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

Improving Visual Working Memory with Cholinergic Deep Brain Stimulation

Acetylcholine is a critical modulatory neurotransmitter for cognitive function. Cholinergic drugs improve cognitive performance and enhance neuronal activity in the sensory and association cortices. An alternative means of improving cognitive function is through the use of deep brain stimulation. Prior animal studies have demonstrated that stimulation of the nucleus basalis of Meynert through DBS improves cognitive performance on a visual working memory task to the same degree as cholinesterase inhibitors. Additionally, unlike current pharmacological treatments for neurocognitive disorders, DBS does not lose efficacy over time and adverse effects are rare. These findings suggest that DBS may be a promising alternative for treating cognitive impairments in neurodegenerative disorders such as Alzheimer's disease. Thus, further research and human trials should be considered to assess the potential of DBS as a therapeutic treatment for these disorders.

Neural and behavioral evidence supporting the relationship between habitual exercise and working memory precision in healthy young adults

Introduction

Working memory (WM) is a well-known fundamental ability related to various high-level cognitive functions, such as executive functioning, decision-making, and problem-solving. Although previous studies have posited that chronic exercise may improve cognitive functions, its underlying neural mechanisms and whether habitual exercise is associated with individual WM ability remain unclear.

Methods

In the current study, 36 participants reported their habitual physical activity through the International Physical Activity Questionnaire (IPAQ). In addition to assessments of intelligence quotient (IQ), WM storage capacity (K score), and visuomotor coordination capacity, electroencephalogram (EEG) signals were recorded while the participants performed a WM precision task fusing conventional visual and motor retrospective cue (retro-cue) WM tasks.

Results

We found that greater amounts of and higher frequencies of vigorous-intensity exercise were highly correlated with smaller recall errors in the WM precision task. Contralateral delay activity (CDA), a well-known WM-related event-related potential (ERP) component evoked by the valid retro-cue, predicted individual behavioral recall error. Participants who met the medium or high level of IPAQ criteria (the regular exercise group) showed smaller behavioral recall error and larger CDA than participants who did not meet the criteria (the irregular exercise group). The two groups did not differ in other assessments, such as IQ, WM storage capacity, and visuomotor coordination ability.

Discussion

Habitual exercise was specifically correlated with individual differences in WM precision, rather than IQ, WM storage capacity, and visuomotor coordination ability, suggesting potential mechanisms of how modulations of chronic exercise improve cognition through visual and/or motor WM precision.

Neuropsychology of posteromedial parietal cortex and conversion factors from Mild Cognitive Impairment to Alzheimer's disease: systematic search and state-of-the-art review

In the present review, we discuss the rationale and the clinical implications of assessing visuospatial working memory (VSWM), awareness of memory deficits, and visuomotor control in patients with mild cognitive impairment (MCI). These three domains are related to neural activity in the posteromedial parietal cortex (PMC) whose hypoactivation seems to be a significant predictor of conversion from MCI to Alzheimer’s disease (AD) as indicated by recent neuroimaging evidence. A systematic literature search was performed up to May 2021. Forty-eight studies were included: 42 studies provided analytical cross-sectional data and 6 studies longitudinal data on conversion rates. Overall, these studies showed that patients with MCI performed worse than healthy controls in tasks assessing VSWM, awareness of memory deficits, and visuomotor control; in some cases, MCI patients’ performance was comparable to that of patients with overt dementia. Deficits in VSWM and metamemory appear to be significant predictors of conversion. No study explored the relationship between visuomotor control and conversion. Nevertheless, it has been speculated that the assessment of visuomotor abilities in subjects at high AD risk might be useful to discriminate patients who are likely to convert from those who are not. Being able to indirectly estimate PMC functioning through quick and easy neuropsychological tasks in outpatient settings may improve diagnostic and prognostic accuracy, and therefore, the quality of the MCI patient’s management.

Structural MRI of the basal forebrain as predictor of cognitive response to galantamine in healthy older adults-A randomized controlled double-blinded crossover study

INTRODUCTION

Cholinesterase inhibitors can enhance cognitive functions in healthy elderly and delay cognitive decline in patients with Alzheimer`s disease (AD). However, not everyone benefits from this treatment (non-responders). Current studies show clinical meaningful improvements only in one third of AD patients treated with cholinesterase inhibitors.

