Contexts and catalysts: a resolution of the localization and integration of function in the brain.

There has been a historical tension between theories of brain function emphasizing regional specialization and those focusing on integration across regions. This tension continues despite the pervasive use of functional neuroimaging, which enables testing of these theories in the human brain. There are instances of agreement, where regions thought to be critical for a given behavior (e.g., Broca's area and language production) do become more active when a person engages in that behavior. However, a number of disconcerting results have also been found. These include activation in areas not thought to be important for the behavior, and lack of activation in regions thought to be critical for particular behaviors based on studies of the damaged brain. A recently proposed Neural Context hypothesis of brain function provides a mechanism that can reconcile these apparently disparate findings. The hypothesis states that the functional relevance of a brain area depends on the status of other connected areas i.e., the context within which the region is operating. A region can participate in several behaviors through variations in its interactions with other areas. It is possible that certain critical nodes serve as Behavioural Catalysts, enabling the transition between behavioral states, without differential alterations in the measured activity. By virtue of its anatomical connections, an area could facilitate a shift in functional connectivity between one set of regions to another. An imaging study on the changing interregional interactions involving the hippocampus in learning and awareness serves as an example of neural context. In this case, the hippocampus may serve to catalyze the transition to awareness.