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Publications (18)

  • Mohsen Mollazadeh · Vikram Aggarwal · Nitish V Thakor · Marc H Schieber
    [Show abstract] [Hide abstract] ABSTRACT: A few kinematic synergies identified by principal component analysis (PCA) account for most of the variance in the coordinated joint rotations of the fingers and wrist used for a wide variety of hand movements. To examine the possibility that motor cortex might control the hand through such synergies, we collected simultaneous kinematic and neurophysiologic data from monkeys performing a reach-to-grasp task. We used PCA, jPCA and isomap to extract kinematic synergies from 18 joint angles in the fingers and wrist, and analyzed the relationships of both single-unit and multi-unit spike recordings, as well as local field potentials (LFPs), to these synergies. For most spike recordings, the maximal absolute cross-correlations of firing rates were somewhat stronger with an individual joint angle than with any PC, any jPC or any isomap dimension. In decoding analyses-where spikes and LFP power in the 100-170 Hz band each provided better decoding than other LFP-based signals-the first PC was decoded as well as the best-decoded joint angle. But the remaining PCs and jPCs were predicted with lower accuracy than individual joint angles. Although PCs, jPCs or isomap dimensions might provide a more parsimonious description of kinematics, our findings indicate that the kinematic synergies identified with these techniques are not represented in motor cortex more strongly than the original joint angles. We suggest that the motor cortex might act to sculpt the synergies generated by subcortical centers, superimposing an ability to individuate finger movements and adapt the hand to grasp a wide variety of objects.
    Article · Jul 2014 · Journal of Neurophysiology
  • Vikram Aggarwal · Mohsen Mollazadeh · Adam G Davidson · [...] · Nitish V Thakor
    [Show abstract] [Hide abstract] ABSTRACT: The performance of Brain-Machine Interfaces (BMIs) that continuously control upper-limb neuroprostheses may benefit from distinguishing periods of posture and movement so as to prevent inappropriate movement of the prosthesis. Few studies, however, have investigated how decoding behavioral states and detecting the transitions between posture and movement could be used autonomously to trigger a kinematic decoder. We recorded simultaneous neuronal ensemble and LFP activity from microelectrode arrays in M1, PMd, and PMv of two male rhesus monkeys performing a center-out reach-and-grasp task, while upper-limb kinematics were tracked using a motion capture system with markers on the dorsal aspect of the forearm, hand, and fingers. A state decoder was trained to distinguish four behavioral states (baseline, reaction, movement, hold), while a kinematic decoder was trained to continuously decode hand endpoint position and 18 joint angles of the wrist and fingers. LFP amplitude most accurately predicted transition into the reaction (61.8%) and movement (72.9%) states, while spikes most accurately decoded arm, hand, and finger kinematics during movement. Using an LFP-based state decoder to trigger a spike-based kinematic decoder (r=0.72, RMSE=0.15) significantly improved decoding of reach-to-grasp movements from baseline to final hold, as compared to either a spike-based state decoder combined with a spike-based kinematic decoder (r=0.70, RMSE=0.17) or a spike-based kinematic decoder alone (r=0.67, RMSE=0.17). Combining LFP-based state decoding with spike-based kinematic decoding may be a valuable step towards the realization of BMI control of a multi-fingered neuroprosthesis performing dexterous manipulation.
    Article · Mar 2013 · Journal of Neurophysiology
  • [Show abstract] [Hide abstract] ABSTRACT: One of the most exciting and compelling areas of research and development is building brain machine interfaces (BMIs) for controlling prosthetic limbs. Prosthetic limb technology is advancing rapidly, and the modular prosthetic limb (MPL) of the Johns Hopkins University/ Applied Physics Laboratory (JHU/APL) permits actuation with 17 degrees of freedom in 26 articulating joints. There are many signals from the brain that can be leveraged, including the spiking rates of neurons in the cortex, electrocorticographic (ECoG) signals from the surface of the cortex, and electroencephalographic (EEG) signals from the scalp. Unlike microelectrodes that record spikes, ECoG does not penetrate the cortex and has a higher spatial specificity, signal-to-noise ratio, and bandwidth than EEG signals. We have implemented an ECoG-based system for controlling the MPL in the Johns Hopkins Hospital Epilepsy Monitoring Unit, where patients are implanted with ECoG electrode grids for clinical seizure mapping and asked to perform various recorded finger or grasp movements. We have shown that low-frequency local motor potentials (LMPs) and ECoG power in the high gamma frequency (70,150 Hz) range correlate well with grasping parameters, and they stand out as good candidate features for closed-loop control of the MPL.
