Memory Deficits in Parkinson’s Disease

Executive dysfunction and cognitive decline, a non-motor symptom of Parkinson's disease captured in animal models

The non-motor symptoms of Parkinson's disease (PD) have gained increasing attention in recent years due to their significant impact on patients' quality of life. Among these non-motor symptoms, cognitive dysfunction has emerged as an area of particular interest where the clinical aspects are covered in Chapter 2 of this volume. This chapter explores the rationale for investigating the underlying neurobiology of cognitive dysfunction by utilising translational animal models of PD, from rodents to non-human primates. The objective of this chapter is to review the various animal models of cognition that have explored the dysfunction in animal models of Parkinson's disease. Some of the more advanced pharmacological studies aimed at restoring these cognitive deficits are reviewed, although this chapter highlights the lack of systematic approaches in dealing with this non-motor symptom at the pre-clinical stages.

Neurocognitive Psychiatric and Neuropsychological Alterations in Parkinson's Disease: A Basic and Clinical Approach

The main histopathological hallmarks of Parkinson's disease (PD) are the degeneration of the dopaminergic neurons of the substantia nigra pars compacta and the loss of neuromelanin as a consequence of decreased dopamine synthesis. The destruction of the striatal dopaminergic pathway and blocking of striatal dopamine receptors cause motor deficits in humans and experimental animal models induced by some environmental agents. In addition, neuropsychiatric symptoms such as mood and anxiety disorders, hallucinations, psychosis, cognitive impairment, and dementia are common in PD. These alterations may precede the appearance of motor symptoms and are correlated with neurochemical and structural changes in the brain. This paper reviews the most crucial pathophysiology of neuropsychiatric alterations in PD. It is worth noting that PD patients have global task learning deficits, and cognitive functions are compromised in a way is associated with hypoactivation within the striatum, anterior cingulate cortex, and inferior frontal sulcus regions. An appropriate and extensive neuropsychological screening battery in PD must accurately assess at least five cognitive domains with some tests for each cognitive domain. This neuropsychological screening should consider the pathophysiological and clinical heterogeneity of cognitive dysfunction in PD.

Face name matching and memory complaints in Parkinson's disease

Objective

Memory impairment is a hallmark cognitive deficit in Parkinson's disease (PD). However, it remains unclear which processes underlie this deficit in PD. Also, little is known on these patients' subjective experiences of memory difficulties and their relationship with objective measures. We aim to portray memory deficits in PD by combining objective and subjective memory measures.

Methods

Fifteen PD patients and 15 controls were assessed with an extended version of the Face-Name Associative Memory Exam (FNAME) and the Memory Failures of Everyday Questionnaire (MFE-28). We also explored the relationship among clinical and cognitive variables.

Results

Participants with PD presented with more memory complaints. On the FNAME, these patients exhibited lower performance in free recall, as well as in name recognition and matching. Importantly, when controlling for initial learning, group effects disappeared, except for matching. Associative memory therefore was significantly compromised in PD and correlated with subjective memory complaints (SMC).

Conclusion

Our findings suggest that associative memory may constitute a sensitive measure to detect subtle memory deficits in PD. Moreover, the current study further clarifies the source of memory impairment in PD. Thus, our study highlights the clinical value of including associative memory tests such as the FNAME in PD neuropsychological assessment.

Standardized database of 400 complex abstract fractals

In experimental settings, characteristics of presented stimuli influence cognitive processes. Knowledge about stimulus features is important to manipulate or control the influence of stimuli. To date, there are a lack of standardized data incorporating such information for complex abstract stimuli. Thus, we provide norms for a database of 400 abstract and complex stimuli. Grey-scaled fractals were rated by 512 participants on the stimulus features of abstractness, animacy, verbalizability, complexity, familiarity, favorableness, and memorability. Moreover, 111 participants labeled the fractals, enabling us to calculate indices of naming agreement and modal names. Overall, the results confirmed high abstractness and low verbalizability of the provided stimuli. To establish external validation for selected stimulus features, we evaluated (a) classifier probability of a deep neural network labeling the fractals, negatively correlated with ratings of abstractness and positively with verbalizability and naming agreement; (b) data compression rate of fractal image files, positively correlated with the rating of complexity; and (c) performance of 212 participants in a recognition-memory task, positively correlated with the rating of memorability. The present work fills the gap of a standardized database for abstract stimuli and provides a database with valid norms for abstract and complex stimuli based on ratings and external validation measures. This database can be used to control and manipulate these stimulus features in experimental settings using abstract stimuli. Such a database is essential in experimental research using abstract stimuli for instance to control for verbal influence and strategy or to control for novelty and familiarity.

Development of a Parkinson's disease specific falls questionnaire

BACKGROUND

Falls are a major health burden for older adults with Parkinson's disease (PD), but there is currently no reliable questionnaire to capture the circumstances and consequences of falls in older adults with PD. This study aimed to develop a PD-specific falls questionnaire and to evaluate its test-retest reliability in older adults with PD.

