Tracking Response Dynamics of Sequential Working Memory in Patients With Mild Parkinson's Disease

Impaired Sequential Working Memory in Patients With Young Onset Parkinson's Disease

BACKGROUND

Sequential working memory refers to the cognitive ability to maintain and/or manipulate a set of ordered representations within a short period. It remains unclear whether sequential working memory is impaired in patients with young onset Parkinson's disease (YOPD).

OBJECTIVES

The aim of this study is to evaluate the sequential working memory in patients with YOPD.

METHODS

Sixty-three YOPD patients (29 women) and one hundred age- and education-matched healthy controls participated in three well-established sequential working memory tests. The YOPD patients were categorized into akinetic rigid type (PD-ART) and non-akinetic rigid type (PD-NART). Participants were asked to maintain digit sequences in mind in the digit span forward (DST-F) and to maintain and manipulate digit sequences in mind in the digit span backward (DST-B) and adaptive digit ordering tests (DOT-A).

RESULTS

The PD-ART group scored lower and had higher ordering costs (difference between the DST-F and DOT-A scores) than the healthy control group in the DOT-A. Moreover, in the PD-ART group, the daily levodopa equivalent dose for dopamine D2/3 receptor agonists positively correlated with the DOT-A score and negatively correlated with the DOT-A ordering cost, suggesting that patients who took a greater dose of dopamine D2/3 receptor agonists tended to have higher DOT-A scores and lower DOT-A ordering costs.

CONCLUSIONS

These results indicated that the impaired sequential working memory may be one of markers of identifying early cognitive impairment in patients with YOPD, especially in PD-ART patients. The dopamine D2/3 receptor agonists can recover this impairment to some extent.

Endogenous PTEN-Induced Kinase 1 Regulates Dendritic Architecture and Spinogenesis

Mutations in PTEN-induced kinase 1 (PINK1) contribute to autosomal recessive Parkinson's disease with cognitive and neuropsychiatric comorbidities. Disturbances in dendritic and spine architecture are hallmarks of neurodegenerative and neuropsychiatric conditions, but little is known of the impact of PINK1 on these structures. We used Pink1 -/- mice to study the role of endogenous PINK1 in regulating dendritic architecture, spine density, and spine maturation. Pink1 -/- cortical neurons of unknown sex showed decreased dendritic arborization, affecting both apical and basal arbors. Dendritic simplification in Pink1 -/- neurons was primarily driven by diminished branching with smaller effects on branch lengths. Pink1 -/- neurons showed reduced spine density with a shift in morphology to favor filopodia at the expense of mushroom spines. Electrophysiology revealed significant reductions in miniature EPSC (mEPSC) frequency in Pink1 -/- neurons, consistent with the observation of decreased spine numbers. Transfecting with human PINK1 rescued changes in dendritic architecture, in thin, stubby, and mushroom spine densities, and in mEPSC frequency. Diminished spine density was also observed in Golgi-Cox stained adult male Pink1 -/- brains. Western blot study of Pink1 -/- brains of either sex revealed reduced phosphorylation of NSFL1 cofactor p47, an indirect target of PINK1. Transfection of Pink1 -/- neurons with a phosphomimetic p47 plasmid rescued dendritic branching and thin/stubby spine density with a partial rescue of mushroom spines, implicating a role for PINK1-regulated p47 phosphorylation in dendrite and spine development. These findings suggest that PINK1-dependent synaptodendritic alterations may contribute to the risk of cognitive and/or neuropsychiatric pathologies observed in PINK1-mutated families.SIGNIFICANCE STATEMENT Loss of PINK1 function has been implicated in both familial and sporadic neurodegenerative diseases. Yet surprisingly little is known of the impact of PINK1 loss on the fine structure of neurons. Neurons receive excitatory synaptic signals along a complex network of projections that form the dendritic tree, largely at tiny protrusions called dendritic spines. We studied cortical neurons and brain tissues from mice lacking PINK1. We discovered that PINK1 deficiency causes striking simplification of dendritic architecture associated with reduced synaptic input and decreased spine density and maturation. These changes are reversed by reintroducing human PINK1 or one of its downstream mediators into PINK1-deficient mouse neurons, indicating a conserved function, whose loss may contribute to neurodegenerative processes.

Altered alpha and theta oscillations correlate with sequential working memory in Parkinson's disease

Daily activities such as preparing a meal rely on the ability to arrange thoughts and actions in the right order. Patients with Parkinson's disease have difficulties in sequencing tasks. Their deficits in sequential working memory have been associated with basal ganglia dysfunction. Here we demonstrate that altered parietal alpha and theta oscillations correlate with sequential working memory in Parkinson's disease. We included 15 patients with Parkinson's disease (6 women, mean age: 66.0 years), 24 healthy young (14 women, mean age: 24.1 years), and 16 older participants (7 women, mean age: 68.6 years). All participants completed a picture ordering task with scalp electroencephalogram (EEG) recording, where they arranged five pictures in a specific order and memorized them over a delay. When encoding and maintaining picture sequences, patients with Parkinson's disease showed a lower baseline alpha peak frequency with higher alpha power than healthy young and older participants. Patients with a higher baseline alpha power responded more slowly for ordered trials. When manipulating picture sequences, patients with Parkinson's disease showed a lower frequency of maximal power change for random versus ordered trials than healthy young and older participants. Healthy older participants showed a higher frequency of maximal power change than healthy young participants. Compared with patients with frequency of maximal power change in the alpha band (8-15 Hz), patients with frequency of maximal power change in the theta band (4-7 Hz) showed a higher ordering-related accuracy cost (random versus ordered) in the main task and tended to respond more slowly and less accurately in an independent working memory test. In conclusion, altered baseline alpha oscillations and task-dependent modulation of alpha and theta oscillations may be neural markers of poor sequential working memory in Parkinson's disease.