Deep brain stimulation of symptom-specific networks in Parkinson's disease

Deep Brain Stimulation can improve tremor, bradykinesia, rigidity, and axial symptoms in patients with Parkinson's disease. Potentially, improving each symptom may require stimulation of different white matter tracts. Here, we study a large cohort of patients (N = 237 from five centers) to identify tracts associated with improvements in each of the four symptom domains. Tremor improvements were associated with stimulation of tracts connected to primary motor cortex and cerebellum. In contrast, axial symptoms are associated with stimulation of tracts connected to the supplementary motor cortex and brainstem. Bradykinesia and rigidity improvements are associated with the stimulation of tracts connected to the supplementary motor and premotor cortices, respectively. We introduce an algorithm that uses these symptom-response tracts to suggest optimal stimulation parameters for DBS based on individual patient's symptom profiles. Application of the algorithm illustrates that our symptom-tract library may bear potential in personalizing stimulation treatment based on the symptoms that are most burdensome in an individual patient.

Efficacy of caudal pedunculopontine nucleus stimulation on postural instability and gait disorders in Parkinson's disease

OBJECTIVES

Gait-related symptoms like postural instability and gait disorders (PIGD) inexorably worsen with Parkinson's disease (PD) deterioration and become refractory to current available medical treatment and deep brain stimulation (DBS) of conventional targets. Pedunculopontine nucleus (PPN) deep brain stimulation (DBS) is a promising method to treat PIGD. This prospective study aimed to clarify the clinical application of PPN-DBS and to explore effects of caudal PPN stimulation on PIGD.

METHODS

Five consecutive PD patients with severe medication-resistant postural instability and gait disorders accepted caudal PPN-DBS. LEAD-DBS toolbox was used to reconstruct and visualize the electrodes based on pre- and postoperative images. Outcomes were assessed with Movement Disorder Society (MDS)-Sponsored Revision of the Unified Parkinson's Disease Rating Scale (MDS-UPDRS), gait-specific questionnaires, and objective gait analysis with GAITRite system.

RESULTS

MDS-UPDRS subitems 35-38 scores were improved at postoperative 6 months (mean, 4.40 vs 11.00; p = 0.0006) and 12 months (mean, 5.60 vs 11.00; p = 0.0013) compared with baseline, and scores at 6 months were slightly lower than scores at 12 months (mean, 4.40 vs 5.60; p = 0.0116). Gait and Falls Questionnaire, New Freezing of Gait Questionnaire, and Falls Questionnaire scores also significantly improved at postoperative 6 months and 12 months compared with baseline. In addition, cadence, bilateral step length, and bilateral stride length significantly increased when PPN On-stimulation compared with Off-stimulation.

CONCLUSIONS

This study suggested that caudal PPN low-frequency stimulation improved PIGD for PD patients at the 6- and 12-month period.

Contribution of different somatosensory afferent input to subcortical somatosensory evoked potentials in humans

OBJECTIVES

To investigate the subcortical somatosensory evoked potentials (SEPs) to electrical stimulation of either muscle or cutaneous afferents.

METHODS

SEPs were recorded in 6 patients suffering from Parkinson's disease (PD) who underwent electrode implantation in the pedunculopontine (PPTg) nucleus area. We compared SEPs recorded from the scalp and from the intracranial electrode contacts to electrical stimuli applied to: 1) median nerve at the wrist, 2) abductor pollicis brevis motor point, and 3) distal phalanx of the thumb. Also the high-frequency oscillations (HFOs) were analysed.

RESULTS

After median nerve and pure cutaneous (distant phalanx of the thumb) stimulation, a P1-N1 complex was recorded by the intracranial lead, while the scalp electrodes recorded the short-latency far-field responses (P14 and N18). On the contrary, motor point stimulation did not evoke any low-frequency component in the PPTg traces, nor the N18 potential on the scalp. HFOs were recorded to stimulation of all modalities by the PPTg electrode contacts.

CONCLUSIONS

Stimulus processing within the cuneate nucleus depends on modality, since only the cutaneous input activates the complex intranuclear network possibly generating the scalp N18 potential.

SIGNIFICANCE

Our results shed light on the subcortical processing of the somatosensory input of different modalities.

