Chp 3: Brain Imaging

Question 1

EEG - Electroencephalography

Answer 1

• Use electrode to understand the brain,
• Electrodes placed on the scalp, device records the pattern of brain waves
• Bonnets can vary number of electrodes

Question 2

EEG Standard Electrode Positions

Answer 2

• F (frontal)
• T (temporal)
• C (central)
• O (occipital)
• A (auricle = ear)

right: even no./ left: odd

Question 3

Synchronous Activity (EEG)

Answer 3

Irregular activity: partial
All 6 neurons are doing sth diff
- Summed signal: a little blip

If all neurons doing the same thing:
Peak is much higher

Amplitude- synchronicity

if synchronised and high amplitude: generalised seizure

Question 4

EEG Rhythms (4)

Answer 4

Theta
Delta
Alpha
Beta

Question 5

Theta EEG

Answer 5

High amplitude waves:
Theta: initial levels of sleep
related to sleep/ drowsy

Question 6

Delta EEG

Answer 6

Deeper waves than theta
Decreasing levels of consciousness
sleep/dreaming

Question 7

Alpha EEG

Answer 7

-not asleep but relaxed
-Low amplitude but emergence of synchronisation
-More neurons doin the same thing

Question 8

Beta EEG

Answer 8

-not very synchronised
-cog activity: calculations, thinking

Question 9

Epilepsy

Answer 9

— Primary symptom is seizures, but not all who have seizures have epilepsy
◦ 7-10% of the general population has had a seizure
— Epileptics have seizures generated by their own brain dysfunction
- Affects about 1% of the population
— Difficult to diagnose due to the diversity and complexity of epileptic
seizures

Question 10

Epilepsy – two categories

Answer 10

Generalised: involves whole brain
Partial: doesn’t involve whole brain

Question 11

2 types of Generalised Seizures

Answer 11

Grand Mal
Petit Mal

Question 12

Grand Mal Seizure (5)

Answer 12

Loss of consciousness and equilibrium

-Tonic-clonic convulsions
– -rigidity (tonus) and tremors (clonus)
–- Cyanosis – turning blue from excessive extraction of oxygen from blood during the convulsion

Resulting hypoxia may cause brain damage

Phases:
-Tonic
-Clonic
-Postictal

Question 13

Petit Mal (4)

Answer 13

◦ not associated with convulsions
◦ a disruption of consciousness associated with a cessation of ongoing behavior
No tonus clonus
- Whatever they do stops for a bit

Question 14

2 types of Partial Seizures

Answer 14

Simple
Complex

Question 15

Simple Partial Seizures

Answer 15

◦ symptoms are primarily sensory or motor or both
◦ symptoms spread as epileptic discharge spreads

Question 16

Complex Partial Seizure

Answer 16

– often restricted to the temporal lobes (temporal lobe epilepsy)
◦ patient engages in compulsive and repetitive simple behaviors - automatisms

Question 17

Computerized Tomography (CT Scan)

Answer 17

— A series of x-ray views of the body/brain are taken from many
different angles and then are combined together by a computer to create cross-sectional images of area of interest and build up a 3D image
— Resolution – can distinguish objects 5mm apart

Question 18

Magnetic Resonance Imaging (MRI)

Answer 18

— Uses a large magnet and a specific radio frequency pulse to generate a brain signal that produces an image

— Magnets - 1.5 teslas in strength
- Tesla = 10 000 guass
- Earth’s magnetic field = 0.5 gauss
- So 1.5 Tesla is a Big Magnet

— High resolution, voxel size better than 1mm3

Question 19

How does the MRI process go? (11)

Answer 19

Based on the idea that a hydrogen atom’s nucleus, which has a single proton, acts like a spinning bar magnet

—Usually oriented at random in tissue
- all tissue contains water and that contains hydrogen

—In a magnetic field the spinning protons orient accordingly and line up in parallel

—Spinning protons generate an electrical current

— A recorder sensitive to such electrical current can produce an image of the brain based on differences between areas in proton density

— Proton density varies amongst nervous tissue
- CSF, myelin, neurons

— Images can also be constructed following proton perturbation

— Brief radiofrequency pulse applied to atoms already vertically aligned in the magnet

— This pulse forms a second magnetic field which pushes protons over on their sides and are said to be tipped

—Differential rates of relaxation from this perturbation over various nervous tissues can be used to generate an image
of the brain
- then tipped over to T2, when turned off it will return to T1 (vertical)
- T2 (horizontal) tend to be better at detecting damage

Question 20

Perturbation: MRI

Answer 20

lining them up in the magnet and pushing them over

Question 21

Functional Magnetic Resonance Imaging (fMRI)

Answer 21

— As neurons become active, they increase their use of oxygen and increase blood flow to the area

— Before neural activation deoxyhemoglobin and oxyhemoglobin are about equal, after activation the amount of oxyhemoglobin is higher

— The different relaxation curves for protons in oxygenated and unoxygenated blood
provides means for obtaining a functional image

BOLD signal: Blood Oxygen Level Dependent Signal

Question 22

Use fMRI to talk to patients in vegetative state

Answer 22

As blood flows to the brain, light up
- Work out what they thinking

Consistencies of the brain:
- All have a different part of the brain being activated
- Imagining playing tennis
- Imagining going around the house

Question 23

Diffusion Tensor Imaging (DTI)

Answer 23

— MRI method that images fiber pathways by detecting directional movement of water molecules
— Movement tends to follow the longitudinal axis, referred to as
anisotropy
— Can detect degeneration of axons, distortion of fibers, and damage to fibers

Question 24

Anisotropy

Answer 24

Water moving in no particular direction
- force the particles to move in one direction
-
When take pic of the brain ask the voxel if there is water moving in any particular direction

• Then start to build up the pathway
• Tractography

Question 25

hypoxia

Answer 25

low levels of oxygen in your body tissues

Question 26

Cyanosis

Answer 26

turning blue from excessive extraction of oxygen from blood during the convulsion