Brain communication & plasticity

MRI function

• A strong magnetic field causes hydrogen atoms to align by orientation - lattice structure. 

• A radio frequency pulse is passed through scanner- Atomic nuclei emit electromagnetic energy

• The scanner detects energy radiated from each spatial location in the chamber

• Computer reconstructs image a 3 dimensional model.

• cooled by liquid helium

advantages to MRI

•  No ionizing radiation exposure

•  Excellent spatial resolution

•  Horizontal, Frontal or Sagittal planes, explore the brain in 3D

Disadvantages to MRI

• Cost to purchase & maintain

• No ferrous metal allowed- subjects have to be screened carefully for internal metals, pacemakers etc.

Structural MRI

• records a signal from each part of the brain by segmenting into tiny chunks (voxels~1mm) 

• signal returned differs depending  on the water content of the region (fatty tissues have lower water content than grey matter, CSF have the most) 

• generates a single, high-resolution depiction of the brains  structure 

• takes 7-10 mins to record 

Functional MRI

• Measures the amount of ‘activation’ in each voxel of the brain (~2-33mm).

• Usually 6000 voxels per 2 second scan

• Looks at oxygen- Oxyhaemoglobin and deoxyhaemoglobin in blood have differing paramagnetic qualities.

• Low-resolution images are generated approximately every 2 seconds

• BOLD signal (Blood Oxygen Level Dependent)- tell us that particular regions required more oxygen at certain times

• Can then infer brain activation

structural versus functional MRI

structural:

• Excellent contrast between tissue types and spatial resolution.

• Suitable for evaluating structural abnormalities

• One scan takes several minutes

functional:

• Indirect measure of neural activity.

• Low resolution image but can be updated frequently to evaluate activity changes associated with experimental conditions

possible errors with MRI

• At  P<0.05 we can expect 360,000 false positives!

  • Risk of TYPE 1 ERROR

• Need to perform many comparisons.

  • GOOD MRI methods compensate for this with statistical corrections

  • E.g., Bennett- Salmon

  • a dead salmon showed statistical \"brain activity\" when uncorrected statistical thresholds were used

Lotze, 2001- lip pursing

• In PL patients, invasion of lip activation profiles seeps into hand area loci.

• Phantom limbs associated with severe chronic pain may result from cortical reorganisation

Guo, 2016

• Scanned before & after (fMRI)

• Shown enhanced bilateral somatomotor activation in patients following MBT

Michielson, 2011

• Also scanned before & after

• Suggested it was deep limbic brain areas which demonstrate changes following MBT

  • More emotional bringing an indirect therapeutic benefit

Rehme, Fink et al, 2011

• fMRI used to observe amount of maladaptive plasticity in stroke patients

• Different levels of impairment

• Showed that patients recovery correlated with the ability of contralateral cortex to activate during movement of affected limb

• Mild= Consistent activation on contralateral side

• Severe= Ipsilateral activation

• 'brain on fire'- activation has expanded on both sides (maladaptive)

CBT

• Depressed patients demonstrate disrupted emotional regulation

  • Also show enhanced brain activity (fMRI) in amygdala during emotional stimuli - 

  • Those with the greatest degree of amygdala dysfunction benefitted from greatest improvement post CBT

  • Connections with insular and anterior cingulate cortex relate to responsiveness to CBT for anxiety related disorder

Transcranial magnetic stimulation

• for treatment of depression

• non-invasive