Pedunculopontine tegmental Nucleus-evoked prepulse inhibition of the blink reflex in Parkinson's disease

OBJECTIVE

To investigate the effects on the blink reflex (BR) of single stimuli applied to the pedunculopontine tegmental nucleus (PPTg).

METHODS

The BR was evoked by stimulating the supraorbital nerve (SON) in fifteen patients suffering from idiopathic Parkinson's disease (PD) who had electrodes monolaterally or bilaterally implanted in the PPTg for deep brain stimulation (DBS). Single stimuli were delivered to the PPTg through externalized electrode connection wires 3-4 days following PPTg implantation.

RESULTS

PPTg stimuli increased the latency and reduced duration, amplitude and area of the R2 component of the BR in comparison to the response recorded in the absence of PPTg stimulation. These effects were independent of the side of SON stimulation and were stable for interstimulus interval (ISI) between PPTg prepulse and SON stimulus from 0 to 110 ms. The PPTg-induced prepulse inhibition of the BR was bilaterally present in the brainstem. The R1 component was unaffected.

CONCLUSIONS

The prepulse inhibition of the R2 component may be modulated by the PPTg.

SIGNIFICANCE

These findings suggest that abnormalities of BR occurring in PD may be ascribed to a reduction of basal ganglia-mediated inhibition of brainstem excitability.

Effects of pedunculopontine nucleus deep brain stimulation on gait disorders in Parkinson's Disease: A meta-analysis of the literature

OBJECTIVES

The pedunculopontine nucleus (PPN) is considered a promising target to alleviate gait disorders. We aimed to evaluate the effects of PPN stimulation on motor symptoms and gait disorders in patients with Parkinson's disease (PD) to help assess the potential role of PPN-DBS treatment in gait disorders.

METHODS

Studies were searched for low-frequency PPN stimulation to treat gait disorders and freezing of gait (FOG) in the PubMed, Embase, Cochrane Library, Web of Science, and ClinicalKey up to April 2020. Outcomes of Unified Parkinson's Disease Rating Scale (UPDRS) part III, subitems 27-30; UPDRS subitems 13 and 14; the Freezing of Gait Questionnaire (FOGQ), and the Gait and Falls Questionnaire (GFQ) were extracted and evaluated during PPN On-stimulation compared to preoperation or Off-stimulation in both Off- and On-medication states.

RESULTS

There was a significant improvement in subitems 27-30 with PPN On-stimulation versus Off-stimulation in Off-medication and On-medication states, but no improvement in UPDRS part III. The occurrence of FOG and falls also declined between PPN On-stimulation and presurgery, with a significant improvement in subitem 13 and subitem 14 in Off-medication and On-medication states, GFQ, and FQGQ. Heterogeneity in stimulation frequency, follow-up, electrode location, and unilateral or bilateral stimulation existed among the included studies.

CONCLUSIONS

In some conditions and in some selective PD patients, low-frequency PPN-DBS has beneficial effects on FOG and falls but no wider benefits on rigidity, resting tremor, or bradykinesia.

Estimating Accurate Target Coordinates with Magnetic Resonance Images by Using Multiple Phase-Encoding Directions during Acquisition

BACKGROUND

Stereotactic procedures are image guided, often using magnetic resonance (MR) images limited by image distortion, which may influence targets for stereotactic procedures.

OBJECTIVES

The aim of this work was to assess methods of identifying target coordinates for stereotactic procedures with MR in multiple phase-encoding directions.

METHODS

In 30 patients undergoing deep brain stimulation, we acquired 5 image sets: stereotactic brain computed tomography (CT), T2-weighted images (T2WI), and T1WI in both right-to-left (RL) and anterior-to-posterior (AP) phase-encoding directions. Using CT coordinates as a reference, we analyzed anterior commissure and posterior commissure coordinates to identify any distortion relating to phase-encoding direction.

RESULTS

Compared with CT coordinates, RL-directed images had more positive x-axis values (0.51 mm in T1WI, 0.58 mm in T2WI). AP-directed images had more negative y-axis values (0.44 mm in T1WI, 0.59 mm in T2WI). We adopted 2 methods to predict CT coordinates with MR image sets: parallel translation and selective choice of axes according to phase-encoding direction. Both were equally effective at predicting CT coordinates using only MR; however, the latter may be easier to use in clinical settings.

