Cognitive neuroscience methods Flashcards
What do axons do?
Connect brain areas
How are messages passed?
Via neurotransmitters
What is an action potential?
Electrical signal initiated when the neuron fires
Excitatory?
Causes the neuron to fire
What is the visual cortex?
The region located at the back of the brain that processes visual information
What is the midbrain?
An area that carries out diverse functions in reward, eye movement, hearing, attention and movement
What is cognitive neuroscience?
The study of how brain structures and processes mediate cognitive behaviour
What are the objectives of cognitive neuroscience?
Understand how the mind is created by the brain and understand the links between cognition and neuroscience
Build models of how the brain works
Establish which brain regions and brain circuits are involved in different tasks and what changes in the brain as a consequence of learnining
Investigate brain imaging and activity produced during cognition
What are some challenges for cognitive neuroscience?
Complex systems - around 1 million neurons in 1 cubic mm of brain
Describe techniques to find brain structure
Anatomical dissection, structural magnetic resonance imaging
Discuss techniques to look at brain function
- Single electrode stimulation
- Scalp-located electrodes- EEG, ERP - Functional MRI - Magnetoencephalography MEG
- Positron emission tomography PET
- Transcranial Magnetic Stimulation TMS
How do MRIs work?
- Atoms (in this case, hydrogen atoms) are like constantly spinning magnets
- These atoms align when in a scanner’s magnetic field
- Then, you send in radiowaves to make them face in a new direction
- When they relax and return to their previous alignment, they emit energy IE resonance
- This energy is what the scanner uses to create an image
Discuss MRI scans
- Static structure of the brain
- Hydrogen atoms in different tissues (such as fat and water) have different relaxation times and can be identified separately
- The lower the water content of an area, the fewer hydrogen atoms there will be emitting signals
- The weaker the signal, the darker the area appears on the scan
The result is shades of grey, fat is light, bone is dark
What are the advantages of MRI scans?
- Excellent spatial resolution
- Allows you to view the brain from multiple angles
- Non invasive
Excellent for looking at soft tissues
What are the disadvantages of MRI scans?
- No temporal information
- Bad experience as noisy, need to stay still, claustrophobic
- Expensive
Older metal implants are not compatible ie pacemaker, brain aneurysm clips
Describe fMRI’s
Not just structure, but function too
Based on same MRI technique but looks at blood flow in the brain
Blood contains haemoglobin which contains iron which is magnetic
Deoxygenated blood is affected by a magnetic field differently than oxygenated blood
When neurons are active, they burn energy. This is automatically replenished via oxygen carried by hemoglobin in the blood stream
Active parts of the brain contain more oxygen-rich blood
By measuring the BOLD (blood oxygen level dependent) response in the MRI scanner, we can work out which parts of the brain were active recently
How does fMRI work?
Oxygen is delivered to neurons by haemoglobin capillary red blood cells
More haemoglobin present in areas of the brain when it needs to replenish the oxygen used by active neurons
Describe haemoglobin and oxygen levels
Haemoglobin is diamagnetic (weak magnetic field) when oxygenated but paramagnetic (strong magnetic field) when deoxygenated.
BOLD response
What are the advantages of fMRI?
- Excellent spatial resolution (get structural data within same session
- Reasonable temporal resolution
- Non-invasive
Tells us which parts of the brain are used in tasks
What are the disadvantages of fMRI?
Bold isn’t a direct measure of activity
Experience
Expensive
Can’t have any metal based equipment for stimulus presentation
Describe positron emission tomography
- Breakthrough brain functional imaging method 1980s
- Measures blood flow in the brain - more blood flower in active areas
- Inject, inhale, or swallow a tracer which is absorbed into the blood stream (mildly radioactive)
- Higher levels of activity show up as bright spots
Can be used to evaluate certain brain disorders such as alzheimers
Advantages of PET
- Reasonable structural resolution
- Direct reflection of activity
- No motions artifacts
- More comfortable experience than MRI Fmri
Disadvantages of PET
No temporal resolution
Expensive
Injection of very weak radioactive substance so ethical issues
May need to do MR or CT scan as well
Describe EEG
- EEG measures electrical signals generated by the brain through electrodes placed at the scalp
- EEG signals are produced by partial synchronisation of cortical field activity and are measured as changes in voltage, recorded at the scalp, over time
Analysis of EEG signals may be task dependent or task independent
How are EEG signals detected?
- Electrodes are placed on the scalp. Connected with gel or conductive solution
- EEG signals are transported to an amplifier
- The amplifier measures the difference in voltage between the active electrode and a reference electrode
Frequency of measurements - upto 2000HZ
Advantages of EEG
Very good temporal resolution
Direct reflection of activity
Not claustrophobic - good with infants
Disadvantages of EEG
Poor spatial resolution, motions artifacts, inverse problems (how can we be sure which brain regions generate the electrical activity
Describe the magnetoencephalogram MEG
- The pyramidal cells of the cortex, when active, generate a significant magnetic field
- MEG records these magnetic fields
- For both EEG and MEG, the synchronous firing of 10000s neurons is required to produce a field which is large enough to measure
Magnetic fields are less distorted by the scalp than electrical fields
What are the advantages of the MEG
Excellent temporal resolution, direct reflection of activity, good spatial resolution
Disadvantages of MEG
Expensive
What is transcranial magnetic stimulation?
Uses a changing magnetic field to induce weak electric currents in the cortex
Noninvasive method causing depolarization or hyperpolarisation of neurons in the brain (i.e. decrease/increase activity).
Can produce a simulated temporary ‘lesion’ of a brain region by preventing normal function of that region.
Invented by Tony Barker and colleagues at University of Sheffield in 1985
Advantages of the TMS
Near portable, can stimulate or lesion
Disadvantages of TMS
Difficult to specify precise regions, only surface regions