METHODS

Here we investigate structural magnetic resonance imaging of the basal forebrain cholinergic system volume (BFvol) as a potential predictor of cognitive response to a single dose of galantamine in healthy adults (n = 18; 59 to 75 years).

RESULTS

We observed that the cognitive response to galantamine, more specifically the attention-dependent filtering performance in a delayed match-to-sample working memory task, correlated with BFvol: Only participants with high BFvol showed a significant positive effect of galantamine on the ability to filter out distracting information during the working memory encoding process.

DISCUSSION

Future studies need to assess whether BFvol may serve as a predictor of the galantamine response in AD patients, too.

From the Gut to the Brain and Back: Therapeutic Approaches for the Treatment of Network Dysfunction in Parkinson's Disease

Parkinson's disease (PD) is a complex, multisystem, progressive, degenerative disorder characterized by severe, debilitating motor dysfunction, cognitive impairments, and mood disorders. Although preclinical research has traditionally focused on the motor deficits resulting from the loss of nigrostriatal dopaminergic neurons, up to two thirds of PD patients present separate and distinct behavioral changes. Loss of basal forebrain cholinergic neurons occurs as early as the loss of dopaminergic cells and contributes to the cognitive decline in PD. In addition, attentional deficits can limit posture control and movement efficacy caused by dopaminergic cell loss. Complicating the picture further is intracellular α-synuclein accumulation beginning in the enteric nervous system and diffusing to the substantia nigra through the dorsal motor neurons of the vagus nerve. It seems that α-synuclein's role is that of mediating dopamine synthesis, storage, and release, and its function has not been completely understood. Treating a complex, multistage network disorder, such as PD, likely requires a multipronged approach. Here, we describe a few approaches that could be used alone or perhaps in combination to achieve a greater mosaic of behavioral benefit. These include (1) using encapsulated, genetically modified cells as delivery vehicles for administering neuroprotective trophic factors, such as GDNF, in a direct and sustained means to the brain; (2) immunotherapeutic interventions, such as vaccination or the use of monoclonal antibodies against aggregated, pathological α-synuclein; (3) the continuous infusion of levodopa-carbidopa through an intestinal gel pad to attenuate the loss of dopaminergic function and manage the motor and non-motor complications in PD patients; and (4) specific rehabilitation treatment programs for drug-refractory motor complications.

Comparing Sensitivity and Specificity of Addenbrooke's Cognitive Examination-I, III and Mini-Addenbrooke's Cognitive Examination in Parkinson's Disease

Background

Parkinson's disease (PD) is the second most common neurodegenerative disorder characterized by numerous motor and nonmotor symptoms. Neurocognitive disorders (NCD) are one of the most troublesome problems and their diagnosis is often challenging.

Methods

We compared the sensitivity and specificity of several versions of Addenbrooke Cognitive Examination (ACE, ACE-III, and Mini-ACE) on 552 subjects with PD. Normal cognition, mild and major NCD were judged in accordance with the respective criteria of the Diagnostic and Statistical Manual of Mental Disorders 5^th edition. Subsequently, we applied the receiver operation characteristic (ROC) analysis in comparison of different education levels.

Results

For subjects with education level 0–8 and 9–12 years, the ACE-III had the best discriminating capabilities for mild NCD (cut-off scores: 83.5 and 85.5 points, respectively), while Mini-ACE was the best for subjects having education > 12 years (cut-off score: 25.5 points). For detecting major NCD, ACE-III had the best diagnostic accuracy in all levels of education (cut-off scores: 70.5, 77.5, and 78.5 points for subjects having education level 0–8, 9–12, and >12 years, respectively).

Conclusion

ACE-III and its nested version, the Mini-ACE, had the best screening abilities for detecting mild and major NCD in PD.