METHODS

A novel PD-specific falls questionnaire (PDF-Q) was developed in two modes (online and paper-based version) and used to assess falls and near-falls events over the past 12-months. Questions were agreed upon by an expert group, with the domains based on previous falls-related questionnaires. The questions included the number and circumstances (activities, location and direction) of falls and near-falls, and consequences (injuries and medical treatment) of falls. The PDF-Q was distributed to 46 older adults with PD (online n = 30, paper n = 16), who completed the questionnaire twice, 4 weeks apart. Kappa (κ) statistics were used to establish test-retest reliability of the questionnaire items.

RESULTS

Pooled results from both questionnaires for all participants were used to assess the overall test-retest reliability of the questionnaire. Questions assessing the number of falls (κ = 0.41) and the number of near-falls (κ = 0.51) in the previous 12-months demonstrated weak agreement, while questions on the location of falls (κ = 0.89) and near-falls (κ = 1.0) demonstrated strong to almost perfect agreement. Questions on the number of indoor (κ = 0.86) and outdoor (κ = 0.75) falls demonstrated moderate to strong agreement, though questions related to the number of indoor (κ = 0.47) and outdoor (κ = 0.56) near-falls demonstrated weak agreement. Moderate to strong agreement scores were observed for the most recent fall and near-fall in terms of the direction (indoor fall κ = 0.80; outdoor fall κ = 0.81; near-fall κ = 0.54), activity (indoor fall κ = 0.70; outdoor fall κ = 0.82; near-fall κ = 0.65) and cause (indoor fall κ = 0.75; outdoor fall κ = 0.62; near-fall κ = 0.56).

CONCLUSIONS

The new PDF-Q developed in this study was found to be reliable for capturing the circumstances and consequences of recent falls and near-falls in older adults with PD.

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.

Correlation between alpha activity and neuropsychometric tests in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease that leads to memory impairment and executive and visuospatial dysfunction as the disease progresses. Alpha activity on EEG has been related to cognition in previous studies. We aimed to investigate the correlation between alpha activity and neuropsychometric tests (NPTs) in PD patients. Fifty-five idiopathic PD patients and 20 healthy controls were included. The Standardized Mini-Mental Test (SMMT), Verbal Learning Memory Test (VLMT), Wechsler Memory Scale (WMS), Stroop Color-Word Test, Categorical Verbal Fluency Test (CVFT), Benton's Face Recognition Test (BFR), and Benton Line Judgment Orientation Test (BLOT) were administered to all participants. Patients were separated into four groups according to NPT results: healthy controls (HC); PD patients with normal cognition (PDNC); PD patients with MCI (PDMCI); and PD patients with dementia (PDD). Analysis of the EEG data showed that HC had the highest alpha activity, and PDD had the lowest. High SMMT scores were correlated with high alpha activity at posterior electrode locations in all PD groups. VLMT and WMS test scores were associated with alpha activity at the parietal sites in PDMCI. VLMT, WMS, and CVFT test scores were correlated with alpha activity at parietooccipital sites in PDD. Verbal and visuospatial memory dysfunction related to low alpha activity was evident in both PDMCI and PDD, whereas executive dysfunction was more strongly associated with low alpha activity in PDD. Analysis of alpha activity could help clinicians predict the progression of cognitive dysfunction in PD patients.

Cognitive Rehabilitation for Individuals With Parkinson's Disease: Developing and Piloting an External Aids Treatment Program

Purpose Cognitive deficits are common in Parkinson's disease (PD) and can have a detrimental effect on daily activities. To date, most cognitive treatments have had an impairment-based focus with primary outcome measures of formal neuropsychological test scores. Few, if any, studies have focused on functional improvement or patient-centered goals. Method Three individuals with idiopathic PD participated in an 8-week pilot treatment program to train for the use of compensatory external aids to achieve personalized goals. Goal attainment scaling was the primary outcome measure, which was independently judged by multiple raters at baseline, postintervention, and 1 month posttreatment and analyzed via T-score analysis. Descriptive measures, including self-report and spouse-report rating scales of cognitive functioning, were employed. Results All 3 participants improved in the majority of their laboratory and home goals posttreatment, as measured by goal attainment scaling, and maintained gains for the majority of goals 1 month posttreatment. Conclusions This is the 1st known study to implement an external aids treatment program with patient-centered goals for individuals with cognitive deficits from PD. Positive outcomes were likely influenced by 3 factors: (a) a theoretically motivated focus on external aids; (b) a well-documented, systematic approach to instruction; and (c) the personalization of goals. Supplemental Material https://doi.org/10.23641/asha.10093493.

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.

