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

TL;DR

This study investigates how altering the ratio of excitatory to inhibitory neurons in cultured neural networks affects their temporal dynamics, revealing that increased inhibition induces structured rhythmic activity.

Contribution

The paper introduces novel neural circuits with varied excitatory-inhibitory ratios and demonstrates how inhibition modulates network temporal organization.

Findings

Inhibitory neurons induce rhythmic oscillations in cultured networks.

Networks with predominantly excitatory neurons lack temporal structure.

Increased inhibition correlates with emergent structured activity.

Abstract

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.