Pedunculopontine and Subthalamic Nucleus Stimulation Effect on Saccades in Parkinson Disease

Novel ways to modulate the vestibular system: Magnetic vestibular stimulation, deep brain stimulation and transcranial magnetic stimulation / transcranial direct current stimulation

BACKGROUND

Advances in neurotechnologies are revolutionizing our understanding of complex neural circuits and enabling new treatments for disorders of the human brain. In the vestibular system, electromagnetic stimuli can now modulate vestibular reflexes and sensations of self-motion by artificially stimulating the labyrinth, cerebellum, cerebral cortex, and their connections.

OBJECTIVE

In this narrative review, we describe evolving neuromodulatory techniques including magnetic vestibular stimulation (MVS), deep brain stimulation (DBS), transcranial magnetic stimulation (TMS), and transcranial direct-current stimulation (tDCS) and discuss current and potential future application in the field of neuro-otology.

RESULTS

MVS triggers both vestibular nystagmic (persistent) and perceptual (lasting ∼1 min) responses that may serve as a model to study central adaptational mechanisms and pathomechanisms of hemispatial neglect. By systematically mapping DBS electrodes, targeted stimulation of central vestibular pathways allowed modulating eye movements, vestibular heading perception, spatial attention and graviception, resulting in reduced anti-saccade error rates and hypometria, improved heading discrimination, shifts in verticality perception and transiently decreased spatial attention. For TMS/tDCS treatment trials have demonstrated amelioration of vestibular symptoms in various neuro-otological conditions, including chronic vestibular insufficiency, Mal-de-Debarquement and cerebellar ataxia.

CONCLUSION

Neuromodulation has a bright future as a potential treatment of vestibular dysfunction. MVS, DBS and TMS may provide new and sophisticated, customizable, and specific treatment options of vestibular symptoms in humans. While promising treatment responses have been reported for TMS/tDCS, treatment trials for vestibular disorders using MVS or DBS have yet to be defined and performed.

Antisaccades in Parkinson's Disease: A Meta-Analysis

The usefulness of eye-tracking tasks as potential biomarkers for motor or cognitive disease burden in Parkinson's disease (PD) has been subject of debate for many years. Several studies suggest that the performance in the antisaccade task may be altered in patients with PD and associated with motor disease severity or executive dysfunction. In this meta-analysis, random effects models were used to synthesize the existing evidence on antisaccade error rates and latency in PD. Furthermore, meta-regressions were performed to assess the role of motor and cognitive disease severity, dopaminergic medication and methodological factors. Additionally, the impact of acute levodopa administration and activation of deep brain stimulation was evaluated in two separate sub-analyses.This meta-analysis confirms that antisaccade latency and error rate are significantly increased in PD. Disease duration, Unified Parkinson's disease rating scale score and Hoehn and Yahr stage mediate the effect of PD on antisaccade latency with higher motor burden being associated with increased antisaccade latency.Acute administration of levodopa had no significant effects on antisaccade performance in a small number of eligible studies. Deep brain stimulation in the subthalamic nucleus, on the other hand, may alter the speed accuracy trade-off supporting an increase of impulsivity following deep brain stimulation in PD.According to the results of the meta-analysis, antisaccade latency may provide a potential marker for disease severity and progression in PD which needs further confirmation in longitudinal studies.

Increased Subthalamic Nucleus Deep Brain Stimulation Amplitude Impairs Inhibitory Control of Eye Movements in Parkinson's Disease

BACKGROUND AND OBJECTIVES

Bilateral subthalamic nucleus deep brain stimulation (STN DBS) in Parkinson's disease (PD) can have detrimental effects on eye movement inhibitory control. To investigate this detrimental effect of bilateral STN DBS, we examined the effects of manipulating STN DBS amplitude on inhibitory control during the antisaccade task. The prosaccade error rate during the antisaccade task, that is, directional errors, was indicative of impaired inhibitory control. We hypothesized that as stimulation amplitude increased, the prosaccade error rate would increase.

MATERIALS AND METHODS

Ten participants with bilateral STN DBS completed the antisaccade task on six different stimulation amplitudes (including zero amplitude) after a 12-hour overnight withdrawal from antiparkinsonian medication.

RESULTS

We found that the prosaccade error rate increased as stimulation amplitude increased (p < 0.01). Additionally, prosaccade error rate increased as the modeled volume of tissue activated (VTA) and STN overlap decreased, but this relationship depended on stimulation amplitude (p = 0.04).

CONCLUSIONS

Our findings suggest that higher stimulation amplitude settings can be modulatory for inhibitory control. Some individual variability in the effect of stimulation amplitude can be explained by active contact location and VTA-STN overlap. Higher stimulation amplitudes are more deleterious if the active contacts fall outside of the STN resulting in a smaller VTA-STN overlap. This is clinically significant as it can inform clinical optimization of STN DBS parameters. Further studies are needed to determine stimulation amplitude effects on other aspects of cognition and whether inhibitory control deficits on the antisaccade task result in a meaningful impact on the quality of life.

Concomitant improvement in anti-saccade success rate and postural instability gait difficulty after rTMS treatment for Parkinson's disease

Parkinson’s disease (PD) is a progressive neurological disorder characterised by motor and non-motor deficits. Repetitive transcranial magnetic stimulation (rTMS) over the bilateral primary motor cortex at a high frequency (5 Hz or higher) is reported to be a potential treatment of PD. We aimed to assess the effect of rTMS on eye movement control in patients with PD in their ‘on’ state. We enrolled 14 patients with PD and assessed motor symptoms (Movement Disorder Society-Sponsored Unified Parkinson’s Disease Rating Scale; MDS-UPDRS) and eye movement performances (visually guided saccades, volitional anti-saccades, and small involuntary saccades during fixation) at baseline and after administering bilateral 10 Hz rTMS on leg region of the motor cortex. We confirmed that rTMS improved the MDS-UPDRS motor scores and found that rTMS improved the anti-saccade success rate, which requires adequate inhibition of the reflexive response. The improvement in anti-saccade success rate was correlated with that of the postural instability gait difficulty (PIGD) sub-scores of MDS-UPDRS and lower baseline Japanese version of the Montreal Cognitive Assessment scores. This result is consistent with previous findings that PIGD and inhibitory control deficits share common brain dysfunctions in PD. rTMS may alleviate dysfunctions of that circuit and have a clinical effect.