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92
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Introduction
Current institution
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August 2016 - October 2016
August 2013 - present
January 2002 - July 2013
Publications
Publications (92)
Neurovascular coupling in response to stimulation of the rat barrel cortex was investigated using concurrent multichannel electrophysiology and laser Doppler flowmetry. The data were used to build a linear dynamic model relating neural activity to blood flow. Local field potential time series were subject to current source density analysis, and the...
We have developed a model of the local field potential (LFP) based on the conservation of charge, the independence principle of ionic flows and the classical Hodgkin-Huxley (HH) type intracellular model of synaptic activity. Insights were gained through the simulation of the HH intracellular model on the nonlinear relationship between the balance o...
It is generally recognised that event related potentials (ERPs) of electroencephalogram (EEG) primarily reflect summed post-synaptic activity of the local pyramidal neural population(s). However, it is still not understood how the positive and negative deflections (e.g. P1, N1 etc) observed in ERP recordings are related to the underlying excitatory...
Background
Although vitamin B-12 (B-12) is known to contribute to the structural and functional development of the brain, it is unclear if B-12 supplementation has any beneficial effect in healthy populations in terms of enhanced neurologic status of the brain or improved cognitive function.
Objectives
We investigated the effect of dietary supplem...
In the resting state, cortical neurons can fire action potentials spontaneously but synchronously (Up state), followed by a quiescent period (Down state) before the cycle repeats. Extracellular recordings in the infragranular layer of cortex with a micro‐electrode display a negative deflection (depth‐negative) during Up states and a positive deflec...
Rodents use their whisker system to discriminate surface texture. Whisker-based texture discrimination tasks are often used to investigate the mechanisms encoding tactile sensation. One such task is the textured Novel Object Recognition Test (tNORT). It takes advantage of a tendency of rodents to explore novel objects more than familiar ones and as...
This research presents the design, development, and validation of a high degree of freedom (DOF) exoskeleton actuated by origami-inspired soft inflatable modules. The objective was to create reliable soft actuators to provide safe and compliant movement assistance. Utilising lightweight 3D printing materials and origami-inspired soft flexible modul...
Objective:
Vitamins B6 and B12 are involved in metabolic processes that decrease neural excitation and increase inhibition. This double-blind study investigated the effects of supplementation for 1 month with a high-dose of B6 or B12, compared to placebo, on a range of behavioural outcome measures connected to the balance between neural inhibition...
The balance between neural excitation and inhibition has been shown to be crucial for normal brain function. However, it is unclear whether this balance is maintained through healthy aging. This study investigated the effect of aging on the temporal dynamics of the somatosensory evoked local field potential (LFP) in rats and tested the hypothesis t...
Although electroencephalography (EEG) is widely used as a non-invasive technique for recording neural activities of the brain, our understanding of the neurogenesis of EEG is still very limited. Local field potentials (LFPs) recorded via a multi-laminar microelectrode can provide a more detailed account of simultaneous neural activity across differ...
We aim to evaluate the mechanisms underlying the neuro-vascular/metabolic coupling in the epileptogenic cortices of rats with chronic focal epilepsy.
We performed and analyzed intracranial recordings obtained from the seizure onset zones during ictal periods on epileptic rats and then used these data to fit a metabolically-coupled balloon model. No...
Studies that use prolonged periods of sensory stimulation report associations between regional reductions in neural activity and negative blood oxygenation level-dependent (BOLD) signaling. However, the neural generators of the negative BOLD response remain to be characterized. Here, we use single-impulse electrical stimulation of the whisker pad i...
Characterization of neural and hemodynamic biomarkers of epileptic activity that can be measured using non-invasive techniques is fundamental to the accurate identification of the epileptogenic zone (EZ) in the clinical setting. Recently, oscillations at gamma-band frequencies and above (>30Hz) have been suggested to provide valuable localizing inf...
This paper proposes a new reconstruction method for diffuse optical tomography using reduced-order models of light transport in tissue. The models, which directly map optical tissue parameters to optical flux measurements at the detector locations, are derived based on data generated by numerical simulation of a reference model. The reconstruction...
Although promise exists for patterns of resting-state blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) brain connectivity to be used as biomarkers of early brain pathology, a full understanding of the nature of the relationship between neural activity and spontaneous fMRI BOLD fluctuations is required before such dat...
