6-1 How do neuroscientists study the brain’s connections to behavior and mind?

A century ago, scientists had no tools high powered yet gentle enough to explore the living human brain. Early case studies helped localize some brain functions. Damage to one side of the brain often caused numbness or paralysis on the body’s opposite side, suggesting that the body’s right side is wired to the brain’s left side, and vice versa. Damage to the back of the brain disrupted vision, and to the left-front part of the brain produced speech difficulties. Gradually, these early explorers were mapping the brain.

Now, within a lifetime, a new generation of neural cartographers is probing and mapping the known universe’s most amazing organ. Scientists can selectively lesion (destroy) tiny clusters of brain cells, leaving the surrounding tissue unharmed. In the laboratory, such studies have revealed, for example, that damage to one area of the hypothalamus in a rat’s brain reduces eating, to the point of starvation, whereas damage in another area produces overeating.

Today’s neuroscientists can also stimulate various brain parts—electrically, chemically, or magnetically—and note the effect. Depending on the stimulated brain part, people may—to name a few examples—giggle, hear voices, turn their head, feel themselves falling, or have an out-of-body experience (Selimbeyoglu & Parvizi, 2010). Scientists can even snoop on the messages of individual neurons. With tips small enough to detect the electrical pulse in a single neuron, modern microelectrodes can, for example, now detect exactly where the information goes in a cat’s brain when someone strokes its whisker. Researchers can also eavesdrop on the chatter of billions of neurons and can see color representations of the brain’s energy-consuming activity.

Right now, your mental activity is emitting telltale electrical, metabolic, and magnetic signals that would enable neuroscientists to observe your brain at work. Electrical activity in your brain’s billions of neurons sweeps in regular waves across its surface. An electroencephalogram (EEG) is an amplified readout of such waves. Researchers record the brain waves through a shower-cap-like hat that is filled with electrodes covered with a conductive gel. Studying an EEG of the brain’s activity is like studying a car engine by listening to its hum. With no direct access to the brain, researchers present a stimulus repeatedly and have a computer filter out brain activity unrelated to the stimulus. What remains is the electrical wave evoked by the stimulus (FIGURE 6.1).

“You must look into people, as well as at them,” advised Lord Chesterfield in a 1746 letter to his son. Unlike EEGs, newer neuroimaging techniques give us that Superman-like ability to see inside the living brain. One such tool, the PET (positron emission tomography) scan (FIGURE 6.2), depicts brain activity by showing each brain area’s consumption of its chemical fuel, the sugar glucose. Active neurons are glucose hogs. Our brains, though only about 2 percent of our body weight, consume 20 percent of our calorie intake. After a person receives temporarily radioactive glucose, the PET scan can track the gamma rays released by this “food for thought” as a task is performed. Rather like weather radar showing rain activity, PET-scan “hot spots” show the most active brain areas as the person does mathematical calculations, looks at images of faces, or daydreams.

In MRI (magnetic resonance imaging) brain scans, the person’s head is put in a strong magnetic field, which aligns the spinning atoms of brain molecules. Then, a radio-wave pulse momentarily disorients the atoms. When the atoms return to their normal spin, they emit signals that provide a detailed picture of soft tissues, including the brain. MRI scans have revealed a larger-than-average neural area in the left hemisphere of musicians who display perfect pitch (Schlaug et al., 1995). They have also revealed enlarged ventricles—fluid-filled brain areas (marked by the red arrows in FIGURE 6.3)—in some patients who have schizophrenia, a disabling psychological disorder.

A special application of MRI—fMRI (functional MRI)—can reveal the brain’s functioning as well as its structure. Where the brain is especially active, blood goes. By comparing successive MRI scans, researchers can watch as specific brain areas activate, showing increased oxygen-laden bloodflow. As the person looks at a scene, for example, the fMRI machine detects blood rushing to the back of the brain, which processes visual information.

Such snapshots of the brain’s changing activity are providing new insights into how the brain divides its labor. A mountain of recent fMRI studies suggests which brain areas are most active when people feel pain or rejection, listen to angry voices, think about scary things, feel happy, or become sexually excited. The technology enables a very crude sort of mind reading. One neuroscience team scanned 129 people’s brains as they did eight different mental tasks (such as reading, gambling, or rhyming). Later, they were able, with 80 percent accuracy, to predict which of these mental activities a person was doing (Poldrack et al., 2009). Other studies have explored brain activity associated with religious experience, though without settling the question of whether the brain is producing or perceiving God (Fingelkurts & Fingelkurts, 2009; Inzlicht et al., 2009; Kapogiannis et al., 2009).

You’ve seen the pictures—of colorful brains with accompanying headlines, such as “your brain on music.” Hot brains make hot news. But “neuroskeptics” caution against overblown claims about any ability to predict customer preferences, detect lies, and foretell crime (Satel & Lilienfeld, 2013; Vul et al., 2009a,b). Neuromarketing, neurolaw, neuropolitics, and neurotheology are often neurohype. We can credit brain imaging with illuminating the brain’s structure and activity, and with sometimes helping us test different theories of behavior (Mather et al., 2013). But given that all human experience is brain-based, it’s no surprise that different brain areas become active when one listens to a lecture or lusts for a lover.

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Today’s techniques for peering into the thinking, feeling brain are doing for psychology what the microscope did for biology and the telescope did for astronomy. From them we have learned more about the brain in the last 30 years than in the previous 30,000. And the next decade will reveal much more, as each year massive funding goes into brain research. Europe’s Human Brain Project promises $1 billion for brain computer modeling and the $40 million Human Connectome Project (2013; Gorman, 2014) seeks “neural pathways [that] will reveal much about what makes us uniquely human and what makes every person different from all others.” A new super-powerful diffusion spectrum imaging machine, built as part of the Human Connectome Project, can even map long-distance brain connections.

To be learning about the neurosciences now is like studying world geography while Magellan was exploring the seas. The whole brain mapping effort now underway has been likened to last century’s Apollo program that landed humans on the Moon, and to the Human Genome Project’s mapping our DNA. This truly is the golden age of brain science.