Local and Relayed Effects of Deep Brain Stimulation of the Pedunculopontine Nucleus

Bioelectronic Zeitgebers: targeted neuromodulation to re-establish circadian rhythms

Existing neurostimulation systems implanted for the treatment of neurodegenerative disorders generally deliver invariable therapy parameters, regardless of phase of the sleep/wake cycle. However, there is considerable evidence that brain activity in these conditions varies according to this cycle, with discrete patterns of dysfunction linked to loss of circadian rhythmicity, worse clinical outcomes and impaired patient quality of life. We present a targeted concept of circadian neuromodulation using a novel device platform. This system utilises stimulation of circuits important in sleep and wake regulation, delivering bioelectronic cues (Zeitgebers) aimed at entraining rhythms to more physiological patterns in a personalised and fully configurable manner. Preliminary evidence from its first use in a clinical trial setting, with brainstem arousal circuits as a surgical target, further supports its promising impact on sleep/wake pathology. Data included in this paper highlight its versatility and effectiveness on two different patient phenotypes. In addition to exploring acute and long-term electrophysiological and behavioural effects, we also discuss current caveats and future feature improvements of our proposed system, as well as its potential applicability in modifying disease progression in future therapies.

Role of Microelectrode Recording in Deep Brain Stimulation of the Pedunculopontine Nucleus: A Physiological Study of Two Cases

BACKGROUND

Deep brain stimulation (DBS) of the pedunculopontine nucleus (PPN) has been reported to improve gait disturbances in Parkinson's disease (PD); however, there are controversies on the radiological and electrophysiological techniques for intraoperative and postoperative confirmation of the target and determination of optimal stimulation parameters.

OBJECTIVES

We investigated the correlation between the location of the estimated PPN (ePPN) and neuronal activity collected during intraoperative electrophysiological mapping to evaluate the role of microelectrode recording (MER) in identifying the effective stimulation site in two PD patients.

MATERIALS AND METHODS

Bilateral PPN DBS was performed in two patients who had suffered from levodopa refractory gait disturbance. They had been implanted previously with DBS in the internal globus pallidus and the subthalamic nucleus, respectively. The PPN was determined on MRI and identified by intraoperative MER. Neuronal activity recorded was analyzed for mean discharge rate, bursting, and oscillatory activity. The effects were assessed by clinical ratings for motor signs before and after surgery.

RESULTS

The PPN location was detected by MER. Groups of neurons characterized by tonic discharges were found 9-10 mm below the thalamus. The mean discharge rate in the ePPN was 19.1 ± 15.1 Hz, and 33% of the neurons of the ePPN responded with increased discharge rate during passive manipulation of the limbs and orofacial structures. PPN DBS with bipolar stimulation at a frequency range 10-30 Hz improved gait disturbances in both patients. Although PPN DBS provided therapeutic effects post-surgery in both cases, the effects waned after a year in case 1 and three years in case 2.

CONCLUSIONS

Estimation of stimulation site within the PPN is possible by combining physiological guidance using MER and MRI findings. The PPN is a potential target for gait disturbances, although the efficacy of PPN DBS may depend on the location of the electrode and the stimulation parameters.

Review of the Midbrain Ascending Arousal Network Nuclei and Implications for Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS), Gulf War Illness (GWI) and Postexertional Malaise (PEM)

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS and Gulf War Illness (GWI) share features of post-exertional malaise (PEM), exertional exhaustion, or postexertional symptom exacerbation. In a two-day model of PEM, submaximal exercise induced significant changes in activation of the dorsal midbrain during a high cognitive load working memory task (Washington 2020) (Baraniuk this issue). Controls had no net change. However, ME/CFS had increased activity after exercise, while GWI had significantly reduced activity indicating differential responses to exercise and pathological mechanisms. These data plus findings of the midbrain and brainstem atrophy in GWI inspired a review of the anatomy and physiology of the dorsal midbrain and isthmus nuclei in order to infer dysfunctional mechanisms that may contribute to disease pathogenesis and postexertional malaise. The nuclei of the ascending arousal network were addressed. Midbrain and isthmus nuclei participate in threat assessment, awareness, attention, mood, cognition, pain, tenderness, sleep, thermoregulation, light and sound sensitivity, orthostatic symptoms, and autonomic dysfunction and are likely to contribute to the symptoms of postexertional malaise in ME/CFS and GWI.

