Trial of Lixisenatide in Early Parkinson's Disease

BACKGROUND

Lixisenatide, a glucagon-like peptide-1 receptor agonist used for the treatment of diabetes, has shown neuroprotective properties in a mouse model of Parkinson's disease.

METHODS

In this phase 2, double-blind, randomized, placebo-controlled trial, we assessed the effect of lixisenatide on the progression of motor disability in persons with Parkinson's disease. Participants in whom Parkinson's disease was diagnosed less than 3 years earlier, who were receiving a stable dose of medications to treat symptoms, and who did not have motor complications were randomly assigned in a 1:1 ratio to daily subcutaneous lixisenatide or placebo for 12 months, followed by a 2-month washout period. The primary end point was the change from baseline in scores on the Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) part III (range, 0 to 132, with higher scores indicating greater motor disability), which was assessed in patients in the on-medication state at 12 months. Secondary end points included other MDS-UPDRS subscores at 6, 12, and 14 months and doses of levodopa equivalent.

RESULTS

A total of 156 persons were enrolled, with 78 assigned to each group. MDS-UPDRS part III scores at baseline were approximately 15 in both groups. At 12 months, scores on the MDS-UPDRS part III had changed by -0.04 points (indicating improvement) in the lixisenatide group and 3.04 points (indicating worsening disability) in the placebo group (difference, 3.08; 95% confidence interval, 0.86 to 5.30; P = 0.007). At 14 months, after a 2-month washout period, the mean MDS-UPDRS motor scores in the off-medication state were 17.7 (95% CI, 15.7 to 19.7) with lixisenatide and 20.6 (95% CI, 18.5 to 22.8) with placebo. Other results relative to the secondary end points did not differ substantially between the groups. Nausea occurred in 46% of participants receiving lixisenatide, and vomiting occurred in 13%.

CONCLUSIONS

In participants with early Parkinson's disease, lixisenatide therapy resulted in less progression of motor disability than placebo at 12 months in a phase 2 trial but was associated with gastrointestinal side effects. Longer and larger trials are needed to determine the effects and safety of lixisenatide in persons with Parkinson's disease. (Funded by the French Ministry of Health and others; LIXIPARK ClinicalTrials.gov number, NCT03439943.).

Care of Late-Stage Parkinsonism: Resource Utilization of the Disease in Five European Countries

BACKGROUND

Parkinson's disease (PD) is a neurodegenerative disease that leads to progressive disability. Cost studies have mainly explored the early stages of the disease, whereas late-stage patients are underrepresented.

OBJECTIVE

The aim is to evaluate the resource utilization and costs of PD management in people with late-stage disease.

METHODS

The Care of Late-Stage Parkinsonism (CLaSP) study collected economic data from patients with late-stage PD and their caregivers in five European countries (France, Germany, the Netherlands, UK, Sweden) in a range of different settings. Patients were eligible to be included if they were in Hoehn and Yahr stage >3 in the on state or Schwab and England stage at 50% or less. In total, 592 patients met the inclusion criteria and provided information on their resource utilization. Costs were calculated from a societal perspective for a 3-month period. A least absolute shrinkage and selection operator approach was utilized to identify the most influential independent variables for explaining and predicting costs.

RESULTS

During the 3-month period, the costs were €20,573 (France), €19,959 (Germany), €18,319 (the Netherlands), €25,649 (Sweden), and €12,156 (UK). The main contributors across sites were formal care, hospitalization, and informal care. Gender, age, duration of the disease, Unified Parkinson's Disease Rating Scale 2, the EQ-5D-3L, and the Schwab and England Scale were identified as predictors of costs.

CONCLUSION

Costs in this cohort of individuals with late-stage PD were substantially higher compared to previously published data on individuals living in earlier stages of the disease. Resource utilization in the individual sites differed in part considerably among these three parameters mentioned. © 2024 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Paul Broca: from fame to shame?

In 2016, the University of Bordeaux named its new neuroscience building after Paul Broca. A debate was recently ignited about the appropriateness of this choice, however, given Broca's endorsement of physiological anthropology. Thomas Boraud and Stephanie Forkel discuss this debate and its implications for neurology today.

[Citation misuse and its effects on public health]

In order to effectively contribute to scientific knowledge, biomedical observations have to be validated and debated by scientists in the relevant field. Along this debate that mainly takes place in the scientific literature, citation of previous studies plays a major role. However, only a few academic studies have quantitatively evaluated the suitability and accuracy of scientific citations. Here we review these academic studies. Two types of misuse have been pointed out: Citation bias and citation distortion. First, scientific citations favor positive results and those supporting authors' conclusion. Second, many statements linked to a reference actually misrepresent the referenced findings. About 10% of all citations in biomedicine are strongly inaccurate and misleading for the reader. Finally, we give two examples illustrating how some citation misuses do affect public health: The opioid crisis in the USA and the unjustified fostering of hydroxychloroquine for Covid-19 treatment in France.

Economic behaviours among non-human primates

Do we have any valid reasons to affirm that non-human primates display economic behaviour in a sufficiently rich and precise sense of the phrase? To address this question, we have to develop a set of criteria to assess the vast array of experimental studies and field observations on individual cognitive and behavioural competences as well as the collective organization of non-human primates. We review a sample of these studies and assess how they answer to the following four main challenges. (i) Do we see any economic organization or institutions emerge among groups of non-human primates? (ii) Are the cognitive abilities, and often biases, that have been evidenced as underlying typical economic decision-making among humans, also present among non-human primates? (iii) Can we draw positive lessons from performance comparisons among primate species, humans and non-humans but also across non-human primate species, as elicited by canonical game-theoretical experimental paradigms, especially as far as economic cooperation and coordination are concerned? And (iv) in which way should we improve models and paradigms to obtain more ecological data and conclusions? Articles discussed in this paper most often bring about positive answers and promising perspectives to support the existence and prevalence of economic behaviours among non-human primates. This article is part of the theme issue 'Existence and prevalence of economic behaviours among non-human primates'.

