Long-Term Recording of Subthalamic Aperiodic Activities and Beta Bursts in Parkinson's Disease.

BACKGROUND: Local field potentials (LFPs) represent the summation of periodic (oscillations) and aperiodic (fractal) signals. Although previous studies showed changes in beta band oscillations and burst characteristics of the subthalamic nucleus (STN) in Parkinson's disease (PD), how aperiodic activity in the STN is related to PD pathophysiology is unknown. OBJECTIVES: The study aimed to characterize the long-term effects of STN-deep brain stimulation (DBS) and dopaminergic medications on aperiodic activities and beta bursts. METHODS: A total of 10 patients with PD participated in this longitudinal study. Simultaneous bilateral STN-LFP recordings were conducted in six separate visits during a period of 18 months using the Activa PC + S device in the off and on dopaminergic medication states. We used irregular-resampling auto-spectral analysis to separate oscillations and aperiodic components (exponent and offset) in the power spectrum of STN-LFP signals in beta band. RESULTS: Our results revealed a systematic increase in both the exponent and the offset of the aperiodic spectrum over 18 months following the DBS implantation, independent of the dopaminergic medication state of patients with PD. In contrast, beta burst durations and amplitudes were stable over time and were suppressed by dopaminergic medications. CONCLUSIONS: These findings indicate that oscillations and aperiodic activities reflect at least partially distinct yet complementary neural mechanisms, which should be considered in the design of robust biomarkers to optimize adaptive DBS. Given the link between increased gamma-aminobutyric acidergic (GABAergic) transmission and higher aperiodic activity, our findings suggest that long-term STN-DBS may relate to increased inhibition in the basal ganglia. © 2022 International Parkinson and Movement Disorder Society.

An Overview of Noninvasive Brain Stimulation: Basic Principles and Clinical Applications.

The brain has the innate ability to undergo neuronal plasticity, which refers to changes in its structure and functions in response to continued changes in the environment. Although these concepts are well established in animal slice preparation models, their application to a large number of human subjects could only be achieved using noninvasive brain stimulation (NIBS) techniques. In this review, we discuss the mechanisms of plasticity induction using NIBS techniques including transcranial magnetic stimulation (TMS), transcranial direct current stimulation (tDCS), transcranial alternating current stimulation (tACS), random noise stimulation (RNS), transcranial ultrasound stimulation (TUS), vagus nerve stimulation (VNS), and galvanic vestibular stimulation (GVS). We briefly introduce these techniques, explain the stimulation parameters and potential clinical implications. Although their mechanisms are different, all these NIBS techniques can be used to induce plasticity at the systems level, to examine the neurophysiology of brain circuits and have potential therapeutic use in psychiatric and neurological disorders. TMS is the most established technique for the treatment of brain disorders, and repetitive TMS is an approved treatment for medication-resistant depression. Although the data on the clinical utility of the other modes of stimulation are more limited, the electrical stimulation techniques (tDCS, tACS, RNS, VNS, GVS) have the advantage of lower cost, portability, applicability at home, and can readily be combined with training or rehabilitation. Further research is needed to expand the clinical utility of NIBS and test the combination of different modes of NIBS to optimize neuromodulation induced clinical benefits.

Event-related deep brain stimulation of the subthalamic nucleus affects conflict processing.

