Although EEG is one of the more favorable brain imaging methods for use with infants and children, there is one major caveat of this methodology. The EEG signal has excellent temporal resolution, but it has poor spatial resolution. The skull behaves like a low-pass filter and distorts the underlying brain electrical activity over a large area of the scalp. Furthermore, potentials recorded at the scalp are likely generated by multiple groupings of cortical and subcortical generators spread across a relatively wide area (Pizzagalli, 2007). Thus, a scalp electrode is likely detecting electrical activity generated from non-local groups of neurons, which is why it is better to discuss EEG activity at a specific electrode location rather than resulting from a particular brain area. Use of dense electrode arrays (typically considered to be a minimum of 64 electrodes) may alleviate some of the concerns with spatial resolution. Indeed, dense arrays allow calculation of the source of the electrical signal (Reynolds & Richards, 2009). Of course, the cost of an EEG system is correlated with the number of electrodes.
