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7-1 Measuring and Manipulating Brain and Behavior

The brain’s primary function is to produce behavior, so the fundamental research technique in behavioral neuroscience is to study the direct relationship between brain and behavior. Investigators study healthy humans and other animals as well as human patients and laboratory animals with neurological problems.

Initially, scientists simply observed behavior, but they later developed neuropsychological testing measures designed to study specific functions such as fine movements, memory, and emotion. Today, researchers correlate these behavioral outcomes with anatomical, physiological, chemical, genetic, and other molecular measures of brain organization.

Brain and behavioral relations can be manipulated by altering brain function, either permanently or temporarily. Permanent changes involve damaging the brain directly by ablation or neurotoxins that remove or destroy brain tissue. Transient changes in brain activity can be induced either by use of a mild electrical or magnetic current, as in DBS or TMS, or by administration of drugs. Optogenetics, a transgenic technique, employs light-activated ion channels to excite or inhibit targeted cells in living tissue. Chemogenetic stimulation combines designer receptors and synthetic drugs to excite targeted cells in living tissue.

7-2 Measuring the Brain’s Electrical Activity

Recording from single or multiple cells shows that neurons employ a code and that cortical neurons are organized into functional groups that work as coordinated networks. Neurons in sensory areas respond to specific characteristics of stimuli, such as color or pitch. Other neurons, such as place cells in the hippocampal formation, can code for more complex information, such as an object’s location in space.

Electroencephalographic or magnetoencephalographic recordings measure electrical or magnetic activity from thousands of neurons at once. EEG can reveal a gross relationship between brain and behavior, as when a person is alert and displays the beta wave pattern versus when the person is resting or sleeping, indicated by the slower alpha wave patterns. Event-related potentials tell us, on the other hand, that even though the entire brain is active during waking, certain parts are momentarily much more active than others. ERP records how the location of increased activity changes as information moves from one brain area to another.

EEG and ERP are noninvasive methods that record from electrodes on the scalp; in the case of MEG, from magnetic detectors above the head. Electrocorticography, by contrast, records via electrodes attached directly to the cortex. ECoG and single-cell recording techniques are invasive.

7-3 Anatomical Imaging Techniques: CT and MRI

Computed tomography and magnetic resonance imaging are sensitive to the density of brain structures, ventricles, nuclei, and pathways. CT is a form of three-dimensional X-ray, whereas MRI works on the principle that hydrogen atoms behave like spinning bar magnets in the presence of a magnetic field.

Although CT scans are quicker and less expensive, MRI provides exceptionally clear images, both of nuclei and of fiber pathways in the brain. MRI also indicates that people’s brain structure varies widely. Both CT and MRI can be used to assess brain damage from neurological disease or injury, but MRI is more useful as a research tool.

Diffusion tensor imaging is a form of MRI that makes it possible to identify normal or abnormal fiber tracts and myelin in the brain. Magnetic resonance spectroscopy, another form of MRI, permits practitioners to detect brain metabolites, such as those produced following concussion.

7-4 Functional Brain Imaging

Metabolic imaging shows that any behavior requires the collaboration of widespread neural circuits. Positron emission tomography records blood flow and other metabolic changes in periods measured in minutes, and requires complex subtraction procedures and the averaging of responses across multiple subjects. Records of blood flow obtained using functional magnetic resonance imaging can be combined with anatomical MRI images to locate changes in the individual brain and to complement ERP results. Resting-state fMRI allows investigators to measure connectivity across brain regions.

Functional near-infrared spectroscopy is the form of optical tomography usually used for functional brain imaging studies. It works on the principle that an object, including brain tissue, can be reconstructed by gathering light transmitted through the object. fNIRS is much simpler to use than PET or fMRI, but because light does not penetrate very far into the brain, it can be used only to study cortical function.

7-5 Chemical and Genetic Measures of Brain and Behavior

Analysis of changes in both genes and neurochemicals provides insight into the molecular correlates of behavior. Although genes code all the information needed to construct and regulate cells, epigenetic research reveals that the environment and life experience can modify gene expression. Even identical twins, who have an identical genome at birth, in adulthood have widely differing patterns of gene expression and very different brains.

7-6 Comparing Neuroscience Research Methods

The main consideration in neuroscience research is the question. Whatever the approach, the goal is to understand brain–behavior relationships. Tables 7-1 and 7-2 on pages 238 and 239 summarize the manipulations and measurements used in behavioral neuroscience. Among all the practical issues of measurement resolution and invasiveness, cost may prove the ultimate consideration.

7-7 Using Animals in Brain–Behavior Research

Understanding brain function, in both the healthy and the disordered brain, often benefits from animal models. Investigators develop animal models to manipulate the brain—to determine how experiential factors and neurological treatments affect brain function.

Because animal subjects cannot protect themselves from abuse, governments and researchers have cooperated to develop ethical guidelines for the use of laboratory animals. These guidelines are designed to ensure that discomfort is minimized, as is the number of animals used for invasive procedures.