I am an Aerospace engineer by training with a Ph.D. in Kinesiology (Neuroscience, Biomechanics, and Space Life Sciences curricular tracks). My Ph.D. research was in the area of Biomechanics and Motor Control of human movement, particularly about human posture control and locomotion in healthy as well as special populations, such as the elderly, patients, and astronauts. As part of my Ph.D., I worked at NASA Johnson Space Center's Neurosciences lab on various projects related to sensorimotor control issues that astronauts face during and after spaceflight.
Currently, in the Precision Health and Integrated Diagnostics (PHIND) Center in the Dept. of Radiology of the Stanford School of Medicine, I am part of the Pervasive Wellbeing Technology lab, where I am helping with several studies around wellbeing and stress management in the wild carried out in an unobtrusive way using sensors that already exist, like computer mice, touchpad, steering wheel of a car, etc.
In the recent past, in the Dept. of Neuroscience of Baylor College of Medicine (BCM) in Houston, I worked on predicting stress response using fMRI and physiological signals in veterans with PTSD, using machine learning. I also worked at the inter-disciplinary consortium of advanced motion performance (iCAMP) of Dept. of Surgery of BCM, where I helped with data analyses of several clinical studies related to using different types of wearables for supervised or unsupervised monitoring of daily physical activities in different populations (like older adults, patients who have had a sternotomy, etc.).
Neuroscience, biomechanics, vestibular stimulation, balance and locomotion, artificial gravity, motor control, sensory systems, human performance, sports science, wearable devices, digital health
Non-invasive stimulation (TMS, GVS), non-invasive brain monitoring (EEG, fMRI), structural-MRI, EMG, Force & Motion sensors (e.g., accelerometers, gyroscope etc.), wearable sensors, MATLAB, C++, Python, signal processing, machine learning, statistical modeling, controls and programming, system identification, human factors, multi-sensory interactions
Wearable Sensor-based Digital Biomarker to Estimate Chest Expansion during Sit-to-Stand Transitions – A Practical Tool to Improve Sternal Precautions in Patients undergoing Median Sternotomy
IEEE Transactions on Neural Systems & Rehabilitation Engineering
2020; 28 (1): 165-173
View details for DOI 10.1109/TNSRE.2019.2952076
Balance Confidence and Turning Behavior as a Measure of Fall Risk
Gait & Posture
View details for DOI 10.1016/j.gaitpost.2020.05.020
Fronto-Parietal Brain Areas Contribute to the Online Control of Posture during a Continuous Balance Task
2019; 413: 135–53
Neuroimaging studies have provided evidence for the involvement of frontal and parietal cortices in postural control. However, the specific role of these brain areas for postural control remains to be known. Here, we investigated the effects of disruptive transcranial magnetic stimulation (TMS) over supplementary motor areas (SMA) during challenging continuous balance task in healthy young adults. We hypothesized that a virtual lesion of SMA will alter activation within the brain network identified using electroencephalography (EEG) and impair performance of the postural task. Twenty healthy young adults received either continuous theta burst stimulation (cTBS) or sham stimulation over SMA followed by the performance of a continuous balance task with or without somatosensory input distortion created by sway-referencing the support surface. cTBS over SMA compared to sham stimulation showed a smaller increase in root mean square of center of pressure as the difficulty of continuous balance task increased suggestive of altered postural control mechanisms to find a stable solution under challenging sensory conditions. Consistent with earlier studies, we found sources of EEG activation within anterior cingulate (AC), cingulate gyrus (CG), bilateral posterior parietal regions (PPC) during the balance task. Importantly, cTBS over SMA compared to sham stimulation altered EEG power within the identified fronto-parietal regions. These findings suggest that the changes in activation within distant fronto-parietal brain areas following cTBS over SMA contributed to the altered postural behavior. Our study confirms a critical role of AC, CG, and both PPC regions in calibrating online postural responses during a challenging continuous balance task.
