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The corticothalamocortical circuit drives higher-order cortex in the mouse
Brian B Theyel1, Daniel A Llano2,3 & S Murray Sherman1
An unresolved question in neuroscience relates to the extent to which corticothalamocortical circuits emanating from layer 5B are involved in information transfer through the cortical hierarchy. Using a new form of optical imaging in a brain slice preparation, we found that the corticothalamocortical pathway drove robust activity in higher-order somatosensory cortex.
When the direct corticocortical pathway was interrupted, secondary somatosensory cortex showed robust activity in responseto stimulation of the barrel field in primary somatosensory cortex (S1BF), which was eliminated after subsequently cutting the somatosensory thalamus, suggesting a highly efficacious corticothalamocortical circuit. Furthermore, after chemically inhibiting the thalamus, activation in secondary somatosensory cortex was eliminated, with a subsequent return after washout. Finally, stimulation of layer 5B in S1BF, and not layer 6, drove corticothalamocortical activation. These findings suggest that the corticothalamocortical circuit is a physiologically viable candidate for information transfer to higher-order cortical areas.
2010 Nature America, Inc. All rights reserved.
Much of neocortex can be divided into macroscopic zones: visual, auditory and somatomotor. Each of these is comprised of a number of discrete areas13 that function together to analyze relevant information (for example, visual, etc.). An important first step toward understanding how cortex functions is to elucidate the manner in which information flows between these discrete cortical areas. The prevailing dogma46 is that this flow of information is subserved by direct corticocortical pathways. In the visual system, for example, this implies that once information reaches primary visual cortex from the lateral geniculate nucleus, it remains exclusively in cortex as it flows up the cortical hierarchy. In this scheme, beyond relaying the initial information to cortex (for example, the geniculocortical pathway), the thalamus is not involved beyond modulation of corticocortical information flow6. However, a recent hypothesis suggests that much, and perhaps the vast majority of, information flow between cortical areas involves higher-order thalamic nuclei in the form of corticothalamocortical circuits79.
This latter hypothesis is based partly on the idea that many brain circuits can be divided into drivers, which represent the main information routes, and modulators, which serve to modulate information flow10,11. Well-documented examples of drivers are the retinal...