DENDRITIC IH MODULATES CORTICAL ENGRAM EXCITABILITY AND MEMORY RECALL

The ability to associate stimuli and 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 that are 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 in sensory areas 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. Ex vivo patch-clamp recordings illustrated that engram cells had decreased excitability due to a transient increase in Ih current and were preferentially connected with neighbouring engram cells. Using two-photon calcium imaging, we show that tuft dendrites of engram cells had dampened, but synchronous, activity during recall which was preferentially increased by pharmacological block of Ih. Finally, Ih block increased freezing to the conditioned stimulus, showing a causal link between this form of plasticity and memory recall. Together, these findings reveal Ih-driven intrinsic plasticity which leads to specific information processing in engram cells and effects memory recall.