The adaptive value of probability distortion and risk-seeking in macaques' decision-making

In humans, the attitude toward risk is not neutral and is dissimilar between bets involving gains and bets involving losses. The existence and prevalence of these decision features in non-human primates are unclear. In addition, only a few studies have tried to simulate the evolution of agents based on their attitude toward risk. Therefore, we still ignore to what extent Prospect theory's claims are evolutionarily rooted. To shed light on this issue, we collected data from nine macaques that performed bets involving gains or losses. We confirmed that their overall behaviour is coherent with Prospect theory's claims. In parallel, we used a genetic algorithm to simulate the evolution of a population of agents across several generations. We showed that the algorithm selects progressively agents that exhibit risk-seeking, and has an inverted S-shape distorted perception of probability. We compared these two results and found that monkeys' attitude toward risk is only congruent with the simulation when they are facing losses. This result is consistent with the idea that gambling in the loss domain is analogous to deciding in a context of life-threatening challenges where a certain level of risk-seeking behaviour and probability distortion may be adaptive. This article is part of the theme issue 'Existence and prevalence of economic behaviours among non-human primates'.

What is the true discharge rate and pattern of the striatal projection neurons in Parkinson's disease and Dystonia?

Dopamine and striatal dysfunctions play a key role in the pathophysiology of Parkinson's disease (PD) and Dystonia, but our understanding of the changes in the discharge rate and pattern of striatal projection neurons (SPNs) remains limited. Here, we recorded and examined multi-unit signals from the striatum of PD and dystonic patients undergoing deep brain stimulation surgeries. Contrary to earlier human findings, we found no drastic changes in the spontaneous discharge of the well-isolated and stationary SPNs of the PD patients compared to the dystonic patients or to the normal levels of striatal activity reported in healthy animals. Moreover, cluster analysis using SPN discharge properties did not characterize two well-separated SPN subpopulations, indicating no SPN subpopulation-specific (D1 or D2 SPNs) discharge alterations in the pathological state. Our results imply that small to moderate changes in spontaneous SPN discharge related to PD and Dystonia are likely amplified by basal ganglia downstream structures.

Optimizing Treatment in Undertreated Late-Stage Parkinsonism: A Pragmatic Randomized Trial

BACKGROUND

Treatment of patients with late-stage parkinsonism is often sub-optimal.

OBJECTIVE

To test the effectiveness of recommendations by a movement disorder specialist with expertise in late-stage parkinsonism.

METHODS

Ninety-one patients with late-stage parkinsonism considered undertreated were included in apragmatic a pragmatic multi-center randomized-controlled trial with six-month follow-up. The intervention group received a letter with treatment recommendations to their primary clinician based on an extensive clinical assessment. Controls received care as usual. The primary outcome was the Unified Parkinson Disease Rating Scale (UPDRS)part-II (Activities of Daily Living). Other outcomes included quality-of-life (PDQ-8), mental health (UPDRS-I), motor function (UPDRS-III), treatment complications (UPDRS-IV), cognition (Mini-mental-state-examination), non-motor symptoms (Non-Motor-Symptoms-scale), health status (EQ-5D-5L) and levodopa-equivalent-daily-dose (LEDD). We also assessed adherence to recommendations. In addition to intention-to-treat analyses, a per-protocol analysis was conducted.

RESULTS

Sample size calculation required 288 patients, but only 91 patients could be included. Treating physicians followed recommendations fully in 16 (28%) and partially in 21 (36%) patients. The intention-to-treat analysis showed no difference in primary outcome (between-group difference = -1.2, p = 0.45), but there was greater improvement for PDQ-8 in the intervention group (between-group difference = -3.7, p = 0.02). The per-protocol analysis confirmed these findings, and showed less deterioration in UPDRS-part I, greater improvement on UPDRS-total score and greater increase in LEDD in the intervention group.

CONCLUSIONS

The findings suggest that therapeutic gains may be reached even in this vulnerable group of patients with late-stage parkinsonism, but also emphasize that specialist recommendations need to be accompanied by better strategies to implement these to further improve outcomes.

Do newspapers preferentially cover biomedical studies involving national scientists?

News value theory rates geographical proximity as an important factor in the process of issue selection by journalists. But does this apply to science journalism? Previous observational studies investigating whether newspapers preferentially cover scientific studies involving national scientists have generated conflicting answers. Here we used a database of 123 biomedical studies, 113 of them involving at least one research team working in eight countries (Australia, Canada, France, Ireland, Japan, New Zealand, the United Kingdom, and the United States). We compiled all the newspaper articles covering these 123 studies and published in English, French, and Japanese languages. In all eight countries, we found that newspapers preferentially covered studies involving a national team. Moreover, these "national" studies on average gave rise to a larger number of newspaper articles than "foreign" studies. Finally, our study resolves the conflict with previous conclusions by providing an alternative interpretation of published observations.

Naftazone in advanced Parkinson's disease: An acute L-DOPA challenge randomized controlled trial

INTRODUCTION

There is an unmet need to better control motor complications in Parkinson's disease (PD). Naftazone, which exhibits glutamate release inhibition properties, has shown antiparkinsonian and antidyskinetic activity in preclinical models of PD and in a clinical proof of concept study.

METHODS

We conducted a double-blind randomized placebo-controlled cross-over trial in PD patients with motor fluctuations and dyskinesia testing naftazone 160 mg/day versus placebo for 14 days. The two co-primary endpoints were the area under curve (AUC) of motor (MDS-UPDRS part III) and dyskinesia (AIMS) scores during an acute levodopa challenge performed at the end of each period. Secondary endpoints were UDysRS and axial symptoms scores during the challenge; AIMS, UDysRS, and time spent with or without dyskinesia the day before the challenge. The primary analysis was performed in the per protocol population.

RESULTS

Sixteen patients were included in the analysis. There was no difference between naftazone and placebo for the AUC of MDS-UPDRS III (-89, 95%CI[-1071; 893], p = 0.85), and AIMS (70, 95%CI[-192; 332], p = 0.57). At the end of treatment periods, AIMS score tended to be lower with naftazone than placebo (4.4 ± 3.4 versus 6.7 ± 4.4, p = 0.07), but UDysRS scores and other secondary outcomes were not different. Naftazone was safe and well tolerated.

