Assessment of Metacognition and Reversal Learning in Parkinson's Disease: Preliminary Results

Neuropsychopharmacological Induction of (Lucid) Dreams: A Narrative Review

Lucid dreaming (LD) is a physiological state of consciousness that occurs when dreamers become aware that they are dreaming, and may also control the oneiric content. In the general population, LD is spontaneously rare; thus, there is great interest in its induction. Here, we aim to review the literature on neuropsychopharmacological induction of LD. First, we describe the circadian and homeostatic processes of sleep regulation and the mechanisms that control REM sleep with a focus on neurotransmission systems. We then discuss the neurophysiology and phenomenology of LD to understand the main cortical oscillations and brain areas involved in the emergence of lucidity during REM sleep. Finally, we review possible exogenous substances-including natural plants and artificial drugs-that increase metacognition, REM sleep, and/or dream recall, thus with the potential to induce LD. We found that the main candidates are substances that increase cholinergic and/or dopaminergic transmission, such as galantamine. However, the main limitation of this technique is the complexity of these neurotransmitter systems, which challenges interpreting results in a simple way. We conclude that, despite these promising substances, more research is necessary to find a reliable way to pharmacologically induce LD.

No effect of subthalamic deep brain stimulation on metacognition in Parkinson's disease

Deep brain stimulation of the subthalamic nucleus (STN-DBS) is a powerful treatment in Parkinson's disease (PD), which provides a positive effect on motor symptoms although the way it operates on high cognitive processes such as metacognition remains unclear. To address this issue, we recorded electroencephalogram (EEG) of PD patients treated with STN-DBS that performed a reversal learning (RL) paradigm endowed with metacognitive self-assessment. We considered two stimulation conditions, namely DBS-ON (stimulation on) and DBS-OFF (stimulation off), and focused our EEG-analysis on the frontal brain region due to its involvement on high cognitive processes. We found a trend towards a significant difference in RL ability between stimulation conditions. STN-DBS showed no effect on metacognition, although a significant association between accuracy and decision confidence level held for DBS OFF, but not in the case of DBS ON. In summary, our study revealed no significant effect of STN-DBS on RL or metacognition.

Nicotine-conditioned place preference, reversal learning, and social interaction in MK-801-induced schizophrenia model: Effects of post-weaning enriched environment

Based on the clinical observations of severe cognitive deficits in schizophrenia patients and the relationship between environmental parameters and the severity of schizophrenia symptoms, the present study investigated these parameters in an MK-801-induced schizophrenia model in rats. In addition to, it evaluated whether a post-weaning enriched environment (EE) would affect the nicotine-induced conditioned place preference (CPP) and the motor and cognitive deficits caused by MK-801 treatment. Male Wistar rat pups were injected peritoneally with MK-801 (1 mg/kg) on a daily basis between the 6th and the 10th postnatal days (P) and were exposed to either an enriched or a standard cage from P21 until the end of the experiments. The rats were evaluated in open-field and three-chamber social interaction tests. Moreover, spatial and reversal learning was assessed by the Morris water maze (MWM). Also, the animals were conditioned with 0.6 mg/kg nicotine and tested for CPP. Increased self-grooming, exploratory behavior, potentiated nicotine-CPP, and decreased social behaviors, delayed spatial learning and memory, and impaired reversal learning in the water maze were observed in the MK-801 treatment group. Housing in an EE improved cognitive and behavioral deficits associated with postnatal MK-801 treatment. The results suggested that neonatal N-methyl-D-aspartate (NMDA) receptor hypofunction may cause susceptibility to these behaviors and indicated the importance of environmental conditions in the development of schizophrenia and probably other neuropsychiatric disorders.

Altered awareness of cognitive and neuropsychiatric symptoms in Parkinson's disease and Dementia with Lewy Bodies: A systematic review

OBJECTIVES

Altered awareness of cognitive and neuropsychiatric symptoms is a common feature of neurodegeneration, which can significantly impact on quality of life, medication concordance and personal safety. Elucidating how awareness is affected by common alpha-synucleinopathies therefore has significant clinical relevance. We performed a systematic review of the literature on awareness of cognitive and neuropsychiatric symptoms in Parkinson's disease and Dementia with Lewy Bodies.

METHODS

Searches of PubMed and Web of Science were carried out, using keywords and MeSH subheadings, limited to papers in English dealing with humans. The terms "Parkinson's" or "Lewy body" were used to denote the disease of interest, combined with either "agnosia", "anosognosia", "insight", "metacognition", or "neuropsychology" to denote the neuropsychological area of interest.

RESULTS

21 publications investigating awareness of cognitive symptoms, and 18 publications on awareness of neuropsychiatric symptoms were identified. The large majority focused on Parkinson's disease rather than Dementia with Lewy Bodies. Cognitively intact people with Parkinson's disease may over-report cognitive symptoms, whilst those with cognitive impairment under-report symptoms. Awareness of neuropsychiatric symptoms is likely to decline over time, particularly in those with progressive cognitive impairment.

CONCLUSIONS

Altered awareness of cognitive and neuropsychiatric symptoms is common in Parkinson's disease. Symptom awareness varies significantly between individuals, and appears to be influenced by mood and global cognitive functioning, with executive functioning specifically implicated. There are gaps in our understanding of how dopaminergic medications influence symptom awareness, and a need for longitudinal studies of how awareness changes over time in Parkinson's disease and Dementia with Lewy Bodies.

Effect of conditioning and test stimulus intensity on cortical excitability using triad-conditioning transcranial magnetic stimulation

Cortical facilitation assessed with triad conditioning transcranial magnetic stimulation has been termed triad-conditioned facilitation (TCF). TCF has been supposed to reflect increased intracortical facilitation (ICF) at short interstimulus intervals (ISI) around 10 ms and an intrinsic rhythm of the motor cortex at longer ISI around 25 ms. To gain further insight into the pathophysiological mechanism of TCF, we systematically studied the effect of suprathreshold conditioning stimulus (CS) and test stimulus (TS) intensity on TCF. Various CS intensities and TS intensities were used in a triad-conditioning paradigm that was applied to 11 healthy subjects. ISI between pulses were studied between 5 and 200 ms. TCF at 10 ms ISI enhanced with increasing CS intensity but decreased with increasing TS intensity. The duration of facilitation was longer with higher CS intensity. However, TCF at 25 ms ISI could not be elicited with none of the CS and TS intensities addressed here. Our results are consistent with the notion of TCF at short ISI reflecting ICF. The enhanced and prolonged facilitation with increase of CS without additional isolated facilitation at longer ISI suggest a prolongation of ICF.