Data From: Fear conditioning potentiates the Hippocampal CA1 commissural pathway In vivo and increases awake phase sleep

The hippocampus is essential for spatial learning and memory. To assess
learning we used contextual fear conditioning (cFC), where animals learn
to associate a place with aversive events like foot-shocks. Candidate
memory mechanisms for cFC are long-term potentiation and long-term
depression, but there is little direct evidence of them operating in the
hippocampus in vivo following cFC. Also, little is known about the
behavioral state changes induced by cFC. To address these issues, we
recorded local field potentials in freely behaving mice by stimulating in
the left dorsal CA1 region and recording in the right dorsal CA1 region.
Synaptic strength in the commissural pathway was monitored by measuring
field excitatory postsynaptic potentials (fEPSPs) before and after cFC.
After cFC, the commissural pathway’s synaptic strength was potentiated.
Although recordings occurred during the wake phase of the light/dark
cycle, the mice slept more in the post-conditioning period than in the
pre-conditioning period. Relative to awake periods, in non-rapid eye
movement (NREM) sleep the fEPSPs were larger in both pre- and
post-conditioning periods. We also found a significant negative
correlation between the animal’s speed and fEPSP size. Therefore, to avoid
confounds in the fEFSP potentiation estimates, we controlled for
speed-related and sleep-related fEPSP changes and still found that cFC
induced long-term potentiation, but no significant long-term depression.
Synaptic strength changes were not found in the control group that simply
explored the fear-conditioning chamber, indicating that exploration of the
novel place did not produce the measurable effects caused by cFC. These
results show that following cFC, the CA1 commissural pathway is
potentiated, likely contributing to the functional integration of the left
and right hippocampi in fear memory consolidation. In addition, the cFC
paradigm produces significant changes in an animal’s behavioral state,
which are observable as proximal changes in sleep patterns.