CONCLUSION

Acquiring MR in multiple phase-encoding directions and selecting axes according to the phase-encoding direction allows identification of more accurate coordinates for stereotactic procedures.

A meta-analysis of the pedunculopontine nucleus deep-brain stimulation effects on Parkinson's disease

Postural instability and gait disturbance (PIGD) are common symptoms in patients with advanced Parkinson's disease (PD). The deep-brain stimulation (DBS) of the pedunculopontine nucleus (PPN) shows a promising effect on PIGD. However, the quantitative effects of PPN DBS for PD, especially for PIGD, and the efficacy of PPN DBS combined with levodopa are controversial and ambiguous to clinical practice. We carried out a meta-analysis of original researches on PPN to PIGD/PD from the electronic databases MEDLINE and EMBASE. The scores of united Parkinson's disease rating scores (UPDRS) III were used to evaluate the improvement in motor function and the scores of UPDRS III subitems 27-30 were used to evaluate the improvement in PIGD. The outcome was expressed as the mean difference and the percentage change between the scores of baseline and end point. The quality of studies was assessed using the 'assessing risk of bias' table. Overall, 909 articles were screened and seven studies were included with a total of 45 patients. The improvement in PIGD was significant, but there were no such effects on motor function. All the differences in PIGD scores were greater in the OFF medicine state rather than the ON medicine state, especially in the comparison between postsurgery ON stimulation and presurgery. PPN DBS indeed improved PIGD in advanced PD patients. This result could inspire more researchers to focus on its clinical application.

Deep Brain Stimulation in Parkinson's Disease: New and Emerging Targets for Refractory Motor and Nonmotor Symptoms

Parkinson's disease (PD) is a progressive neurodegenerative condition characterized by bradykinesia, tremor, rigidity, and postural instability (PI), in addition to numerous nonmotor manifestations. Many pharmacological therapies now exist to successfully treat PD motor symptoms; however, as the disease progresses, it often becomes challenging to treat with medications alone. Deep brain stimulation (DBS) has become a crucial player in PD treatment, particularly for patients who have disabling motor complications from medical treatment. Well-established DBS targets include the subthalamic nucleus (STN), the globus pallidus pars interna (GPi), and to a lesser degree the ventral intermediate nucleus (VIM) of the thalamus. Studies of alternative DBS targets for PD are ongoing, the majority of which have shown some clinical benefit; however, more carefully designed and controlled studies are needed. In the present review, we discuss the role of these new and emerging DBS targets in treating refractory axial motor symptoms and other motor and nonmotor symptoms (NMS).

Dopamine and the Brainstem Locomotor Networks: From Lamprey to Human

In vertebrates, dopamine neurons are classically known to modulate locomotion via their ascending projections to the basal ganglia that project to brainstem locomotor networks. An increased dopaminergic tone is associated with increase in locomotor activity. In pathological conditions where dopamine cells are lost, such as in Parkinson's disease, locomotor deficits are traditionally associated with the reduced ascending dopaminergic input to the basal ganglia. However, a descending dopaminergic pathway originating from the substantia nigra pars compacta was recently discovered. It innervates the mesencephalic locomotor region (MLR) from basal vertebrates to mammals. This pathway was shown to increase locomotor output in lampreys, and could very well play an important role in mammals. Here, we provide a detailed account on the newly found dopaminergic pathway in lamprey, salamander, rat, monkey, and human. In lampreys and salamanders, dopamine release in the MLR is associated with the activation of reticulospinal neurons that carry the locomotor command to the spinal cord. Dopamine release in the MLR potentiates locomotor movements through a D1-receptor mechanism in lampreys. In rats, stimulation of the substantia nigra pars compacta elicited dopamine release in the pedunculopontine nucleus, a known part of the MLR. In a monkey model of Parkinson's disease, a reduced dopaminergic innervation of the brainstem locomotor networks was reported. Dopaminergic fibers are also present in human pedunculopontine nucleus. We discuss the conserved locomotor role of this pathway from lamprey to mammals, and the hypothesis that this pathway could play a role in the locomotor deficits reported in Parkinson's disease.

