Behavioral flexibility is the ability of a subject to change its behavior according to contextual cues. In humans, Obsessive Compulsive Disorders (OCD) is characterized by repetitive behavior, performed through rigid rituals. This phenomenological observation has led to explore the idea that OCD patients may have diminished behavioral flexibility. To address this question we developed innovative translational approaches across multiple species, including human patients suffering from obsessive-compulsive disorders, and rodent genetic models of OCD to provide original data in the perspective of enlightening the neurocognitive bases of compulsive behaviors. Behavioral flexibility may be challenged in experimental tasks such as reversal learning paradigms. In these tasks, the subject has to respond to either of two different visual stimuli but only one stimulus is positively rewarded while the other is not. After this first association has been learned, reward contingency are inverted, so that the previously neutral stimulus is now rewarded, while the previously rewarded stimulus is not. Performance in reversal learning is indexed by the number of perseverative errors committed when participants maintain their response towards previously reinforced stimulus in spite of negative reward. Unsurprisingly, this behavioral task has been adapted to mice using various response modalities (T-maze, lever press, nose-poke). Using animal models of compulsive behaviors give much more possibilities to study the deficient functions and their underlying neural basis that could lead to pathological repetitive behaviors. Here we present new behavioral set-ups that we developed in parallel in human (i.e. healthy subjects and OCD patients) and mice (i.e. controls and SAPAP3-KO mice) to study the role of the behavioral flexibility as a possible endophenotype of OCD. We observed that the subjects suffering of compulsive behaviors showed perseverative maladaptive behaviors in these tasks. By comparing the results of a similar task-design in humans and mouse models we will discuss the pertinence of such translational approach to further study the neurocognitive basis of compulsive behaviors.

Deep Brain Stimulation (DBS) has gained a revival for psychiatric disorders after its application in the SubThalamic Nucleus (STN) for neurological disorders such as Parkinson's disease. The involvement of STN in non-motor processes has also been demonstrated and led to target it for the treatment of obsessive-compulsive disorders. In the context of another disease related to loss of impulse control, addiction, we suggest STN to be an appropriate target. We have tested the effects of STN “inactivation” by lesions or DBS in rats on motivation for food (sucrose), cocaine, heroin, alcohol and nicotine. Inactivation of the STN does not affect consummatory processes, but seems to act on incentive motivation (responses to cues associated with a given reward). STN inactivation can induce opposite effects on motivation for natural reward or for various drugs of abuse, decreasing motivation for drugs, while increasing motivation for sweet food reward [1,2]. STN inactivation by either lesion or DBS can also prevent the loss of control over cocaine or alcohol intake, as assessed in the model of escalation of drug intake. These data, in line with clinical observation in Parkinsonian patients suffering from addiction to their dopaminergic treatment, support our hypothesis that STN could be an interesting target for the treatment of addiction and DBS could be the appropriate surgical tool.

Background: Subthalamic nucleus deep brain stimulation (STN–DBS) has become a standard treatment for many patients with Parkinson’s disease (PD). The reported clinical outcome measures for procedures done under general anesthesia (GA) compared to traditional local anesthetic (LA) technique are quite heterogeneous and difficult to compare. The aim of this systematic review and metaanalysis was to determine whether the clinical outcome after STN–DBS insertion under GA is comparable to that under LA in patients with Parkinson’s disease. Methods: The databases of Medline Embase, Cochrane library and Pubmed were searched for eligible studies (human trials, English language, published between 1946 and January of 2016). The primary outcome of this study was to assess the postoperative improvement in the symptoms, evaluated using either Unified Parkinson’s Disease Rating Scale (UPDRS) scores or levodopa equivalent dosage (LEDD) requirement. Results: The literature searches yielded 395 citations and six retrospective cohort studies with a sample size of 455 (194 in GA and 261 in LA) were included in the analysis. Regarding the clinical outcomes, there were no significant differences in the postoperative Unified Parkinson’s disease rating scale and levodopa equivalent drug dosage between the GA and the LA groups. Similarly, the adverse events and target accuracy were also comparable between the groups. Conclusions: This systematic review and meta-analysis shows that currently there is no good quality data to suggest equivalence of GA to LA during STN-DBS insertion in patients with PD, with some factors trending towards LA. There is a need for a prospective randomized control trial to validate our results.

In this review, we have gathered all the available evidence to guide medication management after deep brain stimulation (DBS) in Parkinson’s disease (PD). Surprisingly, we found that almost no study addressed drug-based management in the postoperative period. Dopaminergic medications are usually reduced, but whether the levodopa or dopamine agonist is to be reduced is left to the personal preference of the treating physician. We have summarized the pros and cons of both approaches. No study on the management of cognitive problems after DBS has been done, and only a few studies have explored the pharmacological management of such DBS-resistant symptoms as voice (amantadine), balance (donepezil) or gait disorders (amantadine, methylphenidate). As for the psychiatric problems so frequently reported in PD patients, researchers have directed their attention to the complex interplay between stimulation and reduction of dopaminergic drugs only recently. In conclusion, studies addressing medical management following DBS are still needed and will certainly contribute to the ultimate success of DBS procedures.

During the “DBS Canada Day” symposium held in Toronto July 4-5, 2014, the scientific committee invited experts to discuss three main questions on target selection for deep brain stimulation (DBS) of patients with Parkinson’s disease (PD). First, is the subthalamic nucleus (STN) or the globus pallidus internus (GPi) the ideal target? In summary, both targets are equally effective in improving the motor symptoms of PD. STN allows a greater medications reduction, while GPi exerts a direct antidyskinetic effect. Second, are there further potential targets? Ventral intermediate nucleus DBS has significant long-term benefit for tremor control but insufficiently addresses other motor features of PD. DBS in the posterior subthalamic area also reduces tremor. The pedunculopontine nucleus remains an investigational target. Third, should DBS for PD be performed unilaterally, bilaterally or staged? Unilateral STN DBS can be proposed to asymmetric patients. There is no evidence that a staged bilateral approach reduces the incidence of DBS-related adverse events.

