Week 3 RF-Brain Communication & Plasticity Flashcards
How can we Image the Living Brain?
-Contrast X-rays: cerebral angiography
-Computer Tomography (CT)
-Magnetic Resonance Imaging (MRI)
-(Functional) MRI
-Positron Emission Tomography (PET)
-Electroencephalography
-Magnetoencephalography (MEG)
-Transcranial Magnetic Stimulation (TMS)
Why do we need to know about MRI?
-Psychology is the study of human behaviour and mechanisms which underpin it.
-Neuroimaging offers rare insight into the link between brain and behaviour.
-(f)MRI research has grown year on year since it’s inception.
-Whether your interests are clinical, forensic, basic science or other, you will not avoid neuroimaging research in your reading.
-Neuroimaging is a super prevalence technique
What are the MRI Basics?
-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 (Gives energy to the nuclei)
-The scanner detects fluctuations of magnetic energy radiated from each spatial location in the chamber
-Computer reconstructs image a 3-dimensional model. (We got this much energy from this point and this much energy from that point)
What are the advantages + disadvantages of MRI?
Advantages of MRI:
-No ionizing radiation exposure
-Excellent spatial resolution (nice images)
-Horizontal, Frontal or Sagittal planes, explore the brain in 3D.
Disadvantages:
-Cost
-No ferrous metal! (Magnetic force will cause the ferrous metal to move)
What is the Hardware for MRI?
-The MRI magnet is super cooled by liquid helium. It is extremely powerful, expensive to purchase, and to maintain.
-1 Tesla (T) = 10,000 Gauss
-Earth’s magnetic field = 0.5 Gauss
-3 Tesla = 3 x 10,000 ÷ 0.5 = 60,000X Earth’s magnetic field
-Screen subjects carefully for internal metals, pacemakers etc.
-Internal ferrous metal could be from factory work, hip replacements etc.,
-So if we put someone who potentially have an internal ferrous metal with the strength the magnetic field MRIs have, it could be dangerous as the metal could move
-The electromagnetic field could also stop the pacemaker working
What is the Employability for Neuroimaging?
-Neuroimaging is a methodology which is relevant for a range of career pathways.
-Research imaging – neuroimaging is a cornerstone of ‘behavioural neuroscience’ ‘cognitive psychology’ or ‘clinical neuropsychology’.
-Clinical imaging – Radiographers e.g., diagnostic scanning.
-In the future, clinical neuroimaging could provide tools to improve treatments or diagnostic approaches
What is Structural MRI?
-Structural MRI records a signal from each part of the brain by segmenting it into tiny chunks called voxels (~1mm3).
-The signal returned from each voxel differs depending on the water content of the regions imaged.
-Fatty tissues (e.g., myelin sheath around white matter) are lower in water content than grey matter, whereas the CSF has the greatest water content.
-Structural imaging generates a single, high-resolution depiction of the brains structure and usually takes around 7-10 minutes to record.
-Determines how much water is in each voxel
-Fatty parts have less water
-Dark parts of the brain has cerebral spinal fluid which has a high water content
What is Functional MRI?
-Functional magnetic resonance imaging technique measures the amount of ‘activation’ in each voxel of the brain (~2-33mm).
-Utilises same principle as structural MRI images but condition of magnet and radio pulse are adjusted.
-Oxyhaemoglobin and deoxyhaemoglobin in blood have differing paramagnetic qualities.
-fMRI targets a reading which differs according to the relative balance at each voxel throughout the brain.
-Low-resolution images are generated approximately every 2 seconds and we can passively monitor the brain or run an experimental manipulation.
-Same scanner but we set the parameters differently to scan a different proportion (oxyhaemoglobin and deoxyhaemoglobin)
-Paramagnetic=slightly different signals
-Gives snapshot images (quick images aka low resolution) means we can update on brain activity regularly but won’t be as pretty as seen in the bottom image
What is the BOLD signal?
-In fMRI the measured variable is called the BOLD signal (Blood Oxygen Level Dependent).
-Neural activity is not measured directly, but BOLD fluctuations during an fMRI scan can tell us that particular regions required more oxygen at certain times. Therefore we can infer brain activation.
Blood Oxygen Level Dependent signal:
↑ neural activity 🡺 ↑ blood flow 🡺 ↑ oxyhemoglobin 🡺 ↑ T2* 🡺 ↑ MR signal
-It’s NOT measuring neural activity
What’s the difference between Structural MRI vs functional MRI
Structural MRI:
Excellent contrast between tissue types and spatial resolution. Suitable for evaluating structural abnormalities but one scan takes several minutes.
-High resolution (1mm voxels)
-Single image
fMRI:
Indirect measure of neural activity. Low resolution image but can be updated frequently to evaluate activity changes associated with experimental conditions.
-Low resolution (~2mm voxels)
-Many images e.g., every 2 sec for 5 minutes
sMRI Analysis: Voxel-Based Morphometry?
-Voxel-based morphometry (VBM) is a structural analysis technique. (How we calculate the thickness and volume of the grey matter)
-Used to investigate differences in brain anatomy – grey matter density.
-Results highlight regions of the brain which show significant differences in density, E.g., between 2 groups.
How is MRI illustrated?
-MRI results, both structural and functional, are typically presented on top of a recognisable structural brain (So the reader can determine what’s going on in regards to different parts of the brain)
-Illustrated by overlaying on top of a sample structural image which provides spatial context for the audience
-In the case of fMRI, only the coloured ‘blob’ data actually comes from the study in question.
-Black and white is a template for a rough image of what you’re looking at whereas coloured areas are usually from statistical image (left image)
MRI- Why do we need statistics?
-fMRI studies give a ‘rich’ dataset.
-Typical resolution gives 6000 voxels per 2 second scan.
-20-minute experiment gives 7.2 million data points.
-At P<0.05 we can expect 360,000 false positives! > Risk of TYPE 1 ERROR
-We need to perform many, many comparisons. GOOD MRI methods compensate for this with statistical corrections
-The scientist makes decisions about P-hacking NOT the data
Bennett et al (2010):
-Bennett used a dead salmon and showed emotional and neutral images to the salmon and could see different responses (shows you can find a result from noise but can relay it as a fact)
What is Phantom Limb Pain?
-Maladaptive neuroplasticity can lead to negative consequences
-Witness invasion of lip activation profiles into hand area loci.
-Phantom limbs associated with severe chronic pain may result from cortical reorganisation
What is the Lip Pursing fMRI activation profile study? (Lotze, 2001)
-Face area will invade the area where the hand area was (Lotze used fMRI to study this hypothesis)
-Lotze made 3 different groups (phantom limb pain, amputees without pain and healthy control) to do a lip pursing task under fMRI
-Healthy and amputees shows bilateral activation over lip and face area
-Phantom had spread to other areas