The role of language in exact calculation is the subject of debate. Some behavioral and functional neuroimaging investigations of healthy participants suggest that calculation requires language resources. However, there are also reports of individuals with severe aphasic language impairment who retain calculation ability. One possibility in resolvi...
Detailed understanding of the haemodynamic changes that underlie non-invasive neuroimaging techniques such as blood oxygen level dependent functional magnetic resonance imaging is essential if we are to continue to extend the use of these methods for understanding brain function and dysfunction. The use of animal and in particular rodent research m...
Nonlinear system identification and analysis methods are employed to study the low-frequency oscillations present in time-series data obtained from reflectance imagery of microvasculature. Using the method of surrogate data testing the analysis reveals the deterministic nature of these oscillations believed by many to be chaotic. Further investigat...
Traditionally functional magnetic resonance imaging (fMRI) has been used to map activity in the human brain by measuring increases in the Blood Oxygenation Level Dependent (BOLD) signal. Often accompanying positive BOLD fMRI signal changes are sustained negative signal changes. Previous studies investigating the neurovascular coupling mechanisms of...
Understanding neurovascular coupling is a prerequisite for the interpretation of results obtained from modern neuroimaging techniques. This study investigated the hemodynamic and neural responses in rat somatosensory cortex elicited by 16 seconds electrical whisker stimuli. Hemodynamics were measured by optical imaging spectroscopy and neural activ...
Although there is evidence that exact calculation recruits left hemisphere perisylvian language systems, recent work has shown that exact calculation can be retained despite severe damage to these networks. In this study, we sought to identify a "core" network for calculation and hence to determine the extent to which left hemisphere language areas...
This paper proposes a new fast 3D image reconstruction algorithm for Diffuse Optical Tomography using reduced order polynomial mappings from the space of optical tissue parameters into the space of flux measurements at the detector locations. The polynomial mappings are constructed through an iterative estimation process involving structure detecti...
This paper proposes a new fast 3D image reconstruction
algorithm for Diffuse Optical Tomography using reduced
order polynomial mappings from the space of optical
tissue parameters into the space of flux measurements at
the detector locations. The polynomial mappings are
constructed through an iterative estimation process
involving structure detecti...
An important constraint on how hemodynamic neuroimaging signals such as fMRI can be interpreted in terms of the underlying evoked activity is an understanding of neurovascular coupling mechanisms that actually generate hemodynamic responses. The predominant view at present is that the hemodynamic response is most correlated with synaptic input and...
Modern neuroimaging techniques rely on neurovascular coupling to show regions of increased brain activation. However, little is known of the neurovascular coupling relationships that exist for inhibitory signals. To address this issue directly we developed a preparation to investigate the signal sources of one of these proposed inhibitory neurovasc...
Using previously published data from the whisker barrel cortex of anesthetized rodents (Berwick et al 2008 J. Neurophysiol. 99 787-98) we investigated whether highly spatially localized stimulus-evoked cortical hemodynamics responses displayed a linear time-invariant (LTI) relationship with neural activity. Presentation of stimuli to individual whi...
Dynamic modelling using the traditional least squares method with noisy input/output data can yield biased and sometimes unstable model predictions. This is largely because the cost function employed by the traditional least squares method is based on the one-step-ahead prediction errors. In this paper, the model-predicted-output errors are used in...
We present a dynamic causal model that can explain context-dependent changes in neural responses, in the rat barrel cortex, to an electrical whisker stimulation at different frequencies. Neural responses were measured in terms of local field potentials. These were converted into current source density (CSD) data, and the time series of the CSD sink...
It is well known that there is a dynamic relationship between cerebral blood flow (CBF) and cerebral blood volume (CBV). With increasing applications of functional MRI, where the blood oxygen-level-dependent signals are recorded, the understanding and accurate modeling of the hemodynamic relationship between CBF and CBV becomes increasingly importa...
We describe the use of the three dimensional characteristics of the functional magnetic resonance imaging (fMRI) blood oxygenation level dependent (BOLD) and cerebral blood volume (CBV) MRI signal changes to refine a two dimensional optical imaging spectroscopy (OIS) algorithm. The cortical depth profiles of the BOLD and CBV changes following neura...
The difference between the rate of change of cerebral blood volume (CBV) and cerebral blood flow (CBF) following stimulation is thought to be due to circumferential stress relaxation in veins (Mandeville, J.B., Marota, J.J.A., Ayata, C., Zaharchuk, G., Moskowitz, M.A., Rosen, B.R., Weisskoff, R.M., 1999. Evidence of a cerebrovascular postarteriole...
