L6 - Brain Mapping: Cognitive Neuroscience Toolbox

Question 1

How do we measure Brain Function?

Answer 1

• Lesion studies, Brain stimulation
• Single neuron recording (animals)
• EEG: Electroencephalography
  
  • ERPs: Event-Related Potentials
• MRI: Magnetic Resonance Imaging
  
  • fMRI: Functional Magnetic Resonance Imaging

Question 2

Limitations of Brain Mapping:

Answer 2

• Cannot infer what people were thinking or doing or feeling based on measurement of their brain activity
• Reverse inference: Cannot measure brain activity (dependent variable) to determine the independent variable was (i.e. task people were doing)

Question 3

Neuropsychology– Brain Lesions:

Answer 3

• Lesions: brain tissue can be damaged by injury, stroke, disease or surgery
• Logic: “If area X does function Y, a lesion to X should impair Y”

Problems:

• Injury is often extensive (more than just one tiny and exact area)
• Impairment is often extensive
• “Compensatory” changes in other brain areas
• Convenience sample – hard to control, can’t be generalised
  
  • Eg. There would be a lot of brain injuries during a war
• Doesn’t take into account that the brain is a network

Question 4

Single neuron recording:

Answer 4

• Electrode in animals brain that detects AP firing of a single neuron
• Allows measurement of what that neuron encodes (what causes it to fire); especially visual cortex
• Pros: Most accurate measurement
• Cons: Highly invasive, animals only

Question 5

EEG (electroencephalography):

Answer 5

• Summed activity from action potentials of neurons in the cortex cause electrical voltage changes on the scalp which can be measured with electrodes
• Frequency of oscillations change between different states of alertness (narrow alpha waves which are compressed when concentrating) and sleepiness (wide delta waves)
• Clinical uses: Detecting stages of sleep; monitoring for epileptic seizures

Subdural recording: cutting open the skull and putting a recording net of electrodes straight onto the brain

Scalp Recording: a cap covered in electrodes put on the head

Question 6

ERPs (Event-Related Potentials):

Answer 6

• Average of EEG +100 responses related to a specific event/stimulus
• Peaks represent different stages of processing (e.g. face processing is related to a negative 170 (N170) peak)
• Clinical uses: Detecting deafness in babies (auditory ERP’s)
• Pros: Provide precise time of information processing in the brain; Direct measure of electrical activity (neuron firing)
• Cons: Difficult to accurately localise activity to specific brain areas (poor spatial resolution); hard to determine exactly where in the brain this activity comes from given the electrical potentials are being measured across the scalp

Question 7

Functional brain imaging:

Answer 7

Change in blood flow associated with neural activity (↑ blood = ↑ activity)

• PET (Positron Emission Tomography): Uses radioactive contrasts to map neurotransmitters or receptors (radioactively labelled “tracers”) in the brain
• fMRI (Functional Magnetic Resonance Imaging): Measures changes in BOLD (blood oxygen level signal) rather than the anatomy of the brain (normal MRI)
  • ↑ Brain activity = ↑ Blood flow = Changes blood oxygen level = ↑ fMRI BOLD signal (detects iron in deoxy-Hb)
• Pros: Good localisation of brain activity; non-invasive
• Cons: Indirect measure; blood oxygen change is slowed and delayed (4-5 seconds after activity brain activity and lasts 10-12 seconds after cessation of activity); not very precise timing ; expensive