Recognition memory in Parkinson's disease with and without dementia: evidence inconsistent with the retrieval deficit hypothesis

Sex differences in Parkinson disease-associated episodic memory and processing speed deficits

OBJECTIVES

This study aims to address a gap in the data on cognitive sex differences in persons living with Parkinson disease (PD). There is some evidence that cognitive dysfunction is more severe in male PD, however data on episodic memory and processing speed is incomplete.

METHODS

One hundred and sixty-seven individuals with a diagnosis of PD were included in this study. Fifty-six of those individuals identified as female. The California Verbal Learning Test 1st edition and the Wechsler Memory Scale 3rd edition were used to evaluate verbal and visuospatial episodic memory and the Wechsler Adult Intelligence Scale 3rd edition was used to evaluate processing speed. Multivariate analysis of covariance was used to identify sex-specific differences across groups.

RESULTS

Our results show that males with PD performed significantly worse than females in verbal and visuospatial recall as well as a trend for the processing speed task of coding.

CONCLUSIONS

Our finding of superior performance among females with PD in verbal episodic memory is consistent with reports in both healthy and PD individuals; however, females outperforming males in measures of visuospatial episodic memory is unique to PD. Cognitive deficits preferentially affecting males appear to be associated with frontal lobe-related function. Therefore, males may represent a disease subgroup more susceptible to disease mechanisms affecting frontal lobe deterioration and cognitive disturbances in PD.

Comparison of core and process scores on the California Verbal Learning Test-3 for Parkinson's disease and essential tremor patients

INTRODUCTION

Parkinson's disease (PD) and essential tremor (ET) are two disorders known to lead to executive dysfunction, presumably through distinct pathways to the frontal lobes via the striatum or cerebellum, respectively. Memory functioning in PD and ET patients has been previously suggested to be adversely impacted by executive dysfunction. The aims of this exploratory study were to compare memory performance between and within groups on the California Verbal Learning Test - 3 (CVLT-3) through the analysis of core and process scores and to understand the relationship of these scores with measures of executive functioning.

METHOD

Seventy PD and 54 ET patients completed comprehensive neuropsychological testing. Independent sample t-tests or Mann-Whitney tests were used to compare between group core and process scores on the CVLT-3. Within-subjects analyses were conducted via Wilcoxon Signed Rank Test due to nonparametric data. Spearman's correlations were conducted to explore the relationship between memory process scores and measures of executive functioning.

RESULTS

The ET and PD samples were similar with regard to age, education, gender, and general cognitive functioning. PD patients made more repetition errors (U = 2391.50, p = .01) than ET patients and Normal Memory PD patients made more repetition errors than Low Memory PD patients (U= 711.00, p= .00). Correlational analyses revealed repetition errors were negatively associated with tests of inhibition, set shifting, and working memory (rs = -.293, -.232). ET patients demonstrated a preference for a serial cluster learning strategy (T = 861.00, p = .005), similar to PD patients (T= 1633.00, p = <.001).

CONCLUSIONS

The study revealed presence of higher repetition errors in the PD sample that was demonstrated to have a negative relationship with measures of executive functioning. Implications for investigating process ("qualitative") scores in memory performance to determine extent of executive involvement are discussed.

Memory Phenotypes In Early, De Novo Parkinson's Disease Patients with Mild Cognitive Impairment

BACKGROUND

Memory deficits in mild cognitive impairment related to Parkinson's disease (PD-MCI) are quite heterogeneous, and there is no general agreement on their genesis.

OBJECTIVES

To define memory phenotypes in de novo PD-MCI and their associations with motor and non-motor features and patients' quality of life.

METHODS

From a sample of 183 early de novo patients with PD, cluster analysis was applied to neuropsychological measures of memory function of 82 patients with PD-MCI (44.8%). The remaining patients free of cognitive impairment were considered as a comparison group (n = 101). Cognitive measures and structural magnetic resonance imaging-based neural correlates of memory function were used to substantiate the results.

RESULTS

A three-cluster model produced the best solution. Cluster A (65.85%) included memory unimpaired patients; Cluster B (23.17%) included patients with mild episodic memory disorder related to a "prefrontal executive-dependent phenotype"; Cluster C (10.97%) included patients with severe episodic memory disorder related to a "hybrid phenotype," where hippocampal-dependent deficits co-occurred with prefrontal executive-dependent memory dysfunctions. Cognitive and brain structural imaging correlates substantiated the findings. The three phenotypes did not differ in terms of motor and non-motor features, but the attention/executive deficits progressively increased from Cluster A, through Cluster B, to Cluster C. This last cluster had worse quality of life compared to others.

CONCLUSIONS

Our results demonstrated the memory heterogeneity of de novo PD-MCI, suggesting existence of three distinct memory-related phenotypes. Identification of such phenotypes can be fruitful in understanding the pathophysiological mechanisms underlying PD-MCI and its subtypes and in guiding appropriate treatments. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Clinical value of the Montreal Cognitive Assessment free recall condition alone versus cued recall and recognition conditions to detect true memory impairment

The Montreal Cognitive Assessment (MoCA) is widely used as a screener to characterize cognition. Although only the delayed free recall condition is required for administration, performance on the optional cued recall and multiple-choice recognition conditions may improve diagnostic accuracy over free recall alone. Data on 719 individuals with MCI and 601 controls were obtained from the Alzheimer's Disease Neuroimaging Initiative (ADNI) database. The Rey Auditory Verbal Learning Test (AVLT) delayed free recall condition was used as the gold standard of memory status. Participants with T-scores ≤30 (≤2 SDs below the mean) were classified as memory "impaired." Binary logistic regressions assessed if combined MoCA cued recall/recognition predicted impaired delayed recall on the AVLT beyond the contribution of MoCA free recall. Results showed that MoCA free recall predicted AVLT delayed recall, and that the addition of combined MoCA cued recall/recognition improved the ability to detect impaired AVLT recall, with a better overall model fit. The combined MoCA cued recall/recognition score also had higher specificity and likelihood ratios in detecting memory impairment than MoCA free recall, while higher sensitivity values were present for free recall. Thus, the additional administration of the MoCA cued recall and recognition is recommended.