Synaptic zinc contributes to motor and cognitive deficits in 6-hydroxydopamine mouse models of Parkinson's disease

Hyperactivity of glutamatergic corticostrial pathways is recognized as a key pathophysiological mechanism contributing to development of PD symptoms and dopaminergic neurotoxicity. Subset of corticostriatal projection neurons uses Zn²⁺ as a co-transmitter alongside glutamate, but the role of synaptically released Zn²⁺ in PD remains unexplored. We used genetically modified mice and pharmacological tools in combination with 6-hydroxydopamine (6-OHDA) lesion models of PD to investigate the contribution of synaptic zinc to disease associated behavioral deficits and neurodegeneration. Vesicular zinc transporter-3 (ZnT3) knockout mice lacking releasable Zn²⁺ were more resistant to locomotor deficit and memory impairment of nigrostriatal dopamine (DA) denervation compared to wildtype littermates. The loss of striatal dopaminergic fibers was comparable between genotypes, indicating that synaptically released Zn²⁺ contributes to behavioral deficits but not neurotoxic effects of 6-OHDA. To gain further insight into the mechanisms of Zn²⁺ actions, we used the extracellular Zn²⁺ chelator CaEDTA and knock-in mice lacking the high affinity Zn²⁺ inhibition of GluN2A-containing NMDA receptors (GluN2A-NMDARs). Acute chelation of extracellular Zn²⁺ in the striatum restored locomotor deficit of 6-OHDA lesion, confirming that synaptic Zn²⁺ suppresses locomotor behavior. Disruption of the Zn²⁺-GluN2A interaction had, on the other hand, no impact on locomotor deficit or neurotoxic effect of 6-OHDA. Collectively, these findings provide clear evidence for the implication of striatal synaptic Zn²⁺ in the pathophysiology of PD. They unveil that synaptic Zn²⁺ plays predominantly a detrimental role by promoting motor and cognitive deficits caused by nigrostriatal DA denervation, pointing towards new therapeutic interventions.

A meta-analytic review of prospection deficits in Parkinson's disease

Parkinson's disease (PD) is one of the most common neurodegenerative disorders, and is associated with prominent motor deficits. However, neurocognitive impairment is also a common clinical feature that can contribute greatly to the overall disease burden. In the current study, a meta-analysis was conducted to gain a clearer understanding of how PD affects one of the most functionally important domains of cognition: prospection. The results indicate that, relative to controls, PD is associated with a large deficit in the capacity to engage in planning (g = -0.81, K = 25) and a moderate-sized deficit in prospective memory (g = -0.57, K = 16). Sub-analyses indicated that these deficits are evident for both time and event-based prospective memory, as well as for prospective memory tasks that have relatively limited ecological validity. Significant impairment was also evident for both medicated and non-medicated PD sub-groups, but for planning, these deficits were substantially greater in the unmedicated sub-group. The theoretical and practical implications of these findings are discussed.

Spatial disorientation and executive dysfunction in elderly nondemented patients with Parkinson's disease

OBJECTIVES

Patients with Parkinson's disease (PD) present with a wide range of cognitive deficits. Cognitive impairment is recognized as an independent nonmotor aspect of the disorder and has a critical role in functional outcome and conversion into PD dementia. To date, everyday memory impairment in elderly patients with PD is underinvestigated and its relationship with executive dysfunction was not clearly explained. Our study aims at clarifying the neuropsychological pattern of everyday memory and executive deterioration in elderly patients with PD.

METHODS

Forty nondemented PD patients (mean age 71.2 years; M:F = 29:11) and 30 well-matched controls (mean age 70.7 years; M:F = 15:15) were assessed on everyday memory (Rivermead Behavioral Memory Test [RBMT]) and executive functioning (Frontal Assessment Battery [FAB]) measures. Mann-Whitney U-tests (Bonferroni corrected) were used to compare groups on these measures and Spearman's rank correlations were performed to highlight their associations.

RESULTS

PD patients performed worse than controls on recall for novel tasks and geographic recall (RMBT) as well as lexical fluency and mental flexibility (FAB). Particularly, spatial orientation depending on egocentric navigation seems to be altered in PD patients. The clinical group showed poorer performances than controls in mental flexibility, sensitivity to interference, and inhibitory control. Such measures were associated with immediate and delayed recall, picture recognition, prospective memory, and orientation tasks of everyday memory.

CONCLUSION

Executive-type difficulties and memory-type difficulties have an impact on cognitive performances of elderly patients with PD. We recommend using the RBMT and the FAB as part of routinely neuropsychological battery for assessing PD patients.

Impairment in the Intention Formation and Execution Phases of Prospective Memory in Parkinson's Disease

Objective: Patients with Parkinson's disease have prospective memory impairments. However, little is known about distinct phases of prospective memory in these patients. This study was designed to elucidate the specific phase(s) of prospective memory that are impaired in patients with Parkinson's disease. Methods: The study included 31 Parkinson's disease patients and 27 healthy controls. The four phases of prospective memory (intention formation, retention, initiation, and execution) were examined in a complex prospective memory task. In this task, the participants were asked to form a sophisticated plan for performing six subtasks to obtain the highest score, and then execute the plan following a cue embedded in a questionnaire. Global cognitive function and relevant cognitive abilities, including attention, short-term memory, working memory, and inhibition, were also evaluated during the retention phase of the prospective memory task. Results: Intention formation was impaired in Parkinson's disease patients (p < 0.001 vs. healthy controls). This impairment could not be attributed to deficits in other cognitive functions. The score of intention execution was also lower in Parkinson's disease patients (p = 0.004 vs. healthy controls). Such a difference was related to working memory deficits in Parkinson's disease. The intention retention and initiation were intact in Parkinson's disease patients. The score of intention execution correlated negatively with disease severity and disease duration. Conclusions: Prospective memory in Parkinson's disease patients is impaired at the phase of intention formation. The worsening performance of intention execution in Parkinson's disease may be related to working memory deficits. In addition, prospective memory impairment might progress with increasing disease duration and severity.

