The role of cortico-hippocampal interaction in memory consolidation

System memory consolidation is a brain-wide process that transforms recently encoded
liable memories into more stable and long-term memories. The 'two-stage' theory of
memory process posits that memory consolidation engages bi-directional dialogue
during offline state between the hippocampus, where memory traces are initially
formed, and the neocortex, where memory traces are eventually stored for long-term
retention. During active exploration of a spatial context, sub-populations of neurons in
both CA1 region of hippocampus (HPC) and primary visual cortex (V1) develop spatial
sensitivity with experience such that those spatially-modulated neurons would be
activated sequentially along animal's running trajectory. Strikingly, during offline period,
the neuronal sequences observed in both regions during active spatial experience can be
replayed in a spatiotemporally coordinated fashion. Disruption of such replay in
hippocampus would impair spatial memory performance. These observations led to the
possibility that interaction between the hippocampus and the neocortex around the
time of coherent replay may be instrumental to memory consolidation. However, as of
today, we are unclear about the nature and direction of cortico-hippocampal
information flow around the time of replay. Previous evidence suggested that change in
neocortical activity can precede replay events. Nevertheless, it is unknown if the V1
activity patterns prior to a replay event can selectively influence the memory content to
replay in both hippocampus and V1. Furthermore, we do not know whether
improvement in coherence of hippocampal-cortical interaction during post-training
replay predict the memory performance and fidelity of the learned spatial information
in the V1.
To address these research questions, we aim to record from V1 and CA1 of HPC while
mice learn to discriminate two novel linear tracks in virtual reality (VR). Two VR linear
tracks with visually-identical landmarks in two positions will be used to track
development of spatial modulation in V1 over time. We will also train the animal to lick
for a reward when reaching a designated reward zone for each linear track, which
encourages animals to actively discriminate between two linear tracks. By recording V1
and CA1 neural activities during multiple learning sessions and post-learning rest
sessions over the course of several weeks, we would like to examine how replay
dynamics and cortico-hippocampal interactions during replay change as the
discriminatory memory performance improves over time.