Spontaneous Object Exploration in a Recessive Gene Knockout Model of Parkinson's Disease: Development and Progression of Object Recognition Memory Deficits in Male Pink1-/- Rats

Cognitive impairments appear at or before motor signs in about one third of patients with Parkinson's disease (PD) and have a cumulative prevalence of roughly 80% overall. These deficits exact an unrelenting toll on patients' quality and activities of daily life due in part to a lack of available treatments to ameliorate them. This study used three well-validated novel object recognition-based paradigms to explore the suitability of rats with knockout of the PTEN-induced putative kinase1 gene (Pink1) for investigating factors that induce cognitive decline in PD and for testing new ways to mitigate them. Longitudinal testing of rats from 3-9 months of age revealed significant impairments in male Pink1-/- rats compared to wild type controls in Novel Object Recognition, Novel Object Location and Object-in-Place tasks. Task-specific differences in the progression of object discrimination/memory deficits across age were also seen. Finally, testing using an elevated plus maze, a tapered balance beam and a grip strength gauge showed that in all cases recognition memory deficits preceded potentially confounding impacts of gene knockout on affect or motor function. Taken together, these findings suggest that knockout of the Pink1 gene negatively impacts the brain circuits and/or neurochemical systems that support performance in object recognition tasks. Further investigations using Pink1-/- rats and object recognition memory tasks should provide new insights into the neural underpinnings of the visual recognition memory and visuospatial information processing deficits that are often seen in PD patients and accelerate the pace of discovery of better ways to treat them.

Task-specific effects of biological sex and sex hormones on object recognition memories in a 6-hydroxydopamine-lesion model of Parkinson's disease in adult male and female rats

Many patients with Parkinson's disease (PD) experience cognitive or memory impairments with few therapeutic options available to mitigate them. This has fueled interest in determining how factors including sex and sex hormones modulate higher order function in this disease. The objective of this study was to use the Novel Object Recognition (NOR) and Object-in-Place (OiP) paradigms to compare the effects of a bilateral neostriatal 6-hydroxydopamine (6-OHDA) lesion model of PD in gonadally intact male and female rats, in orchidectomized male rats and in orchidectomized males supplemented with 17β-estradiol or testosterone propionate on measures of recognition memory similar to those at risk in PD. These studies showed that 6-ODHA lesions impaired discrimination in both tasks in males but not females. Further, 6-OHDA lesions disrupted NOR performance similarly in all males regardless of whether they were gonadally intact, orchidectomized or hormone-supplemented. In contrast, OiP performance was disrupted in males that were orchidectomized or 6-OHDA-lesioned but was spared in orchidectomized and orchidectomized, 6-OHDA lesioned males supplemented with 17β-estradiol. The distinct effects that sex and/or sex hormones have on 6-OHDA lesion-induced NOR vs. OiP deficits identified here also differ from corresponding impacts recently described for 6-OHDA lesion-induced deficits in spatial working memory and episodic memory. Together, the collective data provide strong evidence for effects of sex and sex hormones on cognition and memory in PD as being behavioral task and behavioral domain specific. This specificity could explain why a cohesive clinical picture of endocrine impacts on higher order function in PD has remained elusive.

Correlation Between Amygdala Nuclei Volumes and Memory in Cognitively Normal Adults Carrying the ApoE ε3/ε3 Allele

The amygdala is known to be related to cognitive function. In this study, we used an automated approach to segment the amygdala into nine nuclei and evaluated amygdala and nuclei volumetric changes across the adult lifespan in subjects carrying the apolipoprotein E (ApoE) ε3/ε3 allele, and we related those changes to memory function alteration. We found that except the left medial nucleus (Me), whose volume decreased in the old group compared with the middle-early group, all other nuclei volumes presented a significant decline in the old group compared with the young group. Left accessory basal nucleus (AB) and left cortico-amygdaloid transition area (CAT) volumes were also diminished in the middle-late group. In addition, immediate memory recall is impaired by the process of aging, whereas delayed recall and delayed recognition memory functions were not significantly changed. We found significant positive correlations between immediate recall scores and volumes of the bilateral basal nucleus (Ba), AB, anterior amygdaloid area (AAA), CAT, whole amygdala, left lateral nucleus (La), left paralaminar nucleus (PL), and right cortical nucleus (Co). The results suggest that immediate recall memory decline might be associated with volumetric reduction of the amygdala and its nuclei, and the left AB and left CAT might be considered as potential imaging biomarkers of memory decline in aging.

Neuropsychiatric and Cognitive Deficits in Parkinson's Disease and Their Modeling in Rodents

Parkinson’s disease (PD) is associated with a large burden of non-motor symptoms including olfactory and autonomic dysfunction, as well as neuropsychiatric (depression, anxiety, apathy) and cognitive disorders (executive dysfunctions, memory and learning impairments). Some of these non-motor symptoms may precede the onset of motor symptoms by several years, and they significantly worsen during the course of the disease. The lack of systematic improvement of these non-motor features by dopamine replacement therapy underlines their multifactorial origin, with an involvement of monoaminergic and cholinergic systems, as well as alpha-synuclein pathology in frontal and limbic cortical circuits. Here we describe mood and neuropsychiatric disorders in PD and review their occurrence in rodent models of PD. Altogether, toxin-based rodent models of PD indicate a significant but non-exclusive contribution of mesencephalic dopaminergic loss in anxiety, apathy, and depressive-like behaviors, as well as in learning and memory deficits. Gene-based models display significant deficits in learning and memory, as well as executive functions, highlighting the contribution of alpha-synuclein pathology to these non-motor deficits. Collectively, neuropsychiatric and cognitive deficits are recapitulated to some extent in rodent models, providing partial but nevertheless useful options to understand the pathophysiology of non-motor symptoms and develop therapeutic options for these debilitating symptoms of PD.

Subjective organization in the episodic memory of individuals with Parkinson's disease associated with mild cognitive impairment

Word clustering (i.e., the ability to reproduce the same word pairs in consecutive recall trials of an unrelated word list) has been extensively investigated as a proxy of subjective organization (SO) of memorandum. In healthy subjects and in groups of brain-damaged patients, the rate of SO generally predicts accuracy of word list recall. This study aimed at evaluating SO in the performance of patients with Parkinson's disease (PD) on a word list recall task in order to investigate the basic mechanisms of episodic memory impairment that are frequently observed in these patients. For this purpose, 56 PD patients, who were stratified according to the presence and quality of mild cognitive impairment (MCI), and a group of healthy controls (HCs) were administered a word list task and an extensive battery of neuropsychological tests. Results showed that recall accuracy on the word list task progressively decreased passing from HC to PD patients without cognitive impairment, to patients with single-domain dysexecutive MCI and to patients with multiple-domain dysexecutive and amnesic MCI. Conversely, only the latter PD group showed a lower SO score than that achieved by the other groups. In the overall PD group, correlational and regression analyses demonstrated that SO scores and a composite score of executive functions were not reciprocally related, but both provided an independent and significant contribution to the prediction of word list recall accuracy. These data are discussed in terms of the contribution of executive functions and hippocampal storage processes to the onset of memory impairment in PD.

