Class 5,6

Answer 1

Function x is disrupted by lesion to brain region Y, than Y supports function x (ex. fineas gage, HM, Broach (patient TAN))

Question 2

Brain lesioning logic

Answer 2

Function x is disrupted by lesion to brain region Y, than Y supports function x

suggests a causal role of brain region Y in function X

(ex. fineas gage, HM, Broach (patient TAN))

Question 3

Human vs non-human lesion studies

Answer 3

Question 4

Limitations of Lesioning

Answer 4

Is the brain region critical for the task?

Disconnection syndrome

Question 5

Disconnection syndrome

Answer 5

brain region X may not directly participate in function A, but may disconnect two brain regions that are critical for function A

Ex. Split brain patient - Severing the fibers of the corpus callosum leads to certain cognitive impairments BUT the corpus callosum does not carry out those
cognitive functions

Question 6

Split-brain patients and saying what see (and why)

Answer 6

Most people have language centers in left
hemisphere

The visual system is contralaterally organized:
left field of vision is represented in right hemisphere

Shown in L hemisphere, r Hem process, but language in L (cannot say what see) but can pick up (motor control is on R side)

Question 7

Logic/Issue of lesioning studies

Answer 7

Functions may be unrelated to brain region X itself, but related to keeping brain region X intact

Neuroplasticity, reorganizes and compensates for damage

Question 8

Double Dissociation

Answer 8

determine if 2 factors are independent

ex. Brochas area - speach production NOT comp
Werinchek - imarirs speach comp but NOT production

Question 9

Conduction aphasa

Answer 9

damage to arcutate fasciculus (white matter bundle of axions that connect brocha and wernicke;s area)

Question 10

TMS

Answer 10

most common, figure 8 looking, area stimulating in middle

Use localized magnetic field pulses to alter electrical activity of neurons

• TMS coils can activate or deactivate regions of neurons depending on stimulation frequency
• Can be used to determine causal role of brain region

Question 11

tDCS

Answer 11

Trancranial direct current stimulaiton

weak electral currnent between two patch electrodes

stimulation lower than TMS so can avoid adverse side effects

Can INC or DEC activity not compleet inhibit or stumulate
not as regonaly specific as TMS

Question 12

Anodal (tDCS)

Answer 12

Inc activity

Question 13

Cathodal (tDCS)

Answer 13

dec activity

Question 14

tACS

Answer 14

A varation of tDCS that also involves an oscillating current

Question 15

EEG

Answer 15

Measure voltage fluctuations from electrical activity of groups of neurons

NOT action potentals
electral activty through scalp
electroencephalogram

ERPs: brief changes in EEG time-locked to a stimulus event

Individual trials all have lots of background oscillation activity (noise), Take average of many trials to remove noise and get clean ERP signal

Question 16

Betta Band

Answer 16

higher freq

Question 17

Time-frequency analysis

Answer 17

amount of activity for a given frequency band

Question 18

Pro EEG

Answer 18

• Excellent temporal resolution
• ERPs associated with cognitive processes
• Much more affordable than fMRI or MEG

Question 19

Different frequency bands have been correlated with

Answer 19

different cognitive functions

Question 20

Con EEG

Answer 20

• Poor spatial localization
• Not entirely solved with source modeling
• Poor access to deeper brain structures (e.g. MTL)

Question 21

ECoG

Answer 21

Intracranial recording
• Electrode contact grids placed directly on the cortex

• Electrocorticography (ECoG)

• Cleaner signal than EEG, better spatial specificity
• However, invasive technique: recorded in epileptic patients who have grids implanted for medical purposes

Question 22

MEG

Answer 22

Functional brain imaging
• Records magnetic fields generated by electrical currents using SQUIDs (Superconducting quantum interfering devices)

• Excellent temporal resolution, good spatial resolution
• Magnetic signals less distorted by skull

• Can also see ERP-type responses using MEG
• Event-related (magnetic) fields
• To best use spatial information of MEG, structural information needed
• MRI scan used to localize MEG
• Requires a special magnetically shielded room
• Magnetic fields being measured are very small
• Set-up can be quite expensive

Question 23

In what ways are EEG and MEG similar?

Answer 23

• Both measure surface/scalp-level activity of groups of neurons
• Data can be analyzed similarly (e.g. with the event-related potential averaging method)
• Both have high temporal resolution for neural responses

Question 24

what are some considerations for when you’d use EEG over MEG?

