Myelin sheaths determine the electrical properties of axons by reducing the local capacitive load causing a rapid saltatory propagation of action potentials and speeding of the conduction velocity. While oligodendroglial myelination is well established to regulate spike arrival times there is emerging evidence that myelin exerts divergent additional roles, including for example metabolic supply to axons and buffering of extracellular ion concentrations. Recent work also shows that myelin is found both around inhibitory and excitatory axons, which is expected to have a complex influence on the properties of neural information processing. In this talk I will discuss our recent findings from in vitro and in vivo electrophysiological recordings of parvalbumin basket cell-layer 5 pyramidal neuron pairs in the somatosensory cortex. To identify the isolated contribution of interneuron cell types, the experiments were combined with optogenetically targeted activation of parvalbumin interneurons and myelin was experimentally abolished using toxin-induced and genetic demyelination. The results show converging lines of evidence that myelination of parvalbumin interneuron axons shape the properties of cortical rhythms, revealing a role for myelin beyond the scale of individual axons, in the domain of temporal synchronization.