Neuroimaging

  • This diagram characterizes each neuroimaging technique into spatial and temporal resolution


Human neuroimaging:

  • Modern neuroimaging techniques have been intrinsic to the development of cognitive neuroscience

  • Allows us to view brain morphology and activity in vivo in awake behaving humans

  • Based upon the physical properties of tissue in the brain in the space (structural) and over time (dynamic)


  • Structural imaging produces static images of the brain’s physical structure

  • Functional imaging indexes dynamic aspects of brain function

  • How does activation in the brain change over time

  • Provides different types of information applicable to different types of questions


Structural neuroimaging:

  • Most common methods are:

  • Computerized tomography (CT)

  • Magnetic resonance imaging (MRI)

  • For each technique, the signals come from a different mechanism


  • CT constructs a 3D image of the brain based upon x-ray images

  • Different types of tissue eg grey and white matter have different absorption rates for x-ray material

  • Different densities generate different colours

  • CT scans are fast and cheap to acquire

  • Low spatial resolution, 0.5-1cm

  • Similiar absorption rates for grey and white matter makes it difficult to distinguish these on resulting images

  • Averaging in image means it is not possible to discriminate structures that are closer than 5mm


  • MRI scans exploit magnetic properties of living tissue

  • Signals come from protons in hydrogen atoms, they spin around the atoms axis producing a magnetic field

  • In normal circumstances the orientation of these protons is random

  • MRI scanner produces a powerful magnetic field (measured in tesla) to which these protons align

  • A radio pulse passed through the brain will momentarily return the protons to their original orientation

  • Once the radio pulse stops the protons realign with the magnetic field (T1 relaxation time)

  • Variations in the rate of this process differentiate different types of tissue in the brain

  • Radio pulses can be used to excite slices of the brain that are 1-3mm apart


  • MRI scans have high spatial resolution than CT scans

  • Differentiate white from grey matter as well as CSF and bone

  • Produce 3D images

  • Locations of these images are coded in mm on 3 axes with their origin centred upon the anterior commisure (Talairach coordinates)

  • Coronal plane- front and back sections

  • Different spin rates across different types of tissue provide us with information

  • High spatial resolution images


  • Axial plane- upper and lower sections

  • Sagittal plane- left and right sections

  • MRI distinguish really well between the different types of tissue within the brain


Functional neuroimaging:

  • Most common methods are:

  • Positron emission tomography (PET)

  • Functional magnetic resonance imaging (fMRI)

  • Functional imaging indexes the metabolic activity in the brain

  • Neural activity requires oxygen and glucose and these are supplied via the vasculature system of the brain

  • Allows us to measure dynamic changes in the brain metabolism under different situations

  • We can relate these to experimentally manipulated IVS

  • Neural indices of perception, cognition and emotion

  • fMRI measures the ratio of oxygenated to deoxygenated blood

  • Deoxygenated haemoglobin distorts local magnetic fields and effects the spin rates of protons

  • Differences in the magnetic properties of oxygenated and deoxygenated blood forms the basis of fMRI contrasts (T2 spin rate)


  • The function of the BOLD signal against time is known as the haemodynamic response function

  • BOLD- blood oxygenated level dependent

  • Indirect measure of neuronal activity, which assumes a direct relationship between neuronal activity and haemodynamics

  • Simple designs eg subtraction provide information about the anatomical substrates of task perfomance

  • More complex techniques eg PPI provide information about task related activity across cortical networks

  • Allows us to measure dynamic changes in brain metabolism under different situations

  • We can relate these to experimentally manipulated IVS


Subtraction method:

  • Everything is identical except the motion

  • Stimulus array- visual input

  • Stimulus array + motion involves movement

  • So the subtraction is (stimulus array +motion) - (stimulus array) = motion processing

  • Tells you which part of the brain is sensitive to motion


Subliminal priming (masked cues) :

  • Tests whether the brain processes words without conscious awareness

  • Forward mask (≈ 500 ms)

  • A meaningless pattern

  • Prevents pre-activation of the word system

  • Prime word (≈ 29 ms)

  • Example: “RADIO”

  • Shown too briefly to be consciously perceived

  • Backward mask (≈ 29 ms)

  • Immediately wipes out conscious perception of the prime

  • Target word (≈ 271 ms)

  • Example: “radio”

  • This is consciously visible

  • Participant responds to this word (e.g., lexical decision)

  • Because of masking + short duration, the prime is subliminal.

  • Faster reaction times when the prime and target are the same word


  • Neuroimaging techniques provide unique access to the structure and function of the brain

  • Measures of morphology provide basis for comparisons across individuals or groups

  • Functional imaging provides a basis for structures to function deduction and induction

  • One of many convergent techniques that can be used to investigate links between the brain and behaviour