How do we combine fast and slow information processing to perceive the world?
To understand the world around us, we must combine patterns of information that arrive over multiple time-scales. For example, while having a conversation we continuously perceive not only each spoken word, but also the emerging meaning of that word within a larger sentence, and the meaning of each sentence in the context of the conversation. Data from fMRI and ECoG studies suggest that brain regions are organized in a hierarchy according to the time-scale on which they process information. Regions at the lower levels of the hierarchy sustain representations of sensory information (e.g. word acoustics) over short periods of time, while higher-order regions maintain more abstract representations over seconds and minutes. Thus, our unfolding experience of the world arises from activity within a hierarchical network of functionally specific regions.
Which regions organize the flow of information through the brain, and how?
A typical brain region maintains reciprocal connections with more than a dozen others. Therefore, information can potentially flow in all directions within the brain: downward from the top of the functional hierarchy, upward from the bottom, and also laterally. However, some brain regions are especially effective in organizing and switching the flow of information, as occurs for instance when we switch our attention from what somebody is saying to their facial expression. Our neuroimaging and computational modeling studies suggest that these “hub” regions are found near the top of the functional hierarchy and that they maintain anatomical links across many different areas. The mechanisms are uncertain, but system-specific brain rhythms may be involved in regulating the flow of information. Because brain rhythms can suppress the firing of neurons within a region and also align the firing of neurons in different regions, we study the spatial distribution of brain rhythms and how they change across cognitive states.