Increased brain connectivity and activation after cognitive rehabilitation in Parkinson's disease: a randomized controlled trial

Cognitive rehabilitation programs have demonstrated efficacy in improving cognitive functions in Parkinson's disease (PD), but little is known about cerebral changes associated with an integrative cognitive rehabilitation in PD. To assess structural and functional cerebral changes in PD patients, after attending a three-month integrative cognitive rehabilitation program (REHACOP). Forty-four PD patients were randomly divided into REHACOP group (cognitive rehabilitation) and a control group (occupational therapy). T1-weighted, diffusion weighted and functional magnetic resonance images (fMRI) during resting-state and during a memory paradigm (with learning and recognition tasks) were acquired at pre-treatment and post-treatment. Cerebral changes were assessed with repeated measures ANOVA 2 × 2 for group x time interaction. During resting-state fMRI, the REHACOP group showed significantly increased brain connectivity between the left inferior temporal lobe and the bilateral dorsolateral prefrontal cortex compared to the control group. Moreover, during the recognition fMRI task, the REHACOP group showed significantly increased brain activation in the left middle temporal area compared to the control group. During the learning fMRI task, the REHACOP group showed increased brain activation in the left inferior frontal lobe at post-treatment compared to pre-treatment. No significant structural changes were found between pre- and post-treatment. Finally, the REHACOP group showed significant and positive correlations between the brain connectivity and activation and the cognitive performance at post-treatment. This randomized controlled trial suggests that an integrative cognitive rehabilitation program can produce significant functional cerebral changes in PD patients and adds evidence to the efficacy of cognitive rehabilitation programs in the therapeutic approach for PD.

Cognitive sequelae of methanol poisoning involve executive dysfunction and memory impairment in cross-sectional and long-term perspective

Methanol poisoning leads to lesions in the basal ganglia and subcortical white matter, as well as to demyelination and atrophy of the optic nerve. However, information regarding cognitive deficits in a large methanol sample is lacking. The principal aim of the present study was to identify the cognitive sequelae of methanol poisoning and their morphological correlates. A sample of 50 patients (METH; age 48 ± 13 years), 3-8 months after methanol poisoning, and 57 control subjects (CS; age 49 ± 13 years) were administered a neuropsychological battery. Forty-six patients were followed in 2 years' perspective. Patients additionally underwent 1.5T magnetic resonance imaging (MRI). Three biochemical and toxicological metabolic markers and a questionnaire regarding alcohol abuse facilitated the classification of 24 patients with methanol poisoning without alcohol abuse (METHna) and 22 patients with methanol poisoning and alcohol abuse (METHa). All groups were compared to a control group of similar size, and matched for age, education, premorbid intelligence level, global cognitive performance, and level of depressive symptoms. Using hierarchical multiple regression we found significant differences between METH and CS, especially in executive and memory domains. METHa showed a similar pattern of cognitive impairment with generally more severe executive dysfunction. Moreover, all METH patients with extensive involvement on brain MRI (lesions in ≥2 anatomical regions) had a more severe cognitive impairment. From a longitudinal perspective, we did not find any changes in their cognitive functioning after 2 years' follow-up. Our findings suggest that methanol poisoning is associated with executive dysfunction and explicit memory impairment, supposedly due to basal ganglia dysfunction and disruption of frontostriatal circuitry proportional to the number of brain lesions, and that these changes are persistent after 2 years' follow-up.

Partial lesion of the nigrostriatal dopamine pathway in rats impairs egocentric learning but not spatial learning or behavioral flexibility

Degeneration of the nigrostriatal dopaminergic system in Parkinson's disease (PD) causes motor dysfunction and cognitive impairment, but the etiology of the cognitive deficits remains unclear. The present study investigated the behavioral effects of partial lesions of the nigrostriatal dopamine (DA) pathway. Rats received bilateral infusions of either 6-hydroxydopamine (6-OHDA) or vehicle into the dorsolateral striatum and were tested in spatial and procedural learning tasks. Compared with intact rats, DA-depleted rats were impaired when the first task they learned required egocentric responses. Intact rats that received prior training on a spatial task were impaired while learning a subsequent body-turn task, suggesting that prior spatial training may compete with egocentric learning in intact but not DA-depleted rats. Spatial discrimination, reversal learning, and switching between allocentric and egocentric strategies were similar in both groups. The results suggest that DA loss that is not associated with gross motor pathology temporarily impairs egocentric, but not allocentric, learning or subsequent behavioral flexibility. (PsycINFO Database Record

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.

Screening for Cognitive Impairment in Parkinson's Disease: Improving the Diagnostic Utility of the MoCA through Subtest Weighting

Background

Given the high prevalence of cognitive impairment in Parkinson’s disease (PD), cognitive screening is important in clinical practice. The Montreal Cognitive Assessment (MoCA) is a frequently used screening test in PD to detect mild cognitive impairment (PD-MCI) and Parkinson’s disease dementia (PD-D). However, the proportion in which the subtests are represented in the MoCA total score does not seem reasonable. We present the development and preliminary evaluation of an empirically based alternative scoring system of the MoCA which aims at increasing the overall diagnostic accuracy.

