Task 5

Question 1

What is structural imaging?

Answer 1

based on different types of tissue [skull, white matter, grey matter] having differet physiological properties

-> This information can be used to construct static maps of the brain

Question 2

What is functional imaging ?

Answer 2

based on the assumption that neural activity produces local physiological changes in that region of the brain

-> results in dynamic maps of the moment-to-moment activity of the brain during a task

Question 3

What is PET?

Answer 3

• based on blood volume (= indirect)
• involves radioactivity -> tracer
• participants scanned only once
• temporal resolution: 30 seconds (-> slower than fMRI)
• spatial resolution: 10mm (-> bigger than fMRI)
• must use a blocked design
• sensitive to the whole brain
• can use pharmacological tracers

Question 4

What are advantages of PET?

Answer 4

• less distortion around the air cavities (compared to fMRI)
• tracers can be used to follow specific pathways
• sensitive to the whole brain

Question 5

What are disadvantages of PET?

Answer 5

• MRI is less expensive (+ easier to maintain)
• invasive -> radioactive tracers
• individual´s cannot be tested repeatedly
• low spatial resolution (compared to MRI)
• poor temporal resolution (compared to ERP)
• indirect measure
• interpretation difficulties (correlation ≠ causation)

Question 6

What is MRI ?

Answer 6

• structurally depicting the brain through magnetic fields caused by spinning protons (of hydrogen nuclei)
• creating 3D images

Question 7

What is fMRI?

Answer 7

• exploits the increase of local blood flow in active parts of the brain
• deoxygenated hemoglobin is paramagnet (weakly magnetic within a magnetic field) -> oxygenated hemoglobin is not
• detectors measure the BOLD signal
• an active brain area results in an increase in the ratio of oxygenated to deoxygenated hemoglobin

Question 8

What are advantages of fMRI ?

Answer 8

• scanners are less expansive (compared to PET)
• non-invasive -> it is possible to measure participants repeatedly
• better spatial resolution (than PET and CT)
• can be adopted for use in detecting the changes in blood oxygenation associated in neural activity

Question 9

What are disadvantages of fMRI ?

Answer 9

• poor temporal resolution (compared to ERP)
• indirect measure
• interpretation difficulties (correlation ≠ causation)

Question 10

What is BOLD contrast?

Question 11

What is preprocessing?

Question 12

What is BOLD?

Answer 12

• blood oxgen level-dependent
• ratio of oxygenated and deoxygenated hemoglobin
• signal increases are proportional to the underlying neuronal activity
• depends on source: using magnetic field gravity to vary the strength of the magnetic field
• depends on its strength: the number of spins involved allowing the amount of water to be determined at any point within the body
• depends on rate at which the signal decays: the number of factors describing the interaction of the spins with their surroundings

Question 13

What is the hemodynamic response function?

Answer 13

• maps the way that the BOLD signal evolves over time in response to an increase in neural activity
• Initial dip: as neurons consume oxygen -> small rise in the amount of deoxyhaemoglobin = reduction of BOLD signal
• Overcompensation: increase in blood flow in response to the increased consumption of oxygen -> increase > increased consumption of oxygen = increase of BOLD (measured in fMRI)
• undershoot: blood flow and oxygen consumption dip before returing to the original levels -> possibly due to venous system relaxation causing a temporary increase in deoxyhaemoglobin

Question 14

What are Berman´s fMRI approaches? In what ways can fMRI be used in research?

Answer 14

• studies of localisation: discovering brain behaviour correlations (helps understanding the normal organisation of modules + predicting deficits in case of brain damage)
• studies of commonalities in brain activation: if two tasks lead to activation of common brain areas, then those tasks are likely to share some process
• studies of distinctiveness in brain activation:
• documenting individual differences
• testing psychological models: testing model predictions

Question 15

How does PET work?

Answer 15

• a radioactive substace (=tracer) is introduced into the bloodstream
• the radiation emitted from this tracer is motored
• radioactive isotopes of the tracer rapidly decay, by emitting a positron from their nuclei
• when a positron collides with an elextron: two photons (gamma rays) are created
• those photons move in opposing directions and pass through brain tissue, skull, and scalp
• PET scaner determines where the collision took place -> gamma ray detector
• more blood flow = more radiation