Hemodynamic transient and functional connectivity follow structural connectivity and cell type over the brain...

Area of Science:

• Neuroscience
• Systems Neuroscience
• Neuroimaging

Background:

• Brain neural circuits form a hierarchy supporting information flow.
• Structural and functional connectivity show moderate system-level coupling.
• Influence of connection direction and neuronal types on hierarchical activity is unclear.

Purpose of the Study:

• Investigate how feedforward/feedback connections and excitatory/inhibitory (E/I) neurons shape brain activity and functional connectivity across a hierarchy.
• Relate optogenetic-evoked and resting-state activities to axonal projections and E/I distribution in the mouse somatosensory pathway.

Main Methods:

• Functional MRI (fMRI) to detect optogenetic-evoked and resting-state activities.
• High-sensitivity ultrafast imaging.
• Electrophysiological recordings.
• Analysis of axonal projections and E/I neuronal distribution.

Main Results:

• Extensive activation observed up to third-order projections following thalamic excitation.
• Evoked responses and functional connectivity correlated more with feedforward than feedback projections, decreasing with hierarchy.
• Hemodynamic responses showed regional/hierarchical differences, with slower, variable responses in higher-order areas.
• Positive/negative hemodynamic responses correlated with E/I neuronal densities.
• Resting-state connectivity linked to E/I distribution; evoked connectivity to structural wiring.

Conclusions:

• The structure-function relationship in the brain is dependent on projection type, cell type, and hierarchical level.
• Hemodynamic transients may reflect E/I activity and complex hierarchical processing.