Methods

In study 1, the MoCA was administered to 40 patients with PD without cognitive impairment (PD-N), PD-MCI, or PD-D, as defined by a comprehensive neuropsychological test battery. The new MoCA scoring algorithm was developed by defining Areas under the Curve (AUC) for MoCA subtests in a Receiver Operating Characteristic (ROC) and by weighting the subtests according to their sensitivities and specificities. In study 2, an independent sample of 24 PD patients (PD-N, PD-MCI, or PD-D) was tested with the MoCA. In both studies, diagnostic accuracy of the original and the new scoring procedure was calculated.

Results

Diagnostic accuracy increased with the new MoCA scoring algorithm. In study 1, the sensitivity to detect cognitive impairment increased from 62.5% to 92%, while specificity decreased only slightly from 77.7% to 73%; in study 2, sensitivity increased from 68.8% to 81.3%, while specificity stayed stable at 75%.

Conclusion

This pilot study demonstrates that the sensitivity of the MoCA can be enhanced substantially by an empirically based weighting procedure and that the proposed scoring algorithm may serve the MoCA’s actual purpose as a screening tool in the detection of cognitive dysfunction in PD patients better than the original scoring of the MoCA. Further research with larger sample sizes is necessary to establish efficacy of the alternate scoring system.

Self-awareness of memory impairment in Parkinson’s disease: a review of the literature

Purpose

– The purpose of this paper is to review and provide information on the small but growing body of literature that demonstrates that some people with Parkinson’s disease (PD) are unaware of the memory impairment, and this has clinical implications for how family members care for their loved one, and how clinical staff and others may interact with them on a day-to-day perspective.

Design/methodology/approach

– The approach takes the form of a general review.

Findings

– People with PD experience a variety of cognitive impairment including deficits in memory and higher level executive processes. Impairment in these areas can occur early in the disease course and result in adverse consequences including distractibility, trouble recalling information, and problems remembering to execute planned actions like adhering to medication regimes. The literature also suggests heterogeneity in both the memory performance of people with PD and in the definition of awareness used to investigate this phenomenon.

Practical implications

– Strategies for remembering may be of practical importance for people with PD, and/or caregivers should be introduced and educated to the nature of memory impairment in PD, as well as its likely course and natural progression in a non-threatening way before they are later instructed on “tips” for maximising daily functioning as more severe cognitive deficits begin to appear.

Originality/value

– This paper adds to the small body of literature that investigates patients’ awareness of memory impairment in PD and advocates for ongoing research within the area.

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.

The neurotoxin 1-methyl-4-phenylpyridinium (MPP(+)) alters hippocampal excitatory synaptic transmission by modulation of the GABAergic system

The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induces Parkinson's disease-like symptoms following administration to mice, monkeys, and humans. A common view is that MPTP is metabolized to 1-methyl-4-phenylpyridinium ion (MPP(+)) to induce its neurodegenerative effects on dopaminergic neurons in the substantia nigra (SN). Moreover, the hippocampus contains dopaminergic fibers, which are projecting from the ventral tegmental area, SN and pars compacta and contain the whole machinery required for dopamine synthesis making them sensitive to MPTP and MPP(+). Here, we present data showing that acute bath-application of MPP(+) elicited a dose-dependent facilitation followed by a depression of synaptic transmission of hippocampal Schaffer collaterals-CA1 synapses in mice. The effects of MPP(+) were not mediated by D1/D5- and D2-like receptor activation. Inhibition of the dopamine transporters did not prevent but increased the depression of excitatory post-synaptic field potentials. In the search for a possible mechanism, we observed that MPP(+) reduced the appearance of polyspikes in population spikes recorded in str. pyramidale and increased the frequency of miniature inhibitory post-synaptic currents. The acute effect of MPP(+) on synaptic transmission was attenuated by co-application of a GABAA receptor antagonist. Taking these data together, we suggest that MPP(+) affects hippocampal synaptic transmission by enhancing some aspects of the hippocampal GABAergic system.

Event-based prospective memory in patients with Parkinson's disease: the effect of emotional valence

The present study investigated the effect of Parkinson’s disease (PD) on prospective memory (PM) tasks by varying the emotional content of the PM actions. Twenty-one older adults with PD and 25 healthy older adults took part in the present study. Participants performed three virtual days in the Virtual Week task. On each virtual day, participants performed actions with positive, negative or neutral content. Immediately following each virtual day, participants completed a recognition task to assess their retrospective memory for the various PM tasks. PD patients were less accurate than the control group at both PM accuracy and recognition task accuracy. The effect of emotional valence was also evident, indicating that all participants were more accurate on positive PM tasks than both negative and neutral. This study confirmed PM impairment in PD patients and extended previous research showing how positive emotional stimuli can influence PM performance.