OBJECTIVE: Many lines of evidence suggest that response conflict recruits brain regions in the cortical-basal ganglia system. Within the basal ganglia, deep brain recordings from the subthalamic nucleus (STN) have shown that conflict triggers a transient increase in low-frequency oscillations (LFOs; 2-8Hz). Here, we deployed a new method of delivering short trains of event-related deep brain stimulation (DBS) to the STN to test the causal role of the STN and its associated circuits in conflict-related processing. METHODS: In a double-blind design, we stimulated the STN in patients with Parkinson disease by locking brief trains of DBS to specific periods of the trial within a Stroop task. RESULTS: Stimulation had a specific effect on conflict compared to nonconflict trials by relatively speeding responses on conflict trials (ie, reducing the Stroop effect, defined as the difference in reaction time between conflict and nonconflict trials) when it was delivered in the preresponse period in the preparation phase. Stimulation also increased errors when it was delivered early in the response window. This latter result corresponded to the timing of the conflict-induced increase in LFOs observed in the absence of stimulation but was not directly related to the reduction in the Stroop effect. INTERPRETATION: These results support the theory that the time of LFO increase recorded from the STN corresponds to a conflict-processing function. They also provide one of the first demonstrations of event-related DBS of the STN in humans during a cognitive control paradigm. Ann Neurol 2018;84:515-526.

Pallidal deep brain stimulation modulates cortical excitability and plasticity.

OBJECTIVE: Internal globus pallidus (GPi) deep brain stimulation (DBS) relieves symptoms in dystonia patients. However, the physiological effects produced by GPi DBS are not fully understood. In particular, how a single-pulse GPi DBS changes cortical circuits has never been investigated. We studied the modulation of motor cortical excitability and plasticity with single-pulse GPi DBS in dystonia patients with bilateral implantation of GPi DBS. METHODS: The cortical evoked potentials from DBS were recorded with electroencephalography. Transcranial magnetic stimulation with a conditioning test paired-pulse paradigm was used to investigate the effect of GPi DBS on the primary motor cortex. How GPi DBS might modulate the motor cortical plasticity was tested using a paired associative stimulation paradigm with repetitive pairs of GPi DBS and motor cortical stimulation at specific time intervals. RESULTS: GPi stimulation produced 2 peaks of cortical evoked potentials with latencies of ∼10 and ∼25 milliseconds in the motor cortical area. Cortical facilitation was observed at ∼10 milliseconds after single-pulse GPi DBS, and cortical inhibition was observed after a ∼25-millisecond interval. Repetitive pairs of GPi stimulation with cortical stimulation at these 2 time intervals produced long-term potentiation-like effects in the motor cortex. INTERPRETATION: Single-pulse DBS modulates cortical excitability and plasticity at specific time intervals. These effects may be related to the mechanism of action of DBS. Combination of DBS with cortical stimulation with appropriate timing has therapeutic potential and could be explored in the future as a method to enhance the effects of neuromodulation for neurological and psychiatric diseases. Ann Neurol 2018;83:352-362.

Cortical Plasticity Induction by Pairing Subthalamic Nucleus Deep-Brain Stimulation and Primary Motor Cortical Transcranial Magnetic Stimulation in Parkinson's Disease.

Noninvasive brain stimulation studies have shown abnormal motor cortical plasticity in Parkinson's disease (PD). These studies used peripheral nerve stimulation paired with transcranial magnetic stimulation (TMS) to primary motor cortex (M1) at specific intervals to induce plasticity. Induction of cortical plasticity through stimulation of the basal ganglia (BG)-M1 connections has not been studied. In the present study, we used a novel technique of plasticity induction by repeated pairing of deep-brain stimulation (DBS) of the BG with M1 stimulation using TMS. We hypothesize that repeated pairing of subthalamic nucleus (STN)-DBS and M1-TMS at specific time intervals will lead to plasticity in the M1. Ten PD human patients with STN-DBS were studied in the on-medication state with DBS set to 3 Hz. The interstimulus intervals (ISIs) between STN-DBS and TMS that produced cortical facilitation were determined individually for each patient. Three plasticity induction conditions with repeated pairings (180 times) at specific ISIs (∼ 3 and ∼ 23 ms) that produced cortical facilitation and a control ISI of 167 ms were tested in random order. Repeated pairing of STN-DBS and M1-TMS at short (∼ 3 ms) and medium (∼ 23 ms) latencies increased M1 excitability that lasted for at least 45 min, whereas the control condition (fixed ISI of 167 ms) had no effect. There were no specific changes in motor thresholds, intracortical circuits, or recruitment curves. Our results indicate that paired-associative cortical plasticity can be induced by repeated STN and M1 stimulation at specific intervals. These results show that STN-DBS can modulate cortical plasticity. SIGNIFICANCE STATEMENT: We introduced a new experimental paradigm to test the hypothesis that pairing subthalamic nucleus deep-brain stimulation (STN-DBS) with motor cortical transcranial magnetic stimulation (M1-TMS) at specific times can induce cortical plasticity in patients with Parkinson's disease (PD). We found that repeated pairing of STN-DBS with TMS at short (∼ 3 ms) and medium (∼ 23 ms) intervals increased cortical excitability that lasted for up to 45 min, whereas the control condition (fixed latency of 167 ms) had no effects on cortical excitability. This is the first demonstration of associative plasticity in the STN-M1 circuits in PD patients using this novel technique. The potential therapeutic effects of combining DBS and noninvasive cortical stimulation should be investigated further.

