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Brains and Pictures of Brains

An introductory presentation on brain structure and imaging

Dianne Patterson

on 28 September 2018

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Transcript of Brains and Pictures of Brains

A neuron has a cell body
and axons (connecting wires)
Neurons work together in bundles
and their wires (axons) get bundled together too
CSF is the stuff you don't want leaking out of your ears after you crack your head on the pavement.
When a patient has a stroke or tissue loss, CSF fills the empty spaces
DTI: uses color coded direction maps
-Made mostly of neuron bodies
GM structure
WM Structure
GM covers the surface of the brain, along ridges (gyri) and furrows (sulci)
Axons reach target and start to pull strongly interconnected regions together.
Why gyri and sulci?
There are different schemes for dividing the surface GM
You can further define regions by sulci and gyri
First, there are lobes:
Each lobe has a sort of general purpose
For example,
STG (superior temporal gyrus)
MTG (middle temporal gyrus)
ITG (inferior temporal gyrus)
STS (superior temporal sulcus)
ITS (inferior temporal sulcus)
Can you find each one?
A guy named Brodmann, looked at cortex (GM) under the microscope,
and found that the neurons looked different in different regions.
He built a region classification based on this microscopic analysis.
Whenever you see a reference like "BA 44", that's a Brodmann area.
So we know there are short range connections between regions
on 2 sides of a gyrus
But, there are a bunch of long range connections too.
-covers the surface of the brain, like tree bark "cortex".
-Produces the action in fMRI
The neuron body needs energy...(more when it works hard*)
*Imaging techniques take advantage of this increased energy usage: PET identifies cells using more glucose (sugar); fMRI identifies cells using more oxygen
This bundling is good for us, because our instruments don't see individual cells.
DTI to the rescue
Because we are blinded by the White
Axons are like wires
White, because axons are covered in a layer of
If we slice into my brain
Grey Matter
White Matter
We can't tell where the wires go in normal anatomical scans
Diffusion Tensor Imaging allows us to follow axon bundles
Why do you think they call the brain wetware?
Cerebrospinal fluid fills in all the spaces
As we age, there is more space to fill.
What are These?

The dti maps look like this
Sporns, 2011
Early development: New neurons send out axons...
Outward folds appear. Ridges=gyri; furrows=sulci
Brains and Pictures of Brains
Dianne Patterson Fall, 2011
This is my brain
Of 3 tissues, GM, WM and CSF, 2 are
worth further attention: GM and WM
The fat is called "myelin"
There are 3 kinds of brain "tissue":
Grey Matter: cell bodies
White Matter: axons covered in myelin (fat covered wires)
CerebroSpinal Fluid: Why do you think they call it wetware?
Why the emphasis on the 3 types?
Because, the MRI scanner detects the differences between the tissues
The scanner displays the tissue differences as differences in image contrast
Depending on the scanner settings (like TR and TE), we can produce:
T2 images: better tissue contrast (but take longer to acquire).
T1 images: really fast, but less contrast between tissues
There are actually bunches of variations and tricks that can optimize the image in different ways: speed, contrast, resolution. You can't have everything, so you choose a balance of features.
From Mark Cohen's 2007 Lecture
-The brain is made up of 3 tissue types.
-The scanner can contrast the tissue types because of the the differences between them.
-Images we get out of the scanner are brain slices, usually oriented in one of 3 primary directions.
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