W7 - Introduction to Clinical Neuroscience Flashcards
(31 cards)
How does neuroimaging work?
Brain size is proportional to body size.
Each neuron may be connected to up to 10,000 other neurons.
What is the evolution from man to mouse?
The corticle strucure is around 4mm thick and comprised of 6 layers. Convolutions in the brain means layout is bigger.
How did the Greek concepts of the brain develop?
The Encephalocentric theory:
- A seat of sensation and understanding
- Interpreter of thing, understanding, emtions, moral and aesthetic activities, souk
The cardiocentric theory:
- Cooling agent of body heat
- Command centre of body
- Heat at centre
“The weight of Greek heritage was enormous. The controversy between encephalocentrists and cardiocentrists continued well into Renaissance and beyond”
Galen used rational investigative methodology and first-rate anatomical skill, Galen reached the conclusion that the nerves and the spinal cord were composed of the same substance of the brain [17] . He also provided a clear demonstration that the spinal cord originated from the brain.
What does Clinical neuroscience include?
Neuro:
Brain, spine, peripheral nervous system, gut
stroke, tumours, MS, schizophrenia, depression …………
Input from PNS may alter brain function - chronic pain
Toxins can affect brain function
urea (kidney disease)
ammonia (liver disease)
sugar, alcohol, nicotine ………..
Behavourial / environmental factors can be detrimental
stress, isolation, internet use,
Behavourial factors can boost brain function
exercise, education, enjoyment, engagement …..
Clinical:
Human disease: diagnosis, treatment, mechanisms
Science:
Mechanistic studies, biomarkers, cells to whole-body ……..
What are the cellular structures of the brain network?
Skull
dura
SAS space - with arteries supplying blood from CVS. Oxygen supplies penetrate down to the deep grey matter structures.
There is a mix of glial astrocyte cells and neurones in the cortex.
Axons project to white matter and connect to grey matter, cerebral cortex, spine and PNS.
Brain cells:
Cell body -
Dendrites receive signals
Axons transmits the processed signal
Dendrite (grow as you learn) , growth, branching, pruning, plasticity..
What are the artificial neural networks for image analysis mimic brain connectivity?
The brain is hardwired too.
Eg, We are proned to seeing two eyes and a mouth.
Pareidolia is the misinterpretation of sensory input.
Computer neural network:
Input image, convolution layer, pooling layer, artificial network corresponds to the excess neuronal presence indicating infarction, haemorrhage, tumour in brain etc as output.
What is the STROOP test?
Trying to read colours out loud without reading the word.
What are the brain regions of functional localisation?
Map the cortex to:
Sensory homunculus - PNS, sensory info to brain
Motor homunculus - signals to muscles for motor control.
We are verbal and tactile animals - hand controls. We make tools etc.
They did experiments with epileptic patients. Electric shocks to particular parts of the brain that corresponds to control. Eg. they were asked to do finger flections and shocked that part of brain, they found it difficult to do that task after.
What is the cases of Phineas Gage?
He was a railway track worker - dynamites into blast rocks to clear way for railway.
Major frontal lobe damage
Personality changes, fitful, irreverent, impatient….
What is the Moneiur Leborgne case?
………. nicknamed Tan Tan , for that was the only syllable he could utter (save for a swear word or two), died in the care of the neurologist Paul Broca in Paris on April 17, 1861.
The Broca’s area associated with language was damaged.
Neurological condition - facial ignosia - can’t recognise faces.
What did the high resolution 3D MRI of Leborgne’s brain show?
Damage is much deeper than Broca reported from observing the intact
brain, hence why Leborgne’s speech impediments were so severe
What is post-mortem pathology?
Glioblastoma – made fr0m glial cells that have become cancerous - highly infiltrative
Hemmorrhagic Stroke –localised damage
Hippocampal sclerosis – structural change.
can cause seizures, found in Alzheimers and other dementias
How does medical imaging work?
Firs tmedical X-ray by Wilhelm Röntgenof his wife Anna Bertha Ludwig’s hand in 1895
X-rays are helpful to see bones, but not the soft tissue.
What is X-Ray CT?
The X-ray tube rotates around the patient. A beam of X-rays shots gets picked up by detectors on the other side of the body.
This lead to the invention of X-ray CT for the study of the brain. The first CT of a patient was at Atkinson Morley’s Hospital.
Modern day CTs show a lot more detail - able to see skull, blood vessels.
Blood leaking out of the vasculature absorbing x-ray strongly = bright region
Shadow = edematous surrounding region.
This technique just takes up a few mins and gives a contrast agent that absorbs x-rays. Take that intravenously. You don’t get good differentiation between grey and white matters of the brain.
What are the magnets within us?
MRI is a soft tissue imaging technique.
