Development of hemodynamic responses and functional connectivity in rat somatosensory cortex.

Functional magnetic resonance imaging (fMRI) is a valuable method for probing postnatal circuit refinement and plasticity. However, its use during early development has been hindered by uncertainty as to the nature of neurovascular coupling in young individuals. Here we used somatosensory stimulation in rats to determine age-related parameters of the blood oxygenation level-dependent (BOLD) signal from its apparent inception on postnatal day 13 to adulthood. By comparing fMRI measurements with electrophysiological recordings, we determined that the regional BOLD response in these animals undergoes a systematic decline in latency and growth in amplitude over this period. We found no evidence of negative BOLD at any age. Maturation of hemodynamic responses correlated with age-dependent increases in susceptibility to inhibition of carbonic anhydrase. With knowledge of the infant BOLD response characteristics, we showed that interhemispheric and higher-order cortical stimulus responses are enhanced during the first several weeks after birth.