Kyle Puhger

Research Description

Kyle wants to know how the hippocampus associates events that are separated in time and space. To answer this question, he has been recording and manipulating neural activity while mice are trained on a trace fear conditioning task. This is a Pavlovian procedure where animals learn to associate an unconditioned stimulus (US) with a conditioned stimulus (CS) that occurred 20-30 seconds prior. His research tests the novel hypothesis that population burst events in the CA1 subregion of the hippocampus (known as sharp-wave ripples) are critical for the acquisition of trace fear conditioning. In his first experiments, he used fiber photometry to demonstrate that population activity in CA1 (measured via the calcium indicator GCaMP) primarily increases after the foot-shock US. He then used optogenetic methods to silence CA1 neurons during this same period and found that learning was significantly impaired. He is now expanding on these findings by performing electrophysiological recordings during learning to determine if increases in CA1 population activity after the US are driven by sharp wave-ripple oscillations. If they are, he will then determine if sharp-wave ripples are required for trace fear learning by performing closed-loop optogenetic stimulation. This will involve rapid silencing of CA1 neurons every time a sharp-wave ripple is detected after a foot-shock has occurred. If successful, these experiments would be the first to demonstrate that the hippocampus uses sharp-wave ripples to associate events that are separated in time.