apriori that functionally meaningful changes in neuronal activity may occur without significant changes in local metabolism, for example when some neurons reduce while others increase their activity within the same region, or when synchronization of activity changes without the change in the overall number of active neurons. For example, a recent study has shown that the BOLD response is insensitive to substantial changes in neural activity associated with certain aspects of visual processing (Swettenham et al., 2013). Conversely, another study suggested that, in addition to haemodynamic response related to a visual stimuli, additional trial-related haemodynamic signal emerged as an anticipatory adaptation to pending processing demands, and this latter signal was not directly associated with neuronal activity (Cardoso et al., 2012; Sirotin and Das, 2009). Thus, functionally significant changes in local neuronal activity and changes in BOLD signal may not always be related in a straightforward, linear fashion, which underscores the importance of electrophysiology methods.