Parkinson's disease dementia: a neural networks perspective

In the long-term, with progression of the illness, Parkinson's disease dementia affects up to 90% of patients with Parkinson's disease. With increasing life expectancy in western countries, Parkinson's disease dementia is set to become even more prevalent in the future. However, current treatments only give modest symptomatic benefit at best. New treatments are slow in development because unlike the pathological processes underlying the motor deficits of Parkinson's disease, the neural mechanisms underlying the dementing process and its associated cognitive deficits are still poorly understood. Recent insights from neuroscience research have begun to unravel the heterogeneous involvement of several distinct neural networks underlying the cognitive deficits in Parkinson's disease dementia, and their modulation by both dopaminergic and non-dopaminergic transmitter systems in the brain. In this review we collate emerging evidence regarding these distinct brain networks to give a novel perspective on the pathological mechanisms underlying Parkinson's disease dementia, and discuss how this may offer new therapeutic opportunities.

Virtual multiple errands test (VMET): a virtual reality-based tool to detect early executive functions deficit in Parkinson's disease

INTRODUCTION

Several recent studies have pointed out that early impairment of executive functions (EFs) in Parkinson's Disease (PD) may be a crucial marker to detect patients at risk for developing dementia. The main objective of this study was to compare the performances of PD patients with mild cognitive impairment (PD-MCI) with PD patients with normal cognition (PD-NC) and a control group (CG) using a traditional assessment of EFs and the Virtual Multiple Errands Test (VMET), a virtual reality (VR)-based tool. In order to understand which subcomponents of EFs are early impaired, this experimental study aimed to investigate specifically which instrument best discriminates among these three groups.

MATERIALS AND METHODS

The study included three groups of 15 individuals each (for a total of 45 participants): 15 PD-NC; 15 PD-MCI, and 15 cognitively healthy individuals (CG). To assess the global neuropsychological functioning and the EFs, several tests (including the Mini Mental State Examination (MMSE), Clock Drawing Test, and Tower of London test) were administered to the participants. The VMET was used for a more ecologically valid neuropsychological evaluation of EFs.

RESULTS

Findings revealed significant differences in the VMET scores between the PD-NC patients vs. the controls. In particular, patients made more errors in the tasks of the VMET, and showed a poorer ability to use effective strategies to complete the tasks. This VMET result seems to be more sensitive in the early detection of executive deficits because these two groups did not differ in the traditional assessment of EFs (neuropsychological battery).

CONCLUSION

This study offers initial evidence that a more ecologically valid evaluation of EFs is more likely to lead to detection of subtle executive deficits.

Relation between Olfactory Dysfunction and Episodic Verbal Memory in Early Parkinson's Disease

INTRODUCTION

Olfactory dysfunction is an early and common symptom in idiopathic Parkinson's disease (IPD). Recently, the relation between olfactory dysfunction and cognitive loss in IPD has been reported. In our study, we aimed to investigate the relation between olfactory dysfunction and cognitive impairments in early IPD related with this theory.

METHODS

In this study, we included 28 patients with stage 1 and stage 2 IPD according to the Hoehn-Yahr (H-Y) scale and 19 healthy participants. The University of Pennsylvania Smell Identification Test (UPSIT) was performed for evaluating olfactory function. For cognitive investigation in participants, the clock drawing test, Stroop test, verbal fluency test, Benton face recognition test (BFR), Benton line judgment orientation test (BLO), and Auditory Verbal Learning Test (AVLT) were performed.

RESULTS

We found significantly lower UPSIT scores in the patient group compared to controls (p=.018). In the neuropsychological investigation, only Stroop test and BLOT test scores were significantly lower in the patient group compared to controls (p=.003, p=.002, respectively). We found a negative correlation between UPSIT scores and Stroop time (p=.033) and Stroop error (p=.037) and a positive correlation between UPSIT scores and SBST long-term memory scores (p=.016) in patients.

CONCLUSION

In our study, we found mild cognitive impairment related with visuospatial and executive functions in early-stage IPD compared to controls. But, in the patient group, we detected a different impairment pattern of memory and frontal functions that correlated with hyposmia. This different pattern might be indicating a subgroup of IPD characterized by low performance in episodic verbal memory, with accompanying olfactory dysfunction in the early stage.

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.

Prospective memory in Parkinson's disease: a meta-analysis

Prospective memory (PM) refers to the ability to remember to carry out an intended action in the future and it is pervasive in our daily living. A failure to execute an intended action (e.g., take medication) at the appropriate juncture in future (e.g., after dinner) can negatively affect our daily functioning and at times, may have devastating effects (e.g., forgetting to turn off the gas stove before leaving the house). Patients with Parkinson's disease (PD) exhibit widespread cognitive deficits including deficits in PM. The present study provides a meta-analytic review of PM in PD. Results across nine studies indicated time and event-based PM to be similarly impaired in PD, with time-based PM compromised to a slightly larger extent (Hedges' g = -0.71) as compared to event-based PM (Hedges' g = -0.55). The impairment in PM is more likely due to failure in self-initiated retrieval of intention to be executed, rather than forgetting the content of the intention itself. Furthermore, factors such as intervening task complexity and the mediating role of other executive functions have also been proposed to be responsible for impaired PM in PD.

