Chapter 113. Scanning the Brain

Learning Objectives

brain
largest part of the central nervous system; consists of about 80 billion neurons organized into networks for processing sensory information, storing memories, and controlling behavior
cognitive
refers to the mental activities involved in perceiving, remembering, thinking, and reasoning
CT (computed tomography) scan
method of producing a low-resolution scan of brain structure by combining multiple x-rays from different directions; most useful for detecting brain tumors and strokes
electroencephalogram (EEG)
method of measuring the electrical activity of the brain, as recorded from electrodes on the scalp; most useful for tracking moment-to-moment changes in the activity of different areas of the brain
epilepsy
a neurological disorder associated with abnormal synchronized electrical activity in the brain, which can produce seizures
fMRI (functional magnetic resonance imaging)
method of producing a high-resolution scan of brain activity by tracking the flow of oxygen; most useful for identifying the specific brain regions that are most active during different cognitive tasks
glucose
type of sugar found in blood; main fuel burned by muscles and brain cells; low level of glucose triggers hunger
MEG (magnetoencephalography)
method of producing a high-resolution scan of brain activity by measuring magnetic fields generated by the electrical activity of the brain; most useful for tracking moment-to-moment changes in the activity of small areas of the brain
MRI (magnetic resonance imaging)
method of producing a high-resolution scan of brain structure by using radio waves to disrupt magnetically aligned atoms in the brain; most useful for detecting small abnormalities in brain tissue
neuron
a single nerve cell, forming the basic unit of the nervous system
PET (positron emission tomography)
method of producing a low-resolution scan of brain activity by tracking the flow of glucose; most useful for comparing the broad pattern of brain activity during different cognitive tasks
seizures
brief episode of uncontrolled jerking movements (convulsions) and/or loss of conscious awareness; most often associated with epilepsy
Scanning the Brain
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Learning Objectives:

Describe the major methods of studying the structure and functioning of the brain.

Contrast the purpose of each tool for studying the brain.

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1. The human brain is hidden within the skull, but its shape and activity can be observed and measured with the modern tools of neuroscience. Bombarding the brain with x-rays and magnetic pulses can reveal the structure of each brain region and can detect abnormalities, including tumors and damage from strokes. The faint electrical and magnetic signals generated by individual neurons, as well as changes in blood flow to brain areas, can be captured and analyzed to paint a picture of the moment-by-moment pattern of brain activity.

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2. The oldest of these tools is the electroencephalogram (EEG)—an amplified recording of the electrical signals generated by the synchronized activity of thousands of neurons in each region of the brain. These “brain waves” are measured by electrodes placed on the scalp. EEG is used extensively in research on sleep, as it can track the changes in overall brain activity as the sleeper moves through the stages of sleep. EEG can also identify the location of seizures in a patient with epilepsy.

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The image is a black and white x-ray photograph of the brain.  It shows a horizontal slice of the brain, where the skull is white and the inside of the brain is gray.  A large black mass at the front of the brain represents a cyst pressing against the frontal lobe.  A fuzzy dark gray mass near the back of the brain represents damage from a stroke in the occipital lobe.
Neil Borden/Getty Images

3. Next came a type of brain scan called CT (computed tomography). This is a series of x-ray photographs taken from different angles in the same plane and combined by computer to create a single image that shows a “slice” through the brain. CT scans provide a crude view of the structure of the brain, and are used mainly to identify abnormalities in brain tissue caused by cancer, stroke, or fluid-filled cysts.

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There are images of two PET scans of the brain. The first scan has high glucose utilization on the sides of the brain in the temporal lobes.  This is noticeable by the red areas on the scan and demonstrates that someone is listening.  The second scan has high glucose utilization at the back of the brain in the occipital lobe.  This is noticeable by the red area on the scan and demonstrates that someone is looking.  The areas with low glucose utilization in the brain are green and blue.

4. The brain requires glucose as fuel. Researchers developed a way of injecting a radioactive form of glucose into the bloodstream, and then using PET (positron emission tomography) to detect where that glucose flows while the brain performs a cognitive task. A PET scan provides a visual display of brain activity that shows areas of high glucose use in yellow and red, while areas of low glucose use are shown in green and blue. These PET scan images demonstrate that “looking” activates the visual areas at the rear of the brain, while “listening” activates the auditory areas on the sides of the brain.

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The image is a vertical cross-section of the brain with the various components visible, such as the cerebral cortex, corpus callosum, cerebellum, brain stem, and more.  The curves of the cerebral cortex is visible as well as the detailed structures of the rest of the parts of the brain.
ZEPHYR/Science Photo Library/Getty Images

5. MRI (magnetic resonance imaging) provides the clearest, most detailed view of the individual structures within the brain. This technique uses radio waves to disrupt magnetically aligned atoms in the brain. As the atoms snap back into position, the scanner detects the movement and produces a computer-generated image at such high resolution that it looks like a textbook illustration. On this MRI image, can you recognize and name some of the important structures within the brain?

