Interleaved Propofol-Ketamine Maintains DBS Physiology and Hemodynamic Stability: A Double-Blind Randomized Controlled Trial.

BACKGROUND: The gold standard anesthesia for deep brain stimulation (DBS) surgery is the "awake" approach, using local anesthesia alone. Although it offers high-quality microelectrode recordings and therapeutic-window assessment, it potentially causes patients extreme stress and might result in suboptimal surgical outcomes. General anesthesia or deep sedation is an alternative, but may reduce physiological testing reliability and lead localization accuracy. OBJECTIVES: The aim is to investigate a novel anesthesia regimen of ketamine-induced conscious sedation for the physiological testing phase of DBS surgery. METHODS: Parkinson's patients undergoing subthalamic DBS surgery were randomly divided into experimental and control groups. During physiological testing, the groups received 0.25 mg/kg/h ketamine infusion and normal saline, respectively. Both groups had moderate propofol sedation before and after physiological testing. The primary outcome was recording quality. Secondary outcomes included hemodynamic stability, lead accuracy, motor and cognitive outcome, patient satisfaction, and adverse events. RESULTS: Thirty patients, 15 from each group, were included. Intraoperatively, the electrophysiological signature and lead localization were similar under ketamine and saline. Tremor amplitude was slightly lower under ketamine. Postoperatively, patients in the ketamine group reported significantly higher satisfaction with anesthesia. The improvement in Unified Parkinson's disease rating scale part-III was similar between the groups. No negative effects of ketamine on hemodynamic stability or cognition were reported perioperatively. CONCLUSIONS: Ketamine-induced conscious sedation provided high quality microelectrode recordings comparable with awake conditions. Additionally, it seems to allow superior patient satisfaction and hemodynamic stability, while maintaining similar post-operative outcomes. Therefore, it holds promise as a novel alternative anesthetic regimen for DBS. © 2024 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Tonic and phasic changes in anteromedial globus pallidus activity in Tourette syndrome.

BACKGROUND: Tourette syndrome is a hyperkinetic neurodevelopmental disorder characterized by tics. OBJECTIVE: Assess the neuronal changes in the associative/limbic GP associated with Tourette syndrome. METHODS: Neurophysiological recordings were performed from the anterior (associative/limbic) GPe and GPi of 8 awake patients during DBS electrode implantation surgeries. RESULTS: The baseline firing rate of the neurons was low in a state-dependent manner in both segments of the GP. Tic-dependent transient rate changes were found in the activity of individual neurons of both segments around the time of the tic. Neither oscillatory activity of individual neurons nor correlations in their interactions were observed. CONCLUSIONS: The results demonstrate the involvement of the associative/limbic pathway in the underlying pathophysiology of Tourette syndrome and point to tonic and phasic modulations of basal ganglia output as a key mechanisms underlying the abnormal state of the disorder and the expression of individual tics, respectively. © 2017 International Parkinson and Movement Disorder Society.

Corticostriatal Divergent Function in Determining the Temporal and Spatial Properties of Motor Tics.