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.

Subjective states associated with retrieval failures in Parkinson's disease

Instances in which we cannot retrieve information immediately but know that the information might be retrieved later are subjective states that accompany retrieval failure. These are expressed in feeling-of-knowing (FOK) and Tip-of-the-tongue (TOT) experiences. In Experiment 1, participants with Parkinson's disease (PD) and older adult controls were given general questions and asked to report when they experienced a TOT state and to give related information about the missing word. The PD group experienced similar levels of TOTs but provided less correct peripheral information related to the target when in a TOT state. In Experiment 2, participants were given a Semantic (general knowledge questions) and an Episodic (word pairs) FOK task. PD patients failed to accurately predict their future memory performance (FOK) in response to both episodic and semantic cues. Results are interpreted in the context of recent frameworks of memory and metacognition.

Autobiographical memory in Parkinson's disease: a retrieval deficit

This study examined the effects of providing cues to facilitate autobiographical memory retrieval in Parkinson's disease. Previous findings have shown that individuals with Parkinson's disease retrieve fewer specific autobiographical memories than older adult controls. These findings are clinically significant since the quality of autobiographical memory is linked to identity and sense of self. In the current study, 16 older adults with Parkinson's disease without dementia and 16 matched older adult controls were given 3 min in which to recall autobiographical memories associated with five different time periods and to give each memory a short title. Participants were later asked to retrieve the memories in three phases: firstly in a free recall phase; secondly in response to general cues (time periods) and finally in response to specific cues (the short titles previously given). The number of memories and the quality of the memory (general or specific) was recorded in each condition. Compared with matched older adult controls, the Parkinson's disease group was impaired in retrieving the memories that they had previously given in the free recall phase and in response to general cues. The performance of the group with Parkinson's disease was only equivalent to the older adults when they retrieved memories in response to self-generated cues. The findings are discussed in relation to theories of autobiographical memory and the neuropsychology of Parkinson's disease.

Diagnostic and screening power of neuropsychological testing in detecting mild cognitive impairment in Parkinson's disease

Prevalence of mild cognitive impairment (MCI) in Parkinson's disease (PD) is variable likely due to methodological differences in classification criteria and lack of consensus about neuropsychological tests used for cognitive profiling. The main objective of our study was to identify the most suitable neuropsychological tests and determine their screening and diagnostic cutoff scores for PD-MCI. A series of 104 consecutive PD patients performed an extensive neuropsychological evaluation. Individual test values were converted into Z-scores using relative published normative data. According to published criteria, PD patients were categorized as PD-CNT (PD without cognitive impairment), PD-MCI (patients performing -1.5 SDs below the mean score in at least one cognitive domain), and PDD. We used receiver operating characteristic (ROC) curves and K-means clustering analyses to calculate the best discriminating power of each neuropsychological tests in detecting PD-MCI. PD patients were categorized as follows: 55 PD-CNT (53 %), 34 PD-MCI (33 %), and 15 PDD (14 %). PD-MCI had lower education, longer disease duration and greater frequency of hallucinations than PD-CNT. We found that only the Trail Making test, Rey-Osterrieth Complex Figure Test (ROCF) copy, Frontal Assessment Battery (FAB), Digit Span Backward, and Rey's word auditory verbal learning test (RVLT) immediate recall reached significant screening and diagnostic validity in predicting PD-MCI (AUC 0.705-0.795) with cutoff scores calculated by ROC analyses lying within normal range for normative data. Specific neuropsychological tests covering verbal memory, attention/set-shifting, and visual-spatial deficits are the best predictors of MCI in PD if valid cutoff scores are used. These results have consequences for cognitive diagnosis and potentially in establishing the rate of PD cognitive decline.

The epidemiology and clinical manifestations of dysexecutive syndrome in Parkinson's disease

This mini-review summarizes the evidence of the cognitive and behavioral features of dysexecutive syndrome in Parkinson’s disease (PD). Deficits in response inhibition, set-shifting, mental flexibility, and strategy have been frequently described from the earliest stages of PD, although there are inconsistencies in study findings due to the complexity of the executive function (EF) construct and methodological limitations. Behavioral disorders of PD, e.g., apathy, distractibility, perseverative behavior, and impulse-control disorders, may be viewed as the other side of dysexecutive syndrome. Despite the interrelationship between the cognitive and behavioral domains, some reports reveal that the two syndromes may be dissociated, suggesting that both aspects must be clinically assessed. EFs are widely associated with the prefrontal areas, although dysexecutive syndrome may be observed in patients with damage to other brain regions. EFs drive numerous abilities essential to daily life, such as prospective remembering and language comprehension, which may be impaired in PD subjects. Considering the impact of dysexecutive syndrome on independence and quality of life, early detection of executive impairment is crucial in the management of PD.