A probabilistic template of human mesopontine tegmental nuclei from in vivo 7T MRI

Mesopontine tegmental nuclei such as the cuneiform, pedunculotegmental, oral pontine reticular, paramedian raphe and caudal linear raphe nuclei, are deep brain structures involved in arousal and motor function. Dysfunction of these nuclei is implicated in the pathogenesis of disorders of consciousness and sleep, as well as in neurodegenerative diseases. However, their localization in conventional neuroimages of living humans is difficult due to limited image sensitivity and contrast, and a stereotaxic probabilistic neuroimaging template of these nuclei in humans does not exist. We used semi-automatic segmentation of single-subject 1.1mm-isotropic 7T diffusion-fractional-anisotropy and T₂-weighted images in healthy adults to generate an in vivo probabilistic neuroimaging structural template of these nuclei in standard stereotaxic (Montreal Neurological Institute, MNI) space. The template was validated through independent manual delineation, as well as leave-one-out validation and evaluation of nuclei volumes. This template can enable localization of five mesopontine tegmental nuclei in conventional images (e.g. 1.5T, 3T) in future studies of arousal and motor physiology (e.g. sleep, anesthesia, locomotion) and pathology (e.g. disorders of consciousness, sleep disorders, Parkinson's disease). The 7T magnetic resonance imaging procedure for single-subject delineation of these nuclei may also prove useful for future 7T studies of arousal and motor mechanisms.

Functional Neuroanatomy for Posture and Gait Control

Here we argue functional neuroanatomy for posture-gait control. Multi-sensory information such as somatosensory, visual and vestibular sensation act on various areas of the brain so that adaptable posture-gait control can be achieved. Automatic process of gait, which is steady-state stepping movements associating with postural reflexes including headeye coordination accompanied by appropriate alignment of body segments and optimal level of postural muscle tone, is mediated by the descending pathways from the brainstem to the spinal cord. Particularly, reticulospinal pathways arising from the lateral part of the mesopontine tegmentum and spinal locomotor network contribute to this process. On the other hand, walking in unfamiliar circumstance requires cognitive process of postural control, which depends on knowledges of self-body, such as body schema and body motion in space. The cognitive information is produced at the temporoparietal association cortex, and is fundamental to sustention of vertical posture and construction of motor programs. The programs in the motor cortical areas run to execute anticipatory postural adjustment that is optimal for achievement of goal-directed movements. The basal ganglia and cerebellum may affect both the automatic and cognitive processes of posturegait control through reciprocal connections with the brainstem and cerebral cortex, respectively. Consequently, impairments in cognitive function by damages in the cerebral cortex, basal ganglia and cerebellum may disturb posture-gait control, resulting in falling.

Efficacy and Safety of Pedunculopontine Nuclei (PPN) Deep Brain Stimulation in the Treatment of Gait Disorders: A Meta-Analysis of Clinical Studies

BACKGROUND

Pedunculopontine nucleus (PPN) has complex reciprocal connections with basal ganglia, especially with internal globus pallidus and substantia nigra, and it has been postulated that PPN stimulation may improve gait instability and freezing of gait. In this meta-analysis, we will assess the evidence for PPN deep brain stimulation in treatment of gait and motor abnormalities especially focusing on Parkinson disease patients.

METHODS

PubMed and Scopus electronic databases were searched for related studies published before February 2014. Medline (1966-2014), Embase (1974-2010), CINAHL, Web of Science, Scopus bibliographic, and Google Scholar databases (1960-2014) were also searched for studies investigating effect of PPN deep brain stimulation in treatment of postural and postural instability and total of ten studies met the inclusion criteria for this analysis.

RESULTS

Our findings showed a significant improvement in postural instability (p<0.001) and motor symptoms of Parkinson disease on and off medications (p<0.05), but failed to show improvement in freezing of gait.

CONCLUSIONS

Despite significant improvement in postural instability observed in included studies, evidence from current literature is not sufficient to generalize these findings to the majority of patients.