CONCLUSIONS

This study did not confirm previous results on the efficacy of naftazone on dyskinesia nor motor fluctuations highlighting the problem of translating results obtained in preclinical models into clinical trials. Further investigation of naftazone may be conducted in PD with longer treatment duration.

A natural history of skills

The dorsal pallium (a.k.a. cortex in mammals) makes a loop circuit with the basal ganglia and the thalamus known to control and adapt behavior but the who's who of the functional roles of these structures is still debated. Influenced by the Triune brain theory that was proposed in the early sixties, many current theories propose a hierarchical organization on the top of which stands the cortex to which the subcortical structures are subordinated. In particular, habits formation has been proposed to reflect a switch from conscious on-line control of behavior by the cortex, to a fully automated subcortical control. In this review, we propose to revalue the function of the network in light of the current experimental evidence concerning the anatomy and physiology of the basal ganglia-cortical circuits in vertebrates. We briefly review the current theories and show that they could be encompassed in a broader framework of skill learning and performance. Then, after reminding the state of the art concerning the anatomical architecture of the network and the underlying dynamic processes, we summarize the evolution of the anatomical and physiological substrate of skill learning and performance among vertebrates. We then review experimental evidence supporting for the hypothesis that the development of automatized skills relies on the BG teaching cortical circuits and is actually a late feature linked with the development of a specialized cortex or pallium that evolved in parallel in different taxa. We finally propose a minimal computational framework where this hypothesis can be explicitly implemented and tested.

Social decision making in autism: On the impact of mirror neurons, motor control, and imitative behaviors

The Mirror Neuron System (MNS) plays a crucial role in action perception and imitative behavior, which is suggested to be impaired in Autism Spectrum Disorders (ASDs). In this review, we discuss the plausibility and empirical evidence of a neural interaction between the MNS, action perception, empathy, imitative behavior, and their impact on social decision making in ASDs. To date, there is no consensus regarding a particular theory in ASDs and its underlying mechanisms. Some theories have completely focused on social difficulties, others have emphasized sensory aspects. Based on the current studies, we suggest a multilayer neural network model including the MNS on a first layer and transforming this information to a higher layer network responsible for reasoning. Future studies with ASD participants combining behavioral tasks with neuroimaging methods and transcranial brain stimulation as well as computational modeling can help validate and complement this suggested model. Moreover, we propose applying the behavioral paradigms, and the neurophysiological markers mentioned in this review article for evaluating psychiatric treatment approaches in ASDs. The investigation of modulating effects of different treatment approaches on the neurophysiological markers of the MNS can help find specific subgroups of ASDs patients and support tailored psychiatric interventions.

Memories of Opiate Withdrawal Emotional States Correlate with Specific Gamma Oscillations in the Nucleus Accumbens

Affective memories associated with the negative emotional state experienced during opiate withdrawal are central in maintaining drug taking, seeking, and relapse. Nucleus accumbens (NAC) is a key structure for both acute withdrawal and withdrawal memories reactivation, but the NAC neuron coding properties underpinning the expression of these memories remain largely unknown. Here we aimed at deciphering the role of NAC neurons in the encoding and retrieval of opiate withdrawal memory. Chronic single neuron and local field potentials recordings were performed in morphine-dependent rats and placebo controls. Animals were subjected to an unbiased conditioned placed aversion protocol with one compartment (CS+) paired with naloxone-precipitated withdrawal, a second compartment with saline injection (CS-), and a third being neutral (no pairing). After conditioning, animals displayed a typical place aversion for CS+ and developed a preference for CS- characteristic of safety learning. We found that distinct NAC neurons code for CS+ or CS-. Both populations also displayed highly specific oscillatory dynamics, CS+ and CS- neurons, respectively, following 80 Hz (G80) and 60 Hz (G60) local field potential gamma rhythms. Finally, we found that the balance between G60 and G80 rhythms strongly correlated both with the ongoing behavior of the animal and the strength of the conditioning. We demonstrate here that the aversive and preferred environments are underpinned by distinct groups of NAC neurons as well as specific oscillatory dynamics. This suggest that G60/G80 interplay-established through the conditioning process-serves as a robust and versatile mechanism for a fine coding of the environment emotional weight.

Poor replication validity of biomedical association studies reported by newspapers

Objective

To investigate the replication validity of biomedical association studies covered by newspapers.

Methods

We used a database of 4723 primary studies included in 306 meta-analysis articles. These studies associated a risk factor with a disease in three biomedical domains, psychiatry, neurology and four somatic diseases. They were classified into a lifestyle category (e.g. smoking) and a non-lifestyle category (e.g. genetic risk). Using the database Dow Jones Factiva, we investigated the newspaper coverage of each study. Their replication validity was assessed using a comparison with their corresponding meta-analyses.

Results

Among the 5029 articles of our database, 156 primary studies (of which 63 were lifestyle studies) and 5 meta-analysis articles were reported in 1561 newspaper articles. The percentage of covered studies and the number of newspaper articles per study strongly increased with the impact factor of the journal that published each scientific study. Newspapers almost equally covered initial (5/39 12.8%) and subsequent (58/600 9.7%) lifestyle studies. In contrast, initial non-lifestyle studies were covered more often (48/366 13.1%) than subsequent ones (45/3718 1.2%). Newspapers never covered initial studies reporting null findings and rarely reported subsequent null observations. Only 48.7% of the 156 studies reported by newspapers were confirmed by the corresponding meta-analyses. Initial non-lifestyle studies were less often confirmed (16/48) than subsequent ones (29/45) and than lifestyle studies (31/63). Psychiatric studies covered by newspapers were less often confirmed (10/38) than the neurological (26/41) or somatic (40/77) ones. This is correlated to an even larger coverage of initial studies in psychiatry. Whereas 234 newspaper articles covered the 35 initial studies that were later disconfirmed, only four press articles covered a subsequent null finding and mentioned the refutation of an initial claim.