Alzheimer's Disease and Parkinson Dementia Distinguished by Cognitive Marker

BACKGROUND

Temporary memory binding (TMB) has been shown to be specifically affected by Alzheimer's disease (AD) when it is assessed via free recall and titrating the task demands to equate baseline performance across patients.

METHODS

Patients with Parkinson's disease (PD) were subdivided into patients with and without cognitive impairment and compared with AD and amnestic mild cognitive impairment (aMCI) patients on their performance on the TMB.

RESULTS

The results show that only patients with AD dementia present with impaired TMB performance. Receiver operating characteristic curve analyses showed that TMB holds high sensitivity and specificity for aMCI and AD relative to PD groups and healthy controls.

CONCLUSION

The TMB is sensitive to the neurodegenerative mechanisms leading to AD dementia but not to those underpinning PD dementia. As such, TMB task can aid the differential diagnosis of these common forms of dementia.

Episodic Memory Impairment in Parkinson's Disease: Disentangling the Role of Encoding and Retrieval

OBJECTIVE

The source of episodic memory (EM) impairment in Parkinson's disease (PD) is still unclear. In the present study, we sought to quantify specifically encoding, consolidation, and retrieval process deficits in a list-learning paradigm by a novel method, the item-specific deficit approach (ISDA).

METHODS

We applied the ISDA method to the Free and Cued Selective Reminding Test (FCSRT) in a sample of 15 PD patients and 15 healthy participants.

RESULTS

The results revealed differences in free recall performance between PD patients and controls. These patients, however, benefited from cues as much as controls did, and total recall did not differ between groups. When analyzing the ISDA indices for encoding, consolidation, and retrieval deficits, the results showed a general memory deficit, but with a clear focus on encoding and retrieval, as revealed by the sensitivity values. Moreover, controlling for initial learning did not eliminate group effects in retrieval.

CONCLUSIONS

Our findings reveal a mixed pattern in PD patients, with deficits in both encoding and retrieval processes in memory. Also, despite the fact that an encoding dysfunction may explain some of the deficits observed at retrieval, it cannot fully account for the differences, highlighting that both encoding and retrieval factors are necessary to understand memory deficits in PD.

Beyond PD-MCI: objectively defined subtle cognitive decline predicts future cognitive and functional changes

OBJECTIVE

Cognitive impairment is prevalent among individuals with Parkinson's disease (PD). Effort has been made to identify individuals at risk for cognitive decline and dementia. Objectively-defined subtle cognitive decline (Obj-SCD) is a novel classification that may identify individuals at risk for cognitive decline prior to a diagnosis of mild cognitive impairment (MCI). We examined the utility of Obj-SCD criteria to predict future cognitive decline and difficulties with activities of daily living (ADLs) among individuals with PD.

METHOD

The sample included 483 individuals newly diagnosed with PD. Participants were followed for a five-year span with yearly visits where they completed neuropsychological tests. Participants were categorized as cognitively normal (CN), the newly proposed Obj-SCD, PD-MCI or Parkinson's disease dementia (PDD). Analyses determined if utilization of Obj-SCD criteria predicted subsequent cognitive impairment and difficulties with ADLs.

RESULTS

At baseline, 372 (77%) participants were classified as CN, 40 (8.3%) classified as Obj-SCD, and 71 (14.7%) classified as PD-MCI. Analyses revealed that relative to the CN group, participants classified as Obj-SCD at baseline, were more likely to develop PD-MCI or PDD within 5 years (odds ratio 2.413; 95% confidence interval 1.215-4.792). Furthermore, the Obj-SCD represented an intermediate level of impairment, relative to the CN and PD-MCI groups, on an independent measure of cognition (Montreal Cognitive Assessment) and ADL.

CONCLUSIONS

Findings provide evidence that Obj-SCD criteria can identify individuals at risk for cognitive decline and impairments in ADL. Obj-SCD criteria may identify individuals at risk for cognitive impairment who are not detected by PD-MCI criteria.

The Neuropsychological Profile of Mild Cognitive Impairment in Lewy Body Dementias

OBJECTIVES

Dementia with Lewy bodies (DLB) and Parkinson's disease dementia (PDD) have substantial clinical and biological overlap, with cognitive deficits typically observed in the executive and visuospatial domains. However, the neuropsychological profiles of mild cognitive impairment (MCI) associated with these disorders are not well understood.

METHODS

This systematic review examined existing literature on cognition in MCI due to LB disease (MCI-LB) and PD (PD-MCI) using an electronic search of seven databases (Medline, Embase, Psychinfo, PubMed, ProQuest, Scopus, and ScienceDirect). MCI-LB results were reviewed narratively given the small number of resulting papers (n = 7). Outcome variables from PD-MCI studies (n = 13) were extracted for meta-analysis of standardised mean differences (SMD).

RESULTS

In MCI-LB, executive dysfunction and slowed processing speed were the most prominent impairments, while visuospatial and working memory (WM) functions were also poor. MCI-LB scored significantly lower on verbal memory tests relative to controls, but significantly higher than patients with MCI due to Alzheimer's disease. Quantitative analysis of studies in PD-MCI showed a similar profile of impairment, with the largest deficits in visuospatial function (Benton Judgement of Line Orientation, SMD g = -2.09), executive function (Trail Making Test B, SMD g = -1.65), verbal ability (Naming Tests, SMD g = -0.140), and WM (Trail Making Test A, SMD g = -1.20). In both MCI-LB and PD-MCI, verbal and visuospatial memory retrieval was impaired, while encoding and storage appeared relatively intact.

CONCLUSIONS

The findings of this systematic review indicate similar neuropsychological profiles in the MCI stages of DLB and PDD. Executive impairment may at least partially explain poor performance in other domains.