Stop-related subthalamic beta activity indexes global motor suppression in Parkinson's disease.

BACKGROUND: Rapid action stopping leads to global motor suppression. This is shown by studies using transcranial magnetic stimulation to measure corticospinal excitability of task-unrelated effectors (e.g., from the hand during speech stopping). We hypothesize that this global suppression relates to the STN of the basal ganglia. Several STN local field potential studies in PD patients have shown increased ß-band power during successful stopping. OBJECTIVES: Here, we aimed to test whether this STN ß-band activity indexes global motor suppression measured by transcranial magnetic stimulation. METHODS: We studied 9 medicated PD patients (age, 47-67 years; mean, 55.8; 3 female) who were implanted with STN-DBS electrodes. Participants performed a vocal stop-signal task (i.e., they had to occasionally stop a vocal response) while we simultaneously recorded local field potentials from right STN and delivered transcranial magnetic stimulation to primary motor cortex to measure corticospinal excitability from a task-unrelated hand muscle (first dorsal interosseous). RESULTS: Replicating previous results, STN ß-band power was increased (P < 0.005) and corticospinal excitability was reduced (P = 0.024; global motor suppression) during successful stopping. As hypothesized, global motor suppression was greater for successful stop trials with higher STN ß-power (median split: P = 0.043), which was further evident in a negative correlation between single-trial STN ß-power and corticospinal excitability (mean, r = -0.176; P = 0.011). CONCLUSION: These findings link stopping-related global motor suppression to STN ß-band activity through simultaneous recordings of STN and corticospinal excitability. The results support models of basal ganglia function that propose the STN has broad motor suppressive effects. © 2016 International Parkinson and Movement Disorder Society.

Effects of short-latency afferent inhibition on short-interval intracortical inhibition.

Peripheral nerve stimulation inhibits the motor cortex, and the process has been termed short-latency afferent inhibition (SAI) at interstimulus intervals (ISIs) of ∼20 ms. The objective of the present study was to test how SAI interacts with short-interval intracortical inhibition (SICI) under different stimulation conditions. We studied 20 healthy volunteers. Surface electromyogram was recorded from the first dorsal interosseous muscle. Using paired- and triple-pulse paradigms, we investigated how SAI interacts with SICI under these different conditions. The effects of different conditioning stimulus (CS) intensities (0.6-0.9 active motor threshold), SAI latencies (23 and 25 ms), and ISIs (2 and 3 ms) for SICI were examined in rest and active conditions. SAI had inhibitory interactions with SICI at different CS intensities for rest or active SICI, at SAI latencies of 23 and 25 ms. This interaction occurred at weak CS intensities for SICI when there was no inhibition, and SICI became facilitatory in the presence of SAI. This can be explained by SICI inhibiting SAI and not by saturation of inhibition. The interaction between SAI and SICI was greater for SICI at ISI of 3 ms than for ISI of 2 ms, suggesting that different circuits may be activated at these ISIs. We conclude that SAI and SICI have inhibitory interactions that are influenced by factors such as ISI and muscle activities, which should be considered in design and interpretation of cortical interaction studies.

