engage in late phase, fast inhibition of the response and showed minimal proactive inhibition when tested with the contra-lesional hand. These results provide strong evidence that the subthalamic nucleus is involved in response inhibition, in modulating the rate of information accumulation and the response threshold and influencing the balance between speed and accuracy of performance. Accordingly, the subthalamic nucleus can be considered a key component of the cerebral inhibitory network.This research was supported by a PhD studentship from Fundación Caja Madrid, Spain (I.O.), a Post-doctoral Career Development Fellowship from Parkinson’s UK (L.W.) and the UTE-University of Navarra agreement (J.O. and M.C.R-O.).Peer reviewe