Functional techniques

Functional Techniques

Functions

Examine workings of human brain throughout lifespan

Det where+when neural activity in brain is associated with ability to perform a particular cognitive task

Difs in brain activation bet task variants -> isolate brain structures that are implicated in hypothesized cognitive processes

Relies on -> Assumption of 'pure insertion'

Insertion of new task requirement affects cognitive process of interest

spatial res: amt of details
temporal res: speed of detail acquisition
Level of tolerance needed

EEG

non-invasive
oldest fMRI technique

record brain activity - electrical activity on scalp surface
signal picked up by electrodes in multiple locations
Trf mathematically (inverse prob)

Adv:

cheap
somewhat portable
measure brain act at millisec scale

Disadv:

measured only at scalp surface in rel few locations
X provide accurate localisation of brain function

  1. Lowest spatial res
  2. Highest Temp res
  3. lowest tolerance level

MEG

tiny magnetic fields on scalp

complementary with EEG

position head under a helmet-shaped dewar

  • vacuum-filled: contains 100s of magnetometers
    vat of liquid helium cool down the ultra-sensitive detectors
  • highest temp res
  • lowest spatial res
  • medium tolerance

PET

high spatial (whole brain on mm scale)
lowest temporal res: 10/20 sec scales
highest tolerance, most invasive

tissue tracer conc & location - detect gamma rays emitted as byproduct of decay of the injected radioactive tracer
FDG (glucose metabolism)
F-DOPA: dist of dopamine, Parkinson's
tracers have short half-life - decay quickly - produced onsite by cyclotron - expensive

fNIRS

noninvasive. detect changes in brain act - neurovascular coupling - using infra red light

BOLD effect. blood oxygenation level depedent
differential need for red absorption spectra of oxy and de-oxy haemoglobin

indirectly measure changes in blood flow, blood oxygenation levels + blood volume
both refract +reflect light differently

limitation:1. doesn't penetrate deep into skull

  1. relatively small no. of sensors
    adv: masure infant skull (thin and small)

low spatial res (higher than EEG)
high temporal res (not as high as EEG and MEG), > PET&fMRI
low level of tolerance

fMRI

magnetic properties of oxy and deoxy-haemoglobin

oxy: diamagnetic, barely magnetic
deoxy: paramagnetic, interacts more strongly with magnetic field

  • indirectly measure brain activity for regional changes in magnetism
  • study wide range of psychiatric and neurological disorders
  • investigate healthy brain processes

highest spatial res
low temporal res: measures brain activity every few secs
(much slower than EEG & MEG)
medium level of tolerance

1.5 Tesla & 3 Tesla

  1. Direct: EEG, MEG
  2. PET, fMRI, NIRS
  • real time measurements
  • records activity perp to brain
  • pyramidal cells in cortical gyri