arXiv subjects

Rhonda Dzakpasu

Publications and source records attributed to Rhonda Dzakpasu.

5 recordsLinked to original sources

arXiv2012

Synaptic potentiation facilitates memory-like attractor dynamics in cultured in vitro hippocampal networks

Collective rhythmic dynamics from neurons is vital for cognitive functions such as memory formation but how neurons self-organize to produce such activity is not well understood. Attractor-based models have been successfully implemented as a theoretical framework for memory storage in networks of neurons. Activity-dependent modification of synaptic transmission is thought to be the physiological basis of learning and memory. The goal of this study is to demonstrate that using a pharmacological perturbation on in vitro networks of hippocampal neurons that has been shown to increase synaptic strength follows the dynamical postulates theorized by attractor models. We use a grid of extracellular electrodes to study changes in network activity after this perturbation and show that there is a persistent increase in overall spiking and bursting activity after treatment. This increase in activity appears to recruit more "errant" spikes into bursts. Lastly, phase plots indicate a conserved activity pattern suggesting that the network is operating in a stable dynamical state.

q-bio.NC↗

arXiv2010

Observed network dynamics from altering the balance between excitatory and inhibitory neurons in cultured networks

Complexity in the temporal organization of neural systems may be a reflection of the diversity of its neural constituents. These constituents, excitatory and inhibitory neurons, comprise an invariant ratio in vivo and form the substrate for rhythmic oscillatory activity. To begin to elucidate the dynamical mechanisms that underlie this balance, we construct novel neural circuits not ordinarily found in nature. We culture several networks of neurons composed of excitatory and inhibitory cells and use a multi-electrode array to study their temporal dynamics as the balance is modulated. We use the electrode burst as the temporal imprimatur to signify the presence of network activity. Burst durations, inter-burst intervals, and the number of spikes participating within a burst are used to illustrate the vivid dynamical differences between the various cultured networks. When the network consists largely of excitatory neurons, no network temporal structure is apparent. However, the addition of inhibitory neurons evokes a temporal order. Calculation of the temporal autocorrelation shows that when the number of inhibitory neurons is a major fraction of the network, a striking network pattern materializes when none was previously present.

q-bio.NC↗

arXiv2005

Differential Effect of Delays and Network Topology on Temporal Pattern Formation

We investigate the effects of transmission delays on the formation of temporally ordered states in networks of non-identical Rössler oscillators, having SWN topology. We show that incorporation of two different types of delay, length independent and length dependent, leads to dramatically different temporal properties of the network. In the first case formation of global random connections leads to increased temporal ordering, while in the second case it annihilates locally ordered clusters and forms a disordered state.

cond-mat.dis-nn↗

arXiv2004

Transition from local to global phase synchrony in small world neural network and its possible implications for epilepsy

Temporal correlations in the brain are thought to have very dichotomic roles. On one hand they are ubiquitously present in the healthy brain and are thought to underlie feature binding during information processing. On the other hand large scale synchronization is an underlying mechanism of epileptic seizures. In this paper we show a possible mechanism of transition to pathological coherence underlying seizure generation. We show that properties of phase synchronization in the 2-D lattice of non-identical coupled Hindmarsh-Rose neurons change radically depending on the connectivity structure. We modify the connectivity using the small world network paradigm and measure properties of phase synchronization using previously developed measure based on assessment of the distributions of relative interspike intervals. We show that the phase synchronization undergoes a dramatic change as a function of locality of network connections from local coherence strongly dependent on the distance between two neurons to global coherence exhibiting stronger phase locking and spanning the whole network.

physics.bio-ph↗

arXiv2003

Measurement of synchronization properties in systems with different excitation levels

We devised a measure based on the distributions of relative event timings of two coupled units. The measure dynamically evaluates temporal interdependencies between the two coupled units. Using this we show that even in the event of symmetrical coupling, non-identical units (having different control parameters) have small but persistent shifts in their event timings that change dramatically with the relative properties of their internal trajectories. We link that finding with the activity dependent synaptic modification in the brain showing that internally or externally driven excitation levels of the neuron may determine direction of information processing in a network.

nlin.CD↗