    Article · Jan 2012 · IEEE Pulse
  • Mohsen Mollazadeh · Elliot Greenwald · Nitish Thakor · [...] · Gert Cauwenberghs
    [Show abstract] [Hide abstract] ABSTRACT: Electrocorticographic (ECoG) signals have emerged as a prominent neural interface signal modality due to their high bandwidth and availability in human subjects. We present a system for wireless recording of micro-ECoG activity in a primate performing reach-to-grasp movements. The system is comprised of a head-mounted interface, off-the-shelf receiver module, and custom software written in Labview for real-time data monitoring and storage. The head-mounted interface is composed of a custom-designed VLSI neural recording front, a commercially available FSK transmitter module, a digital interface, and a battery. The system offers a fixed gain of 40 dB, programmable bandwidth settings in the 0.1 Hz to 8.2 kHz range, digital gain of 1-16, and ADC resolution of 8-12 bits. The interface consumes 6.7 mA of current from a 3.7 V battery and transmits digitized data at 1 Mbps rate. The system offers less than 0.25% dropped packets at 3m non-line-of-sight distance. We then used the wirelessly recorded ECoG signal from the dorsal premotor cortex region to decode the movement state of the animal. The ECoG spectral features could decode the movement state, achieving close to 70% accuracy as early as 100 ms prior to actual movement onset. Our system offers a new avenue for future ECoG-based brain-machine interface systems.
    Conference Paper · Dec 2011
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    Mohsen Mollazadeh · Vikram Aggarwal · Adam G Davidson · [...] · Marc H Schieber
    [Show abstract] [Hide abstract] ABSTRACT: To examine the spatiotemporal distribution of discriminable information about reach-to-grasp movements in the primary motor cortex upper extremity representation, we implanted four microelectrode arrays in the anterior bank and lip of the central sulcus in each of two monkeys. We used linear discriminant analysis to compare information, quantified as decoding accuracy, contained in various neurophysiological signals. For all signal types, decoding accuracy increased immediately after the movement cue, peaked around movement onset, and declined during the static hold. Spike recordings and local field potential (LFP) time domain amplitude provided more discriminable information than LFP frequency domain power. Discriminable information on movement type was distributed evenly across recording sites by LFP amplitude and 1-4 Hz power but unevenly by 100-170 Hz power and spike recordings. These latter two signal types provided higher decoding accuracies closer to the hemispheric surface than deep in the anterior bank and also provided accuracies that varied along the central sulcus. This variation in the distribution of movement-type information may be related to differences in the rostral versus caudal regions of the primary motor cortex and to its underlying somatotopic organization. The even distribution of information by LFP amplitude and 1-4 Hz power compared with the more localized distribution by 100-170 Hz power and spikes suggest that these different neurophysiological signals reflect different underlying processes that distribute information through the motor cortex during reach-to-grasp movements.
    Full-text Article · Oct 2011 · The Journal of Neuroscience : The Official Journal of the Society for Neuroscience
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    Matthew S Fifer · Mohsen Mollazadeh · Soumyadipta Acharya · [...] · Nathan E Crone
    [Show abstract] [Hide abstract] ABSTRACT: Recent studies in primate neurophysiology have focused on decoding multi-joint kinematics from single unit and local field potential recordings. However, the extent to which these results can be generalized to human subjects is not known. We have recorded simultaneous electrocorticographic (ECoG) and hand kinematics in a human subject performing reach-grasp-hold of objects varying in shape and size. All Spectral features in various gamma bands (30-50 Hz, 70-100 Hz and 100-150 Hz frequency bands) were able to predict the time course of grasp aperture with high correlation (max r = 0.80) using as few as one ECoG feature from a single electrode (max r for single feature = 0.75) in single trials without prior knowledge of task timing. These results suggest that the population activity captured with ECoG contains information about coordinated finger movements that potentially can be exploited to control advanced upper limb neuroprosthetics.
    Full-text Article · Aug 2011 · Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference
  • Elliot Greenwald · Mohsen Mollazadeh · Charles Hu · [...] · V. Thakor
    [Show abstract] [Hide abstract] ABSTRACT: Long-term monitoring of neuronal activity in awake behaving subjects can provide fundamental information about brain dynamics for neuroscience and neuroengineering applications. Here, we present a miniature, lightweight, and low-power recording system for monitoring neural activity in awake behaving animals. The system integrates two custom designed very-large-scale integrated chips, a neural interface module fabricated in 0.5 μm complementary metal-oxide semiconductor technology and an ultra-wideband transmitter module fabricated in a 0.5 μm silicon-on-sapphire (SOS) technology. The system amplifies, filters, digitizes, and transmits 16 channels of neural data at a rate of 1 Mb/s. The entire system, which includes the VLSI circuits, a digital interface board, a battery, and a custom housing, is small and lightweight (24 g) and, thus, can be chronically mounted on small animals. The system consumes 4.8 mA and records continuously for up to 40 h powered by a 3.7-V, 200-mAh rechargeable lithium-ion battery. Experimental benchtop characterizations as well as in vivo multichannel neural recordings from awake behaving rats are presented here.
