L3: Tools To Study The Brain Flashcards
Name the major tools/techniques used to study the brain
- single unit recording
- electroencephalography (EEG)
- event related potentials (ERPs)
- magnetic resonance imaging (structural MRI)
- functional magnetic resonance imaging (fMRI)
- trans cranial magnetic stimulation (TMS)
- transcranial current stimulation (tACS/tDCS)
Outline single unit recording
Involves inserting a micro-electrode into the brain to study single neurons. Very sensitive methods
(-) invasive and so rarely uses with humans
Outline EEG
- electrodes are applied to the scalp and measure electrical activity (millisecond scale)
- these electrodes measure voltage changes on the scalp, and the signal received represents the summed activity of millions of neurons. Signal is main,h generated by large pyramidal cells in the cortex(this is because their axons are all aligned parallel to each other such that the currents they produce don’t cancel each other out)
- the final signal ,ensured is always a difference in voltage between different electrodes, which is why EEG always needs a reference electrode.
What are Event related potentials (ERPs)?
When EEG data is averaged out. Subject is repeatedly exposed to the same stimulus to prevent background brain activity affecting the results
Evaluate EEG
(+) cheap
(+) temporal resolution
(-) spatial resolution
Outline structural MRI
- slices of the brain are taken and put together to construct a 3D image
- MRI scanners, string magnetic field causes protons to align. Brief radio frequency is then applied, causing the aligned protons to spin and regain their original orientations, emitting energy as they do so (brightest areas on the scan have emitted the most energy)
Outline DTI (Diffusion tensor imaging)
- it is an MRI based neuroimaging technique
- makes it possible to estimate th location, orientation and anisotropy of the brains white matter tracts
- can image white matter fibres (bundles of axons) by measuring the direction of water diffusion
- allows us to study how cognition/perception is supported by connections between brain regions
Outline fMRI
- doesn’t measure neural activity directly
- measures the BOLD signal (blood oxygen level dependent contrast)
- when a certain brain area is active more blood/oxygen is supplied to that area (and so there is a relatively high amount of oxygenated blood compared to deoxygenated blood in those areas). Oxygenated blood will cause less mag field disturbance than deoxygenated blood so active regions will have higher signal.
- the way the BOLD signal changes when a stimulus elicits neural activity in an area is called the haemodynamic response function
Evaluate fMRI
(-) lower spatial resolution than structural MRI
(+) better spatial and temporal resolution than PET
(-) only correlational, no conclusions about causation are possible
Evaluate structural MRI
(-) tells only about the structure of the brain, not function (or does it? McGuire 2013)
(+) no radiation, no invasive
Name the different brain stimulation techniques
-TMS (transcranial magnetic stimulation)
-TCS (transcranial current stimulation)
tDCS/tACS
Outline TMS
- utilises electromagnetic induction (changing electric current in a coil generates a magnetic field)
- this magnetic field then induces a secondary electric current in neutrons below the stimulation site (if they have the correct orientation)
- in theory the induced current will cause the neurons to fire more easily
Outline tACS and tDCS
tACS: used to induce oscillations of different frequencies. One application is to ‘force’ the brain into a certain oscillating rhythm, which will make the neurones more likely to fire synchronously
tDCS: areas under the cathode are thought to be inhibited, areas under the anode are excited
Evaluate TMS
(+) can have long term beneficial effects (e.g depression)
(-) can’t be used on epileptic patients
(+)can provide causal evidence that a certain brain region is involved in cognitive function
