chapter 7: imaging the brain's activity

Question 1

Single-cell recording techniques are good for recording (graded/action) potentials.

Answer 1

action

Question 2

Which recording methods are used to observe graded potentials?

Answer 2

Electroencephalography (EEG), event-related potential recordings (ERP), magnetoencephalography (MEG).

Question 3

What are graded potentials?

Answer 3

A collection of individual action potentials, postsynaptic potentials, etc. all graded and measured together. They indicate localized brain activity via electrical signalling.

Question 4

What method of recording the brain’s electrical activity shows how neurons are tuned to specific stimuli?

Answer 4

Single-cell recording.

Question 5

Which recording method summarizes the electrical activity of neurons within specific regions of the brain in a polygraph?

Answer 5

Electroencephalography (EEG).

Question 6

Which pattern of brain waves correlates with/indicates a state of alertness? Describe their frequency amplitude, and coherence.

Answer 6

Beta waves; high-frequency, low-amplitude, low coherence.

Question 7

Which pattern of brain waves correlates with/indicates a state of relaxation? Describe their frequency and amplitude.

Answer 7

Alpha waves; low-frequency, high-amplitude, high coherence.

Question 8

Which pattern of brain waves correlates with/indicates a state of drowsiness/light sleep? Describe their frequency and amplitude.

Answer 8

Theta waves; low-frequency, medium amplitude, high coherence.

Question 9

Which pattern of brain waves correlates with/indicates a state of deep sleep? Describe their frequency and amplitude.

Answer 9

Delta waves; very low frequency, very high amplitude, high coherence.

Question 10

What kind of brain activity is associated with each sleep stage?

Answer 10

Stage 1: theta waves, drowsiness, light sleep
Stage 2: sleep spindles, k-complexes (high-amplitude delta waves)
Stages 3 and 4: delta waves
Stage 5: REM, mixed brain wave signals

Question 11

How is EEG used diagnostically with brain injury and epilepsy?

Answer 11

Used in identification of abnormal brain signals.

partial seizure: coordinated activity limited to some regions of brain

generalized seizure: abnormal activity spread over entire brain

Question 12

What are the symptoms of the tonic and clonic phases of generalized seizures?

Answer 12

tonic phase: loss of consciousness, breathing stops

clonic phase: stereotyped motor behaviour, muscle spasms

Question 13

What is coherence theory and how does high vs low coherence manifest?

Answer 13

Coherence theory: measure of correlation between EEG activity (brain states, brain wave phase correlation) and behaviour

high coherence: low-frequency, high-amplitude waves.
associated with many neurons firing at the same time, low cognitive load

low coherence: high frequency, low-amplitude waves.
associated with many neurons firing at different times, actively processing information

Question 14

What is time-locking?

Answer 14

In ERPs, stimulus presentation sets time t = 0, changes recorded from that time. Findings are recorded and averaged over repeated presentations.

Question 15

How does magnetoencephalography work

Answer 15

Electrical charges moving along neuron generate magnetic field, which is then detected and mapped by SQUIDS (superconducting quantum interference devices)

Question 16

Describe the two brain stimulation techniques (covered in the chapter).

Answer 16

Deep Brain Stimulation (DBS):
Electrodes implanted into region of interest, region is stimulated a different frequencies to treat clinical conditions

Transcranial Magnetic Stimulation (TMS):
Magnetic field used to cause movement in electrical charges of adjacent neurons. TMS used to stimulate or inactivate neurons to clinically treat pain, movement disorders, depression.

Question 17

What are the limitations of x-ray imaging, and how do pneumoencephalography and angiography help?

Answer 17

Traditional x-ray only provides image of structure, main contrast only between bone and tissue, water not visible.

Pneumoencephalography replaces the CSF with air, allows for greater contrast in imaging ventricles

Angiography injects tracer into blood supply that absorbs x-rays, results in higher resolution image of circulatory system in target area

Question 18

What is computed tomography (CT)?

Answer 18

A static brain imaging technique that captures multiple x-ray images of the brain at multiple angles, which are then compiled into a 3D model of the brain via computer software.

Question 19

What is a voxel?

Answer 19

A 3D unit of measure for the smallest resolution discernible in a given measurement technique. For example, 1 cubic millimetre for CT scans

Question 20

MRI, CT, X-Ray imaging, and DTI are all examples of __________ or __________ imaging.

Answer 20

static, structural

Question 21

PET, EEG, ERP, fMRI, and TMS are all examples of __________ or __________ imaging.

Answer 21

dynamic, functional

Question 22

Which functional brain imaging technique involves injecting a radioactive tracer into circulatory system and measuring metabolically active areas?

Answer 22

Positron Emission Tomography (PET).

Question 23

In the context of functional brain imaging, describe the process of subtraction.

Answer 23

Subtraction is used to isolate brain activity related to task of interest. Multiple experimental and control conditions are imaged, the differences are compiled to create the mean difference image.

Question 24

What are Diffusion Tensor Imaging (DTI) and DTI tractography?

Answer 24

DTI uses the polarity of water molecules to map water’s movement.

DTI tractography uses DTI to map tracts (pathways) throughout the brain by inferring the direction and orientation of axons.

Question 25

How does magnetic resonance imaging (MRI) image the brain? What are T1 and T2 in the context of MRI?

Answer 25

MRI uses a strong magnetic field to orient protons in the brain’s water content.

The time taken for protons to orient to the magnetic field (T1), and the time taken for them to desynchronize (T2) indicate water content in different parts of the brain.

Question 26

How does fMRI functionally image the brain? What is a BOLD signal?

Answer 26

functional magnetic resonance imaging (fMRI) maps and contrasts oxygenated vs deoxygenated hemoglobin in the brain to indicate regional metabolic demand.

Blood oxygen level-dependent contrast (BOLD) signals reveals regions that are more active via slower T2 of oxyhemoglobin than deoxyhemoglobin.

Question 27

What are the diagnostic and general uses of rs-fMRI?

Answer 27

Resting-state functional magnetic resonance imaging is useful in diagnosing underlying brain conditions at rest such as Alzheimer’s disease.

In general, it is also used for research on structural brain connections: for example, characterizing cognitive processes of learning, or disease states.

Question 28

How does Optical Tomography work (e.g. fNIRS)?

Answer 28

Functional near-infrared spectroscopy (fNIRS) shines near-infrared light through the skull to detect light refracted by blood (difference in refraction between oxy vs deoxyhemoglobin).