    Article · May 2011 · IEEE Transactions on Biomedical Circuits and Systems
  • Elliot Greenwald · Mohsen Mollazadeh · C. Hu · [...] · Nitish Thakor
    Article · Jan 2011
  • Mohsen Mollazadeh · Elliot Greenwald · Marc Schieber · [...] · Gert Cauwenberghs
    [Show abstract] [Hide abstract] ABSTRACT: Electrocorticography (ECoG), the recording of electrical signals from the surface of cortex, is widely used for monitoring and analysis of epileptic brain activity. However, current ECoG recording methods require tethering of the patient causing discomfort and impeding his or her mobility. We demonstrate a system for wireless multichannel recording of ECoG activity. The system is comprised of a custom made VLSI neural front end, transceiver modules, battery and a custom software written in LabView for real-time data monitoring and storage. The system offers programmable gain, bandwidth and ADC setting while maintaining low noise performance and drawing less than 6.7mA of current from 3.7V battery. We have validated this system by recording micro-ECoG signal from the dorsal premotor cortex region of a primate performing reach to grasp movements. In our demonstration, we will show the wireless operation of the system, transmitting pre-recorded ECoG signals from primates through a saline solution. We will also show real-time recording of electromyography (EMG) signals from a human subject performing motor movements. Our system offers a new platform for wireless health monitoring system in epilepsy units.
    Conference Paper · Jan 2011
  • Elliot Greenwald · Mohsen Mollazadeh · Nitish Thakor · [...] · Eugenio Culurciello
    [Show abstract] [Hide abstract] ABSTRACT: Long term monitoring of neuronal activity in awake behaving subjects can provide fundamental information about brain dynamics for both neuroscience and neuroengineering applications. Recent advances in VLSI systems has focused on designing wireless neural recording systems which can be mounted on animals and acquire neural signals in real time. These advances provide an unparalleled opportunity to study phenomenon such as neural plasticity in both a basic science setting (learning and memory), and also a clinical setting (injury and recovery). Here we present an integrated VLSI system for wireless telemetry of the entire spectrum of neural signals, spikes, local field potentials, electrocorticograms (ECoG) and electroencephalograms (EEG). The system integrates two custom designed VLSI chips, a 16 channel neural interface which can amplify, filter and digitize neural data up to 16 kS/sec and 12 bits and a low power ultra-wideband (UWB) chip which can transmit data at rates up to 14 Mbps. The entire system which includes these VLSI circuits, a digital interface board and a battery, is small, 1.2 × 1.2 × 2.6 in3, and light weight, 33 grams, so it can be chronically mounted on a rat. The system consumes 32.8 mA at 3.3V and can record for 6 hours running from the 200 mAh coin cell battery. Bench-top and in vitro characterization of the system showed comparable performance to the wired recording system.
    Conference Paper · May 2010
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    Mohsen Mollazadeh · Kartikeya Murari · Gert Cauwenberghs · Nitish Thakor
    [Show abstract] [Hide abstract] ABSTRACT: The intricate coupling between electrical and chemical activity in neural pathways of the central nervous system, and the implication of this coupling in neuropathologies, such as Parkinson's disease, motivates simultaneous monitoring of neurochemical and neuropotential signals. However, to date, neurochemical sensing has been lacking in integrated clinical instrumentation as well as in brain-computer interfaces (BCI). Here, we present an integrated system capable of continuous acquisition of data modalities in awake, behaving subjects. It features one channel each of a configurable neuropotential and a neurochemical acquisition system. The electrophysiological channel is comprised of a 40-dB gain, fully differential amplifier with tunable bandwidth from 140 Hz to 8.2 kHz. The amplifier offers input-referred noise below 2 mu V <sub>rms</sub> for all bandwidth settings. The neurochemical module features a picoampere sensitivity potentiostat with a dynamic range spanning six decades from picoamperes to microamperes. Both systems have independent on-chip, configurable DeltaSigma analog-to-digital converters (ADCs) with programmable digital gain and resolution. The system was also interfaced to a wireless power harvesting and telemetry module capable of powering up the circuits, providing clocks for ADC operation, and telemetering out the data at up to 32 kb/s over 3.5 cm with a bit-error rate of less than 10<sup>-5</sup>. Characterization and experimental results from the electrophysiological and neurochemical modules as well as the full system are presented.
