Learning-induced plasticity decreases cortical engram cell dendritic excitability during memory recall

The ability to associate stimuli to create a memory is one of the most fundamental functions of the brain. Research from the past decade has revealed that memory is encoded in sparse neuronal networks active during learning called engram cells. Although the cortex is recognized as playing an important role in memory, the biophysical properties of cortical engram cells are largely unknown. To address this, we tagged engram cells in the auditory cortex during tone fear conditioning and compared their dendritic and somatic properties with neighbouring non-engram cells. Using two-photon calcium imaging, we show that tuft dendrites of engram cells had dampened, but synchronous, activity during recall. Ex vivo patch-clamp recordings illustrated that engram cells were preferentially connected with neighbouring engram cells and had decreased excitability due to a transient increase in Ih current. Together, these findings reveal Ih-driven intrinsic plasticity which leads to specific information processing in engram cells.