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Search Results: 1 - 10 of 131517 matches for " Sridevi V. Sarma "
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Performance Limitations of Relay Neurons
Rahul Agarwal ,Sridevi V. Sarma
PLOS Computational Biology , 2012, DOI: 10.1371/journal.pcbi.1002626
Abstract: Relay cells are prevalent throughout sensory systems and receive two types of inputs: driving and modulating. The driving input contains receptive field properties that must be transmitted while the modulating input alters the specifics of transmission. For example, the visual thalamus contains relay neurons that receive driving inputs from the retina that encode a visual image, and modulating inputs from reticular activating system and layer 6 of visual cortex that control what aspects of the image will be relayed back to visual cortex for perception. What gets relayed depends on several factors such as attentional demands and a subject's goals. In this paper, we analyze a biophysical based model of a relay cell and use systems theoretic tools to construct analytic bounds on how well the cell transmits a driving input as a function of the neuron's electrophysiological properties, the modulating input, and the driving signal parameters. We assume that the modulating input belongs to a class of sinusoidal signals and that the driving input is an irregular train of pulses with inter-pulse intervals obeying an exponential distribution. Our analysis applies to any order model as long as the neuron does not spike without a driving input pulse and exhibits a refractory period. Our bounds on relay reliability contain performance obtained through simulation of a second and third order model, and suggest, for instance, that if the frequency of the modulating input increases or the DC offset decreases, then relay increases. Our analysis also shows, for the first time, how the biophysical properties of the neuron (e.g. ion channel dynamics) define the oscillatory patterns needed in the modulating input for appropriately timed relay of sensory information. In our discussion, we describe how our bounds predict experimentally observed neural activity in the basal ganglia in (i) health, (ii) in Parkinson's disease (PD), and (iii) in PD during therapeutic deep brain stimulation. Our bounds also predict different rhythms that emerge in the lateral geniculate nucleus in the thalamus during different attentional states.
The effects of cues on neurons in the basal ganglia in Parkinson's disease
Sridevi V. Sarma,Uri Eden
Frontiers in Integrative Neuroscience , 2012, DOI: 10.3389/fnint.2012.00040
Abstract: Visual cues open a unique window to the understanding of Parkinson's disease (PD). These cues can temporarily but dramatically improve PD motor symptoms. Although details are unclear, cues are believed to suppress pathological basal ganglia (BG) activity through activation of corticostriatal pathways. In this study, we investigated human BG neurophysiology under different cued conditions. We evaluated bursting, 10–30 Hz oscillations (OSCs), and directional tuning (DT) dynamics in the subthalamic nucleus (STN) activity while seven patients executed a two-step motor task. In the first step (predicted +cue), the patient moved to a target when prompted by a visual go cue that appeared 100% of the time. Here, the timing of the cue is predictable and the cue serves an external trigger to execute a motor plan. In the second step, the cue appeared randomly 50% of the time, and the patient had to move to the same target as in the first step. When it appeared (unpredicted +cue), the motor plan was to be triggered by the cue, but its timing was not predictable. When the cue failed to appear (unpredicted ?cue), the motor plan was triggered by the absence of the visual cue. We found that during predicted +cue and unpredicted ?cue trials, OSCs significantly decreased and DT significantly increased above baseline, though these modulations occurred an average of 640 ms later in unpredicted ?cue trials. Movement and reaction times were comparable in these trials. During unpredicted +cue trials, OSCs, and DT failed to modulate though bursting significantly decreased after movement. Correspondingly, movement performance deteriorated. These findings suggest that during motor planning either a predictably timed external cue or an internally generated cue (generated by the absence of a cue) trigger the execution of a motor plan in premotor cortex, whose increased activation then suppresses pathological activity in STN through direct pathways, leading to motor facilitation in PD.