The dependency of the blood oxygenation level dependent (BOLD) signal on underlying hemodynamics is not well understood. Building a forward biophysical model of this relationship is important for the quantitative estimation of the hemodynamic changes and neural activity underlying functional magnetic resonance imaging (fMRI) signals. We have develo...
The objective of the present study was to build a dynamic model relating changes in neural responses in rat barrel cortex to an electrical whisker stimulation pulse train of varying frequencies. This work is part of a formal mathematical system currently being developed, which links stimulation to the Blood Oxygen Level Dependent (BOLD) functional...
We describe a mathematical model linking changes in cerebral blood flow, blood volume and the blood oxygenation state in response to stimulation. The model has three compartments to take into account the fact that the cerebral blood flow and volume as measured concurrently using laser Doppler flowmetry and optical imaging spectroscopy have contribu...
Recent studies have shown that the haemodynamic responses to brief (<2 secs) stimuli can be well characterised as a linear convolution of neural activity with a suitable haemodynamic impulse response. In this paper, we show that the linear convolution model cannot predict measurements of blood flow responses to stimuli of longer duration (>2 secs),...
Evidence suggests that for relatively weak sensory stimuli, cocaine elevates background haemodynamic parameters but still allows enhanced neural responses to be reflected in enhanced haemodynamic responses. The current study investigated the possibility that for more intense stimuli, the raised background may produce a protracted attenuation of the...
The temporal relationship between changes in cerebral blood flow (CBF) and cerebral blood volume (CBV) is important in the biophysical modeling and interpretation of the hemodynamic response to activation, particularly in the context of magnetic resonance imaging and the blood oxygen level-dependent signal. measured the steady state relationship be...
Functional magnetic resonance images (fMRI) were analyzed to investigate the cortical regions involved in stereoscopic vision
using red/green anaglyphs to present random dot stereograms. Two experiments were conducted both of which required high attentional
demands. In the first experiment the subjects were instructed to follow the path of a squar...
The BOLD MRI signal is a confound of intra vascular and extra vascular effects. We describe experiments in which we investigate the contribution of the intra vascular and extra vascular effects in an animal model.
An analysis method for diffusion tensor (DT) magnetic resonance imaging data is described, which, contrary to the standard method (multivariate fitting), does not require a specific functional model for diffusion-weighted (DW) signals. The method uses principal component analysis (PCA) under the assumption of a single fibre per pixel. PCA and the s...
The emerging sub-field of dynamic medical optical tomography shows great potential for conferring significantly enhanced early diagnosis and treatment monitoring capabilities upon researchers and clinicians. In previous reports we have showed that adoption of elementary time-series analysis techniques can bring about large improvements in localizat...
This article investigates the relation between stimulus-evoked neural activity and cerebral hemodynamics. Specifically, the hypothesis is tested that hemodynamic responses can be modeled as a linear convolution of experimentally obtained measures of neural activity with a suitable hemodynamic impulse response function. To obtain a range of neural a...
We used functional imaging of normal subjects to identify the neural substrate for the perception of voices in external auditory space. This fundamental process can be abnormal in psychosis, when voices that are not true external auditory objects (auditory verbal hallucinations) may appear to originate in external space. The perception of voices as...
We describe a method for imaging the local cortical haemodynamic response to whisker stimulation in the rat without use of anaesthetic or paralytic agents. Female Hooded Lister rats were anaesthetised and a section of skull overlying somatosensory cortex thinned to translucency. A stainless steel chamber was then secured over the thin cranial windo...
A recent nonlinear system by Friston et al. (2000. NeuroImage 12: 466-477) links the changes in BOLD response to changes in neural activity. The system consists of five subsystems, linking: (1) neural activity to flow changes; (2) flow changes to oxygen delivery to tissue; (3) flow changes to changes in blood volume and venous outflow; (4) changes...
Optical imaging spectroscopy was used to measure the hemodynamic response of somatosensory cortex to stimulation of the whiskers. Responses to brief puffs of air were compared in anesthetized and unanesthetized rats. The hemodynamic response was approximately four times larger in the unanesthetized animal than the corresponding anesthetized animal....