Conclusion

Journalists preferentially cover initial findings although they are often contradicted by meta-analyses and rarely inform the public when they are disconfirmed.

Low statistical power in biomedical science: a review of three human research domains

Studies with low statistical power increase the likelihood that a statistically significant finding represents a false positive result. We conducted a review of meta-analyses of studies investigating the association of biological, environmental or cognitive parameters with neurological, psychiatric and somatic diseases, excluding treatment studies, in order to estimate the average statistical power across these domains. Taking the effect size indicated by a meta-analysis as the best estimate of the likely true effect size, and assuming a threshold for declaring statistical significance of 5%, we found that approximately 50% of studies have statistical power in the 0-10% or 11-20% range, well below the minimum of 80% that is often considered conventional. Studies with low statistical power appear to be common in the biomedical sciences, at least in the specific subject areas captured by our search strategy. However, we also observe evidence that this depends in part on research methodology, with candidate gene studies showing very low average power and studies using cognitive/behavioural measures showing high average power. This warrants further investigation.

Decision making under uncertainty in a spiking neural network model of the basal ganglia

The mechanisms of decision-making and action selection are generally thought to be under the control of parallel cortico-subcortical loops connecting back to distinct areas of cortex through the basal ganglia and processing motor, cognitive and limbic modalities of decision-making. We have used these properties to develop and extend a connectionist model at a spiking neuron level based on a previous rate model approach. This model is demonstrated on decision-making tasks that have been studied in primates and the electrophysiology interpreted to show that the decision is made in two steps. To model this, we have used two parallel loops, each of which performs decision-making based on interactions between positive and negative feedback pathways. This model is able to perform two-level decision-making as in primates. We show here that, before learning, synaptic noise is sufficient to drive the decision-making process and that, after learning, the decision is based on the choice that has proven most likely to be rewarded. The model is then submitted to lesion tests, reversal learning and extinction protocols. We show that, under these conditions, it behaves in a consistent manner and provides predictions in accordance with observed experimental data.

Arkypallidal Cells Send a Stop Signal to Striatum

The suppression of inappropriate actions is critical for flexible behavior. Cortical-basal ganglia networks provide key gating mechanisms for action suppression, yet the specific roles of neuronal subpopulations are poorly understood. Here, we examine Arkypallidal (‘‘Arky’’) and Prototypical (‘‘Proto’’) globus pallidus neurons during a Stop task, which requires abrupt cancellation of an imminent action. We first establish that Arky neurons can be identified by their firing properties across the natural sleep/wake cycle. We then show that Stop responses are earlier and stronger in the Arky compared to the Proto subpopulation. In contrast to other basal ganglia neurons, pallidal Stop responses are selective to Stop, rather than Go, cues. Furthermore, the timing of these Stop responses matches the suppression of developing striatal Go-related activity. Our results support a two-step model of action suppression: actions-inpreparation are first paused via a subthalamic-nigral pathway, then cancelled via Arky GABAergic projections to striatum.

The globus pallidus pars interna in goal-oriented and routine behaviors: Resolving a long-standing paradox

BACKGROUND

There is an apparent contradiction between experimental data showing that the basal ganglia are involved in goal-oriented and routine behaviors and clinical observations. Lesion or disruption by deep brain stimulation of the globus pallidus interna has been used for various therapeutic purposes ranging from the improvement of dystonia to the treatment of Tourette's syndrome. None of these approaches has reported any severe impairment in goal-oriented or automatic movement.

METHOD

To solve this conundrum, we trained 2 monkeys to perform a variant of a 2-armed bandit-task (with different reward contingencies). In the latter we alternated blocks of trials with choices between familiar rewarded targets that elicit routine behavior and blocks with novel pairs of targets that require an intentional learning process.

RESULTS

Bilateral inactivation of the globus pallidus interna, by injection of muscimol, prevents animals from learning new contingencies while performance remains intact, although slower for the familiar stimuli. We replicate in silico these data by adding lateral competition and Hebbian learning in the cortical layer of the theoretical model of the cortex-basal ganglia loop that provided the framework of our experimental approach.

CONCLUSION

The basal ganglia play a critical role in the deliberative process that underlies learning but are not necessary for the expression of routine movements. Our approach predicts that after pallidotomy or during stimulation, patients should have difficulty with complex decision-making processes or learning new goal-oriented behaviors. © 2016 Movement Disorder Society.

Lack of additive role of ageing in nigrostriatal neurodegeneration triggered by α-synuclein overexpression

INTRODUCTION

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by the loss of dopaminergic neurons as well as the presence of proteinaceous inclusions named Lewy bodies. α-synuclein (α-syn) is a major constituent of Lewy bodies, and the first disease-causing protein characterized in PD. Several α-syn-based animal models of PD have been developed to investigate the pathophysiology of PD, but none of them recapitulate the full picture of the disease. Ageing is the most compelling and major risk factor for developing PD but its impact on α-syn toxicity remains however unexplored. In this study, we developed and exploited a recombinant adeno-associated viral (AAV) vector of serotype 9 overexpressing mutated α-syn to elucidate the influence of ageing on the dynamics of PD-related neurodegeneration associated with α-syn pathology in different mammalian species.

RESULTS

Identical AAV pseudotype 2/9 vectors carrying the DNA for human mutant p.A53T α-syn were injected into the substantia nigra to induce neurodegeneration and synucleinopathy in mice, rats and monkeys. Rats were used first to validate the ability of this serotype to replicate α-syn pathology and second to investigate the relationship between the kinetics of α-syn-induced nigrostriatal degeneration and the progressive onset of motor dysfunctions, strikingly reminiscent of the impairments observed in PD patients. In mice, AAV2/9-hα-syn injection into the substantia nigra was associated with accumulation of α-syn and phosphorylated hα-syn, regardless of mouse strain. However, phenotypic mutants with either accelerated senescence or resistance to senescence did not display differential susceptibility to hα-syn overexpression. Of note, p-α-syn levels correlated with nigrostriatal degeneration in mice. In monkeys, hα-syn-induced degeneration of the nigrostriatal pathway was not affected by the age of the animals. Unlike mice, monkeys did not exhibit correlations between levels of phosphorylated α-syn and neurodegeneration.