Striatal disinhibition leads to the formation of motor tics resembling those expressed during Tourette syndrome and other tic disorders. The spatial properties of these tics are dependent on the location of the focal disinhibition within the striatum; however, the factors affecting the temporal properties of tic expression are still unknown. Here, we used microstimulation within the motor cortex of freely behaving rats before and after striatal disinhibition to explore the factors underlying the timing of individual tics. Cortical activation determined the timing of individual tics via an accumulation process of inputs that was dependent on the frequency and amplitude of the inputs. The resulting tics and their neuronal representation within the striatum were highly stereotypic and independent of the cortical activity properties. The generation of tics was limited by absolute and relative tic refractory periods that were derived from an internal striatal state. Thus, the precise time of the tic expression depends on the interaction between the summation of incoming excitatory inputs to the striatum and the timing of the previous tic. A data-driven computational model of corticostriatal function closely replicated the temporal properties of tic generation and enabled the prediction of tic timing based on incoming cortical activity and tic history. These converging experimental and computational findings suggest a clear functional dichotomy within the corticostriatal network, pointing to disparate temporal (cortical) versus spatial (striatal) encoding. Thus, the abnormal striatal inhibition typical of Tourette syndrome and other tic disorders results in tics due to cortical activation of the abnormal striatal network. SIGNIFICANCE STATEMENT: The factors underlying the temporal properties of tics expressed in Tourette syndrome and other tic disorders have eluded clinicians and scientists for decades. In this study, we highlight the key role of corticostriatal activity in determining the timing of individual tics. We found that cortical activation determined the timing of tics but did not determine their form. A data-driven computational model of the corticostriatal network closely replicated the temporal properties of tic generation and enabled the prediction of tic timing based on incoming cortical activity and tic history. This study thus shows that, although tics originate in the striatum, their timing depends on the interplay between incoming excitatory corticostriatal inputs and the internal striatal state.

Abnormal neuronal activity in Tourette syndrome and its modulation using deep brain stimulation.

Tourette syndrome (TS) is a common childhood-onset disorder characterized by motor and vocal tics that are typically accompanied by a multitude of comorbid symptoms. Pharmacological treatment options are limited, which has led to the exploration of deep brain stimulation (DBS) as a possible treatment for severe cases. Multiple lines of evidence have linked TS with abnormalities in the motor and limbic cortico-basal ganglia (CBG) pathways. Neurophysiological data have only recently started to slowly accumulate from multiple sources: noninvasive imaging and electrophysiological techniques, invasive electrophysiological recordings in TS patients undergoing DBS implantation surgery, and animal models of the disorder. These converging sources point to system-level physiological changes throughout the CBG pathway, including both general altered baseline neuronal activity patterns and specific tic-related activity. DBS has been applied to different regions along the motor and limbic pathways, primarily to the globus pallidus internus, thalamic nuclei, and nucleus accumbens. In line with the findings that also draw on the more abundant application of DBS to Parkinson's disease, this stimulation is assumed to result in changes in the neuronal firing patterns and the passage of information through the stimulated nuclei. We present an overview of recent experimental findings on abnormal neuronal activity associated with TS and the changes in this activity following DBS. These findings are then discussed in the context of current models of CBG function in the normal state, during TS, and finally in the wider context of DBS in CBG-related disorders.

Common neuronal mechanisms underlying tics and hyperactivity.

Tourette syndrome (TS) and attention deficit hyperactivity disorder (ADHD) are two neurodevelopmental hyper-behavioral disorders that are highly comorbid. The source of this comorbidity and the neuronal mechanisms underlying these disorders are still unclear. We examined the neuronal activity of freely behaving rats before and after striatal disinhibition, to reveal the similar and distinct neuronal components underlying the mechanisms of TS-like and ADHD-like symptom expression. Focal disinhibition induced motor tics, locomotor hyperactivity or a comorbid effect depending on the location of the injection within the different functional domains of the striatum. While injections within the motor domain induced motor tics, injections into the limbic domain induced mainly locomotor hyperactivity. Disinhibition, regardless of its striatal location, led to qualitatively similar macro-scale and micro-scale neuronal changes. These changes were localized to the domain of the manipulation and remained partly segregated, indicating that hyperactivity is induced as a result of changes in the limbic domain without directly activating the motor domain. Despite the general similarity of induced neuronal changes, these changes were associated with different behavioral effects and were more stereotypic and pronounced following motor-domain disinhibition in comparison to limbic-domain disinhibition. Our recordings revealed a disparity in the neuronal input-output transformation of the two models of the disorders. The results suggest that tic expression and hyperactivity states share similar local neuronal activity changes which manifest in different neuronal and behavioral outcomes. These results expose an intriguing link between tics and their comorbid symptoms and hint at striatal disinhibition, resulting from GABAergic alterations, as a potential common mechanism underlying distinct symptoms expressed by hyper-behavioral patients.

