Gaurav Sharma

Scopus Publications

Non-invasive brain technologies and their role in clinical applications
Gaurav Sharma, Shubhajit Roy Chowdhury
Expert Review of Medical Devices, 2025
INTRODUCTION: Noninvasive brain monitoring and stimulation techniques are widely used in research and clinical applications. These techniques allow researchers and clinicians to study and affect brain activity safely, without any risk associated with invasive procedures. AREAS COVERED: The present review paper is focused on noninvasive brain monitoring and stimulation techniques. First, noninvasive brain monitoring techniques that are beneficial for clinical experts to detect neurological disorders are highlighted. These techniques also help to identify the exact locations where cognitive functions are disturbed. Second, noninvasive brain stimulation (NIBS) techniques that are provided to the patient's specific locations to improve the cognitive function by modulating the neuronal excitability are also discussed in this paper. EXPERT OPINION: Several clinical studies provide strong evidence related to the improvement of cognitive functions of patients suffering from neurological disorders using NIBS procedures. Various studies are being carried out to upgrade the noninvasive brain monitoring and stimulation techniques combined with artificial intelligence (AI) as transformative tool for advancing personalized portable home-based care, which may be beneficial to improve the lifestyle of patients suffering from the neurological disorders.
Preclinical Validation of Electrodes for Single Anodal Transcranial Direct Current Stimulation on Rat Model With Chronic Stress-Induced Depression
Gaurav Sharma, Shubham Nilkanth Rahmatkar, Anil Kumar Rana, Pallavi Sharma, Vikram Patial, Damanpreet Singh, Shubhajit Roy Chowdhury
IEEE Sensors Journal, 2023
Transcranial direct current stimulation (tDCS) is an effective and safe noninvasive brain stimulation (NIBS) procedure to modulate neuronal excitability. The present preclinical study was carried out to validate the impact of the innovative high definition (HD) fabricated spiking Au/AgCl electrodes via a noninvasive tDCS procedure on a rat model with depression-like behavior. In this study, a chronic stress-induced depression-like behavior rat model was developed over a period of 14 days. Furthermore, the aftereffects of NIBS procedures were investigated by providing a tDCS dose ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${2.00} \text {mA} \times {5.00} \text {min}$ </tex-math></inline-formula> ) by placing the electrodes on the interested region of the rat brain. This study was performed in healthy rats, control rats with depression-like behavior, and tDCS treated rats, which were used to examine the differential aftereffects of tDCS dose. After single tDCS dose, a significant increase in average band power of electroencephalogram (EEG) has been observed ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {F}{(}{2},{15}{)} = {8.376}; {P} = {0.0036}$ </tex-math></inline-formula> ) alongside a significant increase in the glutamate level of hippocampus (HPC; <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {F}{(}{2},\!{15}{)} = {8.919}; {P} = {0.0028}$ </tex-math></inline-formula> ), a significant reduction in immobility time ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {F}{(}{2},{15}{)} = {7.552}; {P} = {0.0054}$ </tex-math></inline-formula> ), and a significant increase in the percentage sucrose intake has been observed ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {F}{(}{2}, {15}{)} = {5.941}; {P} = {0.0126}$ </tex-math></inline-formula> ). In addition, immunohistochemistry (IHC) showed a significant increase in the Iba1 protein expression in microglia cell in the both cortex and HPC region ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${P} < {0.05}$ </tex-math></inline-formula> ). Hence, the fabricated electrodes can deliver a tDCS dose that can penetrate up to the cortex and HPC regions from the surface of brain noninvasively within tolerable and safety limits.
A Computational Model to Analyse E/I (Excitation/Inhibition) Dynamics for Neural Network Integrated with Astrocyte
Anirban Bandyopadhyay, Gaurav Sharma, Shubhajit Roy Chowdhury
2020 IEEE Conference on Computational Intelligence in Bioinformatics and Computational Biology Cibcb 2020, 2020
Excitatory glutamate and inhibitory GABA dynamics homeostasis, which is often designated as E/I ratio, is regulated by different types of neural inhibitory circuit system. Gliotransmitter released from astrocyte coupled with two main types of the neural network system, feedback and feedforward inhibitory network can render alteration in E/I dynamics. The recent study provides a new model to study the E/I dynamics by integrating the neural circuit with astrocyte, aiming to understand the effect of input synaptic current ranging 20 −40µA/cm2, the effect of two different types of neural inhibition networks on the E/I dynamics and the effect of information transmission from astrocyte to the neural network with different coupling parameters on the E/I dynamics. The simulated result reveals that the frequency of E/I peak and the maximum peak height is increased with increasing the input current. The maximum E/I peak is diminished in the case of feedback inhibition system than the feedforward system with the constant input current. Another important outcome of the model is that the E/I ratio is dependent on the astrocytic glutamate with a limiting coupling parameter value.
