Measuring communication in neural networks

Population neuronal activity measured by the local field potential (LFP) may measure how well long-range synaptic input can drive local spiking due to changes in excitability. However, the need to causally control circuit activity while measuring its large-scale effects means this hypothesis has not been directly tested. We used large-scale recordings in frontal cortex (PFC and Brodmann areas 4 and 6) of awake monkeys to measure responses to optogenetic stimulation in posterior parietal cortex (Brodmann areas 5 and 7).

We found sites in frontal cortex with multi-unit activity (MUA) that was driven by parietal stimulation. For each MUA site, we measured how the phase of the frontal LFP varied with the probability of eliciting a spike in frontal cortex by computing the conditional probability of a spike occurring after stimulation given the phase at the time of stimulation. We found significant modulations in the alpha band (8-12 Hz), in the beta band (15-25 Hz), and in the gamma band (30-50 Hz) .