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Electroencephalograms (EEGs) are recordings of the electrical frequencies and intensities of the living brain, typically recorded over relatively long periods. Through EEGs, it is possible to study brainwave activity indicative of changing mental states such as deep sleep or dreaming. To obtain EEG recordings, electrodes are placed at various points along the surface of the scalp. The electrical activity of underlying brain areas is then recorded. The information, therefore, is not localized to specific cells. The EEG is sensitive to changes over time. For example, EEG recordings taken during sleep reveal changing patterns of electrical activity involving the whole brain. Different patterns emerge during dreaming versus deep sleep. EEGs are also used to diagnose epilepsy because they can indicate whether seizures appear in both sides of the brain at the same time, or whether they originate in one part of the brain and then spread.

To relate electrical activity to a particular event or task (e.g., seeing a flash of light or listening to sentences), EEG waves can be measured when participants are exposed to a particular stimulus. An event-related potential (ERP) is the record of a small change in the brain's electrical activity in response to a stimulating event. The fluctuation typically lasts a mere fraction of a second. ERPs provide good information about the time- course of task-related brain activity. In any one EEG recording, there is a great deal of "noise"—that is, irrelevant electrical activity going on in the brain. ERPs cancel out the effects of noise by averaging out activity that is not task-related. Therefore, the EEG waves are averaged over a large number (e.g., 100) of trials to reveal the ERPs. The resulting wave forms show characteristic spikes related to the timing of electrical activity, but they reveal only general information about the location of that activity (because of low spatial resolution as a result of the placement of scalp electrodes).
The cerebral cortex forms the outer layer of the two halves of the brain—the left and right cerebral hemispheres. Although the two hemispheres appear to be similar, they function differently. The left cerebral hemisphere is specialized for some kinds of activity, whereas the right cerebral hemisphere is specialized for other kinds. For example, receptors in the skin on the right side of the body generally send information through the medulla to areas in the left hemisphere in the brain. The receptors on the left side generally transmit information to the right hemisphere. Similarly, the left hemisphere of the brain directs the motor responses on the right side of the body. The right hemisphere directs responses on the left side of the body. Not all information transmission is contralateral—from one side to another. Some ipsilateral transmission—on the same side— occurs as well. For example, odor information from the right nostril goes primarily to the right side of the brain. About half the information from the right eye goes to the right side of the brain; the other half goes to the left side of the brain. In addition to this general tendency for contralateral specialization, the hemispheres also communicate directly with one another. The corpus callosum is a dense aggregate of neural fibers connecting the two cerebral hemispheres. It transmits information back and forth. Once information has reached one hemisphere, the corpus callosum transfers it to the other hemisphere. If the corpus callosum is cut, the two cerebral hemispheres cannot communicate with each other. Although some functioning, such as language, is highly lateralized, most functioning—even language—depends in large part on integration of the two hemispheres of the brain.
Acetylcholine is associated with memory functions, and the loss of acetylcholine through Alzheimer's disease has been linked to impaired memory functioning in Alzheimer's patients. Acetylcholine also plays an important role in sleep and arousal. When someone awakens, there is an increase in the activity of so called cholinergic neurons in the basal forebrain and the brainstem.

Dopamine is associated with attention, learning, and movement coordination. Dopamine also is involved in motivational processes, such as reward and reinforcement. Schizophrenics show high levels of dopamine. This fact has led to the "dopamine theory of schizophrenia," which suggests that high levels of dopamine may be partially responsible for schizophrenic conditions. Drugs used to combat schizophrenia often inhibit dopamine activity. In contrast, patients with Parkinson's disease show low dopamine levels, which leads to the typical trembling and movement problems associated with Parkinson's. When patients receive medication that increases their dopamine level, they (as well as healthy people who receive dopamine) sometimes show an increase in pathological gambling. Gambling is a compulsive disorder that results from impaired impulse control. When dopamine treatment is suspended, these patients no longer exhibit this behavior. These findings support the role of dopamine in motivational processes and impulse control.

Serotonin plays an important role in eating behavior and body-weight regulation. High serotonin levels play a role in some types of anorexia. Specifically, serotonin seems to play a role in the types of anorexia resulting from illness or treatment of illness. For example, patients suffering from cancer or undergoing dialysis often experience a severe loss of appetite. This loss of appetite is related, in both cases, to high serotonin levels. Serotonin is also involved in aggression and regulation of impulsivity. Drugs that block serotonin tend to result in an increase in aggressive behavior.
The frontal lobe, toward the front of the brain, is associated with motor processing and higher thought processes, such as abstract reasoning, problem solving, planning, and judgment. It tends to be involved when sequences of thoughts or actions are called for. It is critical in producing speech. The prefrontal cortex, the region toward the front of the frontal lobe, is involved in complex motor control and tasks that require integration of information over time.

The parietal lobe, at the upper back portion of the brain, is associated with somatosensory processing. The primary somatosensory cortex receives information from the senses about pressure, texture, temperature, and pain. It is located right behind the frontal lobe's primary motor cortex. If your somatosensory cortex were electrically stimulated, you probably would report feeling as if you had been touched. The parietal lobe also helps you perceive space and your relationship to it—how you are situated relative to the space you are occupying. It is also involved in consciousness and paying attention.

