Oscillators coupled in a network can synchronize with each other to yield a coherent population rhythm. How do multiple such rhythms interact with each other? Do these collective oscillations synchronize like individual oscillators? We show that this is not the case: for strong, inhibitory coupling rhythms can become synchronized by noise. In contrast to stochastic synchronization, this new mechanism synchronizes the rhythms even if the noisy inputs to different oscillators are completely uncorrelated. Key for the synchrony across networks is the reduced synchrony within the networks: it substantially increases the frequency range across which the networks can be entrained by other networks or by periodic pacemaker-like inputs. We demonstrate this type of robust synchronization for different classes of oscillators and network connectivities. The synchronization of different population rhythms is expected to be relevant for brain rhythms.

Neuronal dendritic spine dynamics provide a plasticity mechanism for altering brain circuit connectivity to integrate new information for learning and memory. Previous in vivo studies in the olfactory bulb (OB) showed that regional increases in activity caused localized spine stability, at a population level, yet how activity affects spine dynamics at an individual neuron level remains unknown. In this study, we tracked in vivo the correlation between an individual neuron’s activity and its dendritic spine dynamics of OB granule cell (GC) interneurons. Odor experience caused a consistent correlation between individual GC activity and spine stability. Dissecting the components of the OB circuit showed that increased principal cell (MC) activity was sufficient to drive this correlation, whereas cell-autonomously driven GC activity had no effect. A mathematical model was able to replicate the GC activity-spine stability correlation and showed MC output having improved odor discriminability while retaining odor memory. These results reveal that GC spine plasticity provides a sufficient network mechanism to decorrelate odors and maintain a memory trace.

Cortical GABAergic interneurons (INs) represent a diverse population of locally projecting cells that provide specialized forms of inhibition to pyramidal neurons and other INs. Most recent work on INs has focused on subtypes distinguished by expression of Parvalbumin (PV), Somatostatin (SST), or Vasoactive Intestinal Peptide (VIP), but a fourth group that includes neurogliaform cells (NGFCs) has remained largely enigmatic due to a lack of genetic tools. Here, we show that these INs can be accessed experimentally using intersectional genetics with the gene Id2. We find that outside of layer 1 (L1), the vast majority of Id2 INs are NGFCs that express high levels of neuropeptide Y (NPY) and exhibit a late-spiking firing pattern, with extensive local connectivity. While much sparser, non-NGFC Id2 IN had more variable properties, with most corresponding to a diverse group of INs that strongly express the neuropeptide CCK. In vivo, using silicon probe recordings, we observed several intriguing aspects of NGFC activity, including a strong rebound in activity immediately following the cortical down state during NREM sleep. Our study provides insights into IN diversity and NGFC distribution and properties, and outlines an intersectional genetics approach for further study of this neglected group of INs.