View details for DOI 10.1016/j.neuroscience.2019.05.063
View details for Web of Science ID 000476866600012
View details for PubMedID 31200107
Daily Use of Bilateral Custom-Made Ankle-Foot Orthoses for Fall Prevention in Older Adults: A Randomized Controlled Trial
JOURNAL OF THE AMERICAN GERIATRICS SOCIETY
2019; 67 (8): 1656–61
To examine the effects of bilateral custom-made ankle-foot orthoses (AFOs) to prevent falls for older adults with concern about or at risk for falling over 12-month daily use.Secondary analysis of a randomized controlled trial.Community-dwelling older adults.Half of the participants were randomly allocated to an intervention group (IG) that received fitted walking shoes and bilateral custom-made AFOs, and the other half were randomly allocated to a control group (CG) that only received fitted walking shoes.Self-reported fall history of 12-month duration was investigated at baseline and 12-month follow-up for both groups. Fall incidence rate and proportion of fallers were used as outcome measures to determine effects of 12-month footwear intervention in either group.Adults aged 65 years and older with concern about or at risk for falling (n = 44).No significant between-group differences in participant characteristics were observed at the baseline (P = .144-.882). Within the IG, significant reductions were found in the fall incidence rate (P = .039) and the proportion of fallers (P = .036) at the 12-month follow-up compared to the baseline. Within the CG, no significant change was found at the 12-month follow-up compared to the baseline for the fall incidence rate (P = .217) or the proportion of fallers (P = .757). When comparing the IG with the CG, there was no significant difference in the change from the baseline to the 12-month follow-up for the fall incidence rate (P = .572) or the proportion of fallers (P = .080).This study failed to demonstrate a significant benefit of bilateral custom-made AFOs to reduce falls compared to fitted walking shoes. However, the AFO users had significant reductions in falls compared to the preceding year. A future study with a larger sample size is recommended to confirm these observations. CLINICAL TRIAL REGISTRATION-URL: http://www.clinicaltrials.gov. Unique identifier: NCT02819011.
View details for DOI 10.1111/jgs.15929
View details for Web of Science ID 000478919000018
View details for PubMedID 31018018
Effectiveness of Daily Use of Bilateral Custom-Made Ankle-Foot Orthoses on Balance, Fear of Falling, and Physical Activity in Older Adults: A Randomized Controlled Trial
2019; 65 (3): 299–307
Foot problems are prevalent in older adults, which may increase the risk and concern for falls. Ankle-foot orthoses (AFO) have been shown to be effective in the stabilization of lower extremities, but their long-term effectiveness in improving balance and their potential to encourage older adults to become more physically active are still debated.This randomized controlled trial investigated the effectiveness of daily use of a custom-made AFO on balance, fear of falling, and physical activity in older adults.Forty-four older adults with concern about or at risk for falling were randomly allocated to either the control group (CG; 77.3% female, age 75.6 ± 6.5 years, BMI 29.3 ± 6.4) or the intervention group (IG; 63.6% female, age 73.7 ± 6.3 years, BMI = 27.8 ± 4.8). The IG received walking shoes and bilateral custom-made AFO. The CG received only walking shoes. At the baseline and 6-month follow-ups, balance and physical activity were assessed using validated wearable instrumentation and fear of falling was assessed using the Fall Efficacy Scale-International (FES-I). Adherence and acceptability toward wearing the AFO were assessed using self-reported questionnaires at the 6-month follow-up.No significant between-group difference was observed at baseline (p = 0.144-0.882). Compared to baseline and the CG, hip, ankle, and center-of-mass (COM) sways were significantly reduced at the 6-month follow-up in the IG while standing with the feet together during the eyes-open condition (p = 0.005-0.040). Within the IG, the FES-I was reduced significantly (p = 0.036) and there was an increasing trend in the number of walking bouts with a medium effect size (d = 0.52, p = 0.440) compared to baseline. However, there were no significant changes in FES-I and physical activity measures in the CG (p = 0.122-0.894). The reduction in COM sway in the IG was moderately correlated with adherence (r = -0.484, p = 0.047) and strongly correlated with baseline COM sway (r = -0.903, p < 0.001).Results suggest that bilateral custom-made AFO plus walking shoes is effective in improving balance compared to walking shoes alone, and it significantly reduces the fear of falling, with a nonsignificant but noticeable positive trend in physical activity, compared to baseline. The results also suggest that older adults with poor balance at baseline and higher daily adherence to using the AFO will gain more benefit from the AFO intervention.
