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Tools of Discovery: Having Our Head Examined

1.4-3 How do neuroscientists study the brain’s connections to behavior and mind?
1.4-3 How do neur oscientists study the brain’s connections to behavior and mind?

The mind seeking to understand the brain — that is among the ultimate scientific chal-
lenges. And so it will always be. To paraphrase cosmologist John Barrow, a brain simple
enough to be fully understood is too simple to produce a mind able to understand it.

When you think about your brain, you’re thinking with your brain — by releasing billions

of neurotransmitter molecules across trillions of synapses. Indeed, say neuroscientists, the
mind is what the brain does. In “The Adventure of the Mazarin Stone,” Sherlock Holmes
declared: “I am a brain, Watson. The rest of me is a mere appendix.” Would you agree?
Distributed by Bedford, Freeman & Worth Publishers. Not for redistribution.
For most of human history, scientists had no tools high-powered yet gentle enough
to reveal a living brain’s activity. Early case studies helped localize some brain functions.
Damage to one side of the brain often caused numbness or paralysis on the opposite side,
destruction. Brain lesions may Copyright © Bedford, Freeman & Worth Publishers.
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 damage to the left-front part of the brain pro-
duced speech difficulties. Gradually, these early explorers were mapping the brain.
Now, a new generation of neural mapmakers is charting the known universe’s most

amazing organ. Scientists can selectively lesion (destroy) tiny clusters of normal or defec-
tive brain cells, observing any effect on brain function. In the laboratory, such studies have
revealed, for example, that damage to one area of a rat’s hypothalamus reduces eating to the
point of starvation, whereas damage to another area produces overeating.
Today’s neuroscientists can also stimulate various brain parts — electrically, chemically,
®
AP Science Practice or magnetically — and note the effect. Depending on the stimulated brain part, people
Research may — to name a few examples — giggle, hear voices, turn their head, feel themselves fall-
ing, or have an out-of-body experience ( Selimbeyoglu & Parvizi, 2010 ).
Electrically stimulating a brain Scientists can even snoop on the messages transmitted by individual neurons. With
part to note its effect on behavior
implies an experimental research tips small enough to detect the electrical pulse in a single neuron, modern electrodes can,
design. You cannot infer causality for example, now detect exactly where the information goes in a rat’s brain when someone
from non-experimental designs.
tickles its belly ( Ishiyama & Brecht, 2017 ). They can also eavesdrop on the chatter of billions
of neurons and see color representations of the brain’s energy-consuming activity. Prom-
ising new tools include optogenetics, a technique that allows neuroscientists to control the
activity of individual neurons ( Boyden, 2014 ). By programming neurons to become receptive
to light, researchers can examine the biological bases of sensations, fear, depression, and
substance use disorders ( Dygalo & Shishkina, 2019 ; Firsov, 2019 ; Juarez et al., 2019 ; Nikitin
et al., 2019 ).
lesion [LEE-zhuhn] tissue Right now, your mental activity is emitting telltale electrical, metabolic, and magnetic
signals that would enable neuroscientists to observe your brain at work. Electrical activ-
occur naturally (from disease ity in your brain’s billions of neurons sweeps in regular waves across its surface. An EEG
or trauma), during surgery, or (electroencephalogram) is an amplified readout of such waves. Researchers record the
experimentally (using electrodes
to destroy brain cells). 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 blender’s motor by
EEG (electroencephalogram)
an amplified recording of the listening to its hum. Researchers may lack direct access to the brain, but they can present a
waves of electrical activity stimulus repeatedly and have a computer filter out brain activity unrelated to the stimulus.
sweeping across the brain’s What remains is the electrical wave evoked by the stimulus.
surface. These waves are A related technique, MEG (magnetoencephalography) measures magnetic fields

,
measured by electrodes placed from the brain’s natural electrical activity. To isolate the brain’s magnetic fields, researchers
on the scalp.
create special rooms that cancel out other magnetic signals, such as the Earth’s magnetic

MEG (magnetoencephalography)
a brain-imaging technique that field. Participants sit underneath a head coil that resembles a salon hair dryer. While partic-
measures magnetic fields from the ipants complete activities, tens of thousands of neurons generate electrical pulses, which in
brain’s natural electrical activity. turn create magnetic fields. The speed and strength of the magnetic fields enable research-
ers to understand how certain tasks influence brain activity ( Samuelsson et al., 2020 ).
58 Unit 1 Biological Bases of Behavior

03_myersAPpsychology4e_28116_ch01_002_163.indd 58 15/12/23 9:22 AM