Brain Scans

what are the four types of brain scans?

post mortems, positron emission tomographys (PET), magnetic resonance imaging (MRI) and functional magnetic resonance imaging (fMRI)

how does a post mortem work?

• cut up the brain and observe

• helps explain deaths with no known cause

advantages of post mortems

• basis of early understanding/identification of brain areas (e.g. broca's area)

• helped us gain understanding of the links between language, the brain and behaviour

limitations of post mortems

• the brain is dead

• observed damage may have had no effect on the person

• causation is a guess

• patient (owner of the brain) didn't consent to the autopsy

how does a PET scan work?

• use a small amount of radioactive dye that travels to areas of high metabolic activity

• different dyes are attracted to different types of metabolic activity in different organs

• shows how much activity is taking place by the amount of dye that is detected

strengths of PET scan

one of the first ways detecting brain activity we had

weakness of PET scans

• poor spatial and temporal resolution (doesn't give a clear idea of where the activity is and it takes a long time to get a response)

• radiation is involved

how does an MRI work?

• we have billions of hydrogen atoms in our body

• they respond to MRI magnets and line up with each other

• any not paired atoms are made to vibrate with a sound pulse

• they turn the field on and off and measure the vibrations

• the computer measures these vibrations and uses it to make an image

strengths of an MRI

excellent spatial resolution (good detail)

weakness of an MRI

can't show any actual activity (no temporal resolution, it's a still image)

how does an fMRI work?

• same as an MRI but takes 3D images called activation maps and it measures changes in brain oxygenation

• when any part of your body or brain is active blood flows to the area (haemodynamic response)

• assumed activity is related to the rate of metabolism

strengths of fMRI

• good spatial resolution (detail)

• 3D, shows real time activity

• no radiation

• if administered correctly it is risk free, non-invasive and straightforward

• produces images that have a high spacial resolution (depicts detail by the millimetre)

weaknesses of fMRIs

• very expensive

• poor temporal resolution (see reaction to stimuli after 5 seconds)

• only measures blood flow not neuronal activity

how does an electroencephalogram work?

• measures changes in the polarity of the brain

• your brain is a massive electrical system, therefore has changes in electrical charge

• an EEG measures these changes in polarity

• presented in wave formats

strengths of EEGs

• helps with sleep study research (REM and NREM)

• useful for diagnosing electrical disorders (e.g. epilepsy)

• gave great insight into sleep stages

• good temporal resolution (instant response)

weaknesses of EEGs

• poor spatial resolution

• doesn't give a clear idea of where the activity is

• generalised nature of the information received

• can't distinguish between activities originating in different but adjacent locations

• produces a lot of different data

how does an event related potential work?

• raw data from EEGs are laid on top of each other

• statistical averaging filters out background noise (extra data) allowing the ERPs to give a measurement of electrical activity related to a particular event

• allows us to see how we react to specific stimuli

strengths of ERPs

• same as EEGs but gives a better idea of specific electrical activity

• we form an idea of what activity is associated with different brain functions

weaknesses of ERPs

• lack of standardisation makes confirming findings difficult

• eliminating background noise (other electrical activity) is very difficult