Neurophysiological assessment of fatigue in electrical injury patients.

To investigate for the presence of central and peripheral physiological fatigue in electrical injury (EI) patients with experiential fatigue. Eight EI patients and eight age-matched healthy volunteers were recruited. Motor evoked potentials (MEP) following transcranial magnetic stimulation (TMS) and M-waves from ulnar nerve stimulation at the wrist were measured from the right abductor digiti minimi. Fatigue was induced by 2 min of maximal voluntary contraction, and subjects were followed for 15 min of recovery. The experiment was performed twice for each subject. In one of the two sessions (randomly assigned), a blood pressure (BP) cuff was inflated during the first 75 s of recovery period to prolong muscle ischemia. Baseline measures showed no difference in central and peripheral conduction times. Cortical silent period was prolonged in patients compared to controls with no differences in abduction force. Decrement of MEP amplitude with consecutive TMS pulses was observed in the post-recovery period only with EI patients who had prolonged muscle ischemia induced by the BP cuff. The post-exercise M-wave area during contraction was significantly higher for patients. Prolonged cortical silent period in EI patients suggests that they had increased GABAB receptor-mediated cortical inhibition. The ischemia-induced decrement in consecutive MEP amplitudes post-exercise demonstrates greater physiological fatigue in EI patients after exercise. The greater increase in M-wave area of EI patients post-exercise suggests larger decrease in conduction velocity of muscle action potentials with exercise. These findings provide preliminary physiological correlates for increased central and peripheral fatigue in EI patients with experiential fatigue.

Quality of life assessment in the first episode of acute coronary syndrome.

Background: Assessment of health-related quality of life (HRQoL) is an important measure of a patient's recovery after an illness. However, HRQoL among acute coronary syndrome (ACS) survivors has not been extensively studied following cardiac management. Aim: The purpose of this study was to assess the quality of life (QoL) among ACS patients who have undergone percutaneous coronary intervention (PCI). Methods: This cohort study included 145 consecutive male ACS patients between March 2021 and May 2022. Of these patients, 138 (mean age 54.3 ± 10.7 years) completed the QoL assessment using the short form-12 (SF-12) health survey questionnaire. Seventy (51%) of them presented with ST-segment elevation myocardial infarction (STEMI), 18 (13%) had non-STEMI, 39 (28%) had evolved MI, and 11 (8%) had unstable angina. Recruited patients' QoL data were assessed at various time points post-PCI. Results: At the end of the 12 months of follow-up, major clinical events (MCE) defined as death, sudden death, or re-acute myocardial infarction occurred in 54.9% of patients. Out of 7 MCE, four deaths and three re-AMIs had occurred. SF-12 physical component score was found to be significantly improved when compared to the mental component score, which seems to improve without reaching statistical significance over time. Among event-free ACS patients, we found a significant positive correlation between left ventricular ejection fraction and HRQoL. Conclusion: Improvement in HRQoL (physical component) was seen among ACS patients post-PCI. Relevance for Patients: QoL assessment outcomes should be considered in clinical settings, practice guidelines, and treatment modality post-PCI to improve QoL in post-ACS survivors.

Resting heart rate variability as a diagnostic marker of cardiovascular dysautonomia in postural tachycardia syndrome.