Pedunculopontine Nucleus Region Deep Brain Stimulation in Parkinson Disease: Surgical Techniques, Side Effects, and Postoperative Imaging

The pedunculopontine nucleus (PPN) region has received considerable attention in clinical studies as a target for deep brain stimulation (DBS) in Parkinson disease. These studies have yielded variable results with an overall impression of improvement in falls and freezing in many but not all patients treated. We evaluated the available data on the surgical anatomy and terminology of the PPN region in a companion paper. Here we focus on issues concerning surgical technique, imaging, and early side effects of surgery. The aim of this paper was to gain more insight into the reasoning for choosing specific techniques and to discuss shortcomings of available studies. Our data demonstrate the wide range in almost all fields which were investigated. There are a number of important challenges to be resolved, such as identification of the optimal target, the choice of the surgical approach to optimize electrode placement, the impact on the outcome of specific surgical techniques, the reliability of intraoperative confirmation of the target, and methodological differences in postoperative validation of the electrode position. There is considerable variability both within and across groups, the overall experience with PPN DBS is still limited, and there is a lack of controlled trials. Despite these challenges, the procedure seems to provide benefit to selected patients and appears to be relatively safe. One important limitation in comparing studies from different centers and analyzing outcomes is the great variability in targeting and surgical techniques, as shown in our paper. The challenges we identified will be of relevance when designing future studies to better address several controversial issues. We hope that the data we accumulated may facilitate the development of surgical protocols for PPN DBS.

The primate pedunculopontine nucleus region: towards a dual role in locomotion and waking state

The mesencephalic reticular formation (MRF) mainly composed by the pedunculopontine and the cuneiform nuclei is involved in the control of several fundamental brain functions such as locomotion, rapid eye movement sleep and waking state. On the one hand, the role of MRF neurons in locomotion has been investigated for decades in different animal models, including in behaving nonhuman primate (NHP) using extracellular recordings. On the other hand, MRF neurons involved in the control of waking state have been consistently shown to constitute the cholinergic component of the reticular ascending system. However, a dual control of the locomotion and waking state by the same groups of neurons in NHP has never been demonstrated in NHP. Here, using microelectrode recordings in behaving NHP, we recorded 38 neurons in the MRF that were followed during transition between wakefulness (TWS) and sleep, i.e., until the emergence of sleep episodes characterized by typical cortical slow wave activity (SWA). We found that the MRF neurons, mainly located in the pedunculopontine nucleus region, modulated their activity during TWS with a decrease in firing rate during SWA. Of interest, we could follow some MRF neurons from locomotion to SWA and found that they also modulated their firing rate during locomotion and TWS. These new findings confirm the role of MRF neurons in both functions. They suggest that the MRF is an integration center that potentially allows to fine tune waking state and locomotor signals in order to establish an efficient locomotion.

Deep Brain Stimulation for Movement Disorders of Basal Ganglia Origin: Restoring Function or Functionality?

Deep brain stimulation (DBS) is highly effective for both hypo- and hyperkinetic movement disorders of basal ganglia origin. The clinical use of DBS is, in part, empiric, based on the experience with prior surgical ablative therapies for these disorders, and, in part, driven by scientific discoveries made decades ago. In this review, we consider anatomical and functional concepts of the basal ganglia relevant to our understanding of DBS mechanisms, as well as our current understanding of the pathophysiology of two of the most commonly DBS-treated conditions, Parkinson's disease and dystonia. Finally, we discuss the proposed mechanism(s) of action of DBS in restoring function in patients with movement disorders. The signs and symptoms of the various disorders appear to result from signature disordered activity in the basal ganglia output, which disrupts the activity in thalamocortical and brainstem networks. The available evidence suggests that the effects of DBS are strongly dependent on targeting sensorimotor portions of specific nodes of the basal ganglia-thalamocortical motor circuit, that is, the subthalamic nucleus and the internal segment of the globus pallidus. There is little evidence to suggest that DBS in patients with movement disorders restores normal basal ganglia functions (e.g., their role in movement or reinforcement learning). Instead, it appears that high-frequency DBS replaces the abnormal basal ganglia output with a more tolerable pattern, which helps to restore the functionality of downstream networks.

