Bayesian multilevel hidden Markov models identify stable state dynamics in longitudinal recordings from macaque primary motor cortex.

Neural populations, rather than single neurons, may be the fundamental unit of cortical computation. Analysing chronically recorded neural population activity is challenging not only because of the high dimensionality of activity but also because of changes in the signal that may or may not be due to neural plasticity. Hidden Markov models (HMMs) are a promising technique for analysing such data in terms of discrete latent states, but previous approaches have not considered the statistical properties of neural spiking data, have not been adaptable to longitudinal data, or have not modelled condition-specific differences. We present a multilevel Bayesian HMM addresses these shortcomings by incorporating multivariate Poisson log-normal emission probability distributions, multilevel parameter estimation and trial-specific condition covariates. We applied this framework to multi-unit neural spiking data recorded using chronically implanted multi-electrode arrays from macaque primary motor cortex during a cued reaching, grasping and placing task. We show that, in line with previous work, the model identifies latent neural population states which are tightly linked to behavioural events, despite the model being trained without any information about event timing. The association between these states and corresponding behaviour is consistent across multiple days of recording. Notably, this consistency is not observed in the case of a single-level HMM, which fails to generalise across distinct recording sessions. The utility and stability of this approach is demonstrated using a previously learned task, but this multilevel Bayesian HMM framework would be especially suited for future studies of long-term plasticity in neural populations.

Impact of drug consumption rooms on risk practices and access to care in people who inject drugs in France: the COSINUS prospective cohort study protocol.

INTRODUCTION: The high prevalence of hepatitis C and the persistence of HIV and hepatitis C virus (HCV) risk practices in people who inject drugs (PWID) in France underlines the need for innovative prevention interventions. The main objective of this article is to describe the design of the COSINUS cohort study and outline the issues it will explore to evaluate the impact of drug consumption rooms (DCR) on PWID outcomes. Secondary objectives are to assess how DCR (a) influence other drug-related practices, such as the transition from intravenous to less risky modes of use, (b) reduce drug use frequency/quantity, (c) increase access to treatment for addiction and comorbidities (infectious, psychiatric and other), (d) improve social conditions and (e) reduce levels of violence experienced and drug-related offences. COSINUS will also give us the opportunity to investigate the impact of other harm reduction tools in France and their combined effect with DCR on reducing HIV-HCV risk practices. Furthermore, we will be better able to identify PWID needs. METHODS AND ANALYSIS: Enrollment in this prospective multi-site cohort study started in June 2016. Overall, 680 PWID in four different cities (Bordeaux, Marseilles, Paris and Strasbourg) will be enrolled and followed up for 12 months through face-to-face structured interviews administered by trained staff to all eligible participants at baseline (M0), 3 month (M3), 6 month (M6) and 12 month (M12) follow-up visits. These interviews gather data on socio-demographic characteristics, past and current drug and alcohol consumption, drug-use related practices, access to care and social services, experience of violence (as victims), offences, other psychosocial issues and perception and needs about harm reduction interventions and services. Longitudinal data analysis will use a mixed logistic model to assess the impact of individual and structural factors, including DCR attendance and exposure to other harm reduction services, on the main outcome (HIV-HCV risk practices). ETHICS AND DISSEMINATION: This study was reviewed and approved by the institutional review board of the French Institute of Medical Research and Health (opinion number: 14-166). The findings of this cohort study will help to assess the impact of DCR on HIV-HCV risk practices and other psycho-social outcomes and trajectories. Moreover, they will enable health authorities to shape health and harm reduction policies according to PWID needs. Finally, they will also help to improve current harm reduction and therapeutic interventions and to create novel ones.

Impaired contrast sensitivity at low spatial frequency in cannabis users with early onset.

The regular use of cannabis generates pronounced cognitive disorders, especially in users who begin before the age of 15-16. However, less is known about the impact of regular cannabis on visual function, especially in the case of early onset. Cannabinoid receptors (CB1) are expressed in areas of the visual system, like the thalamus and primary cortex, which might originate sensory disorders. Hence, we measured contrast sensitivity (CS) in three groups, i.e. cannabis users with late onset of cannabis use (after 16 years old), cannabis users with early onset". We used a constant method which allowed us to control for biased responses. Stimuli were presented at high and low spatial frequencies and in both static and dynamic conditions (8Hz). As contrast sensitivity is measured behaviorally based on an explicit response and could thus be impacted by attentional or vigilance disorders, participants' attention and vigilance were carefully monitored by means of the D2 test, CPT-AX for attention and pupillography for vigilance. Cannabis users with early onset were significantly impaired only at low spatial frequency. This effect was independent of response bias, vigilance and attention. These results show for the first time that early cannabis use impacts contrast sensitivity at low spatial frequency.