OBJECTIVES: Postural orthostatic tachycardia syndrome (POTS) is a disorder of the autonomic nervous system characterised by orthostatic intolerance and orthostatic tachycardia without hypotension. Heart rate variability (HRV) is the most reliable and objective tool for assessing autonomic dysfunction severity. In the present study, we aimed to investigate HRV changes in resting supine position, predicting severity and cardiovascular risk in patients with POTS. METHODS: We compared 100 POTS patients with 160 healthy controls matched for age and gender in a case-control design. Along with clinical characterization, heart rate variability was evaluated using ambulatory 5 min ECG in lead II and expressed in frequency and time-domain measures. RESULTS: The resting heart rate of patients with POTS was significantly higher than that of healthy controls. In HRV measures, root mean square successive difference of RR intervals (RMSSD), total and high frequency (HF) powers were statistically lower with an increased low frequency (LF) to high-frequency ratio in patients with POTS compared to healthy controls. Further, stepwise logistic regression analysis showed increased basal HR and LF/HF as significant predictors of POTS and its severity. CONCLUSIONS: This is the first study on a large cohort of patients with POTS from India wherein HRV was assessed. The study showed reduced parasympathetic activity and increased sympathetic activity in patients with POTS compared to healthy controls. These findings of increased resting heart rate and LF/HF were found to be potential predictors of POTS and future cardiovascular risks, which need to be replicated in a larger and more homogenized cohort.

Prognostic value of heart rate variability in acute coronary syndrome.

OBJECTIVES: To assess the predictive value of pre-discharge heart rate variability (HRV) parameters in patients with acute coronary syndrome (ACS) treated by percutaneous coronary intervention (PCI). METHODS: 145 consecutive male patients with ACS (aged 57.12 ± 10.81 years) were included in this study. Fifteen minutes electrocardiogram recording was done to measure time-domain [standard deviation of N-N intervals (SDNN), root-mean square differences of successive R-R intervals (rMSSD)] and frequency-domain [low-frequency (LF) power, high-frequency (HF) power and total power (TP)] HRV parameters before and after PCI. The primary end point was the occurrence of major clinical events (MCE) defined as death, sudden death or re-acute myocardial infarction at the end of 3 months follow-up. RESULTS: At a follow-up of 3 months, MCE occurred in 06 patients (4.14%) (Cardiac death was 3.01%, while that of sudden death was 1.13%). Out of six-MCE, four deaths and two re-AMIs occurred. Pre-discharge HRV values (SDNN, rMSSD, TP, LF and HF) were significantly lower in patients with ACS without MCE. Only total power HRV index (AUC=0.748; p=0.040) showed greater prognostic accuracy. CONCLUSIONS: In conclusion, study showed an increase in SDNN, rMSSD, LF, HF and TP after successful revascularization with PCI in patients who had MCE. The resultant sensitivity, specificity of HRV is still limited in the present study. Particularly, its sensitivity is higher (33-83%) with a modest specificity (61-72%).

Investigation of Autonomic Dysfunction in Alzheimer's Disease-A Computational Model-Based Approach.

(1) Background and Objective: Alzheimer's disease (AD) is commonly accompanied by autonomic dysfunction. Investigating autonomic dysfunction's occurrence patterns and severity may aid in making a distinction between different dementia subtypes, as cardiac autonomic dysfunction and AD severity are correlated. Heart rate variability (HRV) allows for a non-invasive assessment of the autonomic nervous system (ANS). AD is characterized by cholinergic depletion. A computational model of ANS based on the kinetics of acetylcholine and norepinephrine is used to simulate HRV for various autonomic states. The model has the flexibility to suitably modulate the concentration of acetylcholine corresponding to different autonomic states. (2) Methods: Twenty clinically plausible AD patients are compared to 20 age- and gender-matched healthy controls using HRV measures. Statistical analysis is performed to identify the HRV parameters that vary significantly in AD. By modulating the acetylcholine concentration in a controlled manner, different autonomic states of Alzheimer's disease are simulated using the ANS model. (3) Results: In patients with AD, there is a significant decrease in vagal activity, sympathovagal imbalance with a dominant sympathetic activity, and change in the time domain, frequency domain, and nonlinear HRV characteristics. Simulated HRV features corresponding to 10 progressive states of AD are presented. (4) Conclusions: There is a significant difference in the HRV features during AD. As cholinergic depletion and autonomic dysfunction have a common neurological basis, autonomic function assessment can help in diagnosis and assessment of AD. Quantitative models may help in better comprehending the pathophysiology of the disease and assessment of its progress.

