Global brain activity

Question 1

EEG

• Function
• Where it is used

Answer 1

Electroencephalogram
- Measures electrical rhythm in from the brain through electrodes placed on the scalp.

Use:

• Sleep studies
• Diagnosing + monitoring epilepsy

Question 2

Mechanism of EEG

Answer 2

Measures voltage in the small fields generated by pyramidal cells.

Requirements for signal:

• Neurones must be active and synchronised
• Neurones must be parallel so that they summate.

Question 3

Alpha rhythm

Answer 3

8-13 Hz
- Low amplitude

Indicates being awake but with eyes closed.

Question 4

Beta rhythm

Answer 4

14-60 Hz
- Higher amplitude, high frequency.

Indicates being awake with eyes open
- Mental activity and attention is happening

Rhythm in REM sleep

Question 5

Theta rhythm

Answer 5

4-7 Hz
- High amplitude, very low frequency.

Indicates drowsiness/ sleep

Question 6

Delta rhythm

Answer 6

< 4 Hz
- Very low frequency and high amplitude

• Indicates deep sleep [stage 3 NREM]

Question 7

Stages of sleep

Answer 7

Awake [alpha or beta rhythm]

Non REM {NREM]

• Stage 1: Theta waves
• Stage 2: Spindle waves + K complex
• Stage 3: Delta waves

REM: beta + alpha waves, desynchronised. Similar to being awake.

Question 8

Thalamus in generating synchronous brain rhythms

Answer 8

Thalamic pacemaker neurones generate discharge patterns [voltage gated channels]
- Synchronises other thalamic neurones by setting a pace

Cells also become synchronised without pacemaker activity
- Each neurone is set at a frequency to fire, which lines up eventually.

Question 9

Sleep cycle

Answer 9

Awake—> Stage 1 NREM—> 2—> 3—> 4—> 3—>2—> REM

Repeats

Question 10

Behavioural criteria for sleep

Answer 10

Reduced motor activity

Decreased response to stimulation

Relatively easy to reverse

Stereotypical posture.

Question 11

Possible functions of sleep

Answer 11

Conservation of energy

Thermoregulation

Neural maturation

Mental health

Cognition

Question 12

Structural imaging of the brain

Answer 12

Static map of the brain
- Spatial configuration of tissue types.

Examples:

• MRI
• CT

Question 13

Functional imaging of the brain

Answer 13

Dynamic map of the brain
- Indirectly measures neuronal activity.

Examples:

• PET
• fMRI

Question 14

CT and imaging the brain

Answer 14

Used to diagnose:

• Tumours
• Bleeds
• Gross brain anomalies

Question 15

MRI and brain imaging

Answer 15

Used to diagnose:

• Tumours
• Bleeds
• Brain anomalies

Better contrast resolution than CT:

• Better white-grey discrimination.
• Less radiation

Question 16

CT vs MRI

• Spatial resolution
• Radiation
• Time
• Expense

Answer 16

Spatial resolution:
- Higher in CT

Radiation:

• CT has high radiation
• MRI uses no radiation [magnet]

Time:
- MRI takes longer to take image

Expense:
- MRI much more expensive than CT

Question 17

Physiology of MRI

Answer 17

Produces an magnetic resonance signal by orientating the protons inside the body

Helps to produce static maps or dynamic maps [fMRI]

Question 18

fMRI

• Type of imaging
• Mechanism
• BOLD
• HRF

Answer 18

Functional MRI
- Type of functional imaging

Mechanism:
- Measures metabolic activity of tissues by detecting BOLD signal

BOLD [blood oxygen level-dependant] contrast
- Ratio of oxy/deoxyhaemoglobin in the blood

HRF= haemodynamic response function
- Changes in BOLD signal over tie

Question 19

PET

Answer 19

Functional imaging technique that measures blood flow to brain regions.

Question 20

PET vs fMRI

• Radioactivity
• Temporal resolution
• Spatial resolution
• Sensitivity
• Tracers

Answer 20

Radioactivity

• PET is radioactive because of tracers
• fMRI is not

Temporal resolution

• fMRI is quicker [1-4]
• PET = 30

Spatial resolution:
- fMRI has higher spatial resolution [1mm, PET= 10mm]

Sensitivity
- PET sensitive to whole brain, fMRI only to certain regions