CONCLUSIONS

In conclusion, AAV2/9-mediated hα-syn induces robust nigrostriatal neurodegeneration in mice, rats and monkeys, allowing translational comparisons among species. Ageing, however, neither exacerbated nigrostriatal neurodegeneration nor α-syn pathology per se. Our unprecedented multi-species investigation thus favours the multiple-hit hypothesis for PD wherein ageing would merely be an aggravating, additive, factor superimposed upon an independent disease process.

The Michelin red guide of the brain: role of dopamine in goal-oriented navigation

Spatial learning has been recognized over the years to be under the control of the hippocampus and related temporal lobe structures. Hippocampal damage often causes severe impairments in the ability to learn and remember a location in space defined by distal visual cues. Such cognitive disabilities are found in Parkinsonian patients. We recently investigated the role of dopamine in navigation in the 6-Hydroxy-dopamine (6-OHDA) rat, a model of Parkinson’s disease (PD) commonly used to investigate the pathophysiology of dopamine depletion (Retailleau et al., 2013). We demonstrated that dopamine (DA) is essential to spatial learning as its depletion results in spatial impairments. Our results showed that the behavioral effect of DA depletion is correlated with modification of the neural encoding of spatial features and decision making processes in hippocampus. However, the origin of these alterations in the neural processing of the spatial information needs to be clarified. It could result from a local effect: dopamine depletion disturbs directly the processing of relevant spatial information at hippocampal level. Alternatively, it could result from a more distributed network effect: dopamine depletion elsewhere in the brain (entorhinal cortex, striatum, etc.) modifies the way hippocampus processes spatial information. Recent experimental evidence in rodents, demonstrated indeed, that other brain areas are involved in the acquisition of spatial information. Amongst these, the cortex—basal ganglia (BG) loop is known to be involved in reinforcement learning and has been identified as an important contributor to spatial learning. In particular, it has been shown that altered activity of the BG striatal complex can impair the ability to perform spatial learning tasks. The present review provides a glimpse of the findings obtained over the past decade that support a dialog between these two structures during spatial learning under DA control.

Why am I lost without dopamine? Effects of 6-OHDA lesion on the encoding of reward and decision process in CA3

There is growing evidence that Parkinson's disease, generally characterized by motor symptoms, also causes cognitive impairment such as spatial disorientation. The hippocampus is a critical structure for spatial navigation and receives sparse but comprehensive dopamine (DA) innervation. DA loss is known to be the cause of Parkinson's disease and therefore it has been hypothesized that the associated spatial disorientation could result from hippocampal dysfunction. Because DA is involved in the prediction of reward expectation, it is possible to infer that spatial disorientation in DA depleted subjects results from the loss of the ability to detect the rewarding features within the environment. Amongst hippocampal formation subdivisions, CA3 properties such as the high liability of its place fields make it a serious candidate for interfacing DA reward system and spatial information encoding. We addressed this issue using multiple electrode recordings of CA3 in normal and dopamine depleted rats performing a spatial learning in a Y-maze. Our data confirm that DA is essential to spatial learning as its depletion results in spatial impairments. The present work also shows that CA3 involvement in the detection of spatial feature contextual significance is under DA control. Finally, it also shows that CA3 contributes to the decision making processes of navigation tasks. The data also reveal a lateralization effect of DA depletion underlined by neural correlates.

Opiate dependence induces network state shifts in the limbic system

Among current theories of addiction, hedonic homeostasis dysregulation predicts that the brain reward systems, particularly the mesolimbic dopamine system, switch from a physiological state to a new "set point." In opiate addiction, evidence show that the dopamine system principal targets, prefrontal cortex (PFC), nucleus accumbens (NAC) and basolateral amygdala complex (BLA) also adapt to repeated drug stimulation. Here we investigated the impact of chronic morphine on the dynamics of the network of these three interconnected structures. For that purpose we performed simultaneous electrophysiological recordings in freely-moving rats subcutaneously implanted with continuous-release morphine pellets. Chronic morphine produced a shift in the network state underpinned by changes in Delta and Gamma oscillations in the LFP of PFC, NAC and BLA, in correlation to behavioral changes. However despite continuous stimulation by the drug, an apparent normalization of the network activity and state occurred after 2 days indicating large scale adaptations. Blockade of μ opioid receptors was nonetheless sufficient to disrupt this acquired new stability in morphine-dependent animals. In line with the homeostatic dysregulation theory of addiction, our study provides original direct evidence that the PFC-NAC-BLA network of the dependent brain is characterized by a de novo balance for which the drug of abuse becomes the main contributor.

Interaction between cognitive and motor cortico-basal ganglia loops during decision making: a computational study

In a previous modeling study, Leblois et al. (2006) demonstrated an action selection mechanism in cortico-basal ganglia loops based on competition between the positive feedback, direct pathway through the striatum and the negative feedback, hyperdirect pathway through the subthalamic nucleus. The present study investigates how multiple level action selection could be performed by the basal ganglia. To do this, the model is extended in a manner consistent with known anatomy and electrophysiology in three main areas. First, two-level decision making has been incorporated, with a cognitive level selecting based on cue shape and a motor level selecting based on cue position. We show that the decision made at the cognitive level can be used to bias the decision at the motor level. We then demonstrate that, for accurate transmission of information between decision-making levels, low excitability of striatal projection neurons is necessary, a generally observed electrophysiological finding. Second, instead of providing a biasing signal between cue choices as an external input to the network, we show that the action selection process can be driven by reasonable levels of noise. Finally, we incorporate dopamine modulated learning at corticostriatal synapses. As learning progresses, the action selection becomes based on learned visual cue values and is not interfered with by the noise that was necessary before learning.

Why most biomedical findings echoed by newspapers turn out to be false: the case of attention deficit hyperactivity disorder

Context

Because positive biomedical observations are more often published than those reporting no effect, initial observations are often refuted or attenuated by subsequent studies.

Objective

To determine whether newspapers preferentially report on initial findings and whether they also report on subsequent studies.

