ABSTRACT
P robing brain function and its relation with behavior is one of the mostintriguing challenges of our era. Until about 25 years ago the most reliableway to investigate human brain function via its altered states was limited to occurrences of lesions, intra-operatory stimulation, neurosurgical resections, and congenital malformations. In other words, it was not possible to independently manipulate the state of healthy brains in a targeted, reversible, and noninvasive manner as it is today. In the past quasi-experiments (i.e., experiments in which the independent variable had been manipulated by nature itself or based on primarily clinical considerations) were the gold standard. It has now become possible, instead, to experimentally modulate the state of neural circuits in the healthy human brain for basic research purposes.