The nature of working memory gating in Parkinson's disease: A multi-domain signal detection examination

Distractions are ubiquitous; our brains are inundated with task-irrelevant information. Thus, to remember successfully, one must actively maintain relevant information and prevent distraction from entering working memory. Researchers suggest the basal ganglia-prefrontal pathways are vital to this process by acting as a working memory gate. Using Parkinson's disease as a model of frontostriatal functioning and with signal detection analyses, the present study aims to better characterize the contribution of frontostriatal pathways of this gating process and to determine how it operates across multiple domains. To achieve this, Parkinson's disease patients and healthy controls completed verbal and spatial working memory tasks consisting of three conditions: low-load without distraction; low-load with distraction; and high-load without distraction. Patients were tested both ON and OFF dopaminergic medication, allowing for assessment of the contribution of dorsal and ventral frontostriatal pathways. The results demonstrate that when medication is withheld, Parkinson's patients have a response bias to answer "NO" across all conditions and domains, supporting our hypothesis that the basal ganglia-prefrontal pathways allow or prevent updates of working memory. Contrastingly, medication status affects d' in the distraction condition but not in the high- or low-load conditions. We attribute this to stimulus valuation processes that were impaired by dopaminergic medication overdosing the ventral pathway. These findings are both consistent with the hypothesis that the working memory gate filters spatial and verbal information before it enters into the working memory system, adding support for the gate being a domain-general mechanism of the central executive.

Working Memory Network Changes in ALS: An fMRI Study

We used amyotrophic lateral sclerosis (ALS) as a model of prefrontal dysfunction in order to re-assess the potential neuronal substrates of two sub processes of working memory, namely information storage and filtering. To date it is unclear which exact neuronal networks sustain these two processes and the prefrontal cortex was suggested to play a crucial role both for filtering out of irrelevant information and for the storage of relevant information in memory. Other research has attributed information storage to more posterior brain regions, including the parietal cortex and stressed the role of subcortical areas in information filtering. We studied 14 patients suffering from ALS and the same number of healthy controls in an fMRI-task that allowed calculating separate storage and filtering scores. A brain volume analysis confirmed prefrontal atrophy in the patient group. Regarding their performance in the working memory task, we observed a trend toward slightly impaired storage capabilities whereas filtering appeared completely intact. Despite the rather subtle behavioral deficits we observed marked changes in neuronal activity associated with ALS: Compared to healthy controls patients showed significantly reduced hemodynamic responses in the left occipital cortex and right prefrontal cortex in the storage contrast. The filter contrast on the other hand revealed a relative hyperactivation in the superior frontal gyrus of the ALS patients. This hyperactivation might reflect a possible compensational mechanism for the prefrontal degeneration found in ALS. The reduced hemodynamic responses in the storage contrast might reflect a disruption of prefrontal top-down control of posterior brain regions, a process which was especially relevant in the most difficult high load memory task. Taken together, the present study demonstrates marked neurophysiological changes in ALS patients compared to healthy controls during the filtering and storage of information in spite of largely intact behavior. With respect to the neuronal substrates of the two working memory processes under investigation here, the results suggest that it is rather the degree to which top-down control is required for task completion that determines prefrontal cortex involvement than the specific nature of the process, i.e., storage vs. filtering.

Distinct effects of dopamine vs STN stimulation therapies in associative learning and retention in Parkinson disease

Evidence has been provided in Parkinson's disease patients of cognitive impairments including visual memory and learning which can be partially compensated by dopamine medication or subthalamic nucleus stimulation. The effects of these two therapies can differ according to the learning processes involving the dorsal vs ventral part of the striatum. Here we aimed to investigate and compare the outcomes of dopamine vs stimulation treatment in Parkinson patient's ability to acquire and maintain over successive days their performance in visual working memory. Parkinson patients performed conditional associative learning embedded in visual (spatial and non spatial) working memory tasks over two consecutive days either ON or OFF dopaminergic drugs or STN stimulation depending on the group of patients studied. While Parkinson patients were more accurate and faster in memory tasks ON vs OFF stimulation independent of the day of testing, performance in medicated patients differed depending on the medication status during the initial task acquisition. Patients who learnt the task ON medication the first day were able to maintain or even improve their memory performance both OFF and ON medication on the second day after consolidation. These effects were observed only in patients with dopamine replacement with or without motor fluctuations. This enhancement in memory performance after having learnt under dopamine medication and not under STN stimulation was mostly significant in visuo-spatial working memory tasks suggesting that dopamine replacement in the depleted dorsal striatum is essential for retention and consolidation of learnt skill.