Christoforos Papasavvas
Christoforos Papasavvas
PhD
Data Science in Neurology / Computational and Theoretical Neuroscience
About
25
Publications
3,867
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67
Citations
Introduction
Currently working on two projects: 1) intracranial brain stimulation, predictability of its effects and how its effects relate to functional connectivity; 2) neural entrainment in spiking network models and the role of gain modulation and inhibitory diversity in this phenomenon.
Additional affiliations
April 2019 - January 2022
Position
- Research Associate
Description
- Identifying Optimal Neurostimulation for Epilepsy using Computational Approaches
March 2018 - February 2019
Position
- Research Associate
Description
- In vivo electrophysiology of neuronal ensembles in hippocampus. Production of linear place fields in complex mazes
December 2016 - January 2018
University of Sussex
Position
- Research Associate
Description
- In vivo ca-imaging of synaptic activity. Methodology to remove motion artefacts
Education
September 2013 - October 2016
September 2012 - August 2013
September 2011 - August 2012
Publications
Publications (25)
Purpose: Understanding fluctuations of seizure severity within individuals is important for defining treatment outcomes and response to therapy, as well as developing novel treatments for epilepsy. Current methods for grading seizure severity rely on qualitative interpretations from patients and clinicians. Quantitative measures of seizure severity...
Objective:
Targeted electrical stimulation of the brain perturbs neural networks and modulates their rhythmic activity both at the site of stimulation and at remote brain regions. Understanding, or even predicting, this neuromodulatory effect is crucial for any therapeutic use of brain stimulation. The objective of this study was to investigate if...
Epilepsy is recognised as a dynamic disease, where both seizure susceptibility and seizure characteristics themselves change over time. Specifically, we recently quantified the variable electrographic spatio-temporal seizure evolutions that exist within individual patients. This variability appears to follow subject-specific circadian, or longer, t...
The identification of abnormal electrographic activity is important in a wide range of neurological disorders, including epilepsy for localising epileptogenic tissue. However, this identification may be challenging during non-seizure (interictal) periods, especially if abnormalities are subtle compared to the repertoire of possible healthy brain dy...
The universal scaling law of cortical morphology describes cortical folding as a tight relationship between average grey matter thickness, pial surface area, and exposed surface area. It applies for mammalian species, humans, and across lobes, however it remains to be shown that local cortical folding obeys the same rules. Here, we develop a method...
The identification of abnormal electrographic activity is important in a wide range of neurological disorders, including epilepsy for localising epileptogenic tissue. However, this identification may be challenging during non-seizure (interictal) periods, especially if abnormalities are subtle compared to the repertoire of possible healthy brain dy...
Targeted electrical stimulation of the brain perturbs neural networks and modulates their rhythmic activity both at the site of stimulation and at remote brain regions. Understanding, or even predicting, this neuromodulatory effect is crucial for any therapeutic use of brain stimulation. To this end, we analysed the stimulation responses in 131 sti...
The universal scaling law of cortical morphology describes cortical folding as the covariance of average grey matter thickness, pial surface area, and exposed surface area. It applies for mammalian species, humans, and across lobes, however it remains to be shown that local cortical folding obeys the same rules. Here, we develop a method to obtain...
Nonlinear dynamics emerge through either nonlinear interactions between the variables or through nonlinearities imposed on their linear interactions. Their interactions can be conceptualized as modulations of input-output (I/O) functions, where one variable modulates another variable's I/O function. Within this framework, nonlinear interactions are...
Epilepsy is recognised as a dynamic disease, where seizures and their features change over time. Specifically, we recently demonstrated that seizures themselves change in terms of their evolution. However, the underpinning modulators of seizure evolution remain unclear. In this work, we analyse continuous (interictal) intracranial Electroencephalog...
Objective:
Direct electrical stimulation of the brain through intracranial electrodes is currently used to probe the epileptic brain as part of pre-surgical evaluation, and it is also being considered for therapeutic treatments through neuromodulation. In order to effectively modulate neural activity, a given neuromodulation design must elicit sim...
Goal: to investigate the functional role of different GABAergic interneuronal populations in neocortical neural dynamics. We are interested in oscillatory dynamics and specifically in the phenomenon of entrainment: the ability of the circuit to adjust its oscillation frequency to match the frequency of the input.
Studies on spatial coding and episodic memory typically involve recordings of hippocampal place cell activity while rodents navigate in mazes. Linear place fields serve as reduced representations of the activity of place cells, revealing their spatial preference along the tracks of the maze. Sometimes, the experimental designs include complex mazes...
