31 research outputs found
Information recovery from rank-order encoded images
The work described in this paper is inspired by SpikeNET, a system
developed to test the feasibility of using rank-order codes in modelling largescale
networks of asynchronously spiking neurons. The rank-order code theory
proposed by Thorpe concerns the encoding of information by a population of
spiking neurons in the primate visual system. The theory proposes using the order
of firing across a network of asynchronously firing spiking neurons as a neural
code for information transmission. In this paper we aim to measure the perceptual
similarity between the image input to a model retina, based on that originally
designed and developed by VanRullen and Thorpe, and an image reconstructed
from the rank-order encoding of the input image. We use an objective metric
originally proposed by Petrovic to estimate perceptual edge preservation in image
fusion which, after minor modifcations, is very much suited to our purpose. The
results show that typically 75% of the edge information of the input stimulus is
retained in the reconstructed image, and we show how the available information
increases with successive spikes in the rank-order code
Information recovery from rank-order encoded images
The time to detection of a visual stimulus by the primate eye is recorded at
100 ā 150ms. This near instantaneous recognition is in spite of the considerable
processing required by the several stages of the visual pathway to recognise and
react to a visual scene. How this is achieved is still a matter of speculation.
Rank-order codes have been proposed as a means of encoding by the primate
eye in the rapid transmission of the initial burst of information from the sensory
neurons to the brain. We study the efficiency of rank-order codes in encoding
perceptually-important information in an image. VanRullen and Thorpe built a
model of the ganglion cell layers of the retina to simulate and study the viability
of rank-order as a means of encoding by retinal neurons. We validate their model
and quantify the information retrieved from rank-order encoded images in terms
of the visually-important information recovered. Towards this goal, we apply
the āperceptual information preservation algorithmā, proposed by Petrovic and
Xydeas after slight modification. We observe a low information recovery due
to losses suffered during the rank-order encoding and decoding processes. We
propose to minimise these losses to recover maximum information in minimum
time from rank-order encoded images. We first maximise information recovery by
using the pseudo-inverse of the filter-bank matrix to minimise losses during rankorder
decoding. We then apply the biological principle of lateral inhibition to
minimise losses during rank-order encoding. In doing so, we propose the Filteroverlap
Correction algorithm. To test the perfomance of rank-order codes in
a biologically realistic model, we design and simulate a model of the foveal-pit
ganglion cells of the retina keeping close to biological parameters. We use this
as a rank-order encoder and analyse its performance relative to VanRullen and
Thorpeās retinal model
Implementing the cellular mechanisms of synaptic transmission in a neural mass model of the thalamocortical circuitry
A novel direction to existing neural mass modeling technique is proposed where
the commonly used āalpha functionā for representing synaptic transmission is
replaced by a kinetic framework of neurotransmitter and receptor dynamics.
The aim is to underpin neuro-transmission dynamics associated with abnormal
brain rhythms commonly observed in neurological and psychiatric disorders. An
existing thalamocortical neural mass model is modified by using the kinetic
Q1 framework for modeling synaptic transmission mediated by glutamatergic and GABA
(gamma-aminobutyric-acid)-ergic receptors. The model output is compared qualitatively
with existing literature on in vitro experimental studies of ferret thalamic slices, as
well as on single-neuron-level model based studies of neuro-receptor and transmitter
dynamics in the thalamocortical tissue. The results are consistent with these studies:
the activation of ligand-gated GABA receptors is essential for generation of spindle
waves in the model, while blocking this pathway leads to low-frequency synchronized
oscillations such as observed in slow-wave sleep; the frequency of spindle oscillations
increase with increased levels of post-synaptic membrane conductance for AMPA
(alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic-acid) receptors, and blocking this
pathway effects a quiescent model output. In terms of computational efficiency, the
simulation time is improved by a factor of 10 compared to a similar neural mass model
based on alpha functions. This implies a dramatic improvement in computational resources
for large-scale network simulation using this model. Thus, the model provides a platform
for correlating high-level brain oscillatory activity with low-level synaptic attributes, and
makes a significant contribution toward advancements in current neural mass modeling
paradigm as a potential computational tool to better the understanding of brain oscillations
in sickness and in health
Combined study of time-series bifurcation and power spectral behaviour of a thalamo-cortico- thalamic neural mass model
A combined power spectral and time-series bifurcation analysis of a neural mass model is presented. Such 'multimodal' analytical techniques are being used in several researches to understand Electroencephalograph (EEG) anomalies in brain disorder
Assistive Chatbots for healthcare: a succinct review
Artificial Intelligence (AI) for supporting healthcare services has never
been more necessitated than by the recent global pandemic. Here, we review the
state-of-the-art in AI-enabled Chatbots in healthcare proposed during the last
10 years (2013-2023). The focus on AI-enabled technology is because of its
potential for enhancing the quality of human-machine interaction via Chatbots,
reducing dependence on human-human interaction and saving man-hours. Our review
indicates that there are a handful of (commercial) Chatbots that are being used
