PHASE-DEPENDENT SYNAPTIC GAIN CONTROL BY ~10 HZ RHYTHMS IN PRIMATE CORTEX

Neuronal circuits must flexibly regulate communication while operating under tight energetic constraints. Low-frequency ~10 Hz rhythms are among the most prominent cortical oscillations, yet their role in controlling synaptic communication at the level of single neurons remains unclear. Using Neuropixels probes in awake marmosets, we recorded thousands of neurons in posterior parietal cortex during a visual detection task and identified a ~10 Hz rhythm in both spikes and local field potentials whose amplitude predicted reaction times, indicating fluctuations in behavioral state. Leveraging the large simultaneously recorded population, we estimated spike transmission probability between putatively connected neuron pairs and found that periods of strong ~10 Hz activity paradoxically showed increased spike transmission despite reduced firing rates. Analyzing transmission as a function of oscillatory phase revealed rhythmic modulation that lagged firing-rate modulation by ~13 ms, inconsistent with simple postsynaptic depolarization and instead pointing to phase-dependent changes in short-term synaptic efficacy. Together, these findings indicate that ~10 Hz rhythms dynamically gate effective connectivity to enhance synaptic gain while suppressing average spiking, suggesting a circuit mechanism for state-dependent, energy-efficient communication.