Prolonged striatal disinhibition as a chronic animal model of tic disorders.

BACKGROUND: Experimental findings and theoretical models have associated Tourette syndrome with abnormal striatal inhibition. The expression of tics, the hallmark symptom of this disorder, has been transiently induced in non-human primates and rodents by the injection of GABAA antagonists into the striatum, leading to temporary disinhibition. NEW METHOD: The novel chronic model of tic expression utilizes mini-osmotic pumps implanted subcutaneously in the rat's back for prolonged infusion of bicuculline into the dorsolateral striatum. RESULTS: Tics were expressed on the contralateral side to the infusion over a period of multiple days. Tic expression was stable, and maintained similar properties throughout the infusion period. Electrophysiological recordings revealed the existence of tic-related local field potential spikes and individual neuron activity changes that remained stable throughout the infusion period. COMPARISON WITH EXISTING METHODS: The striatal disinhibition model provides a unique combination of face validity (tic expression) and construct validity (abnormal striatal inhibition) but is limited to sub-hour periods. The new chronic model extends the period of tic expression to multiple days and thus enables the study of tic dynamics and the effects of behavior and pharmacological agents on tic expression. CONCLUSIONS: The chronic model provides similar behavioral and neuronal correlates of tics as the acute striatal disinhibition model but over prolonged periods of time, thus providing a unique, basal ganglia initiated model of tic expression. Chronic expression of symptoms is the key to studying the time varying properties of Tourette syndrome and the effects of multiple internal and external factors on this disorder.

Animal Models of Tourette Syndrome-From Proliferation to Standardization.

Tourette syndrome (TS) is a childhood onset disorder characterized by motor and vocal tics and associated with multiple comorbid symptoms. Over the last decade, the accumulation of findings from TS patients and the emergence of new technologies have led to the development of novel animal models with high construct validity. In addition, animal models which were previously associated with other disorders were recently attributed to TS. The proliferation of TS animal models has accelerated TS research and provided a better understanding of the mechanism underlying the disorder. This newfound success generates novel challenges, since the conclusions that can be drawn from TS animal model studies are constrained by the considerable variation across models. Typically, each animal model examines a specific subset of deficits and centers on one field of research (physiology/genetics/pharmacology/etc.). Moreover, different studies do not use a standard lexicon to characterize different properties of the model. These factors hinder the evaluation of individual model validity as well as the comparison across models, leading to a formation of a fuzzy, segregated landscape of TS pathophysiology. Here, we call for a standardization process in the study of TS animal models as the next logical step. We believe that a generation of standard examination criteria will improve the utility of these models and enable their consolidation into a general framework. This should lead to a better understanding of these models and their relationship to TS, thereby improving the research of the mechanism underlying this disorder and aiding the development of new treatments.

Pharmacological animal models of Tourette syndrome.

Pharmacological animal models of Tourette syndrome (TS) are an important tool for studying the neural mechanisms underlying this disorder. Dysfunction of the cortico-basal ganglia (CBG) system has been widely implicated in TS but the exact nature of this dysfunction is unknown. Pharmacological treatments of TS have prompted multiple hypotheses regarding the involvement of different neuromodulators in the disorder. Pharmacological manipulations in animal models were used to investigate the relationships between these neuromodulators and different symptoms of TS, including motor (tics) and non-motor (sensorimotor gating deficits) phenomena. Models initially focused on the direct effects of pharmacology on behavior, and only recently have begun providing neurophysiological data reflecting the neuronal mechanism linking the two. Animal models support the notion of CBG dysfunction as the neural mechanism underlying TS, and suggest that it may be derived from either direct deficits of local striatal GABAergic networks or a dysfunction of the neuromodulator systems controlling them. These findings can provide the much- needed conceptual construct for the TS etiology and point to new therapeutic targets.