for patient support, while there are others (non-commercial) that are in the
clinical trial phases. However, there is a lack of trust on this technology
regarding patient safety and data protection, as well as a lack of wider
awareness on its benefits among the healthcare workers and professionals. Also,
patients have expressed dissatisfaction with Natural Language Processing (NLP)
skills of the Chatbots in comparison to humans. Notwithstanding the recent
introduction of ChatGPT that has raised the bar for the NLP technology, this
Chatbot cannot be trusted with patient safety and medical ethics without
thorough and rigorous checks to serve in the `narrow' domain of assistive
healthcare. Our review suggests that to enable deployment and integration of
AI-enabled Chatbots in public health services, the need of the hour is: to
build technology that is simple and safe to use; to build confidence on the
technology among: (a) the medical community by focussed training and
development; (b) the patients and wider community through outreach
Combined study of time-series bifurcation and power spectral behaviour of a thalamo-cortico-thalamic neural mass model
A combined power spectral and time-series bifurcation analysis of a neural mass model is presented. Such 'multi-modal' analytical techniques are being used in several researches to understand Electroencephalograph (EEG) anomalies in brain disorders [1][2], in contrast to 'power spectra-only' analytical studies that were more common during the early days of EEG analysis. In a recent work, a combined analysis of a simple thalamo-cortical neural mass model in context to EEG abnormality in Alzheimer's disease (AD) is presented [3]. The study shows that 'unimodal' analytical techniques such as power spectra-only studies without a simultaneous observation of the time-series model output may lead to anomalous conclusions and hypotheses. Towards this, in this work, a 'multi-modal' analytical technique is applied on a thalamocorticothalamic (tct) model, which was earlier studied using power-spectra analysis only [4]. The tct model is an enhanced version of that used in [3] and is based on biological data available in current literature. Furthermore, it aims to mimic thalalmocortical oscillations such as observed in the EEG of both healthy and diseased brain.
Here, the power spectra of the tct model output is observed within the Ī“ (1-3 Hz), Īø (4-7 Hz), Ī± (8-13 Hz), Ī² (14-30 Hz) bands, along with a simultaneous analysis of the time series behaviour, the latter showing three behavioural modes: noisy point-attractor, spindle and limit-cycle. With all parameters at their basal values, the output time series is in a noisy point-attractor mode with maximum power within the alpha band (Figure 1). However the model shifts into a limit cycle oscillatory mode with a decrease in inhibitory connectivity parameters in the model (Figure 1); the corresponding power spectra show an increase in peak power within the Īø and Ī“ bands along with a simultaneous decrease in power within the Ī± and Ī² bands. The model behaviour is very much in agreement with in-vitro studies [5] which report an increased theta band power and a simultaneous decreased alpha band power during transition from wakefulness to sleep. Furthermore, the in-vitro time-series are qualitatively very similar to those obtained using the model. Thus, the model indicates a decreased inhibitory activity to be the neural correlate of the transitive state between wakefulness and sleep. On the other hand, increased mean firing activity of the extrinsic model inputs pushes the model, first into a spindling mode, and then into a limit cycle mode. In this state, the power within the delta band shows a significant increase compared to those within the other frequency bands. This behaviour is more similar to in-vivo studies of awake-to-sleep transition as reported in [5]
Introduction to special issue on āRecent computing paradigms, network protocols, and applicationsā
This special issue of Innovations in Systems and Software
Engineering: A NASA Journal is devoted to selected contributions
from the 3rd International Conference on Advanced
Computing, Networking and Informatics (ICACNI-2015),
organized by School of Computer Engineering, KIIT University,
Odisha, India, during 23ā25 June, 2015. The conference
commenced with a keynote by Prof. Nikhil R. Pal (Fellow
IEEE, Vice President for Publications IEEE Computational
Intelligence Society (2015ā2016), Indian Statistical Institute,
Kolkata, India) on āA Fuzzy Rule-Based Approach to Single
Frame Super Resolutionā. Apart from three regular tracks on
advanced computing, networking, and informatics, the conference
hosted three invited special sessions. While a total
of 558 articles across different tracks of the conference were
received, 132 articles are finally selected for presentation
and publication by Smart Innovation, Systems and Technologies
series of Springer as Volume 43 and 44. The conference
showcased a technical talk by Prof. Nabendu Chaki (Senior
Member IEEE, Calcutta University, India) on āEvolution
from Web-based Applications to Cloud Services: A Case
Study with Remote Healthcareā. The conference identified
some wonderful works and has given away eight awards in
different categories
Studying the effects of thalamic interneurons in a thalamocortical neural mass model
Neural mass models of the thalamocortical circuitry are
often used to mimic brain activity during sleep and
wakefulness as observed in scalp electroencephalogram
(EEG) signals [1]. It is understood that alpha rhythms
(8-13 Hz) dominate the EEG power-spectra in the resting-state
[2] as well as the period immediately before
sleep [3]. Literature review shows that the thalamic
interneurons (IN) are often ignored in thalamocortical
population models; the emphasis is on the connections
between the thalamo cortical relay (TCR) and the thalamic
reticular nucleus (TRN). In this work, we look into
the effects of the IN cell population on the behaviour of
an existing thalamocortical model containing the TCR
and TRN cell populations [4]. A schematic of the
extended model used in this work is shown in Fig.1.
