ADVANCES IN METHODOLOGIES

Ethical constraints restrict the scope of psychobiological methods used with living human beings. In other species, one can surgically or chemically destroy selected parts of the brain and observe the effects on behavior. Autopsy can be used to verify the brain alterations. One also can stimulate selected areas of the brain electrically or chemically through canulas to the brain areas. Brain stimulation in humans is usually done through external stimulation of the senses with stimulation varying in intensity, quality, or content. Chemical manipulation is done through infusion or ingestion of drugs, which can produce transient effects in these systems. Most psychopharmacological work with humans is done on abnormal populations with limited generalizability to normal personality variants.

Measurement of responses of specific brain areas to stimulation may be done directly, using implanted electrodes. Until recently, brain study in humans was limited to amplified electrical potentials from the scalp (EEG and cortical evoked potentials) indicating areas of cortical reactivity imprecisely located in areas under the surface electrodes. Newer brain imaging methods such as positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) allow us to view activity at all levels of the brain at specific cortical and subcortical loci.

The peripheral autonomic system has been studied using physiological methods for measuring cardiovascular (heart rate, blood pressure, blood flow), respiratory, and electrodermal (skin conductance) methods. These methods have been widely used in studies of emotion, perception, and cognition, and some have used them to study personality traits such as neuroticism, and emotional traits such as anxiety and hostility.