The temporal lobe is located below the parietal lobe, directly under your temples. It is associated with auditory processing and comprehending language. Some parts are more sensitive to sounds of higher pitch, others to sounds of lower pitch. The auditory region is primarily contralateral. Both sides of the auditory area have at least some representation from each ear. If your auditory cortex were stimulated electrically, you would report having heard some sort of sound. The temporal lobe is also involved in retaining visual memories. For example, if you are trying to keep in memory

The occipital lobe is associated with visual processing. The occipital lobe contains numerous visual areas, each specialized to analyze specific aspects of a scene, including color, motion, location, and form. Projection areas are the areas in the lobes in which sensory processing occurs. These areas are referred to as projection areas because the nerves contain sensory information going to (projecting to) the thalamus. It is from here that the sensory information is communicated to the appropriate area in the relevant lobe. Similarly, the projection areas communicate motor information downward through the spinal cord to the appropriate muscles via the peripheral nervous system (PNS). The visual cortex is primarily in the occipital lobe. Some neural fibers carrying visual information travel ipsilaterally from the left eye to the left cerebral hemisphere and from the right eye to the right cerebral hemisphere. Other fibers cross over the optic chiasma and go contralaterally to the opposite hemisphere. In particular, neural fibers go from the left side of the visual field for each eye to the right side of the visual cortex. Complementarily, the nerves from the right side of each eye's visual field send information to the left side of the visual cortex.
Brain tumors, also called neoplasms, can affect cognitive functioning in serious ways. Tumors can occur in either the gray or the white matter of the brain. Two types of brain tumors can occur. Primary brain tumors start in the brain. Most childhood brain tumors are of this type. Secondary brain tumors start as tumors somewhere else in the body, such as in the lungs. Brain tumors can be either benign or malignant. Benign tumors do not contain cancer cells. They typically can be removed and will not grow back. Cells from benign tumors do not invade surrounding cells or spread to other parts of the body. If, however, they press against sensitive areas of the brain, they can result in serious cognitive impairments. They also can be life-threatening, unlike benign tumors in most other parts of the body. Malignant brain tumors, unlike benign ones, contain cancer cells. They are more serious and usually threaten the victim's life. They often grow quickly. They tend to invade surrounding healthy brain tissue. In rare instances, malignant cells may break away and cause cancer in other parts of the body. Common symptoms of brain tumors include headaches (usually worse in the morning); nausea or vomiting; changes in speech, vision, or hearing; problems balancing or walking; changes in mood, personality, or ability to concentrate; problems with memory; muscle jerking or twitching (seizures or convulsions); and numbness or tingling in the arms or legs. The diagnosis of brain tumor typically is made through neurological examination, CT scan, or MRI. The most common form of treatment is a combination of surgery, radiation, and chemotherapy.
Metabolic imaging techniques rely on changes that take place within the brain as a result of increased consumption of glucose and oxygen in active areas of the brain. The basic idea is that active areas in the brain consume more glucose and oxygen than do inactive areas during some tasks. An area specifically required by one task ought to be more active during that task than during more generalized processing and thus should require more glucose and oxygen.

PET scans measure increases in oxygen consumption in active brain areas during particular kinds of information. To track their use of oxygen, participants are given a mildly radioactive form of oxygen that emits positrons as it is metabolized (positrons are particles that have roughly the same size and mass as electrons, but that are positively rather than negatively charged). Next, the brain is scanned to detect positrons. A computer analyzes the data to produce images of the physiological functioning of the brain in action. PET scans are not highly precise because they require a minimum of about half a minute to produce data regarding glucose consumption. If an area of the brain shows different amounts of activity over the course of time measurement, the activity levels are averaged, potentially leading to conclusions that are less than precise.

Functional magnetic resonance imaging (fMRI) is a neuroimaging technique that uses magnetic fields to construct a detailed representation in three dimensions of levels of activity in various parts of the brain at a given moment in time. This technique builds on MRI, but it uses increases in oxygen consumption to construct images of brain activity. The basic idea is the same as in PET scans, but the fMRI technique does not require the use of radioactive particles. Rather, the participant performs a task while placed inside an MRI machine. This machine typically looks like a tunnel. When someone is wholly or partially inserted in the tunnel, he or she is surrounded by a doughnut-shaped magnet. An fMRI creates a magnetic field that induces changes in the particles of oxygen atoms. More active areas draw more oxygenated blood than do less active areas in the brain. So shortly after a brain area has been active, a reduced amount of oxygen should be detectable in this area. This observation forms the basis for fMRI measurements. These measurements then are computer analyzed to provide the most precise information currently available about the physiological functioning of the brain's activity during task performance.

A related procedure is pharmacological MRI (phMRI). The phMRI combines fMRI methods with the study of psychopharmacological agents. These studies examine the influence and role of particular psychopharmacological agents on the brain. phMRIs have been used to examine the role of agonists (which strengthen responses) and antagonists (which weaken responses) on the same receptor cells. These studies have allowed for the examination of drugs used for treatment. The investigators can predict the responses of patients to neurochemical treatments through examination of the person's brain makeup. Overall, these methods aid in the understanding of brain areas and the effects of psychopharmacological agents on brain functioning.