Evaluation of Cognitive Function in Relation to Progression of Parkinson Disease

OBJECTIVE

Cognitive impairments are among the nonmotor symptoms in patients with Parkinson disease. Understanding the cognitive impairments in patients with Parkinson disease may be critical for developing effective rehabilitation interventions. The aims of this study were to assess cognitive function in patients with Parkinson disease using the Wechsler Adult Intelligence Scale Third Edition, and the Wechsler Memory Scale Revised and to investigate how cognitive impairments relate to progression of disease in patients with Parkinson disease according to the Hoehn and Yahr stages.

DESIGN

Seventy-eight patients with Parkinson disease participated in the present study. Our study consisted of patients in the following Hoehn and Yahr groups: 1 (no disability, n = 11), 2 (mild, n = 34), 3 (moderate, n = 26), and 4 and 5 (severe, n = 7). Cognitive function was assessed using the Wechsler Adult Intelligence Scale Third Edition, and the Wechsler Memory Scale Revised.

RESULTS

The verbal memory was significantly higher in group 1 (106.4 ± 12.0) than in the other groups (2: 90.5 ± 14.0, 3: 89.9 ± 16.9, 4 and 5: 89.6 ± 11.4). Visual memory and delayed recall were similar to the results seen with verbal memory; however, the differences between groups were not statistically significant. The full-scale IQ was not significantly different (1: 107.3 ± 8.1, 2: 96.9 ± 18.2, 3: 96.7 ± 14.8, 4 and 5: 91.7 ± 9.5).

CONCLUSIONS

These results suggest that a comprehensive assessment focused on memory impairments is important for applying the appropriate interventions in patients with early-stage Parkinson disease.

Comparing learning performance on the open trial selective reminding test with the California verbal learning test II in traumatic brain injury

Introduction: Learning and memory deficits are prevalent following moderate to severe traumatic brain injury (TBI), affecting between 54% and 84% of impacted individuals.Objective: The current study examined learning performance on two tests of verbal memory: the OT-SRT and the CVLT-II.Methods: Sixty-eight participants with TBI performed the OT-SRT and the CVLT-II on two different days. Additionally, all participants completed cognitive tests assessing processing speed, working memory and executive functions. By definition, all participants with TBI were identified as having impaired learning on the OT-SRT, however only 38 were also identified as impaired on the CVLT-II. The sample was thus divided into two groups, those who failed both tests (Fail-2) and those who failed only the OT-SRT (Fail-1).Results: The Failed-1 group showed significantly better performance in processing speed, working memory and executive functions compared to the Fail-2 group. On the CVLT-II, the Fail-1 group performed significantly better on the number of words recalled on trials 1 and 5 compared to the Fail-2 group. Both groups performed similarly the OT-SRT.Discussion: The CVLT-II and the OT-SRT are not equivalent tests and should not be used interchangeably.

The Modality Effect on Delayed Free Recall in Non-demented Patients With Mild Parkinson's Disease Progression

Background: The modality effect plays the central role in learning and memory functions. Retrieval failure constitutes a common memory impairment that occurs among patients with Parkinson’s disease (PD). However, little knowledge exists about the relation between modality effect and delayed recall impairment in PD. The primary goal of this study was to compare delayed free recall performance between three different memory modalities (verbal, visual, and cross visual-verbal) in a sample of non-demented patients with mild PD progression. The secondary goal was to explore the frequency of deficient performance on the basis of normative comparisons on each of the three delayed free-recall measures.

Method: A total of 71 non-demented patients with mild PD progression were recruited for the administration of the Montreal Cognitive Assessment (MoCA), the Rey Auditory Verbal Learning Test (RAVLT), the Rey Osterrieth Complex Figure Test (ROCFT), and the Greek Version of Face-Name Associative Memory Examination (GR-FNAME12).

Results: The percentages of deficient-performances for the three delayed free recall measures were 45.1% (32/71), 39.4% (28/71) and 31% (22/71) for the GR-FNAME12, ROFCT and RAVLT, respectively. The results indicated no significant difference between performances of the GR-FNAME12 and ROCFT, both of which were significantly lower than performance on the RAVLT.

Conclusions: In conclusion, delayed free recall appears to be more severely affected in the cross visual-verbal and visual memory modalities than in verbal-memory modalities in the early phase of PD progression.

Episodic recognition memory and the hippocampus in Parkinson's disease: A review

Parkinson's disease is a progressive neurodegenerative disorder of aging. The hallmark pathophysiology includes the development of neuronal Lewy bodies in the substantia nigra of the midbrain with subsequent loss of dopaminergic neurons. These neuronal losses lead to the characteristic motor symptoms of bradykinesia, rigidity, and rest tremor. In addition to these cardinal motor symptoms patients with PD experience a wide range of non-motor symptoms, the most important being cognitive impairments that in many circumstances lead to dementia. People with PD experience a wide range of cognitive impairments; in this review we will focus on memory impairment in PD and specifically episodic memory, which are memories of day-to-day events of life. Importantly, these memory impairments severely impact the lives of patients and caregivers alike. Traditionally episodic memory is considered to be markedly dependent on the hippocampus; therefore, it is important to understand the exact nature of PD episodic memory deficits in relation to hippocampal function and dysfunction. In this review, we discuss an aspect of episodic memory called recognition memory and its subcomponents called recollection and familiarity. Recognition memory is believed to be impaired in PD; thus, we discuss what aspects of the hippocampus are expected to be deficient in function as they relate to these recognition memory impairments. In addition to the hippocampus as a whole, we will discuss the role of hippocampal subfields in recognition memory impairments.

Verbal Memory in Parkinson's Disease: A Combined DTI and fMRI Study

Background:

While significant progress has been made to determine the functional role of specific gray matter areas underlying verbal memory in Parkinson’s disease (PD), very little is known about the relationship between these regions and their underlying white matter structures.

Objective:

The objectives of this study were (1) to investigate verbal memory, fractional anisotropy and brain activation differences between PD patients and healthy controls (HC), (2) to explore the neuroanatomical and neurofunctional correlates of verbal memory in PD, and (3) to investigate the relationship between these neuroanatomical and neurofunctional verbal memory correlates in PD.

Methods:

Functional magnetic resonance imaging (fMRI) while performing a verbal memory paradigm and diffusion tensor imaging data (DTI), were acquired in 37 PD patients and 15 age-, sex-, and education-matched HC.