Background: Direct electrical stimulation of the brain through intracranial electrodes is currently used to probe the epileptic brain as part of pre-surgical evaluation, and it is also being considered for therapeutic treatments through neuromodulation. It is still unknown, however, how consistent intracranial direct electrical stimulation response...
Parvalbumin-expressing interneurons in cortical networks are coupled by gap junctions, forming a syncytium that supports propagating epileptiform discharges, induced by 4-aminopyridine. It remains unclear, however, whether these propagating events occur under more natural states, without pharmacological blockade. In particular, we investigated whet...
Computational studies of the influence of different network parameters on the dynamic and topological network effects of brain stimulation can enhance our understanding of different outcomes between individuals. In this study, a brain stimulation session along with the subsequent post-stimulation brain activity is simulated for a period of one day...
Key points:
Motion artefacts associated with motor behaviour are an inevitable problem of multiphoton imaging in awake behaving animals, particularly when imaging synapses. Correction of axial motion artefacts usually requires volumetric imaging resulting in slower rates of acquisition. We describe a method to correct z-motion artefacts that is ea...
A bstract
Both subtractive and divisive inhibition has been recorded in cortical circuits and recent findings suggest that different interneuronal populations are responsible for the different types of inhibition. This calls for the formulation and description of these inhibitory mechanisms in computational models of cortical networks. Neural mass...
Functional imaging of head-fixed, awake, behaving mice using two-photon imaging of fluorescent activity reporters has become a powerful tool in the studying the function of the brain. Motion artefacts are an inevitable problem during such experiments and are routinely corrected for in x and y dimensions. However, axial (z) shifts of several microns...
In patients with drug resistant focal epilepsy, targeted weak stimulation of the affected brain regions has been proposed as an alternative to surgery. However, the effectiveness of stimulation as a treatment presents great variation from patient to patient. In this study, brain activity is simulated for a period of one day using a network of Wilso...
Parvalbumin-expressing interneurons in cortical networks are coupled by gap-junctions, forming a syncytium that supports propagating epileptiform discharges, induced by 4-aminopyridine. It remains unclear, however, whether these propagating events occur under more natural states, without pharmacological blockade. In particular, we investigated whet...
Unlabelled:
Accurate localization of sound sources is essential for survival behavior in many species. The inferior colliculi (ICs) are the first point in the auditory pathway where cues used to locate sounds, ie, interaural time differences (ITDs), interaural level differences (ILDs), and pinna spectral cues, are all represented in the same locat...
Experimental results suggest that there are two distinct mechanisms of inhibition in cortical neuronal networks: subtractive and divisive inhibition. They modulate the input-output function of their target neurons either by increasing the input that is needed to reach maximum output or by reducing the gain and the value of maximum output itself, re...
Objective:
Proteins are considered to be the most important individual components of biological systems and they combine to form physical protein complexes which are responsible for certain molecular functions. Despite the large availability of protein-protein interaction (PPI) information, not much information is available about protein complexes...
Questions
Questions (4)
Basket cells in neocortex took their name 'basket' from their morphological characteristics. Their axonal arborization forms a basket around the soma of their targets. This clearly applies when they target principal cells (pyramidal) but we also know that they target other basket cells. Do we have any histological evidence that they target other basket cells in the same way, at the soma?
Typically in graph theory we define a graph G as a set of vertices and edges, that is, G={V, E}. What if I define a graph as G={V, E, P} where P is the position of the vertices in 2D space. So P is a set of coordinate pairs where (x_i, y_i) is the coordinates of vertex v_i in 2D space. Is there a specific name for this type of graphs. I checked geometric graphs but that's not it.
I'm wondering if anyone succeeded in washing out gap-junction blockers like mefloquine or carbenoxolone and reversing their effect.
Other than carbenoxolone, what should I try for blocking cx36? Which, would you say, has the least side effects?
Projects
Projects (5)
Understand how different types of nonlinearities dictate the properties of nonlinear dynamics; specifically in terms of adaptability, entrainability and synchronizability.
To reveal how dendritic vs somatic inhibition (somatostatin- vs parvalbumin-mediated inhibition) influences neural entrainment through the simulation of multi-compartmental spiking network models (NEURON).
Working with Dr Yujiang Wang (grant holder) towards the characterisation of intracranial EEG stimulation and its potential as therapeutic neuromodulation technique.Objectives:
1. Investigation of its cross-session consistency
2. Prediction of its effect in band power modulation based on structural and functional connectivity measures.
