For my PPI protocol, the session begins with 5 pulses at 120db, without any pre-pulses. The first response from the mouse has a high amplitude, the second is slightly attenuated, and after that, there is no noticeable response, from the pulses with and without a pre-pulse. Do most people see this phenomenon? If so, how do you analyze the data if the response is not noticeable?
I can't answer this, but will follow the responses to this question with interest. I am about to start a PPI protocol for PTSD. Apparently the honours student who used PPI in his protocol had a similar issue where it wasn't working the way we expected.
Having no observable response after a startling pulse is a really bad situaton, without a startle reflex you cannot calculate PPI. I study with rats and they usually give good response to the 120 dB startling pulse. However there are always one or two non-responders in a study, so to figure out these guys first I run a short acclimation session with pulses and prepulses three days prior to experiment sessions. And I exluded the rats having startle response less than 20 units (I have SR-LAB startle cages).
In your case your mice seem habituate the pulses too quickly or maybe they freeze. If you give more detail about the mice strain, the startle system and the protocols you use I may better help you.
I re-calibrated our chamber, and that seems to have fixed the problem. I am seeing a good response for all 120 dB pulses. However, there seems to be a lot of variability with %PPI between mice within one experimental group.
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