View details for DOI 10.1159/000494114
View details for Web of Science ID 000467677700009
View details for PubMedID 30504728
Calibrating balance perturbation using electrical stimulation of the vestibular system
JOURNAL OF NEUROSCIENCE METHODS
2019; 311: 193–99
Supra-threshold galvanic vestibular stimulation (GVS) can be used to challenge the balance control system by disrupting vestibular inputs. The goal of this study was to propose an objective method to assess variability across subjects in the minimum safe GVS level that causes maximum balance degradation. New method: Thirteen healthy young subjects stood on a compliant foam surface with their eyes closed and tried to maintain a stable upright stance. Variables related to the stability of the trunk and whole body were quantified to characterize the relationship between postural responses and GVS at amplitudes from 0 to 4.5 mA in 0.5 mA increments. The relationship between decrements in postural responses and GVS was linear up to a minimum GVS level (called KNEE). An increase in the stimulation level above that did not lead to any further degradation of balance performance. The KNEE was determined by iteratively performing linear fits to the performance measure at different stimulation levels.There were individual differences in KNEE; it was in the range of 1-2.5 mA across subjects. GVS caused an average performance decrement of 27-99% across six variables at the KNEE level compared to a no-stimulus condition. Comparison to existing methods: We propose a method to consistently attain the maximum level of impairment across subjects using the minimum current intensity, to minimize all types of adverse effects usually observed at high intensities.Individual differences in the disruption of posture control in response to GVS have important implications for testing and training paradigms.
View details for DOI 10.1016/j.jneumeth.2018.10.012
View details for Web of Science ID 000452935000023
View details for PubMedID 30339880
View details for PubMedCentralID PMC6258330
Critical Role of Somatosensation in Postural Control Following Spaceflight: Vestibularly Deficient Astronauts Are Not Able to Maintain Upright Stance During Compromised Somatosensation
FRONTIERS IN PHYSIOLOGY
2018; 9: 1680
The free-fall of orbital spaceflight effectively removes the gravitational vector used as a primary spatial orientation reference on Earth. Sustained absence of this reference drives adaptive changes in the internal perception-action models of the central nervous system (CNS), most notably in the processing of the vestibular otolith inputs. Upon landing, the return of the gravitational signal triggers a re-adaptation that restores terrestrial performance; however, during this period, the individual suffers from a functional vestibular deficiency. Here we provide evidence of a transient increase of the weighting of somatosensory inputs in postural control while the CNS resolves these vestibular deficiencies. Postural control performance was measured before and after spaceflight in 11 Shuttle astronauts and 11 matched controls and nine elderly who did not experience spaceflight. A quiet-stance paradigm was used that eliminated vision, modulated the lower extremity somatosensory cues by subtly modulating the orientation of the support surface beneath feet of subjects in all groups. Additionally, in astronauts and matched controls, we challenged the vestibular system with dynamic head tilts. Postural stability on the landing day (R+0) was substantially decreased for trials with absent visual and altered somatosensory cues, especially those also requiring dynamic head tilts ( ± 5° @ 0.33 Hz) during which 20/22 trials ended prematurely with a fall. In contrast, none of the astronauts fell during eyes-closed, dynamic head tilt trials with unaltered somatosensory cues, and only 3/22 trials resulted in falls with eyes-closed and altered somatosensory cues, but static upright head orientation. Furthermore, postural control performance of astronauts was either statistically not different or worse than that of healthy elderly subjects during the most challenging vestibular conditions on R+0. Overall, our results demonstrate a transient reweighting of sensory cues associated with microgravity-induced vestibular deficiencies, with a significant increase in reliance on somatosensory cues, which can provide an effective reference even without vision and with dynamic vestibular challenges. The translation of these results to aging population suggests that elderly individuals with visual and vestibular deficits may benefit from therapeutic interventions enhancing sensorimotor-integration to improve balance and reduce the risk of falling.
View details for DOI 10.3389/fphys.2018.01680
View details for Web of Science ID 000451478100002
View details for PubMedID 30538640
View details for PubMedCentralID PMC6277541
Effects of speed and direction of perturbation on electroencephalographic and balance responses
EXPERIMENTAL BRAIN RESEARCH
2018; 236 (7): 2073–83
The modulation of perturbation-evoked potential (PEP) N1 as a function of different biomechanical characteristics of perturbation has been investigated before. However, it remains unknown whether the PEP N1 modulation contributes to the shaping of the functional postural response. To improve this understanding, we examined the modulation of functional postural response in relation to the PEP N1 response in ten healthy young subjects during unpredictable perturbations to their upright stance-translations of the support surface in a forward or backward direction at two different amplitudes of constant speed. Using independent components from the fronto-central region, obtained from subject-specific head models created from the MRI, our results show that the latency of onset of the functional postural response after the PEP N1 response was faster for forward than backward perturbations at a constant speed but was not affected by the speed of perturbation. Further, our results reinforce some of the previous findings that suggested that the N1 peak amplitude and peak latency are both modulated by the speed of perturbation but not by the direction of the perturbation. Our results improve the understanding of the relation between characteristics of perturbation and the neurophysiology of reactive balance control and may have implications for the design of brain-machine interfaces for populations with a higher risk of falls.
