Eye movements in ephedrone-induced parkinsonism

Clinical utility of square-wave jerks in neurology and psychiatry

Human eye fixation is steadily interrupted by small, physiological or abnormal, eye movements. Square-wave jerks (SWJ) are the most common saccadic intrusion which can be readily seen at the bedside and also quantified using oculographic techniques. Various neurological, neuropsychiatric and psychiatric disorders display abnormal fixational eye movement patterns characterized by frequent SWJ. For the clinician, SWJ are particularly important because they can be readily observed at the bedside. Here, we will discuss the pathological conditions that present with SWJ and explore the expanding body of literature suggesting that SWJ may serve as a potential indicator for various clinical conditions.

Antisaccades in Parkinson's Disease: A Meta-Analysis

The usefulness of eye-tracking tasks as potential biomarkers for motor or cognitive disease burden in Parkinson's disease (PD) has been subject of debate for many years. Several studies suggest that the performance in the antisaccade task may be altered in patients with PD and associated with motor disease severity or executive dysfunction. In this meta-analysis, random effects models were used to synthesize the existing evidence on antisaccade error rates and latency in PD. Furthermore, meta-regressions were performed to assess the role of motor and cognitive disease severity, dopaminergic medication and methodological factors. Additionally, the impact of acute levodopa administration and activation of deep brain stimulation was evaluated in two separate sub-analyses.This meta-analysis confirms that antisaccade latency and error rate are significantly increased in PD. Disease duration, Unified Parkinson's disease rating scale score and Hoehn and Yahr stage mediate the effect of PD on antisaccade latency with higher motor burden being associated with increased antisaccade latency.Acute administration of levodopa had no significant effects on antisaccade performance in a small number of eligible studies. Deep brain stimulation in the subthalamic nucleus, on the other hand, may alter the speed accuracy trade-off supporting an increase of impulsivity following deep brain stimulation in PD.According to the results of the meta-analysis, antisaccade latency may provide a potential marker for disease severity and progression in PD which needs further confirmation in longitudinal studies.

Manganese Encephalopathy Caused by Homemade Methcathinone (Ephedrone) Prevalence in Poland

Manganese encephalopathy is a known disorder in occupational medicine. A serious phenomenon has been the emergence of manganese encephalopathy in intravenous users of homemade methcathinone (ephedrone). A short survey was developed for clinical environments dealing with people who use psychoactive substances. The data were obtained from 72 rehabilitation therapy centers. Surveys carried out in about a third of Polish centers dealing with providing medical assistance to people addicted to substances other than alcohol and tobacco have shown that over 4% of people treated there had symptoms of manganese encephalopathy, of which more than half are people in whom the probability of a clinical diagnosis of this disorder is significant. It has been shown that knowledge of manganese encephalopathy is none or minimal in more than 70% of the surveyed institutions. An urgent need for personnel training in this field was pointed out. Attention was paid to the importance of disseminating good review articles on new and dynamically developing problem phenomena.

App-based saccade latency and directional error determination across the adult age spectrum

We aid in neurocognitive monitoring outside the hospital environment by enabling app-based measurements of visual reaction time (saccade latency) and directional error rate in a cohort of subjects spanning the adult age spectrum. Methods: We developed an iOS app to record subjects with the frontal camera during pro- and anti-saccade tasks. We further developed automated algorithms for measuring saccade latency and directional error rate that take into account the possibility that it might not always be possible to determine the eye movement from app-based recordings. Results: To measure saccade latency on a tablet, we ensured that the absolute timing error between on-screen task presentation and the camera recording is within 5 ms. We collected over 235,000 eye movements in 80 subjects ranging in age from 20 to 92 years, with 96% of recorded eye movements either declared good or directional errors. Our error detection code achieved a sensitivity of 0.97 and a specificity of 0.97. Confirming prior reports, we observed a positive correlation between saccade latency and age while the relationship between directional error rate and age was not significant. Finally, we observed significant intra- and inter-subject variations in saccade latency and directional error rate distributions, which highlights the importance of individualized tracking of these visual digital biomarkers. Conclusion and Significance: Our system and algorithms allow ubiquitous tracking of saccade latency and directional error rate, which opens up the possibility of quantifying patient state on a finer timescale in a broader population than previously possible.

Measuring Saccade Latency Using Smartphone Cameras

OBJECTIVE

Accurate quantification of neurodegenerative disease progression is an ongoing challenge that complicates efforts to understand and treat these conditions. Clinical studies have shown that eye movement features may serve as objective biomarkers to support diagnosis and tracking of disease progression. Here, we demonstrate that saccade latency-an eye movement measure of reaction time-can be measured robustly outside of the clinical environment with a smartphone camera.

METHODS

To enable tracking of saccade latency in large cohorts of patients and control subjects, we combined a deep convolutional neural network for gaze estimation with a model-based approach for saccade onset determination that provides automated signal-quality quantification and artifact rejection.