Brain activity in humans telling lies has yet to be elucidated. We developed an objective approach to its investigation, utilizing a computer-based interrogation and fMRI. Interrogatory questions probed recent episodic memory in 30 volunteers studied outside and 10 volunteers studied inside the MR scanner. In a counter-balanced design subjects answ...
Previous functional brain imaging studies suggest that the ability to infer the intentions and mental states of others (social cognition) is mediated by medial prefrontal cortex. Little is known about the anatomy of empathy and forgiveness. We used functional MRI to detect brain regions engaged by judging others' emotional states and the forgivabil...
Optical imaging spectroscopy (OIS) and laser Doppler flowmetry (LDF) data sequences from anesthetized rats were used to determine the relationship between changes in oxy-and deoxygenated hemoglobin concentration and changes in blood volume and flow in the presence and absence of stimulation. The data from Jones et al. (accompanying paper) were used...
This research examines the spatial and temporal characteristics of the responses to stimulation of the barrel cortex in anesthetized rats using optical imaging with particular emphasis on methods of analysis which reduce the effects of low-frequency oscillations on localization of the activated cortical region. Image sequences were captured using a...
A 3-Tesla research system has been developed for functional and interventional magnetic resonance imaging (MRI) procedures on animal models based on a low field niche spectrometer. Use of two stages of fourth harmonic frequency multiplication has allowed us to produce a high-frequency spectrometer with good frequency stability based on a low-freque...
This research investigates the hemodynamic response to stimulation of the barrel cortex in anaesthetized rats using optical imaging and spectroscopy (Bonhoeffer and Grinvald, 1996; Malonek and Grinvald, 1996; Mayhew et al., 1999). A slit spectrograph was used to collect spectral image data sequences. These were analyzed using an algorithm that corr...
A 3-Tesla research system has been developed for functional and interventional magnetic resonance imaging (MRI) procedures on animal models based on a low field niche spectrometer. Use of two stages of fourth harmonic frequency multiplication has allowed us to produce a high-frequency spectrometer with good frequency stability based on a low-freque...
Optical imaging of rat barrel cortex has provided detailed spatio-temporal maps of functional cortical architecture. We describe an event-related procedure (ERP) for optical imaging based on selective signal averaging as reported by Burock et al., using an anti-correlative pseudo-random event sequence. The sequence used 1s vibrissal stimulation at...
Imaging of neural activation has been used to produce maps of functional architecture and metabolic activity. There is some uncertainty associated with the sources underlying the intrinsic signals. It has been reported that following increased neural activity there was little increased oxygen consumption (∼5%), although glucose consumption increase...
Optical imaging spectroscopy is a technique for investigating the metabolic effects of brain activity (Jobsis et al., 1977; Malonek and Grinvald, 1996). It exploits the fact that the brain contains chromophores and these affect the spectra of light remitted (transmitted or reflected) from the brain’s surface. Spectrophotometry can be used to estima...
We have previously demonstrated that the performance of tracking algorithms can be improved by integrating information from multiple cues in a model-driven Bayesian reasoning framework. Here we extend our work to active vision tracking, with variable camera geometry. Many existent active tracking algorithms avoid the problem of variable camera geom...
Nonlinear system identification and analysis methods are employed to study the low frequency oscillations present in time series data obtained from reflectance imagery of microvasculature. Using the method of surrogate data testing the analysis reveals the deterministic nature of these oscillations which initially are believed to be chaotic. Furthe...
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Changes in reflectance of light remitted from the cortex can be measured with video microscopy and used to study neural activity and functional cortical architecture (1, 2) These signals are often referred to as intrinsic signals, and arise as the result of activity-induced changes in the scattering properties of neural tissue, and changes due to t...
Numerous studies attest to the fact that low frequency oscillations are present in measurements of blood flow, volume and diameter changes in the microvasculature. The presence of these oscillations has been known and studied for nearly a century (1, 2). While several low frequency oscillations have been detected, the most frequently reported and s...
Sequences of images of the cortical surface can be processed to reveal information about the cortical micro-circulation, regional cerebral blood flow (rCBF) and changes induced by neuronal activity. Images of rat sensory motor cortex and testes were processed using different analysis methodologies. The study examined the generalised linear model (G...
Analysis of the absorption spectra in the visible range has made it possible to monitor the oxygen supply and metabolism of organic tissues continuously and non-invasively. The nonlinear multicomponent analysis (NLMCA) is an evaluation method for the reflection spectra of the tissues. In this report, the derivation of the relation between the refle...