Evaluation of Cardiac, Autonomic Functions in Ambulant Patients with Duchenne Muscular Dystrophy.

Duchenne muscular dystrophy (DMD) is an X-linked genetic disorder caused by dystrophin gene mutation resulting in muscle weakness, motor delays, difficulty in standing, and inability to walk by 12 years. As disease progresses, it leads to cardiac and respiratory failure. Evaluation of cardiac autonomic status and echocardiography in DMD patients at a young age can be a potential biomarker to assess disease progression. This study aimed to investigate the younger DMD population of 5-11years of age with mild to moderate cardiac involvement for early detection using non-invasive and cost-effective tools. Genetically confirmed male DMD patients, aged 5-11 years (n = 47), screened from the outpatient department of a tertiary neuroscience institution were subjected to heart rate variability and echocardiographic analysis, and values were correlated with their clinical variables. DMD patients showed a significantly higher difference in HR, interventricular septum, E m/s, and E-wave to A-wave (E/A) ratio than normal values (p < 0.001). Significantly higher HR indicates initial sinus tachycardia and decreased IVD (d), and increased E m/s and E/A ratio mark the onset of cardiac symptoms in DMD patients even though its chamber dimension remains normal and are associated with cardiac muscle fibrosis.

Effects of an 18-Week Integrated Yoga Program on Cardiac Autonomic Function in Breast Cancer Patients Undergoing Adjuvant Chemotherapy: A Randomized Controlled Trial.

BACKGROUND: Cardiotoxicity is a commonly observed adverse effect seen in breast cancer (BC) patients undergoing chemotherapy with attributes toward cardiac autonomic dysfunction (CAD). Yoga, a mind-body system of medicine that has been shown to improve cardiac autonomic nervous system (ANS) activity in various health conditions, could be an effective adjuvant approach in addressing CAD. OBJECTIVE: This study aims to investigate the protective effects of Integrated Yoga Therapy (IYT) on ANS functioning, assessed using Heart rate variability (HRV) in breast cancer patients undergoing chemotherapy. METHODS: A total of 68 (stage I-III) BC patients were randomly assigned into 2 groups: Treatment as Usual group (TAU) and TAU with Yoga Therapy group (TAUYT). All patients underwent anthracycline-based adjuvant chemotherapy for a total of 6 cycles with 21 days/cycle. During chemotherapy, the TAUYT group received IYT 5 days a week for 18 weeks, compared with usual care alone in the TAU group. Resting heart rate (RHR) and HRV, measured in both the time and frequency domains, were used to assess the cardiac ANS function of each patient before and after 6 cycles of chemotherapy. RESULTS: A total of 30 subjects in the TAU group and 29 subjects in the TAUYT group were included in the analysis. At baseline (before chemotherapy), there were no significant differences between the TAU and TAUYT groups in terms of RHR and HRV indices. However, after chemotherapy, patients in the TAU group had a significantly higher average RHR (P < .02) and lower HRV indices with reduced parasympathetic indices: RMSSD (P < .01), pNN50% (P < .04), high-frequency power (P < .001) and increased sympathetic indices: low-frequency power (P < .001) with sympathovagal imbalance: LF/HF (P < .001) compared with patients in the TAUYT group. CONCLUSION: The study showed the protective effects of yoga therapy on CAD in patients receiving anthracycline-based chemotherapy for BC, proposing yoga as a potential adjuvant intervention in improving cardiac health and preventing cardiovascular-related morbidities. TRIAL REGISTRATION: This trial is registered with the Clinical Trials Registry-India (CTRI) database (CTRI/2020/10/028446; October 16, 2020).

Neuro-Cardio-Autonomic Modulations in Children with Duchenne Muscular Dystrophy.

