Complex sentence: Brain research is not even nearly at a stage at which physiology can be linked to behavior; people naturally want to use brain science to inform policy and practice, but our limited knowledge of the brain places extreme limits on that effort.
Split into simpler sentences: Brain research is not even nearly at a stage at which physiology can be linked to behavior. People naturally want to use brain science to inform policy and practice, but our limited knowledge of the brain places extreme limits on that effort.