Pedunculopontine Nucleus Deep Brain Stimulation Improves Gait Disorder in Parkinson's Disease: A Systematic Review and Meta-analysis

Deep brain stimulation (DBS) of the pedunculopontine nucleus (PPN) has been proposed as a treatment strategy for gait disorder in patients with Parkinson's disease (PD). We thus performed a systematic review and meta-analysis of randomized and nonrandomized controlled trials to assess the effect of this treatment on gait disorder in patients with PD. We systematically searched PubMed, Cochrane, Web of Knowledge, Wan Fang and WIP for randomized and nonrandomized controlled trials (published before July 29, 2014; no language restrictions) comparing PPN-DBS with other treatments. We assessed pooled data using a random effects model and a fixed effects model. Of 130 identified studies, 14 were eligible and were included in our analysis (N = 82 participants). Compared to those presurgery, the Unified Parkinson Disease Rating Scale (UPDRS) 27-30 scores for patients were lowered by PPN-DBS [3.94 (95% confidence interval, CI = 1.23 to 6.65)]. The UPDRS 13 and 14 scores did not improve with levodopa treatment [0.43 (- 0.35 to 1.20); 0.35 (- 0.50 to 1.19)], whereas the UPDRS 27-30 scores could be improved by the therapy [1.42 (95% CI 0.34 to 2.51)]. The Gait and Falls Questionnaire and UPDRS 13 and 14 scores showed significant improvements after PPN-DBS under the medication-off (MED-OFF) status [15.44 (95% CI = 8.44 to 22.45); 1.57 (95% CI = 0.84 to 2.30); 1.34 (95% CI = 0.84 to 1.84)]. PPN-DBS is a potential therapeutic target that could improve gait and fall disorders in patients with PD. Our findings will help improve the clinical application of DBS in PD patients with gait disorder.

Deep Brain Stimulation of the Pedunculopontine Tegmental Nucleus Renders Neuroprotection through the Suppression of Hippocampal Apoptosis: An Experimental Animal Study

The core objective of this study was to determine the neuroprotective properties of deep brain stimulation of the pedunculopontine tegmental nucleus on the apoptosis of the hippocampus. The pedunculopontine tegmental nucleus is a prime target for Parkinson′s disease and is a crucial component in a feedback loop connected with the hippocampus. Deep brain stimulation was employed as a potential tool to evaluate the neuroprotective properties of hippocampal apoptosis. Deep brain stimulation was applied to the experimental animals for an hour. Henceforth, the activity of Caspase-3, myelin basic protein, Bcl-2, BAX level, lipid peroxidation, interleukin-6 levels, and brain-derived neurotrophic factor levels were evaluated at hours 1, 3 and 6 and compared with the sham group of animals. Herein, decreased levels of caspases activity and elevated levels of Bcl-2 expressions and inhibited BAX expressions were observed in experimental animals at the aforementioned time intervals. Furthermore, the ratio of Bcl-2/BAX was increased, and interleukin -6, lipid peroxidation levels were not affected by deep brain stimulation in the experimental animals. These affirmative results have explained the neuroprotection rendered by hippocampus apoptosis as a result of deep brain stimulation. Deep brain stimulation is widely used to manage neuro-motor disorders. Nevertheless, this novel study will be a revelation for a better understanding of neuromodulatory management and encourage further research with new dimensions in the field of neuroscience.

The pedunculopontine nucleus: From posture and locomotion to neuroepigenetics

In this review, we discuss first an example of one of the symptoms of PD, freezing of gait (FOG), then we will turn to the use of deep brain stimulation (DBS) of the pedunculopontine nucleus (PPN) to treat PD, and the original studies that led to identification of the PPN as one source of locomotor control and why stimulation frequency is critical, and then describe the intrinsic properties of PPN neurons that require beta/gamma stimulation in order to fully activate all types of PPN neurons. Finally, we will describe recent findings on the proteomic and molecular consequences of gamma band activity in PPN neurons, with emphasis on the potential neuroepigenetic sequelae. These considerations will provide essential information for the appropriate refining and testing of PPN DBS as a potential therapy for PD, as well as alternative options.

Subthalamic nucleus oscillations correlate with vulnerability to freezing of gait in patients with Parkinson's disease

Freezing of gait (FOG) is a disabling clinical phenomenon often found in patients with advanced Parkinson's disease (PD). FOG impairs motor function, causes falls and leads to loss of independence. Whereas dual tasking that distracts patients' attention precipitates FOG, auditory or visual cues ameliorate this phenomenon. The pathophysiology of FOG remains unclear. Previous studies suggest that the basal ganglia are involved in the generation of FOG. Investigation of the modulation of neuronal activities within basal ganglia structures during walking is warranted. To this end, we recorded local field potentials (LFP) from the subthalamic nucleus (STN) while PD patients performed single-task gait (ST) or walked while dual-tasking (DT). An index of FOG (iFOG) derived from trunk accelerometry was used as an objective measure to differentiate FOG-vulnerable gait from normal gait. Two spectral activities recorded from the STN region were associated with vulnerability to freezing. Greater LFP power in the low beta (15-21 Hz) and theta (5-8 Hz) bands were noted during periods of vulnerable gait in both ST and DT states. Whereas the elevation of low beta activities was distributed across STN, the increase in theta activity was focal and found in ventral STN and/or substantia nigra (SNr) in ST. The results demonstrate that low beta and theta band oscillations within the STN area occur during gait susceptible to freezing in PD. They also add to the evidence that narrow band ~18 Hz activity may be linked to FOG.