BACKGROUND AND OBJECTIVE: Duchenne muscular dystrophy (DMD) is a degenerative X-linked muscle disease. Death frequently results from complications in cardiopulmonary systems. Preclinical/early diagnosis of cardiac autonomic abnormalities may aid initiate cardioprotective therapy and enhance prognosis. METHODS: A cross sectional, prospective study of 38 DMD boys compared with 37 age-matched healthy controls was conducted. Lead II electrocardiography and beat-to-beat blood pressure were recorded to assess heart rate variability (HRV), blood pressure variability (BPV), and baroreceptor sensitivity (BRS) in a standardized environment. Data were analysed and correlated with disease severity and genotype. RESULTS: In the DMD group, the median age at assessment was 8 years [IQR 7-9 years], the median age at disease onset was 3 years [IQR, 2-6 years], and the mean duration of illness was 4 years [IQR, 2.5-5]. DNA sequencing showed deletions in 34/38 (89.5 %) and duplications in 4/38 (10.5%) patients. The median heart rate in DMD children was significantly higher [101.19 (Range, 94.71-108.49)] /min compared to controls [81 (Range, 76.2-92.76)] /min (p < 0.05). All the assessed HRV and BPV parameters were significantly impaired in DMD cases except for the coefficient of variance of systolic blood pressure. Further, BRS parameters were also significantly reduced in DMD, excluding alpha-LF. A positive correlation was found between alpha HF with age at onset and duration of illness. CONCLUSION: This study demonstrates a distinct early impairment of neuro-cardio-autonomic regulation in DMD. Simple yet effective non-invasive techniques such as HRV, BPV, and BRS may help identify cardiac dysfunction in a pre-clinical state, paving the way for early cardio-protective therapies and limiting disease progression in DMD patients.

Exploring the connections between basal ganglia and cortex revealed by transcranial magnetic stimulation, evoked potential and deep brain stimulation in dystonia.

We review the findings for motor cortical excitability, plasticity and evoked potentials in dystonia. Plasticity can be induced and assessed in cortical areas by non-invasive brain stimulation techniques such as transcranial magnetic stimulation (TMS) and the invasive technique of deep brain stimulation (DBS), which allows access to deep brain structures. Single-pulse TMS measures have been widely studied in dystonia and consistently showed reduced silent period duration. Paired pulse TMS measures showed reduced short and long interval intracortical inhibition, interhemispheric inhibition, long-latency afferent inhibition and increased intracortical facilitation in dystonia. Repetitive transcranial magnetic stimulation (rTMS) of the premotor cortex improved handwriting with prolongation of the silent period in focal hand dystonia patients. Continuous theta-burst stimulation (cTBS) of the cerebellum or cTBS of the dorsal premotor cortex improved dystonia in some studies. Plasticity induction protocols in dystonia demonstrated excessive motor cortical plasticity with the reduction in cortico-motor topographic specificity. Bilateral DBS of the globus pallidus internus (GPi) improves dystonia, associated pain and functional disability. Local field potentials recordings in dystonia patients suggested that there is increased power in the low-frequency band (4-12 Hz) in the GPi. Cortical evoked potentials at peak latencies of 10 and 25 ms can be recorded with GPi stimulation in dystonia. Plasticity induction protocols based on the principles of spike timing dependent plasticity that involved repeated pairing of GPi-DBS and motor cortical TMS at latencies of cortical evoked potentials induced motor cortical plasticity. These studies expanded our knowledge of the pathophysiology of dystonia and how cortical excitability and plasticity are altered with different treatments such as DBS.

Efficacy of Non-contact BallistocardiographySystem to Determine Heart Rate Variability.

