Chp 3: Brain Imaging Flashcards
EEG - Electroencephalography
- Use electrode to understand the brain,
- Electrodes placed on the scalp, device records the pattern of brain waves
- Bonnets can vary number of electrodes
EEG Standard Electrode Positions
- F (frontal)
- T (temporal)
- C (central)
- O (occipital)
- A (auricle = ear)
right: even no./ left: odd
Synchronous Activity (EEG)
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
EEG Rhythms (4)
Theta
Delta
Alpha
Beta
Theta EEG
High amplitude waves:
Theta: initial levels of sleep
related to sleep/ drowsy
Delta EEG
Deeper waves than theta
Decreasing levels of consciousness
sleep/dreaming
Alpha EEG
-not asleep but relaxed
-Low amplitude but emergence of synchronisation
-More neurons doin the same thing
Beta EEG
-not very synchronised
-cog activity: calculations, thinking
Epilepsy
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
Epilepsy – two categories
Generalised: involves whole brain
Partial: doesn’t involve whole brain
2 types of Generalised Seizures
Grand Mal
Petit Mal
Grand Mal Seizure (5)
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
Petit Mal (4)
◦ 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
2 types of Partial Seizures
Simple
Complex
Simple Partial Seizures
◦ symptoms are primarily sensory or motor or both
◦ symptoms spread as epileptic discharge spreads
Complex Partial Seizure
– often restricted to the temporal lobes (temporal lobe epilepsy)
◦ patient engages in compulsive and repetitive simple behaviors - automatisms
Computerized Tomography (CT Scan)
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
Magnetic Resonance Imaging (MRI)
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
How does the MRI process go? (11)
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
Perturbation: MRI
lining them up in the magnet and pushing them over
Functional Magnetic Resonance Imaging (fMRI)
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
Use fMRI to talk to patients in vegetative state
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
Diffusion Tensor Imaging (DTI)
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
Anisotropy
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
hypoxia
low levels of oxygen in your body tissues
Cyanosis
turning blue from excessive extraction of oxygen from blood during the convulsion