    Full-text Article · Jan 2010 · IEEE Transactions on Biomedical Circuits and Systems
  • M. Mollazadeh · V. Aggarwal · N. V. Thakor · [...] · M. H. Schieber
    [Show abstract] [Hide abstract] ABSTRACT: Local field potentials (LFP) represent the dendritic activity of a population of cells near the recording electrode. However, how LFP activity is related to single unit activity, and if it provides any additional information has not been well studied. Previously we have shown that temporal spectral modulation of LFP activity can be used to decode dexterous movements of the hand. Here, we analyze simultaneous spike and LFP recordings from M1 cortex in a rhesus monkey performing fine hand movements. Using multitaper spectral analysis, we found that both LFP and spiking activity show an increase in power in the
    Article · Apr 2009
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    Mohsen Mollazadeh · Kartikeya Murari · Gert Cauwenberghs · Nitish Thakor
    [Show abstract] [Hide abstract] ABSTRACT: Electrical activity in the brain spans a wide range of spatial and temporal scales, requiring simultaneous recording of multiple modalities of neurophysiological signals in order to capture various aspects of brain state dynamics. Here, we present a 16-channel neural interface integrated circuit fabricated in a 0.5 mum 3M2P CMOS process for selective digital acquisition of biopotentials across the spectrum of neural signal modalities in the brain, ranging from single spike action potentials to local field potentials (LFP), electrocorticograms (ECoG), and electroencephalograms (EEG). Each channel is composed of a tunable bandwidth, fixed gain front-end amplifier and a programmable gain/resolution continuous-time incremental DeltaSigma analog-to-digital converter (ADC). A two-stage topology for the front-end voltage amplifier with capacitive feedback offers independent tuning of the amplifier bandpass frequency corners, and attains a noise efficiency factor (NEF) of 2.9 at 8.2 kHz bandwidth for spike recording, and a NEF of 3.2 at 140 Hz bandwidth for EEG recording. The amplifier has a measured midband gain of 39.6 dB, frequency response from 0.2 Hz to 8.2 kHz, and an input-referred noise of 1.94 mu V <sub>rms</sub> while drawing 12.2 muA of current from a 3.3 V supply. The lower and higher cutoff frequencies of the bandpass filter are adjustable from 0.2 to 94 Hz and 140 Hz to 8.2 kHz, respectively. At 10-bit resolution, the ADC has an SNDR of 56 dB while consuming 76 muW power. Time-modulation feedback in the ADC offers programmable digital gain (1-4096) for auto-ranging, further improving the dynamic range and linearity of the ADC. Experimental recordings with the system show spike signals in rat somatosensory cortex as well as alpha EEG activity in a human subject.
    Full-text Article · Mar 2009 · IEEE Transactions on Biomedical Circuits and Systems
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    Mohsen Mollazadeh · Kartikeya Murari · Helen Schwerdt · [...] · Gert Cauwenberghs
    [Show abstract] [Hide abstract] ABSTRACT: Implantable brain-machine interfaces for disease diagnosis and motor prostheses control require low-power acquisition of neuropotentials spanning a wide range of amplitudes and frequencies. Here, we present a 16-channel VLSI neuropotential acquisition system with tunable gain and bandwidth, and variable rate digital transmission over an inductive link which further supplies power. The neuropotential interface chip is composed of an amplifier, incremental ADC and bit-serial readout circuitry. The front-end amplifier has a midband gain of 40 dB and offers NEF of less than 3 for all bandwidth settings. It also features adjustable low-frequency cut-off from 0.2 to 94 Hz, and independent high-frequency cut-off from 140 Hz to 8.2 kHz. The Gm-C incremental DeltaSigma ADC offers digital gain up to 4096 and 8-12 bits resolution. The interface circuit is powered by a telemetry chip which harvests power through inductive coupling from a 4 MHz link, provides a 1 MHz clock for ADC operation and transmits the bit-serial data of the neurpotential interface across 4 cm at up to 32 kbps with a BER less than 10<sup>-5</sup>. Experimental EEG recordings using the neuropotential interface and wireless module are presented.