RESULTS

Simultaneous recordings with a smartphone and a high-speed camera resulted in negligible differences in saccade latency distributions. Furthermore, we demonstrated that the constraint of chinrest support can be removed when recording healthy subjects. Repeat smartphone-based measurements of saccade latency in 11 self-reported healthy subjects resulted in an intraclass correlation coefficient of 0.76, showing our approach has good to excellent test-retest reliability. Additionally, we conducted more than 19 000 saccade latency measurements in 29 self-reported healthy subjects and observed significant intra- and inter-subject variability, which highlights the importance of individualized tracking. Lastly, we showed that with around 65 measurements we can estimate mean saccade latency to within less-than-10-ms precision, which takes within 4 min with our setup.

CONCLUSION AND SIGNIFICANCE

By enabling repeat measurements of saccade latency and its distribution in individual subjects, our framework opens the possibility of quantifying patient state on a finer timescale in a broader population than previously possible.

Eye Movements in Parkinson's Disease and Inherited Parkinsonian Syndromes

Despite extensive research, the functions of the basal ganglia (BG) in movement control have not been fully understood. Eye movements, particularly saccades, are convenient indicators of BG function. Here, we review the main oculomotor findings reported in Parkinson’s disease (PD) and genetic parkinsonian syndromes. PD is a progressive, neurodegenerative disorder caused by dopaminergic cell loss within the substantia nigra pars compacta, resulting in depletion of striatal dopamine and subsequent increased inhibitory BG output from the internal globus pallidus and the substantia nigra pars reticulata. Eye movement abnormalities are common in PD: anomalies are more evident in voluntary than reflexive saccades in the initial stages, but visually guided saccades may also be involved at later stages. Saccadic hypometria (including abnormally fragmented saccades), reduced accuracy, and increased latency are among the most prominent deficits. PD patients show also unusually frequent and large square wave jerks and impaired inhibition of reflexive saccades when voluntary mirror saccades are required. Poor convergence ability and altered pursuit are common. Inherited parkinsonisms are a heterogeneous group of rare syndromes due to gene mutations causing symptoms resembling those of PD. Eye movement characteristics of some parkinsonisms have been studied. While sharing some PD features, each syndrome has a distinctive profile that could contribute to better define the clinical phenotype of parkinsonian disorders. Moreover, because the pathogenesis and the underlying neural circuit failure of inherited parkinsonisms are often well defined, they might offer a better prospect than idiopathic PD to understand the BG function.

The Growing Problem of New Psychoactive Substances (NPS)

The term "new psychoactive substances" (NPS) can be defined as individual drugs in pure form or in complex preparations that are not scheduled under the Single Convention on Narcotic Drugs (1961) or the Convention on Psychotropic Substances (1971). NPS may be categorized by chemical structure, by psychoactive properties, by biological targets, or by source (plant, synthetic, or combined). The emergence of hundreds of NPS in the past decade is challenging for public health and drug policies globally. The novelty of NPS, their ambiguous legal status, ability to evade toxicological tests, swift adaptation to legal restrictions, global Internet marketing, and scant public knowledge of their adverse effects are among the key drivers of this twenty-first century phenomenon. Multi-disciplinary research in areas of biology, epidemiology, prevention, and web analytics are needed to develop effective responses in a domain capable of overwhelming current international conventions and national drug control policies. Ultimately, research-guided prevention education will fortify societies against this tidal wave.

A clinical and neurophysiological motor signature of Unverricht-Lundborg disease

OBJECTIVES

Unverricht-Lundborg disease (ULD) is the most common form of progressive myoclonus epilepsy. Cerebellar dysfunction may appear over time, contributing along with myoclonus to motor disability. The purpose of the present work was to clarify the motor and neurophysiological characteristics of ULD patients.

METHODS

Nine patients with genetically proven ULD were evaluated clinically (medical history collected from patient charts, the Scale for the Assessment and Rating of Ataxia and Unified Myoclonus Rating Scale). Neurophysiological investigations included EEG, surface polymyography, long-loop C-reflexes, somatosensory evoked potentials, EEG jerk-locked back-averaging (JLBA) and oculomotor recordings. All patients underwent brain MRI. Non-parametric Mann-Whitney tests were used to compare ULD patients' oculomotor parameters with those of a matched group of healthy volunteers (HV).

RESULTS

Myoclonus was activated by action but was virtually absent at rest and poorly induced by stimuli. Positive myoclonus was multifocal, often rhythmic and of brief duration, with top-down pyramidal temporospatial propagation. Cortical neurophysiology revealed a transient wave preceding myoclonus on EEG JLBA (n=8), enlarged somatosensory evoked potentials (n=7) and positive long-loop C-reflexes at rest (n=5). Compared with HV, ULD patients demonstrated decreased saccadic gain, increased gain dispersion and a higher frequency of hypermetric saccades associated with decreased peak velocity.