Another procedure related to fMRI is diffusion tensor imaging (DTI). DTI examines the restricted dispersion of water in tissue and, of special interest, in axons. Water in the brain cannot move freely, but rather, its movement is restricted by the axons and their myelin sheaths. DTI measures how far protons have moved in a particular direction within a specific time interval. This technique has been useful in the mapping of the white matter of the brain and in examining neural circuits. Some applications of this technique include examination of traumatic brain injury, schizophrenia, brain maturation, and multiple sclerosis

A recently developed technique for studying brain activity bypasses some of the problems with other techniques. Transcranial magnetic stimulation (TMS) temporarily disrupts the normal activity of the brain in a limited area. Therefore, it can imitate lesions in the brain or stimulate brain regions. TMS requires placing a coil on a person's head and then allowing an electrical current to pass through it. The current generates a magnetic field. This field disrupts the small area (usually no more than a cubic centimeter) beneath it. The researcher can then look at cognitive functioning when the particular area is disrupted.

Magnetoencephalography (MEG) measures brain activity from outside the head (similar to EEG) by picking up magnetic fields emitted by changes in brain activity. This technique allows localization of brain signals so that it is possible to know what different parts of the brain are doing at different times. It is one of the most precise of the measuring methods. MEG is used to help surgeons locate pathological structures in the brain.
Functionalism: Seeks to understand what people do and why they do it. This principal question about processes was in contrast to that of the structuralists, who had asked what the elementary contents (structures) of the human mind are. Functionalists held that the key to understanding the human mind and behavior was to study the processes of how and why the mind works as it does, rather than to study the structural contents and elements of the mind.

Structuralism: Seeks to understand the structure (configuration of elements) of the mind and its perceptions by analyzing those perceptions into their constituent components (affection, attention, memory, and sensation).

Pragmatism: Pragmatists believe that knowledge is validated by its usefulness: What can you do with it? Pragmatists are concerned not only with knowing what people do; they also want to know what we can do with our knowledge of what people do.

Synthesis: Associationism: Associationism examines how elements of the mind, such as events or ideas, can become associated with one another to result in a form of learning.

Behaviorism (extreme form of associationism): Behaviorism focuses only on the relation between observable behavior and environmental events or stimuli. The idea was to make physical whatever others might have called "mental." Behaviorism may be considered an extreme version of associationism. It focuses entirely on the association between the environment and an observable behavior. According to strict, extreme ("radical") behaviorists, any hypotheses about internal thoughts and ways of thinking are nothing more than speculation

Gestalt psychology: Gestalt psychology states that we best understand psychological phenomena when we view them as organized, structured wholes. According to this view, we cannot fully understand behavior when we only break phenomena down into smaller parts.

Synthesis: Cognitivism: Cognitivism is the belief that most human behavior explains how people think. It rejects the behavioristic notion that psychologists should avoid studying mental processes just because they are unobservable. Cognitivism is, in part, a synthesis of earlier forms of analysis, such as behaviorism and Gestaltism. Like behaviorism, it adopts precise quantitative analysis to study how people learn and think; like Gestaltism, it emphasizes internal mental processes.
Eyewitness testimony may be the most common source of wrongful convictions in the United States. The proportion of erroneous identifications has been estimated to be low as a few percent to greater than 90%, but even the most conservative estimates of this proportion suggest frightening possibilities. Of the first 180 cases in the United States in which convicts were exonerated through the use of DNA evidence, more than three-quarters involved eyewitness errors.

Eyewitness testimony is often a powerful determinant of whether a jury will convict an accused person. The effect is particularly pronounced if eyewitnesses appear highly confident of their testimony. This is true even if the eyewitnesses can provide few perceptual details or offer apparently conflicting responses. In general, people are remarkably susceptible to mistakes in eyewitness testimony. They are generally prone to imagine that they have seen things they have not seen.
Loftus's eyewitness testimony experiment and other experiments have shown people's great susceptibility to distortion in eyewitness accounts. This distortion may be due, in part, to phenomena other than just constructive memory. But it does show that we easily can be led to construct a memory that is different from what really happened. Questions do not have to be suggestive to influence the accuracy of eyewitness testimony. Lineups also can lead to faulty conclusions. Eyewitnesses assume that the perpetrator is in the lineup.

Eyewitness identification is particularly weak when identifying people of a racial or ethnic group other than that of the witness. Evidence suggests that this weakness is not a problem remembering stored faces of people from other racial or ethnic groups, but rather, a problem of accurately encoding their faces. Eyewitness identification and recall also are affected by the witness's level of stress. As stress increases, the accuracy of both recall and identification declines.

Whatever may be the validity of eyewitness testimony for adults, it clearly is suspect for children. Children's recollections are particularly susceptible to distortion. Such distortion is especially likely when the children are asked leading questions, as in a courtroom setting.