    Full-text Conference Paper · Dec 2008
  • Kartikeya Murari · Mohsen Mollazadeh · Nitish Thakor · Gert Cauwenberghs
    [Show abstract] [Hide abstract] ABSTRACT: Information processing and propagation in the central nervous system is mostly electrical in nature. At synapses, electrical signals cause the release of neurotransmitters like dopamine, glutamate etc., that are sensed by post-synaptic neurons resulting in signal propagation or inhibition. It can be very informative to monitor electrical and neurochemical signals simultaneously to understand the mechanisms underlying normal or abnormal brain function. We present an integrated system for the simultaneous wireless acquisition of neurophysiological and neurochemical activity. Applications of the system to neuroscience include monitoring EEG and glutamate in rat somatosensory cortex following global ischemia.
    Article · Aug 2008 · Proceedings of SPIE - The International Society for Optical Engineering
  • Mohsen Mollazadeh · Vikram Aggarwal · Girish Singhal · [...] · Nitish Thakor
    [Show abstract] [Hide abstract] ABSTRACT: Recent studies have shown that cortical local field potentials (LFP) contain information about planning or executing hand movement. While earlier research has looked at gross motor movements, we investigate the spectral modulation of LFP activity and its dependence on recording location during dexterous motor actions. In this study, we recorded LFP activity from the primary motor cortex of a primate as it performed a fine finger manipulation task involving different switches. The event-related spectral perturbations (ERSP) in four different frequency bands were considered for the analysis; 4 Hz, 6-15 Hz, 17-40 Hz and 75-170 Hz. LFPs recorded from electrodes in the hand area showed the largest change in ERSP for the highest frequency band (75-170 Hz) (p 0.05), while LFPs recorded from electrodes placed more medially in the arm area showed the largest change in ERSP for the lowest frequency band (4 Hz) (p 0.05). Furthermore, the spectral information from the <4 Hz and 75-150 Hz frequency bands was used to successfully decode the three dexterous grasp movements with an average accuracy of up to 81%. Although previous research has shown that multi-unit neuronal activity can be used to decode fine motor movements, these results demonstrate that LFP activity can also be used to decode dexterous motor tasks. This has implications for future neuroprosthetic devices due to the robustness of LFP signals for chronic recording.
    Article · Aug 2008 · Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference
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    Mohsen Mollazadeh · Kartikeya Murari · Gert Cauwenberghs · Nitish Thakor
    [Show abstract] [Hide abstract] ABSTRACT: Electrical signals recorded from the brain cover a wide range of amplitudes, frequencies, and spatial scales, from spikes and local field potentials (LFP) inside the brain to electrocorticograms (ECoG) and electroencepalograms (EEG) outside. Each of these signal modalities represent different aspects of neural dynamics that can be combined to infer brain state and function in a broader context.We present a 16-channel interface circuit fabricated in a 0.5 mum CMOS process for the selective acquisition and digitization of any of the modalities. Each channel features a fixed gain bandpass amplifier with a tunable frequency response which allows isolation of the signal of interest without hardware modification and a programmable gain/resolution analog to digital converter (ADC). The bandpass amplifier analog front end has an input referred noise of 1.94 microV(rms) for a bandwidth of 8.2 kHz while drawing 12.2 microA of current from a 3.3 V supply. Experimental recordings with the system show spike signals in rat somatosensory cortex as well as alpha EEG activity in a human subject.
    Full-text Article · Feb 2008 · Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference
  • Mohsen Mollazadeh · Kartikeya Murari · Christian Sauer · [...] · Gert Cauwenberghs
    [Show abstract] [Hide abstract] ABSTRACT: Central Nervous System (CNS) uses the interplay between signals of different modalities to transfer and process information. Neurological events are characterized by changes in both neurochemical concentrations and the electrical activity of neurons. Electro physiological and neurochemical events are highly correlated as one causes the other and vice-versa. The ability to simultaneously record electrical and chemical activity is of considerable research and diagnostic importance. Here, we present a hardware implementation for wireless power and clock transfer to and serial transmission of digitized neurochemical and electro physiological data from sensors over one RF link. The idea can be extended to sensors of different modalities having widely different data rates. Neurochemical data are acquired in real-time from a custom multichannel very large scale integrated (VLSI) potentiostat chip at 5 Hz. Field potential data were sampled at 400 Hz. A custom VLSI chip powers up and supplies clocks to the potentiostat and telemeters the multiplexed data. All the chips were fabricated in AMI 3M-2P 0.5¿ CMOS process. We demonstrate successful operation of the system with wireless powering and telemetry of the multiplexed data.
    Conference Paper · Aug 2006