The Effect of Home-based Working Memory Updating Training on Cognition and Health in Patients With Parkinson's Disease

Parkinson's Disease (PD) is after Alzheimers disease (AD) the most common neurodegenerative disease with a prevalence of 1% of the population over 60 years of age. The cardinal symptoms are motoric and are believed to be caused by depletion of dopamine in the brain with severe depletion in the striatum. In addition to the motor impairments, there are several non-motor functions also affected, where cognitive decline and dementia are among the most common problems. Some claim that up to 75% of the total PD population will eventually develop dementia. Prior to dementia, milder cognitive problems are common and already at the time of diagnosis up to 42.5% of patients with PD are affected by decline in different cognitive functions. Early cognitive deficits seen is inhibition, shifting, working memory and planning, but a cognitive profile of visuospatial decline, semantic fluency and episodic memory has been connected to Parkinson's Disease Dementia (PDD). The occurrence of Lewy-bodies and Alzheimer type brain pathology is common in PDD but dopamine depletion has also been connected to cognitive decline in healthy elderly and in PD.

Although prescription of dementia medication in PD most likely has increased during the last decade there are limited evidence of treatment effects . This particular patient group is already burdened by polypharmacy and therefore investigating non-pharmacological interventions is of crucial importance. A recent systematic review of cognitive intervention studies in PD suggests that there is evidence of clinically meaningful improvements in overall cognition and moderate to large effect sizes on measures of working memory, processing speed and executive functions. Another review on the topic suggested that the results are promising, at least in the immediate or short term for some cognitive domains, but due to inconsistencies between studies and lack of methodological salience there are still a lot of questions unanswered. Baseline factors such as cognitive functioning, Hoehn and Yahr stage, premorbid intelligence all can have contributing effects on individual differences in training gain. Therefore it is important to thoroughly investigate baseline characteristics.

In the future, studies need to include more participants, be hypothesis driven and include more detail of the cognitive profile, training intervention and outcome measures.

One approach to cognitive training that has received a lot of attention and critique is process-based cognitive training, such as training focusing on working memory (WM) and executive functions (EF). The purpose of the process based approach is to strengthen general cognitive processes important to global cognitive functioning. WM and EF play central roles in several different functions such as episodic memory, reading comprehension and problem solving to mention a few. Research has also shown that WM and EF is negatively affected both in normal and pathological aging, such as PD.

Training of executive functioning and working memory have gained some promising results in healthy adults, showing improvements in working memory and executive functioning but there is also an indication of broader generalizations of training gain. Previously the effect of process-based updating training in healthy young and older individuals has been studied. Results showed that a period of updating training increased Blood Oxygen Level Dependent (BOLD) activity in striatum related to increased cognitive performance in both groups. Also a corresponding effect of training on dopaminergic neurotransmission was detected.