| How do variations in the structure of brain activity relate to subjective perception, thought, and behavior? The notion that physical processes in the brain correspond to inward experience and outward behavior is the basic premise of modern neuroscience. Technological advances in non-invasive brain imaging, such as functional magnetic resonance imaging (fMRI), have presented new and profound opportunities to study this question empirically.;At its root, the brain is a highly dynamic information processing system that integrates computations performed in spatially distributed areas. The foremost advantage of brain imaging is its capacity to monitor activity throughout every region in the brain simultaneously. The primary drawback of current techniques is that the measured activity is based on hemodynamic signals such as blood flow, rather than direct measurement of electrophysiological signals associated with the action potentials of individual neurons. The field of neurovascular coupling has emerged to describe the relationship between these neural and hemodynamic signals, a fortuitous relationship linked to supply and demand energy requirements of neuronal activity.;A complementary technique for investigating the relationship between structure and function is brain stimulation, for example using electrical current applied through implanted microelectrodes or through electrical fields induced noninvasively via transcranial magnetic stimulation (TMS). Combined with functional imaging, brain stimulation can be used to perform an experimental manipulation of neural activity in one region while observing the result of that manipulation in functionally connected areas.;We have conducted a series of experimental investigations designed to explore the relationship between hemodynamic brain imaging signals and neural activity, during visual stimulation as well as during externally applied electrical brain stimulation using TMS. We demonstrate a tight coupling between hemodynamic and neural signals under a wide variety of experimental conditions. These results reveal the potential of combining non-invasive brain imaging and brain stimulation for the study of structure-function relationships in human cortex. |
