TO EXPLAIN AN ORGANISM’S BEHAVIOR in biological terms, it is necessary to reconcile measures of biological processes (eg, action potentials, blood flow, release of neurotransmitters) with measures of cognitive and motor outputs. Relating biological and behavioral measures is challenging, however. Precise neural measurements and invasive techniques are possible in nonhuman animals, but many of these species have a relatively constrained behavioral repertory. Moreover, it is far more difficult to directly measure or invasively manipulate neural activity in healthy humans, the species with the most advanced and varied behavior. Thus, a central effort of modern neuroscience has been to develop new methods for obtaining precise biological measures from the human brain and for modeling human behaviors in nonhuman animals.
The dominant approach in humans for measuring biological processes and linking them to behavior is functional magnetic resonance imaging (fMRI). Other imaging methods for measuring human brain function such as electroencephalography, positron emission tomography, and near-infrared spectroscopy have their own strengths. However, fMRI is particularly well suited for studying the neural underpinnings of human behavior for several reasons. First, it is noninvasive: It does not require surgery, ionizing radiation, or other disruptive intervention. Second, it can measure brain function over short periods of time (in seconds), which allows it to capture dynamic aspects of mental processes and behavior. Third, it measures activity across the whole brain simultaneously, providing the opportunity to examine how multiple brain regions interact to mediate complex behaviors. Thus, the focus of this chapter is fMRI.
We start by explaining the technicalities of how an fMRI experiment works and how the data are typically collected. We then explain how fMRI data are analyzed and how they provide insight into human behavior and thought. We then turn to a more conceptual overview of what has been learned from fMRI, using examples from the fields of perception, memory, and decision- making. Finally, we consider the strengths and limitations of fMRI and discuss what kinds of inferences about brain and behavior it can support.
Although the focus of this chapter is on imaging and behavior in the healthy brain, fMRI also has the potential to change the way we diagnose and treat psychiatric and neurological disorders. Virtually all such disorders (eg, autism, schizophrenia, depression, eating disorders) involve changes in large-scale circuit dynamics, in addition to the disruption of particular brain regions and cell types. Basic research into how healthy brain circuits mediate mental processes and behavior, combined with the ability to measure activity in these same circuits in clinical populations, holds tremendous promise for understanding disease and dysfunctional behavior.
Functional MRI Experiments Measure Neurovascular Activity
fMRI experiments enable investigators to track brain function based on changes in local blood oxygen levels that occur in response to neural activity. Like all forms of magnetic resonance imaging (MRI), fMRI requires both highly specialized equipment and sophisticated computer ...