Neurostimulation to improve level of consciousness in patients with epilepsy

When drug-resistant epilepsy is poorly localized or surgical resection is contraindicated, current neurostimulation strategies such as deep brain stimulation and vagal nerve stimulation can palliate the frequency or severity of seizures. However, despite medical and neuromodulatory therapy, a significant proportion of patients continue to experience disabling seizures that impair awareness, causing disability and risking injury or sudden unexplained death. We propose a novel strategy in which neuromodulation is used not only to reduce seizures but also to ameliorate impaired consciousness when the patient is in the ictal and postictal states. Improving or preventing alterations in level of consciousness may have an effect on morbidity (e.g., accidents, drownings, falls), risk for death, and quality of life. Recent studies may have elucidated underlying networks and mechanisms of impaired consciousness and yield potential novel targets for neuromodulation. The feasibility, benefits, and pitfalls of potential deep brain stimulation targets are illustrated in human and animal studies involving minimally conscious/vegetative states, movement disorders, depth of anesthesia, sleep-wake regulation, and epilepsy. We review evidence that viable therapeutic targets for impaired consciousness associated with seizures may be provided by key nodes of the consciousness system in the brainstem reticular activating system, hypothalamus, basal ganglia, thalamus, and basal forebrain.

Cholinergic excitation from the pedunculopontine tegmental nucleus to the dentate nucleus in the rat

In spite of the existence of pedunculopontine tegmental nucleus (PPTg) projections to cerebellar nuclei, their nature and functional role is unknown. These fibers may play a crucial role in postural control and may be involved in the beneficial effects induced by deep-brain stimulation (DBS) of brainstem structures in motor disorders. We investigated the effects of PPTg microstimulation on single-unit activity of dentate, fastigial and interpositus nuclei. The effects of PPTg stimulation were also studied in rats whose PPTg neurons were destroyed by ibotenic acid and subsequently subjected to iontophoretically applied cholinergic antagonists. The main response recorded in cerebellar nuclei was a short-latency (1.5-2 ms) and brief (13-15 ms) orthodromic activation. The dentate nucleus was the most responsive to PPTg stimulation. The destruction of PPTg cells reduced the occurrence of PPTg-evoked activation of dentate neurons, suggesting that the effect was due to stimulation of cell bodies and not due to fibers passing through or close to the PPTg. Application of cholinergic antagonists reduced or eliminated the PPTg-evoked response recorded in the dentate nucleus. The results show that excitation is exerted by the PPTg on the cerebellar nuclei, in particular on the dentate nucleus. Taken together with the reduction of nicotinamide adenine dinucleotide phosphate-diaphorase-positive neurons in lesioned animals, the iontophoretic experiments suggest that the activation of dentate neurons is due to cholinergic fibers. These data help to explain the effects of DBS of the PPTg on axial motor disabilities in neurodegenerative disorders.

Long-term follow-up of deep brain stimulation of peduncolopontine nucleus in progressive supranuclear palsy: Report of three cases

Background:

Progressive supranuclear palsy (PSP) is a neurodegenerative disease due to mitochondrial dysfunction. The PSP syndrome presents generally with gait disorder, Parkinsonism, ophthalmoparesis and cognitive alteration. Few reports exist on deep brain stimulation (DBS) in patients with atypical Parkinsonism. The aim of our study was to evaluate further the potential role of DBS in PSP.

Case Description:

We report three patients with PSP with long-term follow up undergoing DBS. Two patients had right peripedunculopontine nucleus (PPN) stimulation and one patient had simultaneous right PPN and bilateral globus pallidus internus DBS. DBS of the PPN alone or combined with globus pallidus internus (GPi) determined an improvement in gait and a reduction in falls sustained over time. Combined target stimulation (GPi-PPN) was correlated with better clinical outcome than single target (PPN) DBS for PSP.

Conclusions:

Although few data on DBS for PSP exist, reported clinical results are encouraging. DBS might be considered as an alternative therapeutic option for patients with PSP presenting with relevant gait imbalance and frequent falls, who fail to respond to pharmacological treatment. Larger cohorts with longer follow-ups are needed to evaluate more exhaustively the efficacy of DBS in PSP.