The use of deep brain stimulation has become increasingly common for the treatment of movement disorders, including Parkinson disease. Although deep brain stimulation is generally very successful in alleviating the extrapyramidal symptoms of Parkinson disease, side effects can occur. This case report describes a patient presenting to the emergency department in a state of extreme aggression 3 days after a change in the parameters of his bilateral subthalamic nucleus stimulator. We review the complications of deep brain stimulation relevant to the emergency physician and provide some practical information on stimulator adjustment in an emergency.

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) in individuals with Parkinson's disease (PD) has often been associated with reduced verbal fluency performance. This study aimed to directly assess semantic switching as a function of STN stimulation in PD participants with the Homophone Meaning Generation Test (HMGT). Seventeen participants with PD who had received STN DBS completed the HMGT in on and off stimulation conditions. Twenty-one non-neurologically impaired participants acted as controls. PD participants (in both on and off stimulation conditions) generated significantly fewer meanings than control participants and consistent with the previous reports of verbal fluency impairment, PD participants produced fewer definitions in the on stimulation condition. PD participants (in both on and off stimulation conditions) also had greater difficulty generating definitions for nonhomographic homophones compared with homographic homographs. The results of this study indicate that STN stimulation exacerbates impairment in semantic switching. (JINS, 2008, 14, 890–894.)

Parkinson’s disease (PD) is characterized by nigral degeneration of dopaminergic neurons in the pars compacta of the substantia nigra. Rather than treating only the symptomatic aspects of Parkinson’s disease, one may also consider treatments designed to retard, arrest, or even reverse this degenerative process. Such strategies could include preventive or restorative treatments instead of purely palliative treatments. A recent hypothesis states that glutamate output from the subthalamic nucleus (STN) to the substantia nigra contributes to the neurotoxic process underlying dopaminergic cell death in Parkinson’s disease. Furthermore, high-frequency stimulation (HFS) of the STN inhibits neurons resulting in the suppression of their glutamate output. Experiments in both rats and monkeys provide preliminary data supporting this hypothesis. Kainic acid (KA) lesions of the STN prevent the loss of dopaminergic neurons in the substantia nigra after intrastriatal injection of 6-hydroxydopamine (6-OHDA) in rats, and after systemic administration of MPTP in monkeys. In PD patients, the background level of their disease is evaluated in the off medication/off stimulation state (UPDRS III score), over a period of 5 years. Thirty percent of the patients are stabilized and 18% have persistent improvement of their disease-related impairment. Further experiments are needed, including controlled clinical trials utilizing functional imaging of the dopamine transporters and post-synaptic receptors.

Subthalamic nucleus (STN) neurons have a pivotal role in basal ganglia, as a result of their intrinsic membrane properties, connections within the circuit and glutamatergic nature. Their innate pacemaker activity, consisting of a single-spike tonic mode of discharge, is abolished in the case of hemiballism, profoundly disrupted in the Parkinsonian state and replaced by a regular bursting mode under treatment (high-frequency stimulation, HFS). We propose that control STN activity represents a clock, an internal measure of time allowing the correct automatic execution of learned movements and, in particular, the automatic switch from one movement to the next in a sequential motor pattern. STN neuronal activity would be able to reset the frequency of oscillations of motor thalamo-cortical loops, notably in the γ band.

This work is focused on the study of neuronal circuits arising from the rodent caudal intralaminar nuclei and their presumed role on basal ganglia function. Emphasis was placed on the analysis of the architecture of thalamostriatal and thalamo-subthalamic projections in albino rats. Our major interest was to elucidate whether thalamic inputs were related to projection neurons or local circuit neurons within targeted structures (striatum and subthalamic nucleus). Projections coming from the parafascicular nucleus (PF) to the striatum displayed a patchy organization throughout the matrix compartment. These patches are composed by dense terminal axonal arborizations, often containing striatal neurons projecting to the entopeduncular nucleus (ENT) (medial globus pallidus in primates) and neurons projecting to the substantia nigra reticulata (SNR). The thalamostriatal projections under scrutiny were also seen to be in register with all the major classes of striatal interneurons (nitrergic neurons, neurons containing the calcium binding protein parvalbumin (PV) and cholinergic interneurons). Subthalamic neurons projecting to the ENT are the presumed postsynaptic target for fibers coming from the sensorimotor part (dorsolateral) of the PF. In summary, glutamatergic axons arising from the PF might exert a dual control of the striatal output, either by directly exciting striatal projection neurons or indirectly by means of a previous synaptic contact onto an striatal interneuron which in turn modulates the activity of projection neurons. Furthermore, thalamic inputs can also gain access to basal ganglia output nuclei via subthalamo-pallidal projecting neurons, neurons receiving glutamatergic thalamo-subthalamic projections. Thus, activation of either circuit has an opposite physiological effect on the basal ganglia output nucleus. Taken together, these data suggest that the PF may influence neuronal activity in the direct and indirect circuits and could be considered as an additional component of the basal ganglia motor loops.

Advances in the neurosciences and functional neurosurgery have led to a renaissance in the use of brain stimulation technology. A number of intractable neurological disorders can now be safely and successfully treated with brain stimulation. Although this technique was first performed over 50 years ago, it has only now begun to reach its vast clinical potential. This article will provide a historical overview of brain stimulation, describe state-of-the-art clinical applications, and discuss future prospects in this rapidly advancing field.