Neuropsychology

Experimental neuropsychology employs a wide range of scientific methods in an attempt to understand basic brain-behavior-mind relationships. Some of these methods involve the study of non-human animals, observing behavior changes following experimental damage, electrical stimulation, or drug injection within various brain regions, and recording the electrical activity of nerve cells while the animal performs different tasks. In the study of humans, the major method has been the careful measurement of behavioral and mental changes following accidental brain injury, neurosurgery, or the unfortunate occurrence of neurological diseases that affect particular brain regions.

Within the late-twentieth and early-twenty-first centuries, a variety of technologies have been added to the methodology of experimental neuropsychology. Each of these technologies allows a noninvasive (without entering the body) or minimally invasive measurement of brain structure or physiology which can be correlated to measures of behavior, cognition, or emotion during the performance of a specified task. These technologies include: (1) Electroencephalography (EEG; fluctuations in brain electrical activity recorded from sensors placed on the scalp); (2) Event-related potentials (ERP; brain electrical in response to a sensory stimulus or preceding a voluntary movement, recorded from scalp sensors and enhanced by computer averaging); (3) Magnetoencephalography (MEG) recording, from outside the head, of the magnetic field fluctuations generated by nerve-cell activity; (4) computerized tomography (CT), which allows the visualization of brain structure by computer-assisted measures of tissue density calculated by the average absorption of X-rays; (5) magnetic resonance imaging (MRI), which makes a highly detailed visualization of brain structure through computer-assisted measures of cellular composition, calculated from radiowave signal changes following a radio-frequency pulse while the head is within the field of a powerful magnet; (6) functional magnetic resonance imaging (fMRI), which involves the use of MRI technology to visualize changes in blood oxygen content that reflect the metabolic demands of active brain cells; and (7) positron emission tomography (PET), which allows measures of blood flow or metabolic activity of different brain regions, based on emitted subatomic particles from radioactively labeled substances injected into blood vessels that supply the brain.

Overall, the most confident conclusions concerning what brain regions contribute to any particular aspect of behavior, cognition, or emotion are obtained when results from several of these scientific methods converge. As technological developments have allowed increasingly fine-grained measurement of brain structure and processes, a more detailed and sophisticated understanding of human brain-behavior-mind relationships has emerged.