The interpretation of functional imaging studies of development is dependent on the sensitivity and accuracy of the imaging methods used to detect these changes (Kotsoni et al., 2006). As the blood oxygen level dependent (BOLD) signal is used as a measure of brain activity in most fMRI studies, a variety of variables including heart rate, heart rate variability and respiration can influence the hemodynamic response. For instance, heart rate and respiratory rate in children are nearly twice those in adults (Kotsoni et al., 2006). These physiological differences across development are a significant concern in developmental neuroimaging studies because they can introduce greater noise in echo planar and spiral imaging due to movement of lungs and diaphragm (van de Moortele et al., 2002). As such, these developmental differences should be taken into consideration when identifying an appropriate baseline. Thomason et al. (2005) examined how developmental differences in respiration influenced the fMRI signal while participants breathed normally in the scanner without engaging in a task. They found that in addition to greater noise in the children's data, this noise contributed to increased