Background: Functions of the autonomic nervous system have cardinal importance in day-to-day life. Heart rate variability (HRV) has been shown to estimate the functioning of the autonomic nervous system. Imbalance in the functioning of the autonomic nervous system is seen to be associated with chronic conditions such as chronic kidney disease, cardiovascular diseases, diabetes mellitus, and so on. Purpose: To evaluate the efficacy of a non-contact ballistocardiography (BCG) system to calculate HRV parameters by comparing them to the parameters derived from a standard commercial software that uses an electrocardiogram (ECG). Methods: Current study captured an ECG signal using a three-channel ECG Holter machine, whereas the BCG signal was captured using a BCG sensor sheet consisting of vibroacoustic sensors placed under the mattress of the participants of the study. Results: The study was conducted on 24 subjects for a total of 54 overnight recordings. The proposed method covered 97.92% epochs of the standard deviation of NN intervals (SDNN) and 99.27% epochs of root mean square of successive differences (RMSSD) within 20 ms and 30 ms tolerance, respectively, whereas 98.84% of two-min intervals for low-frequency (LF) to high-frequency (HF) ratio was covered within a tolerance of 1. Kendall's coefficient of concordance was also calculated, giving a P < .001 for all the three parameters and coefficients 0.66, 0.55, and 0.44 for SDNN, RMSSD, and LF/HF, respectively. Conclusion: The results show that HRV parameters captured using unobtrusive and non-invasive BCG sensors are comparable to HRV calculated using ECG.

Parkinson's disease: Alterations of motor plasticity and motor learning.

This chapter reviews the alterations in motor learning and motor cortical plasticity in Parkinson's disease (PD), the most common movement disorder. Impairments in motor learning, which is a hallmark of basal ganglia disorders, influence the performance of motor learning-related behavioral tasks and have clinical implications for the management of disturbance in gait and posture, and for rehabilitative management of PD. Although plasticity is classically induced and assessed in sliced preparation in animal models, in this review we have concentrated on the results from non-invasive brain stimulation techniques such as transcranial magnetic stimulation (TMS), transcranial alternating current stimulation (tACS) and transcranial direct current stimulation (tDCS) in patients with PD, in addition to a few animal electrophysiologic studies. The chapter summarizes the results from different cortical and subcortical plasticity investigations. Plasticity induction protocols reveal deficient plasticity in PD and these plasticity measures are modulated by medications and deep brain stimulation. There is considerable variability in these measures that are related to inter-individual variations, different disease characteristics and methodological considerations. Nevertheless, these pathophysiologic studies expand our knowledge of cortical excitability, plasticity and the effects of different treatments in PD. These tools of modulating plasticity and motor learning improve our understanding of PD pathophysiology and help to develop new treatments for this disabling condition.

Immediate Effects of OM Chanting on Heart Rate Variability Measures Compared Between Experienced and Inexperienced Yoga Practitioners.

Background: Chanting "OM" is a form of meditation that has numerous health benefits. However, the neurophysiological mechanisms underpinning its effect are surprisingly scarce. The present study aimed to investigate the effect of OM chanting on autonomic modulation, using heart rate variability (HRV), on experienced yoga practitioners and yoga naïve persons. Methods: This prospective study included 19 yoga practitioners (9 females and 10 males; group mean age ± standard deviation [SD]; 25.9 ± 3.2 years) and 17 yoga naïve persons (8 females and 9 males; group mean age ± SD; 24.8 ± 3.6 years) of both sexes and similar age range. Both the groups were assessed for HRV indices (time and frequency domain measures) before and after loud OM chanting for 5 min. Results: Baseline comparison using Mann-Whitney U test between groups showed yoga practitioners had significantly increased high frequency (HF) power (P < 0.029) than nonyoga practitioners, signifying a state of tranquility before the chanting of OM. After 5 min of loud chanting of OM, a comparison between groups assessed using Wilcoxon Signed Ranks test revealed: HF Power, a component of the parasympathetic nervous system, was further amplified with a significantly increase (P < 0.001) in the yoga practitioners group compared to nonyoga practitioners. Furthermore, this increase in HF power was positively correlated with the years of experience in yoga. Conclusion: The present study showed that a brief chanting of OM (5 min) might enhance parasympathetic nervous system activity, promote relaxation, and provide calmness. Further, this experience may be achieved effectively in individuals experienced in yoga than nonyoga practitioners.