L9.5 - Techniques

Question 1

When are invasive perturbations used?

Answer 1

in clinical cases

Question 2

Name two types of non-invasive perturbations

Answer 2

~ Transcranial magnetic stimulation (TMS)

~ Transcranial direct-current stimulation (tDCS)

Question 3

TMS

Answer 3

Transcranial magnetic stimulation
~ electric current in coil generates magnetic field
~ magnetic field generates focal electric field in brain
~ depolarises neurons locally
~ briefly interferes with cognitive processing
~ stimulus needs to follow pulse by 70-130ms for participant to be unable to recognise it
~ devise looks like number 8

Question 4

TMS pros

Answer 4

~ non-invasive
~ good temporal and spacial resolution
~ harmless
~ subjects act as their own control

Question 5

TMS cons

Answer 5

~ cortical effect - doesn’t reach deep brain areas

~ neurophysiological effect not clear

Question 6

tDCS

Answer 6

Transcranial direct-current stimulation
~ low-level current that results in action potentials under the anodes
~ hyperpolarisation (inhibited activity) under cathodes

Question 7

tDCS pros

Answer 7

~ non-invasive
~ poor spacial resolution
~ cheap + portable
~ subjects act as their won controls
~ clinical applications (depression)

Question 8

tDCS cons

Answer 8

~ Cortical effect - dines’t reach deeper brain areas

~ neurophysiological effect not clear

Question 9

Computed Tomography (CT)

Answer 9

~ 3D construction computed from multiple 2D X-ray images from all angles
~ low resolution, low precision but good at finding tumours

Question 10

Magnetic resonance imaging (MRI)

Answer 10

~ measures presence of water (73%) in brain - specifically protons within the water
~ combination of strong magnetic field + radio pulses leads to protons emitting radio signal
~ MRI picks ups he radio waves
~ high resolution

Question 11

Diffusion tensor imaging

Answer 11

~ MRI variant
~ MRI equipment can be ‘tuned’ to detect water diffusion
~ diffusion in the bran is anisotropic
~ water diffusion is highest within axons (water pipes)
~ myelin sheath creates a tight lipid boundary
~ high resolution

Question 12

anisotropic

Answer 12

restricted

Question 13

Problems with real data

Answer 13

~ invasive recordings –> only record activity in small samples, no access to whole system
~ non-invasive recording –> no access to individual neurones
~ no access to many variables e.g. synaptic strength

Question 14

General scheme of modelling

Answer 14

~ experiment
~ data (link to S&A)
~ define variables and parameters
~ build model
~ simulate and analyse (computers)
~ repeat

Question 15

What are the markers of model success? (3)

Answer 15

1. does the model explain existing data?
2. does it produce correct predictions?
3. does it give us new insight into what is going on?

Question 16

How do you counteract the complexity of the brain when creating models?

Answer 16

~ make a simpler version, retaining features which may be important for whatever is to be explained
~ full understanding of simpler system is possible

Question 17

Who introduces the current axon model?

Answer 17

Hodgkin & Huxley (1952)

Question 18

The virtual brain project

Answer 18

~ first open simulation of the human brain based on individual large-scale connectivity
~ goal = to explain brain activity
~ current emphasis = modelling he brain’s ‘resting state’