Lecture 7

Question 1

Manipulating brain-behaviour interactions

Answer 1

DBS, TMS

Question 2

Measuring the brain’s electrical activity

Answer 2

EEG, MEG

Question 3

Anatomical imaging techniques

Answer 3

CT, MRI

Question 4

Functional brain imaging

Answer 4

fMRI, fNRI, PET

Question 5

Postmortem examination in humans with brain lesions

Answer 5

• Focus on the substantia nigra
• Healthy SN will show cell bodies of dopamine neurons
• Weakened SN will show degenerated dopamine neurons - contributing to symptoms of Parkinson’s disease

Question 6

Neuropsychological testing of humans with brain lesions

Answer 6

• Examiner taps out a sequence of blocks. The block numbers are visible in the examiner’s side of the board but not the participants side.
• Participants’ task is the trace between the two outlines of the star like looking at their hand in a mirror. Crossing a line constitutes an error.
• Participants’ task is to identify which picture they saw most recently.

Question 8

Brain research techniques (5)

Answer 8

• Spatial resolution
• Temporal resolution
• Invasiveness
• Anatomical (static)
• Functional (dynamic)

Question 9

Sterotaxic appartus

Answer 9

Allows targeting of a specific part of the brain.

• Psychosurgery (ablation, lesions, gamma “knife” radiation)
• Deep brain stimulation

Question 10

Psychosurgery

Answer 10

1. Irreversible lesion techniques
2. Reversible lesion techniques

Question 11

Irreversible lesion techniques

Answer 11

• Electrolytic
• Neurotoxic
• High-intensity focused ultrasound (HIFU)
• Permanent lesions lead to compensation (neuroplasticity)

Question 12

Reversible lesion techniques

Answer 12

• Regional cooling
• Local administration of a GABA agonist

Question 13

Electrolytic

Answer 13

Burning by passing current through electrode

Question 14

Neurotoxic

Answer 14

Intoxication through infusion of neuron-killing chemical

Question 15

High intensity focused ultrasound

Answer 15

Heating with focused ultrasonic beams

Question 16

Deep-brain stimulation (DBS)

Answer 16

Electrodes implanted in the brain stimulate a target area with continuous pulses of low-voltage electrical current to facilitate behaviour

Question 17

Four major techniques for measuring the brains electrical activity

Answer 17

1. Single cell recording (action potentials)
2. EEGs (graded potentials)
3. ERPs
4. MEGs

Question 18

Single cell recording

Answer 18

• Extracellular: record electrical activity of multiple neurons at once (clusters)
• Intracellular: allows study and recording of electrical activity of a single neuron

Main disadvantage is that it works well for dish grown neurons but requires surgery when recording brain cells in living organisms

Question 19

EEG

Answer 19

Measures graded potentials (EPSP & IPSP) of similarly orientated neurons that are simultaneously active

• High temporal resolution
• Poor spatial resolution

Question 20

Why can EEG not record action potentials?

Answer 20

Potentials can only be recorded at the scalp if they occur at approximately the same time across thousands or millions of neurons.

• Action potentials have very short duration (1ms)
• Neurons rarely fire at exactly the same time
  Axons are relatively randomly orientated

Question 21

EEG recording postsynaptic potentials

Answer 21

• EPSPs and IPSPs typically last longer (10s-100s ms)
• EPSPs and IPSPs occur instantaneously
• EPSPs and IPSPs occur at dendrites and cell bodies, which are typically orientated perpendicular to the surface of the cortex

NB: graded potentials recorded at the scalp reflect summed EPSPs and IPSPs

Question 22

MEGs

Answer 22

Magnetic counterpart of EEG and ERP.
Main disadvantage: more expensive than EEG, ERP

• High temporal resolution
• High spatial resolution

Question 23

Why does MEG have a higher spatial resolution than EEG?

Answer 23

Magnetic waves undergo less distortion through brain tissue and scalp compared to EEG or ERP

Question 24

Source localisation in EEG and MEG

Answer 24

Record data first, the ntry to infer what sources ‘caused’ data.

Inverse problem: no unique solution - multiple sources might yield the same data
Possible solutions can be derived using models involving prior knowledge of brain functioning

Question 25

CT scan

Answer 25

- Low temporal resolution - High spatial resolution Appropriate for localising bone fractures, brain tumours and lesions. - Grey and white matter cannot be distinguished on CT scan. - Main advantage: relatively inexpensive - Main disadvantage: uses X-ray radiation.

Question 26

MRI

Answer 26

Magnetic counterpart of CT More expensive, slower compared to CT. Based on the principle that hydrogen atoms behave like spinning bar magnets in the presence of a magnetic field. - Low temporal resolution - High spatial resolution - Disadvantage: subjects must lie motionless in a noisy tube for a long time - NB: grey and white matter can be distinguished

Question 27

DTI

Answer 27

MRI method that detects directional movements of water molecules - Water can move relatively free along the axon but less freely across cell membranes - Used to create visual images of nerve fibre tracts in the brain and identify changes in axon myelination

Question 28

MRA

Answer 28

MRI focused on blood vessels

Question 29

fMRI

Answer 29

Functional MRI When the brain region is active, the amount of blood, oxygen and glucose flowing to the region increases. NB: oxygen-rich blood is less magnetic than oxygen poor blood. - Low temporal resolution - High spatial resolution

Question 30

fNIRS

Answer 30

Functional near-infrared spectroscopy - Good temporal resolution - Fairly high spatial resolution - Main advantage: inexpensive, noninvasive Main disadvantage: max dept of 2cm so only superficial layers.

Question 31

PET

Answer 31

Positron emission tomography Used to study metabolic activity of the brain cells by injecting a small amount of water labeled with radioactive molecules into the blood stream. - Low temporal resolution - Fairly high spatial resolution - Often combined with CT, MRI or EEG. - NB: biggest disadvantage: required preparation of radiochemicals = very expensive.