Brain imaging has made great strides in understanding the mechanisms of normal human brain function, and the changes associated with brain and mental illness.  However, this work has been mostly observational, obtaining correlations that cannot be used to prove causation, and with limited direct benefits for patients.  

Brain stimulation has shown early promise for improving human behavior and reducing symptoms of brain and mental illness, and also for testing hypotheses derived from brain imaging data. However, it is still mostly empirical, with little understanding of its underlying mechanisms, or of methods to optimize its effects. Some  recent failures of clinical trials using DBS to reduce depression  suggest that we still have much to learn.

The combination of brain imaging and stimulation could lead to many advances in both fields, providing a better understanding of human brain organization, optimization of neuroenhancement in healthy people, an improved understanding of the mechanisms of neurostimulation, and improved treatments for brain and mental illness.