Travelling spindles create necessary conditions for spike-timing-dependent plasticity in humans

Sleep spindles facilitate memory consolidation in the cortex during mammalian non-rapid eye movement (NREM) sleep. In rodents, phase-locked firing during spindles may facilitate spike-timing-dependent plasticity (STDP) by grouping pre- and post-synaptic cell firing within [~]25ms. Currently, microphysiological evidence in humans for conditions conducive for STDP during spindles is absent. We analyzed local field potentials and supragranular unit spiking during spindles from 10x10 arrays of microelectrodes at 400{micro}m pitch in humans. We found strong tonic and phase-locked increases in firing and co-firing within 25ms during spindles. Co-firing, spindle co-occurrence, and spindle coherence were greatest between sites within [~]2mm, and high co-firing of units on different electrodes was largely restricted to moments of high spindle coherence between those electrodes. Spindles propagated at [~]0.23m/s in distinct patterns, with correlated cell co-firing sequences. These results suggest that spindles may organize spatiotemporal patterns of neuronal co-firing which promote memory consolidation during NREM sleep.