The model equations are solved in Matlab using the
Runge-Kutta method of the 4th/5th order. The model
shows high sensitivity to the forward and reverse rates
of reactions during synaptic transmission as well as on
the membrane conductance of the cell populations. The
input to the model is a white noise signal simulating
conditions of resting state with eyes closed, a condition
well known to be associated with dominant alpha band
oscillations in EEG e.g. [5]. Thus, the model parameters
are calibrated to obtain a set of basal parameter values
when the model oscillates with a dominant frequency
within the alpha band. The time series plots and the
power spectra of the model output are compared with
those when the IN cell population is disconnected from
the circuit (by setting the inhibitory connectivity parameter
from the IN to the TCR to zero). We observe
(Fig. 2 inset) a significant difference in time series output
of the TRN cell population with and without the IN
cell population in the model; this in spite of the IN
having no direct connectivity to and from the TRN cell
population (Fig. 1). A comparison of the power spectra
behaviour of the model output within the delta
(1-3.5Hz), theta (3.75-7.5Hz), alpha (7.75-13.5Hz) and
beta (13.75-30.5Hz) bands is shown in Fig. 2. Disconnecting
the IN cell population shows a significant drop in the
alpha band power and the dominant frequency of oscillation
now lies within the theta band. An overall āslowingā
(left-side shift) of the power spectra is observed with an
increase within the delta and theta bands and a decrease
in the alpha and beta bands. Such a slowing of EEG is a
signature of slow wave sleep in healthy individuals, and
this suggests that the IN cell population may be centrally
involved in the phase transition to slow wave sleep [6]. It
is also characteristic of the waking EEG in Alzheimerās
disease, and may help us to understand the role of the IN
cell population in modulating TCR and TRN cell behaviour
in pathological brain conditions
Causal role of thalamic interneurons in brain state transitions: a study using a neural mass model implementing synaptic kinetics
Experimental studies on the Lateral Geniculate Nucleus (LGN) of mammals and rodents show that the inhibitory interneurons (IN) receive around 47.1% of their afferents from the retinal spiking neurons, and constitute around 20ā25% of the LGN cell population. However, there is a definite gap in knowledge about the role and impact of IN on thalamocortical dynamics in both experimental and model-based research. We use a neural mass computational model of the LGN with three neural populations viz. IN, thalamocortical relay (TCR), thalamic reticular nucleus (TRN), to study the causality of IN on LGN oscillations and state-transitions. The synaptic information transmission in the model is implemented with kinetic modeling, facilitating the linking of low-level cellular attributes with high-level population dynamics. The model is parameterized and tuned to simulate alpha (8ā13 Hz) rhythm that is dominant in both Local Field Potential (LFP) of LGN and electroencephalogram (EEG) of visual cortex in an awake resting state with eyes closed. The results show that: First, the response of the TRN is suppressed in the presence of IN in the circuit; disconnecting the IN from the circuit effects a dramatic change in the model output, displaying high amplitude synchronous oscillations within the alpha band in both TCR and TRN. These observations conform to experimental reports implicating the IN as the primary inhibitory modulator of LGN dynamics in a cognitive state, and that reduced cognition is achieved by suppressing the TRN response. Second, the model validates steady state visually evoked potential response in humans corresponding to periodic input stimuli; however, when the IN is disconnected from the circuit, the output power spectra do not reflect the input frequency. This agrees with experimental reports underpinning the role of IN in efficient retino-geniculate information transmission. Third, a smooth transition from alpha to theta band is observed by progressive decrease of neurotransmitter concentrations in the synaptic clefts; however, the transition is abrupt with removal of the IN circuitry in the model. The results imply a role of IN toward maintaining homeostasis in the LGN by suppressing any instability that may arise due to anomalous synaptic attributes