Chunk #41 — Open questions in layer-fMRI connectivity analyses — Inherent connectivity across layers — Functional connectivity is not the same thing as structural connectivity.
Only because the layers are structurally connected, doesn’t guarantee that these connections functionally are engaged. It usually depends on the content of the neural activity fluctuation. In the context of conventional fMRI resolutions, the difference between structural and functional connectivity has been extensively discussed and widely established (Bullmore and Sporns 2009; Friston 2011). While functional connectivity depends on structural connectivity, structural connectivity is not a guarantee of functional connectivity. For example, at the spatial scale of large brain areas, it is well established that V1 and V5 are highly interconnected. However, the engagement of this connectivity depends on the motion energy of the stimulus. Thus, when the visual stimulus contains a lot of motion components, the connection is more engaged as opposed to static stimuli. Thus, despite the high structural connectivity between V1 and V5, in resting-state analyses, these areas can be investigated as two separate entities. This reasoning can be extended from the scale of Brodman areas to the scale of layers too (Sotero et al. 2010). Despite the fact that individual layers in every column have many structural connections, layer-specific functional connections can still be extracted from isolated cortical depths (Fig. 3–7).
