Trust Game
Average transferby investors
6.5 6 7.0 7.5 8.0 8.5
Oxytocin Placebo
Before Feedback After Feedback
Data from J. A. Bartz & E. Hollander, The neuroscience of affiliation: Forging links between basic and clinical research on neuropeptides and social behavior, Hormones and Behavior, 50, pp. 518–528.
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Phineas Gage is shown holding the pole that caused his injury. Why were doctors so fascinated by Gage’s changes in personality?
application of intense heat, cold, or electricity. As you would guess, experimental work with permanent lesions is carried out exclusively with nonhuman animals. (Recall the discussion in Chapter 2 that the ethics of this type of animal research has now come under heightened scrutiny.) Our conception of the brain has been radically changed as researchers have repeatedly compared and coordinated the results of lesioning experiments on animals with the growing body of clinical findings on the effects of brain damage on human behavior.
In recent years, scientists have developed a procedure called repetitive transcranial magnetic stimulation (rTMS) that uses pulses of magnetic stimulation to create temporary, reversible “lesions” in human participants—without any dam-age being done to tissue, brain regions can be briefly inactivated.
This new technique enables researchers to address a range of questions that would not have been possible with nonhuman experiments (Sandrini et al., 2011). Consider an application of rTMS to study how your brain responds to nouns and verbs.
If you’ve spent any time studying languages, you’re likely aware that nouns and verbs serve very different functions. A team of researchers used rTMS to test the hypothesis that different brain regions are at work when you produce the two parts of speech (Cappelletti et al., 2008). In the experi-ment, participants completed simple phrases presented by computer. For example, participants would read, “today I walk,” and then complete, “yesterday I . . .” Similarly, they would read “one child,” and then complete “many. . . .” Un-der ordinary circumstances, participants should be relatively quick to respond “walked” and “children.” Suppose, how-ever, that the researchers are able to use rTMS to “lesion”
brain regions that help make these responses possible.
Then, we’d expect participants’ responses to be slowed down. In fact, the researchers identified one brain region (in the vicinity of Broca’s area) that, when stimulated by rTMS, yielded slower performance for verbs but not for nouns.
These data support the hypothesis that your brain processes make distinctions between nouns and verbs.
You can see why this experiment would not be possible with nonhuman participants: Humans are the only species that habitually produces nouns and verbs.
On other occasions, neuroscientists learn about the func-tion of brain regions by directly stimulating them. For example, in the mid-1950s, Walter Hess (1881–1973) pioneered the use of electrical stimulation to probe structures deep in the brain.
For example, Hess put electrodes into the brains of freely mov-ing cats. By pressmov-ing a button, he could then send a small electri-cal current to the point of the electrode. Hess carefully recorded the behavioral consequences of stimulating each of 4,500 brain sites in nearly 500 cats. Hess discovered that, depending on the location of the electrode, sleep, sexual arousal, anxiety, or terror could be provoked by the flick of the switch—and turned off just as abruptly. For example, electrical stimulation of certain regions of the brain led the otherwise gentle cats to bristle with rage and hurl themselves on a nearby object.
Recording and Imaging Brain Activity Other neurosci-entists map brain function by using electrodes to record the electrical activity of the brain in response to environmental Gage’s injury came at a time when scientists were just
beginning to form hypotheses about the links between brain functions and complex behavior. The behavioral changes fol-lowing the dramatic piercing of his brain prompted his doctor to hypothesize brain bases for aspects of personality and ra-tional behavior.
At about the same time that Gage was convalescing from his injury, Paul Broca was studying the brain’s role in lan-guage. His first research in this area involved an autopsy of a man whose name was derived from the only word he had been able to speak, “Tan.” Broca found that the left front portion of Tan’s brain had been severely damaged. This finding led Broca to study the brains of other persons who suffered from lan-guage impairments. In each case, Broca’s work revealed similar damage to the same area of the brain, a region now known as Broca’s area. As you will see as Psychology and Life unfolds, contemporary researchers still attempt to correlate patterns of behavior change or impairment with the sites of brain damage.
