The Nature and Source of the Signal Change

Neuroimaging studies measure changes in signal magnitude. However, many processes in the brain may be characterized by changes in firing patterns or synchronization among neurons, rather than changes in overall firing rates (Lestienne, 2001; Neuenschwander, Castelo-Branco, Baron, & Singer, 2002). Neuroimaging studies will often be insensitive to such changes.

Equally important is a consideration of the source of rCBF/BOLD changes, which in addition to the neuronal output signals are also significantly associated with input to a region and local processing within the activated region (Logothetis, 2002). Thus, when an area shows increased rCBF or BOLD signal, the finding may not directly inform us about the region's output. This differs from many electrophysiological techniques that solely examine a brain region's output.

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