Neuronal plasticity has been shown to be causally linked to coincidence detection through dendritic spikes (dSpikes). We demonstrate the existence of SPW-R-associated, branch-specific, local dSpikes and their computational role in hippocampal PV+ interneurons in awake animals.
To measure long thin dendrites during SPW-Rs, we used fast 3D acousto-optical imaging through an eccentric deep-brain adapter and focal electropysiological recordings. This unique combination enabled, for the first time, fast access to long, thin dendritic segments simultaneously in multiple locations along the entire 3D dendritic arbour of the PV+ cells during locally-detected SPW-R events in awake mice, with orders-of-magnitude higher speed and better signal-to-noise ratio than previous two-dimensional imaging methods.
Our approach revealed the existence of SPW-R-dSpikes which were initiated in a minority of dendrites in distal dendritic regions at variable, NMDA-AMPA-dependent, hot-spots and propagated at a high amplitude beyond a sharp distance threshold (~150 µm).
A novel supralinear summation emerged during SPW-R doublets when two successive SPW-R events coincide within a short temporal window (~150 ms), e.g. during more complex association tasks. Our results indicate that doublet-associated dSpikes are the smallest computational unit in the brain functioning as a coincidence detector during SPW-R-related computation.