Computational analysis of NIRS and BOLD signal from neurovascular coupling with three neuron-system feedforward inhibition network
Anirban Bandyopadhyay, Gaurav Sharma, Shubhajit Roy Chowdhury
Journal of Theoretical Biology, 2020
Corrigendum to “P41 a preliminary study to classify healthy and lesioned hemisphere of ischemic stroke patients with anodal transcranial direct current stimulation technique” [Clin. Neurophysiol. 131 (2020) e199–e200] (Clinical Neurophysiology (2020) 131(4) (e199–e200), (S1388245719314130), (10.1016/j.clinph.2019.12.047))
G. Sharma, A. Bandyopadhyay, S. Roy Chowdhury
Clinical Neurophysiology, 2020
High-definition transcranial direct current stimulation device for targeting cerebral cortex
Gaurav Sharma, Rakshit Raj, Shubhajit Roy Chowdhury
I2mtc 2020 International Instrumentation and Measurement Technology Conference Proceedings, 2020
Non-invasive brain stimulation (NIBS) devices are progressively used as neuromodulator and are showing optimistic potential in the field of point care medical technology. The main aim of this study is to develop a prototype device, which helps in improving various neurological disorders, by increasing or decreasing neuronal excitability, depending upon the selection of a weak intensity of direct current. Conventionally, high definition transcranial direct current stimulation (HD-tDCS) device mainly depends upon three factors, viz, small size of high definition electrodes, multi-electrode configurations and optimized distribution of weak direct currents to the active and return electrodes. The proposed prototype HD-tDCS device is mainly focused on the internal circuit of the device, which provides precise distribution of direct current to both active and return electrodes, considering selected configurations. In this paper, HD-tDCS device has been designed which provides a weak direct current in the range of 1.00mA to 4.00mA with a measured error of +0.06mA to 0.06mA in the output direct currents. The % error between the theoretical and the measured values is less than 2%.
Statistical Analysis to Find out the Optimal Locations for Non Invasive Brain Stimulation
Gaurav Sharma, Shubhajit Roy Chowdhury
Journal of Medical Systems, 2020
Non-invasive brain electrical stimulation (NIBES) techniques are progressively used for modulation of neuronal membrane potentials, which alters cortical excitability. The neuronal activity depends on position of channel locations for electrodes and the amount and direction of injected weak current through the target neurons area. In the present paper hybrid near infrared spectroscopy and electroencephalogram (NIRS-EEG) open access dataset for brain computer interface (BCI) has been used to find the best locations for NIBES. The percentage oxygen saturation has been calculated with the help of provided NIRS experimental dataset of changes in concentration of oxy-hemoglobin (HbO 2 ) and deoxy-hemoglobin (Hb) in thirty-six scalp site locations of twenty-eight healthy subjects. The variation in standard deviation have been calculated for given pre-processed EEG signals of thirty locations for same twenty-eight healthy subjects. The statistical one-way ANOVA method has been used to find out the best channels and locations which are having less variation in all motion artifacts. In this method, F value is calculated for these locations and those locations are selected which are significant at 99% confidence interval (P < 0.01). In this study, out of sixty-six locations sixteen best locations have been selected for non-invasive brain electrical stimulation. This pilot study has been used to find out the appropriate locations on the scalp sites to place the electrodes to provide weak direct current stimulation which are less affected by motion artifacts.
Fabrication of Dual Purpose Spiking Electrode for Sensing Electroencephalogram Signal and High Definition Transcranial Direct Current Stimulation
Gaurav Sharma, Ravinder Kumar, Shubhajit Roy Chowdhury
IEEE Sensors Journal, 2020
The present article aims to fabricate spiking electrodes for EEG signal sensing and stimulating at interested region of the brain, using two different materials such as Au/AgCl and Pt/AgCl, which are synthesized by simple single step precipitation method. These electrodes can also play a significant role in maintaining high focality of high definition transcranial direct current stimulation (HD-tDCS) of the brain. The morphology of the fabricated electrodes are studied using field emission scanning electron microscopy (FESEM), its crystalline properties are studied using powdered X-ray diffraction (XRD), functional groups associated with AgCl nanoparticles are studied using Fourier-transform infrared (FTIR) spectroscopy and photo-sensitivity using UV-Vis spectroscopy. Elemental study of the material using energy dispersive X-ray analyzer (EDX) and spikes of the electrodes using optical profilometer are investigated. The calculated maximum current density for Au/AgCl electrode is measured to be 1.37 <inline-formula> <tex-math notation="LaTeX">$\\mu { {A/m}}^{{2}}$ </tex-math></inline-formula> and for Pt/AgCl electrode is 0.555 <inline-formula> <tex-math notation="LaTeX">$\\mu { {A/m}}^{{2}}$ </tex-math></inline-formula>. Using the known values of electrical conductivities of different tissues, it has been confirmed that the electrical field produced by the spiking electrodes reach both the gyri and sulci present in the cerebral cortex. Experimental trial is used to authenticate or validate the fabricated sensing electrodes for recording electroencephalogram (EEG) signal after required impedance matching which is less than <inline-formula> <tex-math notation="LaTeX">$50~{ {KOhm}}$ </tex-math></inline-formula>. The main benefit of these sensing and stimulating fabricated electrodes is to record EEG signal before and after injecting the weak amount of direct current on targeted locations of brain with same fabricated electrodes.