Results:

PD patients showed verbal recognition memory impairment, lower fractional anisotropy in the anterior cingulate tract, and lower brain activation in the inferior orbitofrontal cortex compared to HC. Brain activation in the inferior orbitofrontal cortex correlated significantly with verbal recognition memory impairment in PD patients. In addition, a relationship between brain activation in the inferior orbitofrontal cortex and fractional anisotropy of the uncinate fasciculus was found in PD.

Conclusions:

These results reveal that deficits in verbal memory in PD are accompanied by functional brain activation changes, but also have specific structural correlates related to white matter microstructural integrity.

Markers of cognitive decline in PD: The case for heterogeneity

Cognitive impairment is highly prevalent and has a severe negative effect on health related and perceived quality of life in Parkinson's disease (PD). It is now established that 20-40% of persons with PD will develop cognitive deficits early in the disease. Moreover, the risk of developing dementia is six times higher in PD patients than in age-matched controls and it is estimated that 80% of patients will develop dementia after 20 years of the disease. In order to address these symptoms properly it is crucial to identify very early in the disease the patients who are most likely to develop dementia rapidly. Persons who meet criteria for mild cognitive impairment (MCI) exhibit measurable cognitive deficits but those deficits are not severe enough to interfere significantly with daily life. While the presence of MCI in PD increases the chance of developing dementia, various studies suggest that PD-MCI might consist of distinct subtypes with different pathophysiologies and prognoses. In this paper we comment on various biomarkers associated with cognitive decline in PD, specifically clinical, neuropathological, genetic and neuroimaging ones. We also discuss disrupted functional connectivity in PD-MCI and reveal preliminary results from our own group. We propose that the current studies looking at different types of biomarkers provide support for different causes being associated with cognitive decline in PD. Large-scale multi-disciplinary and multi-modal longitudinal studies are required to identify more specifically the different phenotypes associated with different cognitive profiles and evolution in PD.

Decreased synaptic plasticity in the medial prefrontal cortex underlies short-term memory deficits in 6-OHDA-lesioned rats

Parkinson's disease (PD) is characterized by motor dysfunction associated with dopaminergic degeneration in the dorsolateral striatum (DLS). However, motor symptoms in PD are often preceded by short-term memory deficits, which have been argued to involve deregulation of medial prefrontal cortex (mPFC). We now used a 6-hydroxydopamine (6-OHDA) rat PD model to explore if alterations of synaptic plasticity in DLS and mPFC underlie short-term memory impairments in PD prodrome. The bilateral injection of 6-OHDA (20μg/hemisphere) in the DLS caused a marked loss of dopaminergic neurons in the substantia nigra (>80%) and decreased monoamine levels in the striatum and PFC, accompanied by motor deficits evaluated after 21 days in the open field and accelerated rotarod. A lower dose of 6-OHDA (10μg/hemisphere) only induced a partial degeneration (about 60%) of dopaminergic neurons in the substantia nigra with no gross motor impairments, thus mimicking an early premotor stage of PD. Notably, 6-OHDA (10μg)-lesioned rats displayed decreased monoamine levels in the PFC as well as short-term memory deficits evaluated in the novel object discrimination and in the modified Y-maze tasks; this was accompanied by a selective decrease in the amplitude of long-term potentiation in the mPFC, but not in DLS, without changes of synaptic transmission in either brain regions. These results indicate that the short-term memory dysfunction predating the motor alterations in the 6-OHDA model of PD is associated with selective changes of information processing in PFC circuits, typified by persistent changes of synaptic plasticity.

Time-based prospective memory functioning in mild cognitive impairment associated with Parkinson's disease: relationship with autonomous management of daily living commitments

OBJECTIVE

Prospective memory (PM), that is, the ability to keep in memory and carry out intentions in the future, is reported to be impaired in individuals with Parkinson's disease (PD). PM failure may be also associated with reduced daily living functioning in these patients. Little is known, however, about the relationship between mild cognitive impairment (MCI) and time-based PM functioning in PD patients and the possible impact of PM deficits on patients' autonomy in daily living. Here we aimed to investigate whether MCI associated with PD affects time-based PM. We also wished to determine whether PM impairment accounts for reduced autonomous management of medication in these patients.

METHOD

The study included 48 PD patients with MCI, 33 PD patients without cognitive disorders (PDN) and 20 healthy controls. The time-based PM procedure required that subjects perform an action after a fixed time. The PM procedure was incorporated in the standard neuropsychological assessment. One score was computed for the ability to retrieve the intention (prospective component) and one for remembering the action to be executed (retrospective component). The Pill Questionnaire was administered to assess the ability to manage medication.

RESULTS

PD patients with MCI performed less accurately in the PM procedure than HC and tended to perform poorer than PDN. Moreover, in PD patients with MCI, accuracy on the prospective component of the PM task and performance on the Modified Card Sorting Test significantly predicted the ability to manage medication.

CONCLUSIONS

RESULTS document that reduced efficiency of time-based PM processes in PD is specifically related to the presence of MCI. The same data indicate that PM weakness may be associated with impaired daily living functioning and decreased autonomy.

Structural MRI Correlates of Episodic Memory Processes in Parkinson's Disease Without Mild Cognitive Impairment

BACKGROUND

Changes in episodic memory are common early in Parkinson's disease (PD) and may be a risk factor for future cognitive decline. Although medial temporal lobe (MTL) memory and frontostriatal (FS) executive systems are thought to play different roles in distinct components of episodic memory impairment in PD, no study has investigated whether different aspects of memory functioning are differentially associated with MTL and FS volumes in nondemented patients without mild cognitive impairment (PD-woMCI).

OBJECTIVES

The present study investigated MRI markers of different facets of memory functioning in 48 PD-woMCI patients and 42 controls.

METHODS

Regional volumes were measured in structures comprising the MTL and FS systems and then correlated with key indices of memory from the California Verbal Learning Test.

RESULTS

In PD-woMCI patients, memory was impaired only for verbal learning, which was not associated with executive, attention/working memory, or visuospatial functioning. Despite an absence of cortical atrophy, smaller right MTL volumes in patients were associated with poorer verbal learning, long delayed free recall, long delayed cued recall, and recognition memory hits and false positives. Smaller right pars triangularis (inferior frontal) volumes were also associated with poorer long delayed cued recall and recognition memory hits. These relationships were not found in controls.

