Lecture 20

Question 1

What is diffusor tensor imaging?

Answer 1

Detects directional movement of water molecules to image nerve fibre pathways in the brain (structural imaging).

Question 2

What is a connectome?

Answer 2

A comprehensive map of neural connections in the brain

Question 3

What is the human connectome project?

Answer 3

Aim is to build a network model of the human brain in healthy subjects-compare the normal network to those suffering from a number of disease states including Alzheimers, MS, Autism, schizophrenia. Concern is about major pathways.

Question 4

How many neurons does C. Elegans have and how long did it take us to figure out every single connection?

Answer 4

302 neurons, 12 years to complete.

Question 5

How many neurons does the human brain have and how long would it take us to figure out every single connection?

Answer 5

Neocortex 10 billion neurons, 100 trillion connections. Around 397 million years to complete a whole connectome map.

Question 6

How does an fMRI differ from an MRI?

Answer 6

Infers brain activity-provides spatial depiction of some process that is at least indirectly related to brain activity.

Question 7

How is an fMRI measured?

Answer 7

Indirectly using blood oxygenation- changes in ratio of oxygenated blood vs deoxygenated.

Question 8

Why would we measure blood oxygenation? (4 reasons)

Answer 8

1) Onset of a stimulus changes local blood oxygenation
2) More cellular activity requires more oxygen in the local area
3) Changes in the oxygenation of blood alter magnetic properties of the hydrogen protons
4) We can convert this into a visual signal.

Question 9

How does the onset of a stimulus change local blood oxygenation?

Answer 9

Decrease in oxygen initially then an OVERSHOOT after the stimulus

Question 10

What does it mean when something is dephased?

Answer 10

Anything that changes the field at 1 proton will cause it to dephase and give off less of an echo.

Question 11

What are the properties of oxygenated hemoglobin?

Answer 11

Diamagnetic- no magnetic effects on surrounding molecules

Question 12

What are the properties of deoxygenated hemoglobin?

Answer 12

Paramagnetic (gives less MR echo because protons dephase quickly). Where there’s oxygen, then, theres a bright spot of activity.

Question 13

How do we actually end up seeing the activated brain region?

Answer 13

Through coregistration of MRI and fMRI

Question 14

What is BOLD?

Answer 14

Blood oxygenated level dependent contrast- what an fMRI really sees.

Question 15

What is a block design?

Answer 15

How fMRI activity is designed- alternation between active and rest conditions. Subtract the rest state from the active state.

Question 16

What is positron emission tomography?

Answer 16

Measures the uptake of oxygen and glucose by brain tissue (metabolic activity). Breakdown of radioactive substance into positrons-photons.

Question 17

What are some advantages of the PET scan?

Answer 17

Can detect the decay of hundreds of radiochemicals, mapping of wide range of activity (changes and conditions), can detect relative amounts of a given neurotransmitter, density of receptors, metabolic activities associated with learning, and degenerative processes.

Question 18

What are the disadvantages of PET scan?

Answer 18

Expensive (2.5-6million). Requires cyclotron/particle accelorator.

Question 19

What is microdialysis?

Answer 19

Used to determine the chemical constituents of extracellular fluid-direct measures of brains chemistry.