A mechanism for hippocampal memory recall based on excitatory-inhibitory fluctuations in neocortex

Abstract

The brain has a remarkable capacity to acquire and store memories that can later be selectively recalled. These processes are supported by the hippocampus which is thought to index memory recall by reinstating information stored across distributed neocortical circuits. However, the mechanism that supports this interaction remains unclear. Here, in humans, we show that recall of a visual cue from a paired associate is accompanied by a transient increase in the ratio between glutamate and GABA in visual cortex. Moreover, these excitatory-inhibitory fluctuations are predicted by activity in the hippocampus. These data suggest the hippocampus gates memory recall by indexing information stored across neocortical circuits using a disinhibitory mechanism.

Memories in a network with excitatory and inhibitory plasticity are encoded in the spiking irregularity

“…Similarly, in Yger et al [5], strengthening of the assembly led to stronger neural response upon stimulation. Since neurons belonging to an EI assembly receive increased excitation and inhibition, memories encoded by the EI assembly could also be reactivated by disinhibition [17,18]. A transient decrease in inhibitory drive leads to a net increase in excitatory input to excitatory neurons belonging to the assembly, resulting in an increase in their activity.…”