CONCLUSIONS

The findings indicate that MTL volumes are sensitive to subtle changes in almost all facets of memory in PD-woMCI, whereas FS volumes are sensitive only to memory performances in cued-testing formats.

Cognitive Impairment in Parkinson’s Disease: More than a Frontostriatal Dysfunction

Cognitive deficit in Parkinson’s disease has been traditionally considered as being mainly related to executive dysfunction secondary to frontostriatal affectation. However, this traditional consideration has recently been challenged. Forty-three nondemented PD patients (mean age = 59.19; SD = 9.64) and twenty control group subjects (mean age = 60.85; SD = 12.26) were studied. They were assessed on a wide range of cognitive functions. Patients showed motor slowing (p = .012), along with alterations in visuoperceptive (p = .001), visuospatial (p = .007) and visuoconstructive functions (p = .017), as well as in visual span (direct: p = .008; inverse: p = .037). Regarding executive functions, differences were not observed in classical measures for verbal fluency (phonetic: p = .28; semantic: p = .27) or in response inhibition (Stroop test: p = .30), while execution was altered in other prefrontal tasks (Wisconsin Test: p = .003; action fluency: p = .039). Patients showed altered performance in verbal learning processes (p = .005) and delayed memory (free: p = .032; cued: p = .006), visuospatial learning (p = .016) and linguistic functions (naming: p < .001; comprehension: p = .007). Poor performance in visuospatial memory is predicted by deficits in working memory and visuospatial perception. Taken together, the observed alterations not only suggest prefrontal affectation, but also temporal and parietal systems impairment. Thus, cognitive dysfunction in nondemented PD patients cannot be exclusively explained by frontostriatal circuit affectation and the resulting executive dysfunction.

Exploring recollection and familiarity impairments in Parkinson's disease

There is conflicting evidence on whether patients diagnosed with Parkinson's disease (PD) have cognitive deficits associated with episodic memory and particularly with recognition memory. The aim of the present study was to explore whether PD patients exhibit deficits in recollection and familiarity, the two processes involved in recognition. A sample of young healthy participants (22) was tested to verify that the experimental tasks were useful estimators of recognition processes. Two further samples--one of elderly controls (16) and one of PD patients (20)--were the main focus of this research. All participants were exposed to an associative recognition test aimed at estimating recollection followed by a two-alternative forced-choice (2AFC) test designed to estimate familiarity. The analyses showed a deficit in associative recognition in PD patients and no difference between elderly controls and PD patients in the 2AFC test. By contrast, young healthy participants were better than elderly controls and PD patients in both components of recognition. Further analyses of results of the 2AFC test indicated that the measure chosen to estimate conceptual familiarity was adequate.

Free and cued recall memory in Parkinson's disease associated with amnestic mild cognitive impairment

The hypothesis has been advanced that memory disorders in individuals with Parkinson's disease (PD) are related to either retrieval or consolidation failure. However, the characteristics of the memory impairments of PD patients with amnestic mild cognitive impairment have not been clarified. This study was aimed at investigating whether memory deficits in PD patients with amnestic mild cognitive impairment (PDaMCI) are due to failure of retrieval or consolidation processes. Sixteen individuals with PDaMCI, 20 with amnestic mild cognitive impairment without PD (aMCINPD), and 20 healthy controls were recruited. Participants were administered the Free and Cued Selective Reminding Test. An index of cueing was computed for each subject to capture the advantage in retrieval of cued compared to free recall. Individuals with PDaMCI performed worse than healthy controls on the free recall (p<0.01) but not the cued recall (p>0.10) task, and they performed better than aMCINPD subjects on both recall measures (p<0.01). The index of cueing of subjects with PD was comparable to that of healthy controls (p>0.10) but it was significantly higher than that of the aMCINPD sample (p<0.01). Moreover, PD patients' performance on free recall trials was significantly predicted by scores on a test investigating executive functions (i.e., the Modified Card Sorting Test; p = 0.042). Findings of the study document that, in subjects with amnestic mild cognitive impairment associated to PD, episodic memory impairment is related to retrieval rather than to consolidation failure. The same data suggest that, in these individuals, memory deficits might be due to altered frontal-related executive functioning.

Neuropsychologic assessment in collaborative Parkinson's disease research: a proposal from the National Institute of Neurological Disorders and Stroke Morris K. Udall Centers of Excellence for Parkinson's Disease Research at the University of Pennsylvania and the University of Washington

Cognitive impairment (CI) and behavioral disturbances can be the earliest symptoms of Parkinson's disease (PD), ultimately afflict the vast majority of PD patients, and increase caregiver burden. Our two Morris K. Udall Centers of Excellence for Parkinson's Disease Research were supported by the National Institute of Neurological Disorders and Stroke (NINDS) in an effort to recommend a comprehensive yet practical approach to cognitive and behavioral assessment to further collaborative research. We recommend a stepwise approach with two levels of standardized evaluation to establish a common battery, as well as an alternative testing recommendation for severely impaired subjects, and review supplemental tests that may be useful in specific research settings. Our flexible approach may be applied to studies with varying emphasis on cognition and behavior, does not place undue burden on participants or resources, and has a high degree of compatibility with existing test batteries to promote collaboration.

Cognitive effects of dopamine depletion in the context of diminished acetylcholine signaling capacity in mice

A subset of patients with Parkinson’s disease acquires a debilitating dementia characterized by severe cognitive impairments (i.e. Parkinson’s disease dementia; PDD). Brains from PDD patients show extensive cholinergic loss as well as dopamine (DA) depletion. We used a mutant mouse model to directly test whether combined cholinergic and DA depletion leads to a cognitive profile resembling PDD. Mice carrying heterozygous deletion of the high-affinity, hemicholinium-3-sensitive choline transporter (CHT^HET) show reduced levels of acetylcholine throughout the brain. We achieved bilateral DA depletion in CHT^HET and wild-type (WT) littermates via intra-striatal infusion of 6-hydroxydopamine (6-OHDA), or used vehicle as control. Executive function and memory were evaluated using rodent versions of cognitive tasks commonly used with human subjects: the set-shifting task and spatial and novel-object recognition paradigms. Our studies revealed impaired acquisition of attentional set in the set-shifting paradigm in WT-6OHDA and CHT^HET-vehicle mice that was exacerbated in the CHT^HET-6OHDA mice. The object recognition test following a 24-hour delay was also impaired in CHT^HET-6OHDA mice compared with all other groups. Treatment with acetylcholinesterase (AChE) inhibitors physostigmine (0.05 or 0.1 mg/kg) and donepezil (0.1 and 0.3 mg/kg) reversed the impaired object recognition of the CHT^HET-6OHDA mice. Our data demonstrate an exacerbated cognitive phenotype with dual ACh and DA depletion as compared with either insult alone, with traits analogous to those observed in PDD patients. The results suggest that combined loss of DA and ACh could be sufficient for pathogenesis of specific cognitive deficits in PDD.

