Respiratory cycle as time basis: An improved method for averaging olfactory neural events

In the mammalian olfactory system, neural activity appears largely modulated by respiration. Accurate analysis of respiratory synchronized activity is precluded by the variability of the respiratory frequency from trial to trial. Thus, the use of respiratory cycle as the time basis for measuring cell responses was developed about 20 years ago. Nevertheless, averaging oscillatory component of the activity remains a challenge due to their rhythmic features. In this paper, we present a new respiratory monitoring setup based on the measurement of micropressure changes induced by nasal airflow in front of the nostril. Improvements provided by this new monitoring setup allows automatic processing of respiratory signals in order to extract each respiratory period (expiration and inspiration). The time component of these periods, which can differ from trial to trial, is converted into a phase component defined as [-pi, 0] and [0, pi] for inspiration and expiration, respectively. As opposed to time representation, the phase representation is common to all trials. Thus, this phase representation of the respiratory cycle is used as a normalized time basis permitting to collect results in a standardized data format across different animals and providing new tools to average oscillatory components of the activity.