Читать книгу Lifespan Development - Tara L. Kuther - Страница 87

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Modern brain imaging techniques enable us to measure brain activity as individuals think and solve problems.

Phanie / Alamy Stock Photo

What parts of the brain are active when we solve problems or feel emotions? How does the brain change with development? Until recently, the brain was a mystery. Over the past hundred years, researchers have devised several ways of studying brain activity that have increased our understanding of how the brain functions and how it develops.

The earliest instrument created to measure brain activity was the electroencephalogram, first used with humans in the 1920s (Collura, 1993). Electroencephalography (EEG) measures electrical activity patterns produced by the brain via electrodes placed on the scalp. Researchers study fluctuations in activity that occur when participants are presented with stimuli or when they sleep. EEG recordings measure electrical activity in the brain, but they do not provide information about the location of activity.

Not until the invention of positron emission tomography (PET) in the early 1950s did researchers obtain the first glimpse of the inner workings of the brain (Portnow, Vaillancourt, & Okun, 2013). Researchers inject a small dose of radioactive material into the participant’s bloodstream and detected by the PET scan. The radioactive material enables researchers to monitor the flow of blood. Blood flows more readily to active areas of the brain, and the resulting images can illustrate what parts of the brain are active as participants view stimuli and solve problems. Developed in 1971, computerized tomography, known as the CT scan, produces X-ray images of brain structures (Cierniak, 2011). A movable X-ray unit rotates around a person’s head as it records images of the brain (Herman, 2009). The images are then combined to make a three-dimensional picture of the person’s brain, providing images of bone, brain vasculature, and tissue. CT scans can provide researchers with information about the density of brain structures to illustrate, for example, how the thickness of the cortex changes with development.

Functional magnetic resonance imaging (fMRI) measures brain activity by monitoring changes in blood flow in the brain (Bandettini, 2012). Developed in the 1990s, MRI machines house a powerful magnet that uses radio waves and to measure blood oxygen level. Active areas of the brain require more oxygen-rich blood. Like PET scans, fMRI enables researchers to determine what parts of the brain are active as individuals complete cognitive tasks. However, fMRI images are much more detailed than PET scans. An important advantage of fMRI over PET scans is that it does not rely on radioactive molecules, which can only be administered a few times before becoming unsafe.

Another imaging process, called diffusion tensor imaging (DTI), uses an MRI machine to track how water molecules move in and around the fibers connecting different parts of the brain (Soares, Marques, Alves, & Sousa, 2013). DTI gauges the thickness and density of the brain’s connections, permitting researchers to measure the brain’s white matter and determine changes that occur with development and with age-related illnesses, such as Alzheimer’s disease.