Clock test deficits related to the global cognitive state in Alzheimer's and Parkinson's disease

BACKGROUND/AIMS

Clock drawing (CD) seems to be impaired quite early in the process of cognitive decline in Parkinson's disease (PD).

METHODS

We assessed performance on the CD test (CDT), clock setting test (CST) and clock reading test (CRT) in 32 elderly healthy controls, 41 patients with PD, 23 patients with amnestic mild cognitive impairment (aMCI) and 40 patients with Alzheimer's dementia (AD). Our focus was on comparing the performance of PD and aMCI/AD patients in relation to their global cognitive states (operationalized by the Mini Mental Status Examination). We also analyzed qualitative differences in errors of drawing, setting and reading clocks.

RESULTS

We found that performance in CDT, but not in the CST or CRT, was impaired earlier in PD than in aMCI/AD. Incorrect placement of the minute hand was the most prominent error in both patient groups. We found no specific influence of visuospatial dysfunction in PD on clock drawing.

CONCLUSION

Our findings suggest that executive function related to retrieval of semantic memory about the minute hand is compromised early in PD.

Clinical differences among mild cognitive impairment subtypes in Parkinson's disease

Mild cognitive impairment is increasingly recognized as a construct in Parkinson's disease (PD) and occurs in about 25% of nondemented PD patients. Although executive dysfunction is the most frequent type of cognitive deficit in PD, the cognitive phenotype of PD mild cognitive impairment (PD-MCI) is broad. PD-MCI subtypes are represented by amnestic and nonamnestic domain impairment as well as single- and multiple-domain impairment. However, it is unclear whether patients with different PD-MCI subtypes also differ in other clinical characteristics in addition to cognitive profile. We studied 128 PD-MCI subjects at our Movement Disorders center, comparing clinical, motor, and behavioral characteristics across the PD-MCI subtypes. We found varying proportions of impairment subtypes: nonamnestic single domain, 47.7%; amnestic multiple domain, 24.2%; amnestic single domain, 18.8%; and nonamnestic multiple domain, 9.5%. Attentional/executive functioning and visuospatial abilities were the most frequently impaired domains. PD-MCI subtypes differed in their motor features, with nonamnestic multiple-domain PD-MCI subjects showing particularly pronounced problems with postural instability and gait. Differences among PD-MCI subtypes in age, PD duration, medication use, mood or behavioral disturbances, and vascular disease were not significant. Thus, in addition to differing cognitive profiles, PD-MCI subtypes differed in motor phenotype and severity but not in mood, behavioral, or vascular comorbidities. Greater postural instability and gait disturbances in the nonamnestic multiple-domain subtype emphasize shared nondopaminergic neural substrates of gait and cognition in PD. Furthermore, increased burden of cognitive dysfunction, rather than type of cognitive deficit, may be associated with greater motor impairment in PD-MCI.

Cognitive impairment and dementia in Parkinson's disease: clinical features, diagnosis, and management

Parkinson’s disease (PD) is a common, disabling, neurodegenerative disorder. In addition to classical motor symptoms, non-motor features are now widely accepted as part of the clinical picture, and cognitive decline is a very important aspect of the disease, as it brings an additional significant burden for the patient and caregivers. The diagnosis of cognitive decline in PD, namely mild cognitive impairment (MCI) and dementia, can be extremely challenging, remaining largely based on clinical and cognitive assessments. Diagnostic criteria and methods for PD dementia and MCI have been recently issued by expert work groups. This manuscript has synthesized relevant data in order to obtain a pragmatic and updated review regarding cognitive decline in PD, from milder stages to dementia. This text will summarize clinical features, diagnostic methodology, and therapeutic issues of clinical decline in PD. Relevant clinical genetic issues, including recent advances, will also be approached.

Entorhinal cortex atrophy differentiates Parkinson's disease patients with and without dementia

Volumetric measures of mesial temporal lobe structures on MRI scans recently have been explored as potential biomarkers of dementia in patients with PD, with investigations primarily focused on hippocampal volume. Both in vivo MRI and postmortem tissue studies in Alzheimer's disease, however, demonstrate that the entorhinal cortex (ERC) is involved earlier in disease-related pathology than the hippocampus. The ERC, a region integral in declarative memory function, projects multimodal sensory information to the hippocampus through the perforant path. In PD, ERC atrophy, as measured on MRI, however, has received less attention, compared to hippocampal atrophy. We compared ERC and hippocampal atrophy in 12 subjects with PD dementia including memory impairment, 14 PD subjects with normal cognition, and 14 healthy controls with normal cognition using manual segmentation methods on MRI scans. Though hippocampal volumes were similar in the two PD cognitive groups, ERC volumes were substantially smaller in the demented PD subjects, compared to cognitively normal PD subjects (P < 0.05). In addition, normalized ERC and hippocampal volumes for right and left hemispheres were significantly lower in the demented PD group, compared to healthy controls. Our findings suggest that ERC atrophy differentiates demented and cognitively normal PD subjects, in contrast to hippocampal atrophy. Thus, ERC atrophy on MRI may be a potential biomarker for dementia in PD, particularly in the setting of memory impairment.

Cognitive deficits in a mouse model of pre-manifest Parkinson's disease

Early cognitive deficits are increasingly recognized in patients with Parkinson's disease (PD), and represent an unmet need for the treatment of PD. These early deficits have been difficult to model in mice, and their mechanisms are poorly understood. α-Synuclein is linked to both familial and sporadic forms of PD, and is believed to accumulate in brains of patients with PD before cell loss. Mice expressing human wild-type α-synuclein under the Thy1 promoter (Thy1-aSyn mice) exhibit broad overexpression of α-synuclein throughout the brain and dynamic alterations in dopamine release several months before striatal dopamine loss. We now show that these mice exhibit deficits in cholinergic systems involved in cognition, and cognitive deficits in domains affected in early PD. Together with an increase in extracellular dopamine and a decrease in cortical acetylcholine at 4-6 months of age, Thy1-aSyn mice made fewer spontaneous alternations in the Y-maze and showed deficits in tests of novel object recognition (NOR), object-place recognition, and operant reversal learning, as compared with age-matched wild-type littermates. These data indicate that cognitive impairments that resemble early PD manifestations are reproduced by α-synuclein overexpression in a murine genetic model of PD. With high power to detect drug effects, these anomalies provide a novel platform for testing improved treatments for these pervasive cognitive deficits.