Enhancement in Focality of Non-Invasive Brain Stimulation through High Definition (HD) Anodal Transcranial Direct Current Stimulation (tDCS) Techniques
Gaurav Sharma, Shubhajit Roy Chowdhury
2019 IEEE Conference on Computational Intelligence in Bioinformatics and Computational Biology Cibcb 2019, 2019
The current work aims to provide conventional and high definition (HD) transcranial direct current stimulation (tDCS) for the rehabilitation of patients, suffering from cerebrovascular accident or impaired hemodynamic conditions. The paper presents a computational model to study the electric field distribution on the targeted brain cortex. The proposed computational model is used to find out the electric field distribution due to conventional tDCS and HD-tDCS electrode configuration. The main objective of this computational model is to find out the focality in terms of affected surface area due to electric field distribution in the region of targeted brain cortex. In the present work, different sizes (4 × 4, 3 × 3 and 2 × 2 cm2) of rectangular sponge pads are used to compute the electric field distribution at the targeted brain cortex by using bipolar tDCS method. The percentage pixels of affected area because of different sized electrode configurations used in bipolar tDCS has been estimated. Instead of large sponge pad, the small size electrode is used for high definition multi-electrode configurations to compute electric field distribution on same target region and also estimate the percentage of affected pixel surface area. In conventional bipolar tDCS method as the size of sponge pad decreases, focality in the affected surface area improves slightly. However, in case of multi-electrode HD-tDCS configuration, focality in the affected surface area is improved with high rate. In current work 4 × 1 HD-tDCS multi-electrode configuration is used to compute the electric field distribution and estimate percentage affected pixel surface area of the targeted region of interest. Focality in terms of affected percentage pixel surface area is better in 4 × 1 HD-tDCS method with 0.7323% affected skull tissue pixels area as compared to different sized rectangular sponge pad based bipolar conventional tDCS where 17.4059% affected pixel area has been achieved with 2×2 cm2rectangular sponge pad electrode.
Non Invasive Brain Stimulation Study Based on Ischemic Stroke Patients
Gaurav Sharma, Om Karwal, Shubhajit Roy Chowdhury
Proceedings of the Annual International Conference of the IEEE Engineering in Medicine and Biology Society EMBS, 2019
Non-invasive brain stimulation (NIBS) methods are progressively used as neuromodulator and showing optimistic potential for medical practice. In present study experimental NIRS-tDCS raw dataset of twenty-two sub-acute ischemic stroke patients has been used to explore the significant variation in measured NIRS signal namely cerebral oxygenation, oxy-hemoglobin and deoxy-hemoglobin before and after tDCS. Pearson correlation statistical method is used to determine the strength and relationship between hemodynamic responses. The negative correlation has been shown between oxy-hemoglobin and deoxy-hemoglobin before and after tDCS at 99% confidence interval (P<0.01). One sample t-test is used to determine the pre to post tDCS significant change in regional cerebral oxygenation, oxy-hemoglobin and deoxy-hemoglobin independently at 99% confidence interval (P<0.01). On the basis of significant change in the NIRS measurement parameters (HbO2, Hb and rSO2) the healthy and lesioned hemisphere of patients suffering from sub-acute ischemic stroke have been classified. A significant increase in pre to post rSO2 has been found in the healthy hemispheres of patients. For the lesioned hemisphere, the two cases were found. One is due to the decrease in rSO2 after tDCS and significant change from pre to post rSO2. The second is negligible pre to post change in the rSO2 and insignificant variation in rSO2.
Design of NIRS Probe Based on Computational Model to Find Out the Optimal Location for Non-Invasive Brain Stimulation
Gaurav Sharma, Shubhajit Roy Chowdhury
Journal of Medical Systems, 2018
Studies on rat brain phantoms for the development of near-infrared spectroscopy (NIRS) system
Gaurav Sharma, Yashika Arora, Shubhajit Roy Chowdhury
Biodevices 2018 11th International Conference on Biomedical Electronics and Devices Proceedings Part of 11th International Joint Conference on Biomedical Engineering Systems and Technologies Biostec 2018, 2018
A 4X1 high-definition transcranial direct current stimulation device for targeting cerebral micro vessels and functionality using NIRS
Gaurav Sharma, Yashika Arora, Shubhajit Roy Chowdhury
Proceedings 2016 IEEE International Symposium on Nanoelectronic and Information Systems Inis 2016, 2017