Methods

We focused on attention deficit hyperactivity disorder (ADHD). Using Factiva and PubMed databases, we identified 47 scientific publications on ADHD published in the 1990s and soon echoed by 347 newspapers articles. We selected the ten most echoed publications and collected all their relevant subsequent studies until 2011. We checked whether findings reported in each “top 10” publication were consistent with previous and subsequent observations. We also compared the newspaper coverage of the “top 10” publications to that of their related scientific studies.

Results

Seven of the “top 10” publications were initial studies and the conclusions in six of them were either refuted or strongly attenuated subsequently. The seventh was not confirmed or refuted, but its main conclusion appears unlikely. Among the three “top 10” that were not initial studies, two were confirmed subsequently and the third was attenuated. The newspaper coverage of the “top 10” publications (223 articles) was much larger than that of the 67 related studies (57 articles). Moreover, only one of the latter newspaper articles reported that the corresponding “top 10” finding had been attenuated. The average impact factor of the scientific journals publishing studies echoed by newspapers (17.1 n = 56) was higher (p<0.0001) than that corresponding to related publications that were not echoed (6.4 n = 56).

Conclusion

Because newspapers preferentially echo initial ADHD findings appearing in prominent journals, they report on uncertain findings that are often refuted or attenuated by subsequent studies. If this media reporting bias generalizes to health sciences, it represents a major cause of distortion in health science communication.

Oscillatory entrainment of subthalamic nucleus neurons and behavioural consequences in rodents and primates

We investigated the functional role of oscillatory activity in the local field potential (LFP) of the subthalamic nucleus (STN) in the pathophysiology of Parkinson's disease (PD). It has been postulated that beta (15-30 Hz) oscillatory activity in the basal ganglia induces PD motor symptoms. To assess this hypothesis, an LFP showing significant power in the beta frequency range (23 Hz) was used as a stimulus both in vitro and in vivo. We first demonstrated in rat brain slices that STN neuronal activity was driven by the LFP stimulation. We then applied beta stimulation to the STN of 16 rats and two monkeys while quantifying motor behaviour. Although stimulation-induced behavioural effects were observed, stimulation of the STN at 23 Hz induced no significant decrease in motor performance in either rodents or primates. This study is the first to show LFP-induced behaviour in both rats and primates, and highlights the complex relationship between beta power and parkinsonian symptoms.

Basal Ganglia preferentially encode context dependent choice in a two-armed bandit task

Decision is a self-generated phenomenon, which is hard to track with standard time averaging methods, such as peri-event time histograms (PETHs), used in behaving animals. Reasons include variability in duration of events within a task and uneven reaction time of animals. We have developed a temporal normalization method where PETHs were juxtaposed all along task events and compared between neurons. We applied this method to neurons recorded in striatum and GPi of behaving monkeys involved in a choice task. We observed a significantly higher homogeneity of neuron activity profile distributions in GPi than in striatum. Focusing on the period of the task during which the decision was taken, we showed that approximately one quarter of all recorded neurons exhibited tuning functions. These so-called coding neurons had average firing rates that varied as a function of the value of both presented cues, a combination here referred to as context, and/or value of the chosen cue. The tuning functions were used to build a simple maximum likelihood estimation model, which revealed that (i) GPi neurons are more efficient at encoding both choice and context than striatal neurons and (ii) context prediction rates were higher than those for choice. Furthermore, the mutual information between choice or context values and decision period average firing rate was higher in GPi than in striatum. Considered together, these results suggest a convergence process of the global information flow between striatum and GPi, preferentially involving context encoding, which could be used by the network to perform decision-making.

Misrepresentation of neuroscience data might give rise to misleading conclusions in the media: the case of attention deficit hyperactivity disorder

BACKGROUND

There is often a huge gap between neurobiological facts and firm conclusions stated by the media. Data misrepresentation in the conclusions and summaries of neuroscience articles might contribute to this gap.

METHODOLOGY/PRINCIPAL FINDINGS

Using the case of attention deficit hyperactivity disorder (ADHD), we identified three types of misrepresentation. The first relies on prominent inconsistencies between results and claimed conclusions and was observed in two scientific reports dealing with ADHD. Only one out of the 61 media articles echoing both scientific reports adequately described the results and, thus questioned the claimed conclusion. The second type of misrepresentation consists in putting a firm conclusion in the summary while raw data that strongly limit the claim are only given in the results section. To quantify this misrepresentation we analyzed the summaries of all articles asserting that polymorphisms of the gene coding for the D4 dopaminergic receptor are associated with ADHD. Only 25 summaries out of 159 also mentioned that this association confers a small risk. This misrepresentation is also observed in most media articles reporting on ADHD and the D4 gene. The third misrepresentation consists in extrapolating basic and pre-clinical findings to new therapeutic prospects in inappropriate ways. Indeed, analysis of all ADHD-related studies in mice showed that 23% of the conclusions were overstated. The frequency of this overstatement was positively related with the impact factor of the journal.

CONCLUSION/SIGNIFICANCE

Data misrepresentations are frequent in the scientific literature dealing with ADHD and may contribute to the appearance of misleading conclusions in the media. In synergy with citation distortions and publication biases they influence social representations and bias the scientific evidence in favor of the view that ADHD is primarily caused by biological factors. We discuss the social consequences and the causes of data misrepresentations and suggest a few corrective actions.

The translational value of the MPTP non-human primate model of Parkinsonism for deep brain stimulation research

Deep brain stimulation (DBS) has been applied in more than 70000 patients worldwide during the last two decades. The main target is the subthalamic nucleus (STN) for the treatment of motor complications in late stage Parkinson's disease (PD). Positive results in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated non-human primates have set the grounds for its successful translation to PD patients. Since then, this model has allowed gaining significant insights in the underlying mechanisms of action of DBS and is currently being used for the development of new stimulation techniques. Altogether, this underpins the high potential of this preclinical model for future translation of DBS research in PD.