Predictors of HVOT performance in Parkinson's disease

Evidence suggests that the Hooper Visual Organization Test (HVOT) has naming and executive components that vary in size depending on neurological diagnosis. The current study used a sample of individuals with Parkinson's disease (PD) to demonstrate for the first time that an executive measure can be the best predictor of HVOT performance. Forty-eight nondemented and nondepressed individuals with idiopathic PD completed the HVOT and other measures of visuoperception, executive function, and visual confrontation naming. Despite average performance on all neuropsychological measures, an executive measure, time to complete Trail-Making Test Part B minus time to complete Part A, was clearly the best predictor of HVOT performance in a standard regression. The pattern of neurocognitive predictors is unlike that reported in healthy individuals and other patient samples. This finding suggests that the presence of a neuropathological process can alter neurocognitive correlates even when performance is intact, and supports the contention that executive function is paramount in the cognitive profile associated with PD.

Dysfunctions of cerebral networks precede recognition memory deficits in early Parkinson's disease

We aimed to investigate changes in the verbal recognition memory network in patients with early Parkinson's disease (PD) without overt recognition memory alteration. Verbal recognition memory was assessed in 24 PD patients in early stages of the disease and a control group of 24 healthy subjects during fMRI data acquisition. Participants were presented with a list of 35 words before imaging, and later during fMRI scanning they were required to recognize these previously presented words. Both model-based (FEAT) and model-free (MELODIC) analyses of the fMRI data were carried out with FSL software. Memory was also assessed by means of Rey's Auditory Verbal Learning Test (RAVLT). PD patients showed no difference in the fMRI recognition memory task and recognition memory assessed by the RAVLT compared to healthy controls. Model-based analysis did not show significant differences between groups. On the other hand, model-free analysis identified components that fitted the task-model and were common to all the participants, as well as components that differed between PD and healthy controls. PD patients showed decreased task-related activations in areas involved in the recognition memory network and decreased task-related deactivations in the default mode network in comparison with controls. In conclusion, model-free fMRI analysis detected alterations in functional cerebral networks involved in a verbal memory task in PD patients without evident recognition memory deficit.

Sharpening the boundaries of Parkinson-associated dementia: recommendation for a neuropsychological diagnostic procedure

Older adults suffering from Parkinson's disease (PD) frequently present with an additional form of severe neurodegenerative and/or vascular pathology. Findings of differential clinical manifestations of cognitive impairment, depending on presence and nature of such coexisting brain pathology, raise the question for neuropsychological procedures that are capable not only of distinguishing between non-demented PD patients and patients with Parkinson-associated dementia (PDD), but also of detecting other types of cognitive decline, most likely Alzheimer's disease (AD) or vascular dementia (VD), superimposing PD. The aim of this article is to review the literature on neuropsychological processes at risk in developing PDD, to introduce comorbid causes of cognitive decline in the presence of PD, to discuss the scope of the "cortical versus subcortical dementia"-concept in view of its capability of differentiating dementias, and to scrutinize existing diagnostic criteria concerning the toleration of comorbidity. Additionally, we derive an evidence-based neuropsychological diagnostic procedure for assessing PDD under special consideration of these comorbid aspects.

Impaired verbal memory in Parkinson disease: relationship to prefrontal dysfunction and somatosensory discrimination

Objective

To study the neurocognitive profile and its relationship to prefrontal dysfunction in non-demented Parkinson's disease (PD) with deficient haptic perception.

Methods

Twelve right-handed patients with PD and 12 healthy control subjects underwent thorough neuropsychological testing including Rey complex figure, Rey auditory verbal and figural learning test, figural and verbal fluency, and Stroop test. Test scores reflecting significant differences between patients and healthy subjects were correlated with the individual expression coefficients of one principal component, obtained in a principal component analysis of an oxygen-15-labeled water PET study exploring somatosensory discrimination that differentiated between the two groups and involved prefrontal cortices.

Results

We found significantly decreased total scores for the verbal learning trials and verbal delayed free recall in PD patients compared with normal volunteers. Further analysis of these parameters using Spearman's ranking correlation showed a significantly negative correlation of deficient verbal recall with expression coefficients of the principal component whose image showed a subcortical-cortical network, including right dorsolateral-prefrontal cortex, in PD patients.

Conclusion

PD patients with disrupted right dorsolateral prefrontal cortex function and associated diminished somatosensory discrimination are impaired also in verbal memory functions. A negative correlation between delayed verbal free recall and PET activation in a network including the prefrontal cortices suggests that verbal cues and accordingly declarative memory processes may be operative in PD during activities that demand sustained attention such as somatosensory discrimination. Verbal cues may be compensatory in nature and help to non-specifically enhance focused attention in the presence of a functionally disrupted prefrontal cortex.

Correlations between gray matter reductions and cognitive deficits in dementia with Lewy Bodies and Parkinson's disease with dementia

There is controversy regarding whether Dementia with Lewy Bodies (DLB) and Parkinson's disease with dementia (PDD) may or not be different manifestations of the same disorder. The purpose of the present study was to investigate possible correlations between brain structure and neuropsychological functions in clinically diagnosed patients with DLB and PDD. The study sample consisted of 12 consecutively referred DLB patients, 16 PDD patients, and 16 healthy control subjects recruited from an outpatient setting, who underwent MRI and neuropsychological assessment. Voxel-based morphometry results showed that DLB patients had greater gray matter atrophy in the right superior frontal gyrus, the right premotor area and the right inferior frontal lobe compared to PDD. Furthermore, the anterior cingulate and prefrontal volume correlated with performance on the Continuous Performance Test while the right hippocampus and amygdala volume correlated with Visual Memory Test in the DLB group. In conclusion, DLB patients had more fronto-temporal gray matter atrophy than PDD patients and these reductions correlated with neuropsychological impairment.