Synaptic depression depends on charge delivered to network

In vitro neuronal networks cultured on microelectrode arrays enable the study of network electrophysiology on a fundamental level. Neuronal response to electrical stimulation is an area of interest at the laboratory bench and in the clinic, given its wide application for remedying neurological disorders. Here we investigated the change in cortical network response over time to varied amounts of charge used for stimulation, which may lead to a phenomenon known as selective adaptation. There is a charge threshold that invokes a reverberating network response; when stimulating at 900 mV, five stimulation electrodes were required to elicit a response across the entire network. Stimulating with more charge leads to greater synaptic depression over time when constant periodic stimulation is applied. Stimulating with 5 electrodes led to a decrease in network response to stimulation, whereas stimulating with 12 electrodes led to an extinction of network response. The previously hypothesized selective adaptation mechanism was not observed, implying that our random cortical assemblies have homogeneous excitatory and inhibitory subnetworks.