Dynamic Changes in the Cortex-Basal Ganglia Network After Dopamine Depletion in the Rat

It is well established that parkinsonian syndrome is associated with alterations in the temporal pattern of neuronal activity and local field potentials in the basal ganglia (BG). An increase in synchronized oscillations has been observed in different BG nuclei in parkinsonian patients and animal models of this disease. However, the mechanisms underlying this phenomenon remain unclear. This study investigates the functional connectivity in the cortex-BG network of a rodent model of Parkinson's disease. Single neurons and local field potentials were simultaneously recorded in the motor cortex, the striatum, and the substantia nigra pars reticulata (SNr) of freely moving rats, and high-voltage spindles (HVSs) were used to compare signal transmission before and after dopaminergic depletion. It is shown that dopaminergic lesion results in a significant enhancement of oscillatory synchronization in the BG: the coherence between pairs of structures increased significantly and the percentage of oscillatory auto- and cross-correlograms. HVS episodes were also more numerous and longer. These changes were associated with a shortening of the latency of SNr response to cortical activation, from 40.5 ± 4.8 to 10.2 ± 1.07 ms. This result suggests that, in normal conditions, SNr neurons are likely to be driven by late inputs from the indirect pathway; however, after the lesion, their shorter latency also indicates an overactivation of the hyperdirect pathway. This study confirms that neuronal signal transmission is altered in the BG after dopamine depletion but also provides qualitative evidence for these changes at the cellular level.

Late emergence of synchronized oscillatory activity in the pallidum during progressive parkinsonism

Parkinson's disease is known to result from basal ganglia dysfunction. Electrophysiological recordings in parkinsonian patients and animals have shown the emergence of abnormal synchronous oscillatory activity in the cortico-basal ganglia network in the pathological condition. In addition, previous studies pointed out an altered response pattern during movement execution in the pallidum of parkinsonian animals. To investigate the dynamics of these changes during disease progression and to relate them to the onset of the motor symptoms, we recorded spontaneous and movement-related neuronal activity in the internal pallidum of nonhuman primates during a progressive dopamine depletion process. Parkinsonian motor symptoms appeared progressively during the intoxication protocol, at the end of which both animals displayed severe akinesia, rigidity and postural abnormalities. Spontaneous firing rates did not vary significantly after intoxication. During the early phase of the protocol, voluntary movements were significantly slowed down and delayed. At the same time, the neuronal response to movement execution was modified and inhibitory responses disappeared. In contrast, the unitary and collective dynamic properties of spontaneous neuronal activity, as revealed by spectral and correlation analysis, remained unchanged during this period. Spontaneous correlated activity increased later, after animals became severely bradykinetic, whereas synchronous oscillatory activity appeared only after major motor symptoms developed. Thus, a causality between the emergence of synchronous oscillations in the pallidum and main parkinsonian motor symptoms seems unlikely. The pathological disruption of movement-related activity in the basal ganglia appears to be a better correlate at least to bradykinesia and stands as the best candidate to account for this motor symptom.

Shaping of motor responses by incentive values through the basal ganglia

The striatum is a key neural interface for cognitive and motor information processing in which associations between reward value and visual stimulus can be used to modify motor commands. It can guide action-selection processes that occur farther downstream in the basal ganglia (BG) circuit, by encoding the reward value of an action. Here, we report on the study of simultaneously recorded neurons in the dorsal striatum (input stage of the BG) and the internal pallidum (output stage of the BG) in two monkeys performing a center-out motor task in which the visual targets were associated with different reward probabilities. We show that the tuning curves of motor-related neurons in both structures are modulated by the value of the action before movement initiation and during its execution. The representations of values associated with different actions change dynamically during the task in the internal globus pallidus, with a significant increase in the number of encoding neurons for the chosen target at the onset of movement. This report sheds additional light on the functional differences between the input and output structures of the BG and supports the assertion that the dorsal basal ganglia are involved in movement-related decision-making processes based on incentive values.

Synchronous high-voltage spindles in the cortex-basal ganglia network of awake and unrestrained rats

Synchronous oscillations in various frequency ranges have been recorded in several nuclei of the basal ganglia (BG) and are thought to be an information processing mechanism. High-voltage spindles (HVSs) are 5-13 Hz spike-and-wave oscillations, which are commonly recorded in rats and which have been reported in some recent studies where their occurrence in the BG has been investigated. We recorded single neurons and local field potentials (LFPs) simultaneously in the motor cortex, striatum and substantia nigra pars reticulata (SNr) of the freely moving rat. We took advantage of the high level of synchronization observed during HVSs to study signal transmission in the cortex-BG network in the awake animals. The results show that LFPs are synchronized in the motor cortex, striatum and SNr during HVS episodes and that the latter propagate from the cortex to the SNr via the striatum. Moreover, > 50% of single neurons in each of these structures are triggered by the HVS. Following the discharge of cortical cells, SNr neurons are first inhibited after approximately 19 ms and then activated after approximately 45 ms. This response is probably driven by the direct and indirect pathways, respectively, without any involvement of the hyperdirect pathway. Here, it is shown that cortex-BG connectivity can be studied using physiological signals in the freely moving animal as opposed to artificial stimulation under anaesthetized conditions. This opens the door to further studies under various experimental conditions, such as animal models of basal ganglia disorders.

Temporal and spatial alterations in GPi neuronal encoding might contribute to slow down movement in Parkinsonian monkeys

Although widely investigated, the exact relationship between changes in basal ganglia neuronal activity and parkinsonian symptoms has not yet been deciphered. It has been proposed that bradykinesia (motor slowness) is related either to a modification of the activity of the globus pallidus internalis (GPi), the main output structure, or to a loss of spatial selectivity of the extrapyramidal motor system. Here we investigate the relationship between movement initiation and GPi activity in parkinsonian non-human primates. We compare neuronal encoding of movement in the normal and pathological conditions. After dopamine depletion, we observe an increased number of neurons responding to movement, with a less specific somato-sensory receptive field and a disruption of the selection mechanism. Moreover, the temporal order of the response of GPi neurons in parkinsonian animals is reversed. Indeed, whereas muscle activity and movement are delayed in parkinsonian animals, GPi neuronal responses to movement occur earlier and are prolonged, compared with normal conditions. Parkinsonian bradykinesia could thus result from an impairment of both temporal and spatial specificity of the GPi response to movement.