Imaging of scattered and reflected light from the surface of neural structures can reveal the functional architecture within large populations of neurons. These techniques exploit, as one of the principal signal sources, reflectance changes produced by local variation in blood volume and oxygen saturation related to neural activity. We found that a...
Motion parameter recovery for AGVs based on landmarks (or corners)
has been widely used in stereo navigation. Existing methods use weighted
least-squares algorithms to recover motion parameters, but these
estimates usually yield a zigzagged vehicle trajectory. Based on the
idea that vehicle motion must be constrained by the vehicle dynamics, a
new...
We have built a simulation to model the intrinsic signal sources. It uses estimates of parameter values derived from the published data from the optical imaging, the functional brain neuroimaging literature and textbook physiology.The temporal dynamics of the intrinsic signals are modelled by gamma functions to give delays with the appropriate time...
A method of vehicle control is described. Visual feedback from a micro-saccadic tracker is used to provide a docking competence. The vehicle is thereby capable of arriving at goal position with a specified head-ing angle. The vehicle uses a beacon to estimate it's trajectory and position in the ground plane. This information is used to control the...
The paper describes the use of biologically plausible neural network architectures to address some of the issues associated with the use of stereopsis under variable camera geometry. We report an implementation of a layered (subsumption) architecture for the adaptive control of microsaccadic tracking, and show experimental results demonstrating the...
The paper describes a 3-layered architecture for the control of the stereoscopic eye-saccade system of a stereo-camera head1 mounted on an autonomous vehicle.
The 02-level is a proportional feedback controller providing a microsaccadic 2 control for eye movements enabling the head to foveate and track targets but requiring iteration through the vis...
A method of motion parameter estimation for AGV’s is developed based on a new trajectory constraint algorithm. It is assumed that the vehicle will follow a circular path over the vision sampling interval. The algorithm has been found to be more effective and consistent than least squares estimators when the motion obeys the trajectory constraint. R...
A stereo algorithm for detecting and locating obstacles raised above a ground plane is described. It is based on applying a simple multi-model approach using hypothesis tests to the grey levels of preprocessed stereo images. The algorithm has been successfully applied to real images captured from a moving vehicle to recover putative obstacle locati...
The stabilization of a class of sampled-data systems by slow sampling is studied. A relationship is obtained between the minimum sampling period and an estimated domain of attraction of the system.
A system has been developed for integrating informa- tion from sequences of stereo images suitable for use in visual control. The method exploits multiple sources of information to obtain a subset of correctly matched corner features in temporal pairs of stereo images. These have been used to determine the ego- motion of a stereo camera system and...
The objective of this paper is to investigate how the choice of sampling interval is related to the stability of a class of
nonlinear sampled-data systems, and in particular how fast sampling may stabilize a sampled-data system when the underlying
continuous system is known to be stable. In this, the first, part of the paper, two fast sampling theo...
This paper uses a time-domain approach to study the effect of fast sampling on the stability of a class of nonlinear sampled-data
systems which have the property that their underlying continuous system are stable on a certain domain. In this, the second,
part of the paper, a relationship between sampling rate and an estimated domain of attraction o...
This paper uses a time-domain approach to study the effect of fast sampling on the stability of a class of nonlinear sampled-data systems which have the property that their underlying continuous systems are stable on a certain domain. In this, the second part of the paper, a relationship between sampling rate and an estimated domain of attraction o...
The VW model was finally published in 2009 but it was first submitted in 2007, and rejected (twice!). I wrote it in a tutorial style because I found the literature in this area very confusing and sometimes misleading. I thought I would be doing a service to clarify various concepts and bring material science and biology together. But the reviewers...
This paper demonstrates the potential of diffuse optical to-mography for estimating the temporal evolution of the haemodynamic re-sponse following cortical activation is small animals. In order to improve the spatial resolution and quantitative accuracy, a priori anatomical and functional information, derived from MR scans and prior physiological e...
Questions
Question (1)
Does someone have measurements of (or know papers that have) electrical conductivity of rat's barrel cortex across cortical layers? I have read various papers, some say it is almost homogenous, others seem to suggest large (vertical) conductance in layers II and V but small conductance in layer III. This will clearly affect CSD calculations. Is there a consensus on this? Thanks.
