Neuroscience methods

Neuroimaging techniques

MRI - Magnetic Resonance Imaging

• Magnet - most important component, runs throughout the entire scanner, strength is measured using Tesla (T), 3T scanners are 30,000 as strong as the earth's magnetic pull; scanners are very expensive, cost rougly £1M per T.
• MRI is a medical technique used to: Create pictures of anatomy (structual MRI); To view functioning of the brain (Functional MRI)

Structural MRI

• Meausres hydrogren protons in various tissue types
• These hydrogen protons spin at different rates in various tissue types
• Very complex 
• Smoking is associated with decreased prefrontal volume

Functional MRI

• Can be used to determine which brain regions are important for various tasks
• Visual attention task - visual cortex activated
• Auditory attention task - activates the auditory cortex
• Decision-making task - activates the prefrontal cortex
• fMRI is used to measure brain function
• It does this by measuring levels of oxygen in the blood
• BOLD - Blood-Oxygen Level Dependent

 

Hemodynamic Response Function (HRF)

Present a stimulus

1. Oxygenated blood - rushes to the active region - peak is ~6 seconds after stimulus presentation
2. Oxygenated blood then disappears
3. Followed by a simultaneous increase in deoxygenated blood

 

Positron Emission Tomography

• Nuclear imaging technique
• Molecule ('ligand') is radio-labelled - usually with flourine-18 or carbon-11 - and injected 
• This 'radioligand' binds to certain receptors
• Gamma rays emitted from the ligand and detected by the scanner
• Areas of yellow and red show high binding, and thus high levels of receptors
• Receptors are important components of neurotransmitter systems
• Can image amount of receptors of various neurotransmitter systems
• Most common to examine dopamine receptors; easier to measure, dopamine dsyfunction is involved in many neuropsychiatric disorders
• Having less (or more) receptors indicates dysfunction in that neurotransmitter system
• Compared to non-smokers, smokers exhibit less dopamine in the striatum

 

Transcranial Magnetic Stimulations (TMS) - brain stimulation technique

• Is non-invasive
• Induces rapid and strong magnetic fields to induce a current in the brain
• TMS causes neurons under the site of stimulation to discharge an action potential
•  can cause long-lasting changes in brain function and behaviour
• TMS of the prefrontal cortex reduces Impulsivity