Increased slow oscillatory activity in substantia nigra pars reticulata triggers abnormal involuntary movements in the 6-OHDA-lesioned rat in the presence of excessive extracelullar striatal dopamine

Since electrophysiological correlates of L-dopa-induced dyskinesia (LID) are almost unknown, changes of striatal dopamine (DA) transmission and electrophysiological activity of the substantia nigra pars reticulata (SNr) were recorded before and after acute L-dopa administration in sham-operated and 6-hydroxydopamine (6-OHDA)-lesioned rats that were previously treated with vehicle or L-dopa for 10 days. Abnormal involuntary movements occurred only in the L-dopa-primed 6-OHDA-lesioned rats that showed after acute l-dopa administration a decrease in firing rate, the highest local field potential power in the theta/alpha band, a consequent oscillatory activity in the same frequency band at the single neuron level and an excessive increase in striatal DA release associated with the lowest level of DA metabolism. These results suggest that increased synchronised afferent activity may drive SNr oscillations in the same frequency band and is associated with abnormal involuntary movements, further suggesting the potential use of desynchronising drugs for managing LID in Parkinson's disease.

Competition between feedback loops underlies normal and pathological dynamics in the basal ganglia

Experiments performed in normal animals suggest that the basal ganglia (BG) are crucial in motor program selection. BG are also involved in movement disorders. In particular, BG neuronal activity in parkinsonian animals and patients is more oscillatory and more synchronous than in normal individuals. We propose a new model for the function and dysfunction of the motor part of BG. We hypothesize that the striatum, the subthalamic nucleus, the internal pallidum (GPi), the thalamus, and the cortex are involved in closed feedback loops. The direct (cortex-striatum-GPi-thalamus-cortex) and the hyperdirect loops (cortex-subthalamic nucleus-GPi-thalamus-cortex), which have different polarities, play a key role in the model. We show that the competition between these two loops provides the BG-cortex system with the ability to perform motor program selection. Under the assumption that dopamine potentiates corticostriatal synaptic transmission, we demonstrate that, in our model, moderate dopamine depletion leads to a complete loss of action selection ability. High depletion can lead to synchronous oscillations. These modifications of the network dynamical state stem from an imbalance between the feedback in the direct and hyperdirect loops when dopamine is depleted. Our model predicts that the loss of selection ability occurs before the appearance of oscillations, suggesting that Parkinson's disease motor impairments are not directly related to abnormal oscillatory activity. Another major prediction of our model is that synchronous oscillations driven by the hyperdirect loop appear in BG after inactivation of the striatum.

Emerging patterns of neuronal responses in supplementary and primary motor areas during sensorimotor adaptation

Acquisition and retention of sensorimotor skills have been extensively investigated psychophysically, but little is known about the underlying neuronal mechanisms. Here we examine the evolution of neural activity associated with adaptation to new kinematic tasks in two cortical areas: the caudal supplementary motor area (SMA proper), and the primary motor cortex (MI). We investigate the hypothesis that adaptation starts at premotor areas, i.e., higher in the hierarchy of computation, until a stable representation is formed in primary areas. In accordance with previous studies, we found that adaptation can be characterized by two phases: an early phase that is accompanied by fast and substantial reduction of errors, followed by a late phase with slower and more moderate improvements in behavior. We used unsupervised clustering to separate the activity of the single cells into groups of cells with similar response patterns, under the assumption that each such subpopulation forms a functional unit. We specifically observed the number of clusters in each cortical area during early and late phases of the adaptation and found that the number of clusters is higher in the SMA during early phases of adaptation. In contrast, a higher number of clusters was observed in MI only during late phases. Our results suggest a new approach to analyze responses of large populations of neurons and use it to show a hierarchy of dynamic reorganization of functional groups during adaptation.

Subthalamic high frequency stimulation resets subthalamic firing and reduces abnormal oscillations

High frequency stimulation (HFS) of the subthalamic nucleus (STN) is a well-established therapeutic approach for the treatment of late-stage Parkinson's disease. Although the underlying cause of this illness remains a mystery, changes in firing rate and synchronized activity in different basal ganglia nuclei have been related to its symptoms. Here we investigated the impact of STN-HFS on firing rate as well as correlated and oscillatory activity in the STN network in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned non-human primates by using simultaneous extracellular single-unit recordings. STN-HFS reduced (i) the firing rate of STN neurons, (ii) the oscillatory activity at an individual STN neuron level as well as (iii) the correlated and oscillatory activity between pairs of STN neurons, while contralateral rigidity was improved. A detailed analysis showed that the decrease of mean firing rate resulted from the resetting of firing probability to virtually zero by the stimulus pulse. Subsequently, STN neurons resumed their activity after a mean duration of 2.9 +/- 0.1 ms and their firing probability returned to baseline values approximately 7 ms after the onset of the stimulus pulse, the recovery of the firing probability being represented by a sigmoid function. Thus, the overall decrease of the mean firing rate resulted from the repetition of this dynamical process with a frequency of 130 Hz (interstimulus interval approximately 7.7 ms), allowing the neuron to fire with its baseline firing rate only for a very short period. Although the mechanisms underlying the desynchronization of neuronal activity in the STN network remain unclear, the resetting of STN neuron firing probability by the electrical stimulus would rather be expected to increase oscillatory activity at an individual neuron level as well as correlated and oscillatory activity between pairs of STN neurons. However, assuming the resetting of firing rate to be the consequence of a transient GABAergic inhibition through excitation of presynaptic GABAergic axon terminals, different recovery periods of STN neurons might delay the appearance of synchronized oscillations, particularly if they are not generated locally. In conclusion, our study provides new evidence that STN-HFS decreases oscillatory activity in the STN network. Although the exact relation between oscillatory activity and Parkinson's disease symptoms remains to be determined, the present results suggest that STN-HFS might at least partially exert its beneficial effects through the reduction of oscillatory activity in the STN network and consequently in the entire cortex-basal ganglia-cortex network.