The problem with studying accidentally damaged brains, of course, is that researchers have no control over the loca-tion and extent of the damage. To produce a well-founded understanding of the brain and its relationship to behavioral and cognitive functioning, scientists need methods that allow them to specify precisely the brain tissue that has been inca-pacitated. Researchers have developed a variety of techniques to produce lesions, highly localized brain injuries. They may, for example, surgically remove specific brain areas, cut the neu-ral connections to those areas, or destroy those areas through
Broca’s area The region of the brain that translates thoughts into speech or signs.
lesion Injury to or destruction of brain tissue.
repetitive transcranial magnetic stimulation (rTMS) A technique for producing temporary inactivation of brain areas using repeated pulses of magnetic stimulation.
Featured Study
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computerized axial tomography (CT or CAT) A technique that uses narrow beams of X-rays passed through the brain at several angles to assemble complete brain images.
How have new imaging techniques expanded the range of questions researchers can ask?
use CT scans to determine the location and extent of brain damage or brain abnormalities.
In research with positron emission tomography, or PET, subjects are given different kinds of radioactive (but safe) sub-stances that eventually travel to the brain, where they are taken up by active brain cells. Recording instruments outside the skull can detect the radioactivity emitted by cells that are active during different cognitive or behavioral activities. This infor-mation is then fed into a computer that constructs a dynamic portrait of the brain, showing where different types of psycho-logical activities are actually occurring.
Magnetic resonance imaging, or MRI, uses magnetic fields and radio waves to generate pulses of energy within the brain. As the pulse is tuned to different frequencies, some at-oms line up with the magnetic field. When the magnetic pulse is turned off, the atoms vibrate (resonate) as they return to their original positions. Special radio receivers detect this reso-nance and channel information to a computer, which generates images of the locations of different atoms in areas of the brain.
By looking at the image, researchers can link brain structures to psychological processes.
stimulation. The brain’s electrical output can be monitored at different levels of precision. At the most specific, research-ers can insert ultrasensitive microelectrodes into the brain to record the electrical activity of a single brain cell. Such record-ings can illuminate changes in the activity of individual cells in response to stimuli in the environment.
For human subjects, researchers often place a number of electrodes on the surface of the scalp to record larger, inte-grated patterns of electrical activity. These electrodes provide the data for an electroencephalogram (EEG), or an ampli-fied tracing of the brain activity. EEGs can be used to study the relationship between psychological activities and brain response. For example, in one experiment, researchers used EEGs to demonstrate that people’s brains respond differently when they view emotionally charged images (Hajcak & Olvet, 2008). While their brain activity was being recorded, partici-pants viewed a series of pleasant (e.g., smiling faces), neutral (e.g., household objects), and unpleasant (e.g., violent images) pictures on a computer screen. The EEGs revealed distinct pat-terns for the neutral versus emotional pictures: Participants ap-peared to devote more attention to the pleasant and unpleasant pictures, and that greater attention lingered even after the pic-tures left the computer screen.
Some of the most exciting technological innovations for studying the brain are machines originally developed to help neurosurgeons detect brain abnormalities, such as damage caused by strokes or diseases. These devices produce images of the living brain without invasive procedures that risk damaging brain tissue.
To obtain three-dimensional images of the brain, researchers may use computerized axial tomography (CT or CAT). When an individual undergoes a CT scan, his or her head is placed in a doughnut-shaped ring that contains an X-ray source and an X-ray detector. During the scan, focused X-ray beams pass through the individual’s head from several different angles. The computer assembles those separate X-ray images into coherent pictures of the brain. Researchers often
electroencephalogram (EEG) A recording of the electrical activity of the brain.
positron emission tomography (PET) scanBrain image produced by a device that obtains detailed pictures of activity in the living brain by recording the radioactivity emitted by cells during different cognitive or behavioral activities.
magnetic resonance imaging (MRI) A technique for brain imaging that scans the brain using magnetic fields and radio waves.
What can psychologists learn by looking at PET scans?
Chapter 3 The Biological and Evolutionary Bases of Behavior 64
central nervous system (CNS) The part of the nervous system consisting of the brain and spinal cord.
of your brain’s most important secrets. The remainder of this chapter describes some of those secrets.