Nonparametric Estimation of Band-limited Probability Density Functions
Rahul Agarwal,Zhe Chen,Sridevi V. Sarma
Statistics , 2015,
Abstract: In this paper, a nonparametric maximum likelihood (ML) estimator for band-limited (BL) probability density functions (pdfs) is proposed. The BLML estimator is consistent and computationally efficient. To compute the BLML estimator, three approximate algorithms are presented: a binary quadratic programming (BQP) algorithm for medium scale problems, a Trivial algorithm for large-scale problems that yields a consistent estimate if the underlying pdf is strictly positive and BL, and a fast implementation of the Trivial algorithm that exploits the band-limited assumption and the Nyquist sampling theorem ("BLMLQuick"). All three BLML estimators outperform kernel density estimation (KDE) algorithms (adaptive and higher order KDEs) with respect to the mean integrated squared error for data generated from both BL and infinite-band pdfs. Further, the BLMLQuick estimate is remarkably faster than the KD algorithms. Finally, the BLML method is applied to estimate the conditional intensity function of a neuronal spike train (point process) recorded from a rat's entorhinal cortex grid cell, for which it outperforms state-of-the-art estimators used in neuroscience.
Mutual Dependence: A Novel Method for Computing Dependencies Between Random Variables
Rahul Agarwal,Pierre Sacre,Sridevi V. Sarma
Statistics , 2015,
Abstract: In data science, it is often required to estimate dependencies between different data sources. These dependencies are typically calculated using Pearson's correlation, distance correlation, and/or mutual information. However, none of these measures satisfy all the Granger's axioms for an "ideal measure". One such ideal measure, proposed by Granger himself, calculates the Bhattacharyya distance between the joint probability density function (pdf) and the product of marginal pdfs. We call this measure the mutual dependence. However, to date this measure has not been directly computable from data. In this paper, we use our recently introduced maximum likelihood non-parametric estimator for band-limited pdfs, to compute the mutual dependence directly from the data. We construct the estimator of mutual dependence and compare its performance to standard measures (Pearson's and distance correlation) for different known pdfs by computing convergence rates, computational complexity, and the ability to capture nonlinear dependencies. Our mutual dependence estimator requires fewer samples to converge to theoretical values, is faster to compute, and captures more complex dependencies than standard measures.
Electrical neurostimulation for chronic pain: on selective relay of sensory neural activities in myelinated nerve fibers
Pierre Sacré,Sridevi V. Sarma,Yun Guan,William S. Anderson
Quantitative Biology , 2015,
Abstract: Chronic pain affects about 100 million adults in the US. Despite their great need, neuropharmacology and neurostimulation therapies for chronic pain have been associated with suboptimal efficacy and limited long-term success, as their mechanisms of action are unclear. Yet current computational models of pain transmission suffer from several limitations. In particular, dorsal column models do not include the fundamental underlying sensory activity traveling in these nerve fibers. We developed a (simple) simulation test bed of electrical neurostimulation of myelinated nerve fibers with underlying sensory activity. This paper reports our findings so far. Interactions between stimulation-evoked and underlying activities are mainly due to collisions of action potentials and losses of excitability due to the refractory period following an action potential. In addition, intuitively, the reliability of sensory activity decreases as the stimulation frequency increases. This first step opens the door to a better understanding of pain transmission and its modulation by neurostimulation therapies.
A Signal-to-Noise Ratio Estimator for Generalized Linear Model Systems
Gabriela Czanner,Sridevi V. Sarma,Uri T. Eden,Emery N. Brown
Lecture Notes in Engineering and Computer Science , 2008,
Non-stationary discharge patterns in motor cortex under subthalamic nucleus deep brain stimulation
Sabato Santaniello,Erwin B. Montgomery Jr.,John T. Gale,Sridevi V. Sarma
Frontiers in Integrative Neuroscience , 2012, DOI: 10.3389/fnint.2012.00035
Abstract: Deep brain stimulation (DBS) of the subthalamic nucleus (STN) directly modulates the basal ganglia (BG), but how such stimulation impacts the cortex upstream is largely unknown. There is evidence of cortical activation in 6-hydroxydopamine (OHDA)-lesioned rodents and facilitation of motor evoked potentials in Parkinson's disease (PD) patients, but the impact of the DBS settings on the cortical activity in normal vs. Parkinsonian conditions is still debated. We use point process models to analyze non-stationary activation patterns and inter-neuronal dependencies in the motor and sensory cortices of two non-human primates during STN DBS. These features are enhanced after treatment with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which causes a consistent PD-like motor impairment, while high-frequency (HF) DBS (i.e., ≥100 Hz) strongly reduces the short-term patterns (period: 3–7 ms) both before and after MPTP treatment, and elicits a short-latency post-stimulus activation. Low-frequency DBS (i.e., ≤50 Hz), instead, has negligible effects on the non-stationary features. Finally, by using tools from the information theory [i.e., receiver operating characteristic (ROC) curve and information rate (IR)], we show that the predictive power of these models is dependent on the DBS settings, i.e., the probability of spiking of the cortical neurons (which is captured by the point process models) is significantly conditioned on the timely delivery of the DBS input. This dependency increases with the DBS frequency and is significantly larger for high- vs. low-frequency DBS. Overall, the selective suppression of non-stationary features and the increased modulation of the spike probability suggest that HF STN DBS enhances the neuronal activation in motor and sensory cortices, presumably because of reinforcement mechanisms, which perhaps involve the overlap between feedback antidromic and feed-forward orthodromic responses along the BG-thalamo-cortical loop.