Answer 24

• EEG is more portable and not as sensitive to small disruptions in magnetic field, so you can take it for more ‘field studies’
• EEG is also way cheaper, so if you’re strapped for a budget and still want time sensitive data

Question 25

CT Scan

Answer 25

Computerized Axial Tomography (CAT / CT) * Allows for localization of brain damage * Uses X-rays for visualization • Requires exposure to radiation * Different tissues have different densities * X-rays pass through fluid easily but are absorbed by higher densities like bone * Density gradient: CSF \< brain tissue \< blood \< bone

Question 26

MRI

Answer 26

Magnetic resonance imaging * Uses a large magnet measured in Tesla (strength of magnetic field) • 1 Tesla (T) = 10 000 Gauss • Earth’s magnetic field = 0.5 Gauss • 3T magnet = 60 000 times Earth’s field * Combined with radio frequency pulse

Question 27

How MRI Works

Answer 27

* Many organic elements in the body are magnetic * Hydrogen is the most abundant in the body • Protons spin around a random axis * When placed in magnetic field the protons become aligned in parallel * A radio frequency pulse is used to push protons out of alignment with magnetic field * The time it takes for protons to revert back to original orientation is measured through head coil * Protons relax at different rates in different tissues, which makes a gradient that can be reconstructed as an image

Question 28

DTI

Answer 28

Diffusion tensor imaging (DTI): measurement of connectivity * Uses slightly different MRI protocol based on what direction water diffuses in nerve fibers * **Based on axis of water diffusion, DTI models connectivity of white matter tracts: tractography maps**

Question 29

MRI vs. fMRI

Answer 29

* MRI: High resolution (1mm), one image * fMRI: Low resolution (~3mm), many images over time

Question 30

BOLD

Answer 30

used in fMRI BOLD: blood oxygen level-dependent • Neurons get oxygen from hemoglobin in red blood cells • When neuronal activity increases, blood flow increases to the area • More oxygenated blood flows to region • Differences in magnetism of blood depends on oxygenation • Make differences in MR signal • Use differences in signal to infer activity

Question 31

HR

Answer 31

Hemodynamic response **• Change in regional cerebral blood flow over time** * Slow response compared to the actual neural signal: * Neural response happens on the scale of milliseconds • HR starts after 2 seconds and peaks around 6-8 seconds after stimulus onset

Question 32

Block design

Answer 32

for fMRI Examine extended HR across the same trial type

Question 33

Event-related design

Answer 33

* HR for different, individual trials * Can examine trial-specific HR

Question 34

fMRI Analisis

Answer 34

* Detects change in signal from one condition to another * Must always contrast two images • Functional images subtracted from each other and superimposed onto anatomical image • Choice of baseline depends on research question

Question 35

MRI and fMRI: Pros

Answer 35

PROS: • Non-invasive • No radiation • Can do multiple scans on the same person • Excellent spatial resolution, temporal resolution is okay

Question 36

MRI and fMRI: Cons

Answer 36

CONS: • Very expensive • Correlational measure (in that what we see could be due to several different factors)

Question 37

PET

Answer 37

* Measures local changes in cerebral blood flow over a few minutes * Radioactive isotope tracers introduced into body • Isotopes rapidly decay, which is measured to produce signal

Question 38

PET Pros

Answer 38

* Tracking multiple metabolic processes * Can label specific neurotransmitters with isotopes that will go to receptor sites

Question 39

PET Cons

Answer 39

* Invasive: Radioactive isotopes * Can only be done limited number of times * Limited temporal resolution • Depends on half-life of isotope • E.g. oxygen-15 gives average of activity over 1.5 minutes

Question 40

Optical Imaging

Answer 40

* Laser of infrared light * Sensors detect distortions in light * Slow signal: measures absorption from blood * Fast signal: measures scattering of light related to neuronal firing * High temporal and spatial resolution * Only cortical activity can be detected • Too much light gets absorbed at deeper levels to be measured

Question 41

Simultaneous EEG - fMRI

Answer 41

Originally applied to improve localization of sources for epileptic EEG activity (Ives et al., 1993) • Combining the relative strengths of each modality

Question 42

Disconnection syndrome

Answer 42

general term for a collection of neurological symptoms caused -- via lesions to *associational or commissural nerve fibres* -- by damage to the white matter axons of communication pathways in the cerebrum

Question 43

Density gradient:

Answer 43

CSF \< brain tissue \< blood \< bone