Unilateral deep brain stimulation of the pedunculopontine tegmental nucleus in idiopathic Parkinson's disease: effects on gait initiation and performance

The pedunculopontine tegmental nucleus (PPTg) is a component of the locomotor mesencephalic area. In recent years it has been considered a new surgical site for deep brain stimulation (DBS) in movement disorders. Here, using objective kinematic and spatio-temporal gait analysis, we report the impact of low frequency (40 Hz) unilateral PPTg DBS in ten patients suffering from idiopathic Parkinson's disease with drug-resistant gait and axial disabilities. Patients were studied for gait initiation (GI) and steady-state level walking (LW) under residual drug therapy. In the LW study, a straight walking task was employed. Patients were compared with healthy age-matched controls. The analysis revealed that GI, cadence, stride length and left pelvic tilt range of motion (ROM) improved under stimulation. The duration of the S1 and S2 sub-phases of the anticipatory postural adjustment phase of GI was not affected by stimulation, however a significant improvement was observed in the S1 sub-phase in both the backward shift of centre of pressure and peak velocity. Speed during the swing phase, step width, stance duration, right pelvic tilt ROM phase, right and left hip flexion-extension ROM, and right and left knee ROM were not modified. Overall, the results show that unilateral PPTg DBS may affect GI and specific spatio-temporal and kinematic parameters during unconstrained walking on a straight trajectory, thus providing further support to the importance of the PPTg in the modulation of gait in neurodegenerative disorders.

Continuous stimulation of the pedunculopontine tegmental nucleus at 40 Hz affects preparative and executive control in a delayed sensorimotor task and reduces rotational movements induced by apomorphine in the 6-OHDA parkinsonian rat

The pedunculopontine tegmental nucleus (PPTg) relays basal ganglia signals to the thalamus, lower brainstem and spinal cord. Using the 6-hydroxydopamine (6-OHDA) rat model of parkinsonism, we investigated whether deep brain stimulation (DBS) of the PPTg (40 Hz, 60 μs, 200-400 μA) may influence the preparative and executive phases in a conditioned behavioural task, and the motor asymmetries induced by apomorphine. In the conditioned task, rats had to press two levers according to a fixed delay paradigm. The 6-OHDA lesion was placed in the right medial forebrain bundle, i.e. contralaterally to the preferred forepaw used by rats to press levers in the adopted task. The stimulating electrode was implanted in the right PPTg, i.e. contralateral to left side, which was expected to be most affected. The lesion significantly reduced correct responses from 63.4% to 16.6%. PPTg-DBS effects were episodic; however, when rats successfully performed in the task (18.9%), reaction time (468.8 ± 36.5 ms) was significantly increased (589.9 ± 45.9 ms), but not improved by PPTg-DBS (646.7 ± 33.8 ms). Movement time was significantly increased following the lesion (649.2 ± 42.6 ms vs. 810.9 ± 53.0 ms), but significantly reduced by PPTg-DBS (820.4 ± 39.4 ms) compared to sham PPTg-DBS (979.8 ± 47.6 ms). In a second group of lesioned rats, rotations induced by apomorphine were significantly reduced by PPTg-DBS compared to sham PPTg-DBS (12.2 ± 0.6 vs. 9.5 ± 0.4 mean turns/min). Thus, it appears that specific aspects of motor deficits in 6-OHDA-lesioned rats may be modulated by PPTg-DBS.

The role of frontostriatal impairment in freezing of gait in Parkinson's disease

Freezing of gait (FOG) is a disabling symptom of advanced Parkinson's disease (PD) that leads to an increased risk of falls and nursing home placement. Interestingly, multiple lines of evidence suggest that the manifestation of FOG is related to specific deficits in cognition, such as set shifting and the ability to process conflict-related signals. These findings are consistent with the specific patterns of abnormal cortical processing seen during functional neuroimaging experiments of FOG, implicating increased neural activation within cortical structures underlying cognition, such as the Cognitive Control Network. In addition, these studies show that freezing episodes are associated with abnormalities in the BOLD response within key structures of the basal ganglia, such as the striatum and the subthalamic nucleus. In this article, we discuss the implications of these findings on current models of freezing behavior and propose an updated model of basal ganglia impairment during FOG episodes that integrates the neural substrates of freezing from the cortex and the basal ganglia to the cognitive dysfunctions inherent in the condition.