For more than two decades, the single channel measurement technique of NIR spectroscopy (NIRS) has been successfully used to measure the haemodynamic response to brain activity in both adults and neonates (Hoshi 2003, Ferrari 2004). It has been used to record functional activity for research into brain cognition, and to examine brain development in infants (Obrig and Villringer 2003). An obvious limitation of NIRS is the lack of any spatial information. It is natural to consider combining multiple NIRS measurements in order to localise the origin of signals in the brain; indeed, the first optical topography studies were carried out in this way (Gratton et al. 1995).