Metacognitive Performance, the Tip-of-Tongue Experience, Is Not Disrupted in Parkinsonian Patients

The present study investigated whether a form of metamemory, the tip-of-tongue phenomenon (TOT), was affected in patients with Parkinson's disease (PD). The PD patient (n = 22), age-matched elderly control (n = 22), and college student control (n = 46) groups were compared on a motor timing task and TOT measures. Motor timing was assessed using a cued hand-clapping task, whereas TOT was assessed using general knowledge questions. The results indicated that motor timing was significantly impaired in the PD group relative to both control groups. However, all of the TOT metacognitive measures: frequency, strength, and accuracy were statistically equivalent between the PD patients and elderly control groups, both of whom showed significantly better memory performance than college controls. These findings demonstrate that TOT metamemory is not compromised in PD patients, and that further insight into TOT mechanisms in PD may prove helpful in developing novel intervention strategies to enhance memory and general cognitive functions in these patients.

Cognitive impairment and dementia in Parkinson's disease

Relatively subtle cognitive disturbances may be present from the initial stages of Parkinson's disease (PD) that progress in many patients to a more severe cognitive impairment and dementia. Several of the initial deficits are ascribed to failure in the frontal-striatal basal ganglia circuits and involve executive defects in planning, initiation, monitoring of goal-directed behaviors and working-memory. Other non-demented PD patients also exhibit visuospatial and memory deficits more representative of posterior cortical functioning and fail performing naming or copying tasks. Major differences in the overall rate of cognitive decline among PD patients support the co-existence of at least two patterns of involution, differentiating a relatively slow decline of fronto-striatal deficits from a more rapid decline of posterior-cortical deficits, with different pathophysiological substrates, genetics, prognosis and response to drugs used to treat the motor symptoms of PD.

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.

Event-based prospective memory in newly diagnosed, drug-naive Parkinson's disease patients

The present study investigated memory for intention in individuals with Parkinson's disease (PD) who were newly diagnosed and not yet treated to avoid the effect of therapy as a potential confounding variable. A comprehensive neuropsychological battery and an event-based prospective memory task were administered to 41 subjects with de novo PD and 40 control subjects. Separate scores were computed for correct execution of intended action (prospective component) and recall of intention (retrospective component). PD patients performed marginally worse (p = .053) than controls on the prospective component of the task. On the other hand, the performance of the two groups was comparable for the retrospective component. Neuropsychological findings revealed lower performance of the PD group in episodic memory and in some measures of executive functions. These results suggested a subtle prospective memory dysfunction present at the initial stage of PD, which may be related to disruption of fronto-striatal circuitry.

Mild cognitive impairment in Parkinson's disease

Prospective studies conducted during the last decade have shown that the majority of patients with Parkinson's disease (PD) develop dementia. In addition, using a variety of definitions and methods, more recent research suggests that approximately a quarter of PD patients without dementia have mild cognitive impairment (PD-MCI). Furthermore, several studies have shown that approximately 20% have MCI even at time of diagnosis of PD. The typical cognitive deficits include visuospatial, attentional, and executive deficits, but memory deficits have also been shown. The etiology of PD-MCI is not known, but it is likely that mechanisms known to contribute to dementia in PD (ie, limbic and cortical Lewy bodies, amyloid plaques, and cholinergic deficits) play a role, in addition to dysfunction of dopaminergic frontostriatal circuits. PD-MCI predicts a shorter time to dementia, and preliminary evidence suggests that this is particularly true for posterior cognitive deficits. There are currently no systematic clinical trials in PD-MCI.

The role of the basal ganglia in learning and memory: insight from Parkinson's disease

It has long been known that memory is not a single process. Rather, there are different kinds of memory that are supported by distinct neural systems. This idea stemmed from early findings of dissociable patterns of memory impairments in patients with selective damage to different brain regions. These studies highlighted the role of the basal ganglia in non-declarative memory, such as procedural or habit learning, contrasting it with the known role of the medial temporal lobes in declarative memory. In recent years, major advances across multiple areas of neuroscience have revealed an important role for the basal ganglia in motivation and decision making. These findings have led to new discoveries about the role of the basal ganglia in learning and highlighted the essential role of dopamine in specific forms of learning. Here we review these recent advances with an emphasis on novel discoveries from studies of learning in patients with Parkinson's disease. We discuss how these findings promote the development of current theories away from accounts that emphasize the verbalizability of the contents of memory and towards a focus on the specific computations carried out by distinct brain regions. Finally, we discuss new challenges that arise in the face of accumulating evidence for dynamic and interconnected memory systems that jointly contribute to learning.

Cognitive impairment in nondemented Parkinson's disease

A substantial percentage of patients with newly diagnosed Parkinson's disease without dementia are reported to be affected by cognitive impairment (CI). In practice, however, CI is underrecognized, as the signs may not be apparent in early-stage disease and many routine assessment tools lack the sensitivity to detect subtle cognitive dysfunction. Patients with PD and mild CI (MCI) may have a higher risk of developing dementia than cognitively intact PD patients; however, it is not currently known which patients with CI are at increased risk of developing dementia. This review summarizes current knowledge about CI in nondemented PD; it discusses the structural and functional changes associated with CI and addresses areas of unmet needs. We focus on questions that should be addressed in future studies to achieve consensus on its characteristics and definition, pathophysiology, epidemiology, diagnosis and assessment, and treatment and management.

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.