We have 75% water in us and water has H2O molecules. The H atoms at their core has a proton, which spins on its own axis letting it have a magnetic moment. The billions of these in the body are what’s used to generate that image.
What is NMR to MRI?
These were used before MRI.
A chemical sample was placed between a strong magnetic field, we then have a radio wave input, which interacts with the chemical sample we are interested in. We have a second coil where we pick up the radio frequency output. This is detected and amplified and turned into an NMR spectrum.
The peaks relate to different chemicals and relate to signals coming from sample at different frequencies.
They came up with the idea of picking up signals that relate to the location of the signals. They used a finger.
What is the MRI signal source?
A strong magnetic field creates magnetisation in
all the tissue
This magnetisation is from the protons of
hydrogen in water and fat in the tissue
The magnetisation direction can be manipulated
by radiofrequency pulses to produce an MRI signal
to create an image
The intensity in the image depends on water
content, tissue structure, blood flow, perfusion,
diffusion, paramagnetics, T1 and T2 etc
What happens along with increased water content?
T2w MRI – signal intensity increases with increased water content.Increased tissue water and loss of cellular structure all lead to increased T2. T2 is a measure of how long the MRI lasts.
Brain tissues shows up darker.
In areas with a brighter signal intensity, in that image the middle cerebral artery shows up bright due to oedema.
High-grade glioma - at the core, there are tumour cells rather than brain tissue. It is a less structured tissue, so it is more fluid and shows up brightly. Surrounding that, there is a region of bright due to the oedema because of more fluid in the tissue. The whole tumour region and the damage to the surrounding tissue shows up bright.
Multiple sclerosis - causes demyelination. You lose the white matter structure and you get inflammation. You get bright spots related to the multiple sclerosis regions.
How does an MRI investigate anatomical structure?
These are T1 weighted images.
You put radio frequency signals in that interact with the magnetisation. They are effectively knocking the magnetisation out of alignment and the magnetisation comes back into alignment with the magnetic field.
T1 image is related to the time it takes to realign.
The CFS shows up very dark - takes a long time for magnetisation to align. White matter shows up very bright and grey matter inbetween.
*1mm spatial resolution
*Grey and white matter
*Volumetry
*Degenerative change - like aging and dementia
*Developmental abnormalities - like early development of a child
*Disease specific changes
What is Grey and white matter?
Grey:
In grey matter water in both the intra- and
extracellular compartments has relatively
free motion.
- Cell body, dendtrite, H2O intracellular and extracellular
White:
In white matter approximately 50% of the
tissue volume is accounted for by myelin
structures, within which T1 relaxation of 1H
in lipid structures is very short.
Hence the average T1 of WM < GM
- axonal pathways with myelin sheaths which is fatty tissue, CH3 and CH2 in terms of structure.
In a patient with Alzheimer’s dementia, the brain itself has shrunk tremendouslty. CFS spaces in the ventricles get larger and the CFS space between brain and dura also gets larger.
Grey and white matter have very different T1 relaxation times because the water generating the signal are in a different structural environment between the two tissue types. Protons in water moving up and down axonal pathways themselves can exchange with the myelinated protons. This means myelinated protons have a very short T1, reduce the average T1 of the water in white matter.
How can you make a surface rendering of the cortex with T1 weighted image data sets?
Aim is to find how the cortex changes with development.
Genes a key early factor in development; environment, education, emotional, nutrition, toxins…all major affectors
Synaptic pruning and myelination changes: sensory & motor systems complete first (pre and early school), higher order functions still developing up to early adulthood.
A baby born at 26 weeks has a much smoother cortex than one born at 34 weeks.
How does the brain connectivity work? White matter tracts?
These can be observed via Diffusion MRI.
Looking at the structure of the neurone, there is the cell body and the axon with myelin. Within the axon are neurofibrils with the water that picks up the NMR signal to create the image.
With MRI, you can measure how freely water can diffuse in different directions. Can determine direction of maximum and minimum diffusion. With that info, can work out the orientation of the axon within brain.
These diffusion MRIs show an anisotropy map.
High anisotropy means diffusion is very high in one direction and low in the other.
In grey matter, don’t have myelinated structures = dark
In white matter, very high diffusion orientation and restricted diffusion orientation.
What is White Matter Anatomy from diffusion tensor MRI?
Colour coding shows direction of maximum diffusion. Superior to inferior in blue. Anterior to posterior in green and left to right in red.
What is a 3D MR angiography of the brain?
Radio frequency passes - Very short TR of about 10ms used - flowing blood provides a high signal against a darker background tissue signal.
Signal in static tissue = very weak
Signal from water in blood flowing through that tissue = high
Important for detecting strokes, in surgical procedures like thrombectomy, it tells whether the surgical intervention has been successful or not.
