Cognition following bilateral deep brain stimulation surgery of the subthalamic nucleus for Parkinson's disease.

OBJECTIVE: Parkinson's disease (PD) is a neurodegenerative disorder characterized by significant motor dysfunction and various non-motor disturbances, including cognitive alterations. Deep brain stimulation (DBS) is an increasingly utilized therapeutic option for patients with PD that yields remarkable success in alleviating disabling motor symptoms. DBS has additionally been associated with changes in cognition, yet the evidence is not consistent across studies. The following review sought to provide a clearer understanding of the various cognitive sequelae of bilateral subthalamic nucleus (STN) DBS while taking into account corresponding neuroanatomy and potential confounding variables. DESIGN: A literature search was performed using the following inclusion criteria: (1) at least five subjects followed for a mean of at least 3 months after surgery; (2) pre- and postoperative cognitive data using at least one standardized measure; (3) adequate report of study results using means and standard deviations. RESULTS: Two recent meta-analyses found mild post-operative impairments in verbal learning and executive function in patients who underwent DBS surgery. However, studies have revealed improved working memory and psychomotor speed in the 'on' vs 'off' stimulation state. A deficit in language may be a consequence of the surgical procedure. CONCLUSIONS: While cognitive decline has been observed in some domains, our review of the data suggests that STN DBS is a worthwhile and safe method to treat PD.

Decision-making capacity and competency in the elderly: a clinical and neuropsychological perspective.

With our ageing population, the number of older adults with cognitive impairment has also increased. There is both an acute and growing need for evidence-based assessments to identify their decision making capacity and competence. In the present article we (1) present definitions of decision-making capacity and competence, (2) review cognitive functions that are central to decision-making capacity as well as the methods and procedures commonly used to assess these domains, and (3) address the communication of assessment findings to patients and their loved ones. The importance of assessing decision-making capacity in the context of specific functions and of respecting the values and interests of older adults are emphasized.

Dopamine receptor blockade and extinction differentially affect behavioral variability.

Dopamine (DA) neurons respond to unexpected food delivery and are inhibited during the omission of expected reward. DA receptor blockade mimics some, but not all, aspects of non-reward (extinction) conditions. It was therefore of interest to ask whether DA receptor blockade produces extinction-like increases in behavioral variability in addition to its well-known operant response-suppressing effects. In the current experiment, rats were trained drug-free on an operant task in which they pressed on a keyboard. Two of the keys led to food on a continuous reinforcement schedule. Both response rates and behavioral variability were measured. Test day administration of D(1) and D(2) antagonists SCH23390 and raclopride, like extinction, suppressed responding but, unlike extinction, did not lead to an increase in variability.

Phenylthiocarbamide (PTC) perception in Parkinson disease.

OBJECTIVE: To examine phenylthiocarbamide (PTC) sensitivity in Parkinson disease (PD) patients and healthy volunteers to determine whether taster status represented a simple vulnerability marker for PD. BACKGROUND: The inability to taste PTC has been associated with a number of medical illnesses not typically associated with taste impairment. Abnormalities in the function/expression of G protein-signaling pathways have been implicated in PTC perception and also in dopamine expression and regulation in PD. No study has yet probed whether PTC tasting is disrupted in PD. METHOD: PTC sensitivity was assessed in a small sample of 36 male PD patients and 20 healthy male comparison subjects using a standardized psychophysical method. RESULTS: A higher proportion of nontasters were found in patients relative to healthy comparison subjects. These differences were not explained by alterations in perception of basic taste intensity or age. Among patients, nontasters and tasters of PTC did not differ with regard to duration of illness, age of onset, severity of motor symptoms, or overall illness severity. CONCLUSIONS: These data suggest an increase in the frequency of PTC nontaster status in PD. As phenotypic variation in PTC sensitivity is genetic in origin, this may represent a surrogate risk factor for the development of PD.