Chapter 2: Techniques used to study the brain

Question 1

Describe the CAT scan (computerized axial tomography).

Answer 1

Slides into the cylindrical apparatus where a moving source of x-rays scans the subject’s head. This reveals structural features of the brain. It’s strengthened by it’s non-invasive nature and it records images of both hard and soft tissue and blood vessels. Additionally, it is a quick process and can scan subjects with metal implants. The CAT scan is limited by a limited amount of radiation exposure.

Question 2

MRI (magnetic resonance imaging)

Answer 2

Based on hydrogen’s ability to emit energy when placed in an external magnetic field. By analyzing these emissions, the brain can be mapped.
The MRI scan is strengthened by: non-exposure and a better resolution than CAT.
Weakened by: cost, fear (children and claustrophobics have to stay still for a long time), metal in body, incidental findings due to the sensitivity of the MRI.

Question 3

fMRI (functional magnetic resonance imaging)

Answer 3

Functional due to the fact that it is dynamic, captures brain processes over time.
Usually, a subject is instructed to complete a task, and hence areas of the brain are activated and blood flow increases in said areas. A signal is then obtainable from the oxygenated blood, known as the BOLD signal.
The (spatial) resolution is measured in voxels (volumetric pixels), where one voxel contains several million neurons. The ‘FPS’ of the scan is called temporal resolution, and currently lies at about 1 second.
FMRI is strengthened by good spatial resolution and that it allows to see brain processes.
Limited by poor temporal resolution (no fast brain processes) and the fear (random noise), similar to MRI.

Question 4

PET (positron emission tomography)

Answer 4

Uses blood flow as an indicator by tracking a radioactive tracer with a short half-life (such as glucose), and hence it is invasive.
An advantage for PET scans is that it is minimal in size, but it is not regularly utilzed due to its invasive nature and an incredibly low temporal resolution of 30-45 seconds.

Question 5

EEG (electroencephalography)

Answer 5

Electrodes applied to scalp measure the electric impulses along the axons emitted by neurons and mapped into “brainwaves”.
It has perfect temporal resolution but poor spatial resolution. Therefore it is not used to locate the origin of the signals.
Advantages: low cost, mobile, silent non-invasive
Limited by: poor spatial resolution, can not detect subcortical areas, it takes a lot of experience to read an encephalogram due to the noise.