View details for DOI 10.1007/s00221-018-5284-5
View details for Web of Science ID 000435783300021
View details for PubMedID 29752486
Assessing Somatosensory Utilization during Unipedal Postural Control
FRONTIERS IN SYSTEMS NEUROSCIENCE
2017; 11: 21
Multisensory-visual, vestibular and somatosensory information is integrated for appropriate postural control. The primary goal of this study was to assess somatosensory utilization during a functional motor task of unipedal postural control, in normal healthy adults. Assessing individual bias in the utilization of individual sensory contributions during postural control may help customization of rehabilitation protocols. In this study, a test paradigm of unipedal stance control in supine orientation with and without vision was assessed. Postural control in this test paradigm was hypothesized to utilize predominantly contributions of somatosensory information from the feet and ankle joint, with minimal vestibular input. Fourteen healthy subjects "stood" supine on their dominant leg while strapped to a backpack frame that was freely moving on air-bearings, to remove available otolith tilt cues with respect to gravity that influences postural control when standing upright. The backpack was attached through a cable to a pneumatic cylinder that provided a gravity-like load. Subjects performed three trials each with Eyes-open (EO) and Eyes-closed (EC) while loaded with 60% body weight. There was no difference in unipedal stance time (UST) across the two conditions with EC condition challenging the postural control system greater than the EO condition. Stabilogram-diffusion analysis (SDA) indicated that the critical mean square displacement was significantly different between the two conditions. Vestibular cues, both in terms of magnitude and the duration for which relevant information was available for postural control in this test paradigm, were minimized. These results support our hypothesis that maintaining unipedal stance in supine orientation without vision, minimizes vestibular contribution and thus predominantly utilizes somatosensory information for postural control.
View details for DOI 10.3389/fnsys.2017.00021
View details for Web of Science ID 000399476100001
View details for PubMedID 28443004
View details for PubMedCentralID PMC5387047
Motor Control Performance During Rapid Voluntary Movements of Elbow and Knee
JOURNAL OF MOTOR BEHAVIOR
2016; 48 (4): 348–56
Knowledge of motor control differences during rapid goal-directed movements of the upper and lower limbs could be useful in improving rehabilitation protocols. The authors investigated performance and control differences between elbow and knee joints and between different contraction types (concentric vs. eccentric) during rapid movements under externally applied load. There were no significant differences in performance and control with respect to joint (elbow vs. knee) but the performance during concentric contractions was better than eccentric for both the joints. The findings indicate that despite anatomical and functional differences, the CNS is finely tuned for both the joints to maximize the efficiency of movement during a dynamic environment, but there are differences in control strategies between the 2 contraction types.
View details for DOI 10.1080/00222895.2015.1098585
View details for Web of Science ID 000378751600007
View details for PubMedID 26731048
Using low levels of stochastic vestibular stimulation to improve locomotor stability
FRONTIERS IN SYSTEMS NEUROSCIENCE
2015; 9: 117
Low levels of bipolar binaural white noise based imperceptible stochastic electrical stimulation to the vestibular system (stochastic vestibular stimulation, SVS) have been shown to improve stability during balance tasks in normal, healthy subjects by facilitating enhanced information transfer using stochastic resonance (SR) principles. We hypothesize that detection of time-critical sub-threshold sensory signals using low levels of bipolar binaural SVS based on SR principles will help improve stability of walking during support surface perturbations. In the current study 13 healthy subjects were exposed to short continuous support surface perturbations for 60 s while walking on a treadmill and simultaneously viewing perceptually matched linear optic flow. Low levels of bipolar binaural white noise based SVS were applied to the vestibular organs. Multiple trials of the treadmill locomotion test were performed with stimulation current levels varying in the range of 0-1500 μA, randomized across trials. The results show that subjects significantly improved their walking stability during support surface perturbations at stimulation levels with peak amplitude predominantly in the range of 100-500 μA consistent with the SR phenomenon. Additionally, objective perceptual motion thresholds were measured separately as estimates of internal noise while subjects sat on a chair with their eyes closed and received 1 Hz bipolar binaural sinusoidal electrical stimuli. The optimal improvement in walking stability was achieved on average with peak stimulation amplitudes of approximately 35% of perceptual motion threshold. This study shows the effectiveness of using low imperceptible levels of SVS to improve dynamic stability during walking on a laterally oscillating treadmill via the SR phenomenon.
