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Fear & the Brain

Revealing the Brain’s Secrets

Since the end of the 19th century, curious researchers have used a variety of techniques to try to figure out what happens beneath the folded exterior of the brain. Before computerized imaging techniques made it possible to analyze intact brains, scientists relied on observations of people and animals with damaged or altered brains paired with dissections after the subjects died.

By implanting electrodes into a subject’s brain, a researcher can electrically stimulate a particular brain area and then observe how the person or animal reacts.

Another approach, called lesion analysis, is basically the opposite of electrical stimulation. Rather than seeing what happens when a brain area is activated, lesion analysis involves watching what happens when a brain area is not working. Neuroscience has benefited greatly from the study of subjects, including animals, with damaged or missing brain areas. Sometimes the damage is the product of disease or an accident; other times, subjects have had parts of their brains surgically removed.

Perhaps the most famous case of lesion analysis involves a patient known as H.M. As a young man, in 1953, H.M. had the temporal lobes of his brain surgically removed in an attempt to limit his severe epileptic attacks. Though the operation stopped the seizures, H.M. was left with anterograde amnesia – just like the main character in the film, Memento, he can no longer form long-term memories.

Researchers found an ideal lesion analysis subject in H.M. Since his amnesia was caused by an operation, they knew exactly which brain structures he was missing. And although H.M. maintained his intelligence after surgery, he can no longer consciously remember anything for more than about a minute or two.

Since his operation so many years ago, H.M. has improved scientists’ understanding of memory tremendously. Both of his hippocampi were removed. These structures are now considered crucial to the formation and storage of new, long-term memories, such as facts, interactions and details of events that most of us can recall at will.

Unlike his long-term memory, researchers have found that H.M.’s procedural memory is intact. This type of memory allows us to learn and retain new skills, such as riding a bike. It operates below the level of consciousness, which is why we don’t have to struggle like beginners once we’ve learned to ride a bike the first time. The fact that H.M. can master new skills, but cannot remember ever having learned to do them, provided scientists with strong evidence that different types of memory are regulated by different neural pathways in the brain. Another famous patient provided additional evidence.

Brain Imaging

New imaging technologies, introduced in the last 40 years, have provided scientists with powerful, extremely effective tools to better understand how normal brains function.

One particularly useful imaging technique used extensively by neurobiologists today is functional magnetic resonance imaging, or fMRI. Using magnetic fields and radio waves, fMRI scanners show changes in blood flow, allowing researchers to see which areas of the brain subjects use most during a particular task. In this way, they can measure brain function in near real-time, providing a method to test theories about which brain structures are activated during various tasks and emotions.

Fear Conditioning

Scientists can reliably produce fear in the lab through a process known as fear conditioning. Conditioning has provided researchers with an important tool for tracing fear in the brain. After all, before they can study fear and its effects, scientists have to know, with confidence, that what they're looking at is actually fear.

You might associate the term "conditioning" with Ivan Pavlov's famous salivating dogs experiment. If so, you're well on your way to understanding the technique. As in Pavlov's experiment, fear conditioning involves the pairing of a stimulus with a response.

Pavlov noted that dogs naturally salivate in preparation for a feeding. After feeding the dogs for a while only after ringing a bell, Pavlov showed that the dogs had come to associate the sound of the bell with food. They salivated as soon as they heard the bell ringing.

The difference is that in fear conditioning, the association is negative – a researcher can make a subject respond fearfully to a normally neutral stimulus. For example, people are born with a fear of loud noises. If a researcher plays a loud noise while flashing a light, her subjects will quickly come to pair the flash with the negative experience of the loud noise. Later, the subjects will demonstrate measurable fear of a flash of light, even without the loud noise.

Such associations are reversible through a process called extinction. For example, if the same subjects are shown soothing images while the lights flash, they can eventually dissociate the flashes from the negative experience of the loud noises.