Development of intrinsic optical signal in somatosensory cortex of neonatal rat

Functional imaging is a perspective and promising way to study how the brain works. Modern imaging techniques are widely used both in clinic and fundamental science. One of the imaging techniques is based on registration of intrinsic optical signal (IOS), which is considered to be a functional analogue to the BOLD fMRI, i. e. both techniques are registering hemodynamic responses in active region. However we have already shown a presence of IOS in neonatal rats, whereas BOLD fMRI response appears significantly later in development, thus raising a question whether both techniques use similar parameters of active tissue. To answer it we focused on detection and analysis of IOS in vivo in anesthetized newborn rats using whisker stimulation during first three weeks after birth. To improve signal-noise ratio of IOS we used video preprocessing (light and motion corrections, spatial and temporal filtering), which allowed us to observe IOS presence since P3 (P0 corresponds to the day of birth). Analysis of developmental profile revealed significant correlation between optimal stimulation and animal age: the older the animal the more frequent stimulation it supports. The bell shape of IOS dependence on age with maximum at P9-P10 was equally found. We performed simultaneous IOS and EEG recording from the principal barrel and established a relationship between IOS and electrical neuronal activity. Our findings suggest that in neonatal rats IOS and fMRI have different origins, thus making IOS suitable for brain imaging early in development.