Abstract| Volume 16, ISSUE 1, P115, January 2023

Measuring inhibitory engrams in memory storage and recall using concurrent tDCS-fMRI

      Memories are thought to be represented in the brain by activity in groups of neurons described as memory engrams. Although memory engrams are typically thought to be made up of excitatory neurons, several recent studies suggest that inhibitory neurons also play a critical role. Indeed, by matching their excitatory counterparts, selective inhibitory interneurons may facilitate a stable storage system that allows memories to lie quiescent unless the balance between excitation and inhibition is perturbed. Here I will present a set of studies that show evidence for selective neocortical inhibition in the human brain using ultra-high field 7T MRI and concurrent non-invasive brain stimulation. I will show that matched excitatory-inhibitory engrams provide a stable storage mechanism for neocortical associations, and protect memories from interference. I will then show how neocortical memory engrams interact with brain regions such as the hippocampus during recall, to selectively perturb excitatory-inhibitory balance. To conclude, I will discuss how concurrent MRI and non-invasive brain stimulation can be used as a tool to demonstrate the importance of neural inhibition for computations that underlie higher-order cognition.