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 response to 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.
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