A specific shifting deficit in Parkinson's disease: a reversal shift of consistent stimulus-response mappings

The effect of age on task switching: updated and extended meta-analyses

Cognitive flexibility is one of the crucial abilities for human survival. As people get older, whether their flexibility ability will be affected is one of the core research topics in aging research. Researchers have developed a task-switch paradigm in laboratories to mimic daily-life shifting task-set scenarios. However, the empirical evidence is equivocal. Considering every single study may have a biased sample; therefore, we hoped to combine smaller studies, making them into one extensive investigation, which may help show an actual effect. In the current study, we used two meta-analysis techniques, the Brinley plot (along with the State-trace plot) and conventional meta-analysis, to re-evaluate whether healthy aging influences cognitive flexibility. The results of the Brinley plot analysis showed no evidence of switch-specific age-related impairment as indexed by the local switch cost. Yet, older adults performed more slowly than younger adults across task conditions. The conventional meta-analysis further showed that the currently available findings were heterogenous and exhibited publication bias. Therefore, this study suggests that researchers should interpret their results cautiously while using a task-switching paradigm to address older adults' shifting abilities. More parametric variables must be considered and developed in a task-switching paradigm to enhance its sensitivity and reveal older adults' actual shifting ability.

Effect of cognitive and motor tasks on postural stability in Parkinson's disease: a posturographic study

To analyse the effect of concomitant cognitive or motor task performance on balance control in Parkinson's disease (PD), we performed a posturographic study in 24 PD patients and in 20 sex- and age-matched control subjects. Postural sway was measured with eyes open (EO) and eyes closed (EC) during quiet stance and during performance of calculation or motor sequence of thumb opposition to the other fingers. No difference of centre of foot pressure (COP) parameters was observed during quiet standing (either EO or EC) between patients and controls, but visual deprivation induced in both groups a worsening of postural stability. COP area was significantly increased in PD patients during dual task performance, whereas no difference of COP path and x-y axes was observed. The effects induced by the performance of cognitive or motor task were significantly more evident in PD patients with clinical evidence of postural instability (presence of prior falls in the history). This study demonstrates that dual task interference on postural control can be observed in PD patients during performance of cognitive as well as motor tasks. The balance deterioration during dual task performance was significantly enhanced in patients with history of prior falls. These findings have some implications for the strategies to be used in reducing the risk of fall in PD.

Working memory in mild Alzheimer's disease and early Parkinson's disease

Alzheimer's disease (AD) and Parkinson's disease (PD) impair working memory (WM). It is unclear, however, whether the deficits seen early in the course of these diseases are similar. To address this issue, the authors compared the performance of 22 patients with mild AD, 20 patients with early PD and without dementia, and 112 control participants on tests of inhibition, short-term memory, and 2 commonly administered tests of WM. The results suggest that although mild AD and early PD both impair WM, the deficits may be related to the interruption of different processes that contribute to WM performance. Early PD disrupted inhibitory processes, whereas mild AD did not. The WM deficits seen in patients with AD may be secondary to deficits in other cognitive capacities, including semantic memory.

The psychological refractory period in Parkinson's disease

The Psychological Refractory Period paradigm was used to investigate whether patients with Parkinson's disease showed disproportional deficits in regulating responses to two sequential presented stimuli. The first task required a speeded key-press response to an auditory stimulus, and the second task required a speeded key-press response to a visual stimulus. The stimulus onset asynchrony (SOA) between Task 1 and Task 2 was 50 msec., 150 msec., and 650 msec. According to the bottleneck model, the SOA manipulation should not affect performance on Task 1, but reaction time for Task 2 should increase as the SOA between the two tasks decreased. The increase in reaction time for Task 2 was referred to as the Psychological Refractory Period. In this study, both patients with Parkinson's disease and normal controls showed classical effects. More importantly, although the 22 patients with Parkinison's disease took longer to respond to both Tasks 1 and 2 than the 20 normal controls, the effects of the Psychological Refractory Period for the two groups were of the same magnitude. The results suggest that Parkinson's disease affects only the response-execution stages rather than the response-selection stages, based on the central bottleneck model.