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The image is a side picture of the brain.  Different areas are highlighted showing higher levels of blood flow and oxygen.

6. A single MRI scan shows the structure of the brain, but also can detect the blood concentration of oxygen, another type of fuel that neurons require. By performing multiple MRI scans in quick succession, fMRI (functional magnetic resonance imaging) tracks changes in blood flow during different cognitive tasks. This scan shows that, when a person is engaged in a conversation, a high level of oxygen flows to the language areas of the brain.

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7. The newest method of brain scanning is called MEG (magnetoencephalography). It detects the activity of clusters of neurons in specific regions of the brain. Rather than measuring the neurons’ electrical signals directly, MEG uses multiple detectors around the head to measure the magnetic fields generated by that electrical activity. Like EEG, MEG can track moment-by-moment changes in brain activity, but does a better job than EEG in identifying the exact location of the activity.

Practice 1: Exploring Brain Scans

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Practice 1: Exploring Brain Scans

Roll over each of the types of brain scans to view a brief description.

CT SCAN

EEG

fMRI SCAN

MEG SCAN

MRI SCAN

PET SCAN

Key aspects:

CT (computed tomography) scan: low-resolution scan of brain structure, produced by combining multiple x-rays from different directions; most useful for detecting brain tumors and strokes

EEG (electroencephalogram): measures the electrical activity of the brain, as recorded from electrodes on the scalp; most useful for tracking moment-to-moment changes in the activity of different areas of the brain

fMRI (functional magnetic resonance imaging): high-resolution scan of brain activity produced by tracking the flow of oxygen; most useful for identifying the specific brain regions that are most active during different cognitive tasks

MEG (magnetoencephalography): high-resolution scan of brain activity produced by measuring magnetic fields generated by electrical activity of the brain; useful for tracking moment-to-moment activity changes in small areas of the brain

MRI (magnetic resonance imaging): high-resolution scan of brain structure produced by using radio waves to disrupt magnetically aligned atoms in the brain; most useful for detecting small abnormalities in brain tissue

PET (positron emission tomography): low-resolution scan of brain activity produced by tracking the flow of glucose; most useful for comparing the broad pattern of brain activity during different cognitive tasks

Practice 2: Recognizing Brain Scans

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Practice 2: Recognizing Brain Scans

Roll over each of the images to view the name of the brain scan along with a brief description.

Human head, MRI and 3D CT scans
This axial (cross sectional) CT of the head in a person with the sudden onset of visual loss shows a typical infarct in the right (on your left) occipital lobe. Incidentally noted is a typical arachnoid cyst in the right frontal region with bony remodellin
Description:

EEG (electroencephalogram): measures the electrical activity of the brain; typically shown as individual waves from each electrode

MRI (magnetic resonance imaging): high-resolution scan of brain structure; measures repositioning of magnetically aligned atoms; typically shown as monochrome side view or sagittal slice

CT (computed tomography) scan: low-resolution scan of brain structure; typically monochrome scan shown as horizontal slice of brain

fMRI (functional magnetic resonance imaging): high-resolution scan of brain activity; measures flow of oxygen; typically shown as small splotches of color superimposed on an MRI scan

PET (positron emission tomography): low-resolution scan of brain activity; measures flow of glucose; typically a horizontal slice with large splotches of bright colors

MEG (magnetoencephalography): high-resolution scan of brain activity; measures magnetic fields generated by electrical activity of the brain; typically shown as color splotches superimposed on a head

Quiz 1

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Quiz 1

Match the terms to their descriptions by dragging each colored circle to the appropriate gray circle. When all the circles have been placed, select the CHECK ANSWER button.

Select the NEXT button and move to Quiz 2.
Perhaps you should go back and review the types of brain scans.
CT (computed tomography) scan
EEG (electroencephalogram)
fMRI (functional magnetic resonance imaging)
MEG (magnetoencephalography)
MRI (magnetic resonance imaging)
PET (positron emission tomography)
measures the electrical activity of the brain, as recorded from electrodes on the scalp
high-resolution scan of brain structure produced by using radio waves to disrupt magnetically aligned atoms in the brain
low-resolution scan of brain structure, produced by combining multiple x-rays from different directions
high-resolution scan of brain activity produced by tracking the flow of oxygen
high-resolution scan of brain activity produced by measuring magnetic fields generated by electrical activity of the brain
low-resolution scan of brain activity produced by tracking the flow of glucose

Quiz 2

dnd_test

Quiz 2

Classify the types of brain scans by dragging each label to a gray area in the appropriate section of the chart. When all the labels have been placed, select the CHECK ANSWER button.

Perhaps you should go back and review the types of brain scans.
Select the NEXT button and move to the Conclusion.
Structure Activity
Rough
Detailed
CT scan
EEG
MRI scan
PET scan
MEG scan
fMRI scan

Conclusion

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