Design and Analysing the Various Parameters of CMOS Circuit’s under Bi-Triggering Method Using Cadence Tools  [PDF]
A. Sridevi, V. Lakshmiprabha, N. Prabhu
Circuits and Systems (CS) , 2016, DOI: 10.4236/cs.2016.79227
Abstract: Reducing the power and energy required by the device/circuit to operate is the main aim of this paper. Here the new design is implemented to reduce the power consumption of the device using the triggering pulses. The proposed triggering method uses a complementary MOS transistor (pMOS and nMOS) as a voltage divider and ground leakage suppressor (i.e.); these designs are named as Trig01 and Trig10 designs. In Trig01 design the pair of CMOS is placed in the voltage divider part; similarly in Trig10 design the pair of CMOS is placed at the ground leakage suppressor part. Standard CMOS gates like NOT, NAND, NOR, EX-OR etc. are designed with these technologies and these gates are designed with 180 nm technology file in the cadence tool suite; compared to the normal CMOS gates, the Bi-Trig gate contains 4 inputs and 2 outputs. The two extra inputs are used as Bi-Trig control signaling inputs. There are 2 control inputs and thus 22= 4 combination of controlling is done (i.e.); both pMOS and nMOS are ON, both pMOS and nMOS are OFF, pMOS ON and nMOS OFF and pMOS ON and nMOS ON. Depending on the usage of the circuit, the mode of operation is switched to any one of the combination. If the output of the circuit is not used anywhere in the total block, that specified circuit can be switched into idle mode by means of switched OFF both the pMOS and nMOS transistor in the control unit. This reduces the leakage current and also the power wastage of the circuits in the total block. Bi-Trig controlled circuit reduces the power consumption and leakage power of the circuit without affecting a performance of the circuits.
CNTFET Parallel in Parallel out Shift Register
T. Jayanthy,V. Sridevi
Indian Streams Research Journal , 2012,
Abstract: In this paper, a compact model for carbon nanotube field effect transistor has been designed by considering various device parameters such as length, number of tubes, chiral vector etc. The modeled CNTFET is used to design various digital circuits in particular parallel in parallel out shift register. The results of Hspice simulation performed on the designed PIPO shift register shows superior performance over conventional MOSFET in terms of power dissipation, power delay product, size etc.
Review of Research , 2012,
Abstract: A study was undertaken to study the awareness of adolescent teacher trainees of Awassa College of teacher education, South Ethiopia regarding reproductive health aspects through a questionnaire. The study adopted a survey method. A total of 200 teacher trainees were selected randomly from Awassa College of Teacher Education, South Ethiopia. The tool for assessment consisted of Awareness test on ARHA consisting of sixty five items on the aspects of physical changes occurring in male and female during adolescence period(17 items); Reproductive health issue (33items) and HIV/AIDS(15 items). Results showed that the Male teacher trainees have better awareness on ARH when compared to that of female trainees; Trainees from urban background have better awareness than that of rural background; As the educational level of parents increase the awareness level of trainees on Adolescent Reproductive Health (ARH) also increases.; and Trainees whose parents are professionals have better awareness on ARH than non professional parents. Informative and educable interventions would help in bringing out a positive effect on awareness levels which would eventually encourage expansion of knowledge and positive health habits
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