CONCLUSION

A homogeneous motor pattern was delineated that may represent a ULD clinical and neurophysiological signature. Clinical and neurophysiological findings confirmed the pure cortical origin of the permanent myoclonus. Also, oculomotor findings shed new light on ULD pathophysiology by evidencing combined midbrain and cerebellar dysfunction.

Response inhibition in Parkinson's disease: a meta-analysis of dopaminergic medication and disease duration effects

Parkinson's disease is a neurodegenerative disorder involving the basal ganglia that results in a host of motor and cognitive deficits. Dopamine-replacement therapy ameliorates some of the hallmark motor symptoms of Parkinson's disease, but whether these medications improve deficits in response inhibition, a critical executive function for behavioral control, has been questioned. Several studies of Parkinson's disease patients "on" and "off" (12-h withdrawal) dopaminergic medications suggested that dopamine-replacement therapy did not provide significant response inhibition benefits. However, these studies tended to include patients with moderate-to-advanced Parkinson's disease, when the efficacy of dopaminergic drugs is reduced compared to early-stage Parkinson's disease. In contrast, a few recent studies in early-stage Parkinson's disease report that dopaminergic drugs do improve response inhibition deficits. Based on these findings, we hypothesized that Parkinson's disease duration interacts with medication status to produce changes in cognitive function. To investigate this issue, we conducted a meta-analysis of studies comparing patients with Parkinson's disease and healthy controls on tests of response inhibition (50 comparisons from 42 studies). The findings supported the hypothesis; medication benefited response inhibition in patients with shorter disease duration, whereas "off" medication, moderate deficits were present that were relatively unaffected by disease duration. These findings support the role of dopamine in response inhibition and suggest the need to consider disease duration in research of the efficacy of dopamine-replacement therapy on cognitive function in Parkinson's disease.

Eye movements in neurodegenerative diseases

PURPOSE OF REVIEW

Abnormalities of oculomotor control accompany the pathological changes underlying many neurodegenerative diseases. Clinical examination of eye movements can contribute to differential diagnosis, whereas quantitative laboratory measures can provide detailed insight into the disease process. In this review of eye movements in neurodegenerative disease, we summarise recent empirical findings and conceptual advances.

RECENT FINDINGS

Oculomotor researchers continue to be particularly prolific in studying Parkinson's disease but there is also substantial activity in Alzheimer's disease and spinocerebellar ataxia. Interesting findings have been reported in Huntington's, motor neuron disease, and glaucoma. Most studies report laboratory-based investigations but useful progress in clinical description continues to be made.

SUMMARY

Eye movements remain an active field of investigation across a variety of neurodegenerative conditions. Progress continues to be made at the clinical level as well by using laboratory techniques.

CIDER: Enabling Robustness-Power Tradeoffs on a Computational Eyeglass

The human eye offers a fascinating window into an individual's health, cognitive attention, and decision making, but we lack the ability to continually measure these parameters in the natural environment. The challenges lie in: a) handling the complexity of continuous high-rate sensing from a camera and processing the image stream to estimate eye parameters, and b) dealing with the wide variability in illumination conditions in the natural environment. This paper explores the power-robustness tradeoffs inherent in the design of a wearable eye tracker, and proposes a novel staged architecture that enables graceful adaptation across the spectrum of real-world illumination. We propose CIDER, a system that operates in a highly optimized low-power mode under indoor settings by using a fast Search-Refine controller to track the eye, but detects when the environment switches to more challenging outdoor sunlight and switches models to operate robustly under this condition. Our design is holistic and tackles a) power consumption in digitizing pixels, estimating pupillary parameters, and illuminating the eye via near-infrared, b) error in estimating pupil center and pupil dilation, and c) model training procedures that involve zero effort from a user. We demonstrate that CIDER can estimate pupil center with error less than two pixels (0.6°), and pupil diameter with error of one pixel (0.22mm). Our end-to-end results show that we can operate at power levels of roughly 7mW at a 4Hz eye tracking rate, or roughly 32mW at rates upwards of 250Hz.

Methcathinone "Kitchen Chemistry" and Permanent Neurological Damage

Methcathinone abuse is a significant cause of parkinsonism among young patients in the Eastern European countries. The drug is synthesized from over-the-counter cold remedies containing ephedrine or pseudoephedrine. The final mixture contains a high concentration of manganese if potassium permanganate is used as the oxidant agent. Though manganese is an essential trace element and its homeostasis is well maintained, exposure to a high level of manganese is neurotoxic. The use of manganese-contaminated methcathinone may cause permanent neurological damage and severe disability. Drug users develop a distinctive extrapyramidal syndrome that resembles classic manganese intoxication. Methcathinone could have additive neurotoxic effect to the progression of parkinsonism. The most prevalent symptoms are symmetrical bradykinesia, dystonias, and early postural, gait, and speech impairment. After cessation of exposure, the syndrome is generally irreversible and can even progress.