Visual–spatial disembedding in Parkinson's disease

Systematic Review and Meta-Analyses of Word Production Abilities in Dysfunction of the Basal Ganglia: Stroke, Small Vessel Disease, Parkinson's Disease, and Huntington's Disease

Clinical populations with basal ganglia pathologies may present with language production impairments, which are often described in combination with comprehension measures or attributed to motor, memory, or processing-speed problems. In this systematic review and meta-analysis, we studied word production in four (vascular and non-vascular) pathologies of the basal ganglia: stroke affecting the basal ganglia, small vessel disease, Parkinson's disease, and Huntington's disease. We compared scores of these clinical populations with those of matched cognitively unimpaired adults on four well-established production tasks, namely picture naming, category fluency, letter fluency, and past-tense verb inflection. We conducted a systematic search in PubMed and PsycINFO with terms for basal ganglia structures, basal ganglia disorders and language production tasks. A total of 114 studies were included, containing results for one or more of the tasks of interest. For each pathology and task combination, effect sizes (Hedges' g) were extracted comparing patient versus control groups. For all four populations, performance was consistently worse than that of cognitively unimpaired adults across the four language production tasks (p-values < 0.010). Given that performance in picture naming and verb inflection across all pathologies was quantified in terms of accuracy, our results suggest that production impairments cannot be fully explained by motor or processing-speed deficits. Our review shows that while language production difficulties in these clinical populations are not negligible, more evidence is necessary to determine the exact mechanism that leads to these deficits and whether this mechanism is the same across different pathologies.

Social Cognition in Patients with Early-Onset Parkinson's Disease

Social cognition (SC) deficits have been linked to Parkinson's disease (PD) but have been less well researched than general cognitive processes, especially in early-onset PD (EOPD), despite this population often having greater social and family demands. Most studies focus on recognition of facial emotion, theory of mind (ToM), and decision-making domains, with limited research reporting on social reasoning. The main objective of this work was to compare SC ability across four domains: emotional processing, social reasoning, ToM, and decision-making between patients with EOPD and healthy controls. Twenty-five nondemented patients with EOPD and 25 controls matched for sex, age, and educational level were enrolled. A battery that included six SC tests was administered to all study participants; a decision-making scale was completed by participants' partners. Statistically significant differences were found between patients with EOPD and controls in all subtests across the four SC domains studied. The EOPD group demonstrated worse performance on all tasks, with large effect sizes. Differences remained significant after adjusting for Montreal Cognitive Assessment (MoCA) test scores for all SC subtests except the decision-making scale and the Iowa gambling task. No significant correlations between SC and other clinical PD variables were found. Our study shows that patients with EOPD perform significantly below controls in multiple SC domains affecting recognition of facial emotion, social reasoning, ToM, and decision-making. Only decision-making seems to be mediated by overall cognitive ability. The confounding or contributing effect of other clinical PD variables should be studied further.

Cognitive profile of non-demented Parkinson's disease: Meta-analysis of domain and sex-specific deficits

INTRODUCTION

Better awareness of the cognitive domains affected in non-demented Parkinson's Disease (PD) should improve understanding of cognitive disease mechanisms. A complete understanding of the cognitive areas impaired in non-demented PD is hindered because most studies use small clinical samples without comparison to healthy controls. This meta-analysis examined cumulative evidence across studies to determine if there were impairments in non-demented PD in the three cognitive domains thought to be most widely affected in PD: frontal executive, visuospatial, and verbal memory. Because there are well-documented sex differences in PD, a second objective was to explore sex differences in these findings.

METHODS

MEDLINE, EMBASE and PsycINFO databases were searched (1988-March 2017). Random effects models were used to compute and compare effect sizes of differences between PD patients and controls within cognitive domains. Sex differences in effect sizes were also examined in these comparisons. Moderating factors including age, disease duration, motor symptom severity, levodopa dosage, and depression were examined through meta-regression.

RESULTS

PD patients showed deficits of moderate effect sizes in all three cognitive domains relative to controls. Significant sex differences were observed only for frontal executive abilities, with male PD patients showing greater deficits than female PD patients relative to controls. No moderators of effect sizes were identified in the domain specific overall or sex-segregated meta-analyses.

CONCLUSIONS

Results indicate that non-demented PD patients have deficits of moderate magnitude in frontal executive, verbal memory, and visuospatial abilities. Our findings of greater frontal executive deficits in males warrant further confirmation.

The visual kinetic depth effect is altered with Parkinson's disease

BACKGROUND

People with Parkinson's disease (PD) often have visual-perceptual disorders. The goal of this study was to learn if they can develop a three dimensional (3D) percept that depends on the kinetic depth effect; that is, the viewer's ability to spatially integrate over time images that are moving along many trajectories.

METHODS

Sixteen patients with PD and 12 healthy matched controls were presented with stimuli that were comprised of a circular region of randomly placed dots that moved as orthographic projections of a sphere. With a normal kinetic depth effect, the Training stimuli appear as an opaque rotating ball and the Test stimuli appear as a rotating transparent ball.

RESULTS

Whereas all controls and all PD patients reported seeing the Training stimuli as a rotating ball, the patients with PD were significantly less likely to report the Test stimuli appearing as a 3D "ball" than were the healthy participants. Instead, seven PD patients often reported these bidirectional stimuli appeared "flat."

