Dendritic synaptic integration modes under in vivo-like states

Abstract

The neural code remains undiscovered and understanding synaptic input integration under in vivo-like conditions is just the initial step toward unraveling it. Synaptic signals generate fast dendritic spikes through two main modes of temporal summation: coincidence detection and integration. In coincidence detection, dendrites fire only when multiple incoming signals arrive in rapid succession, whereas integration involves summation of postsynaptic potentials over longer periods with minimal membrane leakage. This process is influenced by ionic properties, especially as the membrane potential approaches the firing threshold, where inactivating currents play a critical role. However, the modulation of temporal summation by these currents under in vivo-like conditions has not been thoroughly studied. In our research, we used computer simulations of a single dendritic branch to investigate how three inactivating currents -- A-type potassium, T-type calcium, and transient sodium -- affect temporal summation. We found that calcium and sodium currents promote integrative behavior in dendrites, while potassium currents enhance their ability to act as coincidence detectors. By adjusting the levels of these currents in dendrites, neurons can flexibly switch between integration and coincidence detection modes, providing them with a versatile mechanism for complex tasks like multiplexing. This flexibility could be key to understanding how neural circuits process information in real time. SignificanceNeurons consist of specialized structures that shape computation. The soma processes inputs from dendrites and communicates via its axon. Dendrites have a branched architecture. They receive excitatory signals and generate dendritic spikes. These spikes allow individual branches to convert inputs into spiking patterns prior to somatic integration. Depending on input synchrony, branches operate as coincidence detectors or integrators, which is determined by ionic currents. Our study explores how these currents affect signal summation. We found that potassium currents favor coincidence detection, while calcium and sodium currents promote integration. Cellular mechanisms finely tune these currents, enabling dendrites to adjust processing modes in response to synaptic inputs.