Normal aging affects movement execution but not visual motion working memory and decision-making delay during cue-dependent memory-based smooth-pursuit

How does decisional capacity evolve with normal cognitive aging: systematic review of the literature

PURPOSE

Aging is associated with increased needs related to complex decisions, particularly in medical and social issues. However, the complexity of decision-making involves many neurological functions and structures which are potentially altered by cognitive aging.

METHODOLOGY

A systematic review was conducted in accordance with PRISMA guidelines to examine changes in decision-making occurring in normal cognitive aging. The keywords "decision making" and "normal aging" were used to find the clinical studies and literature reviews focused on these changes.

RESULTS

A total of 97 articles were considered in the review, and ultimately 40 articles were selected, including 30 studies and 10 literature reviews. The data from these studies were of uneven quality and too disparate to allow meta-analysis according to PRISMA criteria. Nevertheless, a key result of the analysis is the decrease of processing speed with aging. In ambiguous decision-making situations, the alteration of the ventromedial system is associated with changes in motivation profiles. These changes can be compensated by experience. However, difficulties arise for older adults in the case of one-off decisions, which are very common in the medical or medico-social domains.

CONCLUSIONS

Cognitive aging is associated with a slowdown in processing speed of decision-making, especially in ambiguous situations. However, decision-making processes which are based on experience and cases in which sufficient time is available are less affected by aging. These results highlight the relativity of decision-making capacities in cognitive aging.

Clinical application of eye movement tasks as an aid to understanding Parkinson's disease pathophysiology

Parkinson's disease (PD) is a progressive neurodegenerative disorder of the basal ganglia. Most PD patients suffer from somatomotor and oculomotor disorders. The oculomotor system facilitates obtaining accurate information from the visual world. If a target moves slowly in the fronto-parallel plane, tracking eye movements occur that consist primarily of smooth-pursuit interspersed with corrective saccades. Efficient smooth-pursuit requires appropriate target selection and predictive compensation for inherent processing delays. Although pursuit impairment, e.g. as latency prolongation or low gain (eye velocity/target velocity), is well known in PD, normal aging alone results in such changes. In this article, we first briefly review some basic features of smooth-pursuit, then review recent results showing the specific nature of impaired pursuit in PD using a cue-dependent memory-based smooth-pursuit task. This task was initially used for monkeys to separate two major components of prediction (image-motion direction memory and movement preparation), and neural correlates were examined in major pursuit pathways. Most PD patients possessed normal cue-information memory but extra-retinal mechanisms for pursuit preparation and execution were dysfunctional. A minority of PD patients had abnormal cue-information memory or difficulty in understanding the task. Some PD patients with normal cue-information memory changed strategy to initiate smooth tracking. Strategy changes were also observed to compensate for impaired pursuit during whole body rotation while the target moved with the head. We discuss PD pathophysiology by comparing eye movement task results with neuropsychological and motor symptom evaluations of individual patients and further with monkey results, and suggest possible neural circuits for these functions/dysfunctions.

Impaired smooth-pursuit in Parkinson's disease: normal cue-information memory, but dysfunction of extra-retinal mechanisms for pursuit preparation and execution

While retinal image motion is the primary input for smooth-pursuit, its efficiency depends on cognitive processes including prediction. Reports are conflicting on impaired prediction during pursuit in Parkinson's disease. By separating two major components of prediction (image motion direction memory and movement preparation) using a memory-based pursuit task, and by comparing tracking eye movements with those during a simple ramp-pursuit task that did not require visual memory, we examined smooth-pursuit in 25 patients with Parkinson's disease and compared the results with 14 age-matched controls. In the memory-based pursuit task, cue 1 indicated visual motion direction, whereas cue 2 instructed the subjects to prepare to pursue or not to pursue. Based on the cue-information memory, subjects were asked to pursue the correct spot from two oppositely moving spots or not to pursue. In 24/25 patients, the cue-information memory was normal, but movement preparation and execution were impaired. Specifically, unlike controls, most of the patients (18/24 = 75%) lacked initial pursuit during the memory task and started tracking the correct spot by saccades. Conversely, during simple ramp-pursuit, most patients (83%) exhibited initial pursuit. Popping-out of the correct spot motion during memory-based pursuit was ineffective for enhancing initial pursuit. The results were similar irrespective of levodopa/dopamine agonist medication. Our results indicate that the extra-retinal mechanisms of most patients are dysfunctional in initiating memory-based (not simple ramp) pursuit. A dysfunctional pursuit loop between frontal eye fields (FEF) and basal ganglia may contribute to the impairment of extra-retinal mechanisms, resulting in deficient pursuit commands from the FEF to brainstem.