CONCLUSIONS

This study has revealed that some patients with PD have impaired spatio-temporal integration of bidirectional visual motions, but the mechanism accounting for this loss, as well as why only some patients had this deficit, needs further study. When the driver of a moving vehicle fixates upon a stationary target in the surroundings, bidirectional retinal image motions may occur. Failure to perceive 3D structure in such moving scenes can be plausibly suspected to contribute to adverse events such as auto accidents.

Gait in Parkinson's disease: A visuo-cognitive challenge

Vision and cognition have both been related to gait impairment in Parkinson's disease (PD) through separate strands of research. The cumulative and interactive effect of both (which we term visuo-cognition) has not been previously investigated and little is known about the influence of cognition on vision with respect to gait. Understanding the role of vision, cognition and visuo-cognition in gait in PD is critical for data interpretation and to infer and test underlying mechanisms. The purpose of this comprehensive narrative review was to examine the interdependent and interactive role of cognition and vision in gait in PD and older adults. Evidence from a broad range of research disciplines was reviewed and summarised. A key finding was that attention appears to play a pivotal role in mediating gait, cognition and vision, and should be considered emphatically in future research in this field.

Visual Attention and Saccadic Oculomotor Control in Parkinson's Disease

BACKGROUND

In patients with Parkinson's disease (PD) we aimed at differentiating the relation between selective visual attention, deficits of programming and dynamics of saccadic eye movements while searching for a target and hand-reaction time as well as hand-movement time. Visual attention is crucial for concentrating selectively on one aspect of the visual field while ignoring other aspects. Eye movements are anatomically and functionally related to mechanisms of visual attention. Saccadic dysfunction might confound selective visual attention in PD.

METHODS

We studied visual selective attention in 22 medicated PD patients (clinical ON status, mild to moderate disease severity) and 22 age matched controls. We looked for possible interferences through oculomotor deficits. Two tasks were compared: free viewing of photographs and time optimal visual search of a hidden target. Visual search times (VST), task related dynamics of saccades, and hand-reaction and hand-movement times were analyzed.

RESULTS

In the free viewing task mild to moderately affected PD patients did not differ statistically from healthy subjects with respect to saccade dynamics. However, patients differed significantly from healthy subjects in the time optimal visual search task with 25% lower rates of successful searches. Hand movement reaction time did not differ in both groups, whereas hand movement execution time was significantly prolonged in PD patients.

CONCLUSION

Saccadic oculomotor control and hand movement reaction times were intact, whereas in our less severely affected treated PD patients, visual selective attention was not. The highly reduced successful search rate might be related to disturbed programming and delayed execution of saccades during time optimal visual search due to decreased execution of serial-order sequential generation of saccades.

Dopamine does not appear to affect mental rotation in Parkinson's disease

Objective

Patients with Parkinson’s disease (PD) often have deficits with mental rotation (MR). The neuropathological factors underlying these deficits, however, remain to be elucidated. One hypothesis suggests that dopamine depletion in nigro-striatal systems adversely influences MR. Another hypothesis suggests that deterioration of cortical (fronto-temporo-parietal basal ganglia) networks that mediate this function are responsible for this deficit. The goal of this study was to test the dopamine hypothesis by determining if dopamine abstinence negatively influences MR performance.

Methods

Thirty three non-demented right-handed individuals with PD were assess for their ability to perform a pencil and paper MR test while “on” and “off” dopaminergic medications. Dopamine abstinence followed the typical overnight withdrawal procedures.

Results

No differences in mental rotation abilities were found between “on” and “off” dopaminergic medications.

Conclusions

These results suggest that other neuropathological factors, such as cortical-basal ganglia neurodegeneration, or dysfunction of other neurotransmitters systems, might account for these cognitive deficits and future research will have to test these alternative hypotheses.

The contribution of acetylcholine and dopamine to subprocesses of visual working memory--what patients with amnestic mild cognitive impairment and Parkinson׳s disease can tell us

Attentional selection, i.e. filtering out of irrelevant sensory input and information storage are two crucial components of working memory (WM). It has been proposed that the two processes are mediated by different neurotransmitters, namely acetylcholine for attentional selection and dopamine for memory storage. However, this hypothesis has been challenged by others, who for example linked a lack in dopamine levels in the brain to filtering deficits. Here we tested the above mentioned hypothesis in two patient cohorts which either served as a proxy for a cholinergic or a dopaminergic deficit. The first group comprised 18 patients with amnestic mild cognitive impairment (aMCI), the second 22 patients with Parkinson׳s disease (PD). The two groups did not differ regarding their overall cognitive abilities. Both patient groups as well as a control group without neurological deficits (n=25) performed a visuo-spatial working memory task in which both the necessity to filter out irrelevant information and memory load, i.e. the number of items to be held in memory, were manipulated. In accordance with the primary hypothesis, aMCI patients displayed problems with filtering, i.e., were especially impaired when the task required ignoring distracting stimuli. PD patients on the other hand showed difficulties when memory load was increased suggesting that they mainly suffered from a storage deficit. In sum, this study underlines how the investigation of neurologic patients with a presumed neurotransmitter deficit can aid to clarify these neurotransmitters׳ contribution to specific cognitive functions.