View details for DOI 10.3389/fnsys.2015.00117
View details for Web of Science ID 000363850500001
View details for PubMedID 26347619
View details for PubMedCentralID PMC4547107
Using Low Levels of Stochastic Vestibular Stimulation to Improve Balance Function
2015; 10 (8): e0136335
Low-level stochastic vestibular stimulation (SVS) has been associated with improved postural responses in the medio-lateral (ML) direction, but its effect in improving balance function in both the ML and anterior-posterior (AP) directions has not been studied. In this series of studies, the efficacy of applying low amplitude SVS in 0-30 Hz range between the mastoids in the ML direction on improving cross-planar balance function was investigated. Forty-five (45) subjects stood on a compliant surface with their eyes closed and were instructed to maintain a stable upright stance. Measures of stability of the head, trunk, and whole body were quantified in ML, AP and combined APML directions. Results show that binaural bipolar SVS given in the ML direction significantly improved balance performance with the peak of optimal stimulus amplitude predominantly in the range of 100-500 μA for all the three directions, exhibiting stochastic resonance (SR) phenomenon. Objective perceptual and body motion thresholds as estimates of internal noise while subjects sat on a chair with their eyes closed and were given 1 Hz bipolar binaural sinusoidal electrical stimuli were also measured. In general, there was no significant difference between estimates of perceptual and body motion thresholds. The average optimal SVS amplitude that improved balance performance (peak SVS amplitude normalized to perceptual threshold) was estimated to be 46% in ML, 53% in AP, and 50% in APML directions. A miniature patch-type SVS device may be useful to improve balance function in people with disabilities due to aging, Parkinson's disease or in astronauts returning from long-duration space flight.
View details for DOI 10.1371/journal.pone.0136335
View details for Web of Science ID 000359926900102
View details for PubMedID 26295807
View details for PubMedCentralID PMC4546608
Effects of five days of bed rest with intermittent centrifugation on neurovestibular function.
Journal of musculoskeletal & neuronal interactions
2015; 15 (1): 60–68
We tested whether intermittent short-radius centrifugation was effective for mitigating alteration in balance and gait following bed rest.Ten male subjects were exposed to 5 days of 6° head-down tilt bed rest with: (a) no countermeasure; (b) daily 1-g centrifugation for a continuous 30-min period; and (c) daily 1-g centrifugation for six periods of 5 min. During and after the bed rest, subjects were asked to scale the severity of neurovestibular symptoms that followed centrifugation or 80° head-up tilt. Following the bed rest, equilibrium scores were derived from anterior-posterior sway while standing on a foam pad with the eyes open or closed while making pitch head movements, and gait was evaluated by grading subjects' performance during various locomotion tasks.At the beginning of bed rest, one single 30-min period of centrifugation induced more severe neurovestibular symptoms than six periods of 5-min centrifugation. After bed rest, although equilibrium scores and gait performance were not significantly altered, subjects felt less neurovestibular dysfunction with orthostatic stress when centrifugation was used.Centrifugation was effective at reducing the severity of neurovestibular symptoms after bed rest, but this decrease was not different between one or multiple daily sessions.
View details for PubMedID 25730653
View details for PubMedCentralID PMC5123609
- Stress wave micro-macro attenuation in ceramic plates made of tiles during ballistic impact INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES 2014; 83: 30–37
- An experimental and numerical study of blast induced shock wave mitigation in sandwich structures APPLIED ACOUSTICS 2013; 74 (1): 1–9
- Shock attenuation of PMMA sandwich panels filled with soda-lime glass beads: A fluid-structure interaction continuum model simulation INTERNATIONAL JOURNAL OF IMPACT ENGINEERING 2012; 47: 48–59
- Modeling the benefits of an artificial gravity countermeasure coupled with exercise and vibration ACTA ASTRONAUTICA 2012; 70: 43–51
- Design/Development of Mini/Micro Air Vehicles through Modelling and Simulation: Case of an Autonomous Quadrotor DEFENCE SCIENCE JOURNAL 2011; 61 (4): 337–45
- Effect of back pressure on impact and compression-after-impact characteristics of composites COMPOSITE STRUCTURES 2011; 93 (2): 944–51
Evaluating the Performance of Helmet Linings Incorporating Fluid Channels
Journal of ASTM International
2010; 7 (10)
View details for DOI 10.1520/JAI102821
- Stress wave attenuation in ceramic plates JOURNAL OF APPLIED PHYSICS 2008; 103 (10)