Deconstructing the 10% myth

Deconstructing the 10% myth

• Does it refer to 10% of brain tissue or 10% of a more abstract “functional capacity”?

• If it refers to 10% of brain tissue, then which 10%!?• Does it mean “at any moment” or “ever in your

life”?• If it means “at any moment” (and it were true),

would it be a good thing to boost this number to 100%!?

• What does “use” mean?

The Methods of Cognitive Neuroscience

• Is the 10% “myth” true in any way? • More importantly, how could you go about

testing the theory?

Goals and Methods

• Broad goal is to understand the brain activity associated with

specific cognitive processes such as attention, memory, language

and consciousness

• There are several smaller questions in this. For example:– What structures do what jobs?– How is information represented in these structures?– How is information passed between these structures?– How is information transformed by these structures?– How are the structures transformed by information!?

Anatomy

• What is the difference between Structural Anatomy and Functional Anatomy?

• What roles do each play in our understanding of the brain?

Structural Anatomy

• Brain structures are identified in a hierarchical fashion• Hemispheres -> Lobes -> Sulci & Gyri• Sulci and Gyri are all named

– but somewhat variable across individuals

• But remember – THE CORTEX IS A FLAT SHEET of tissue

Structural Anatomy

• Brodmann Areas defined by cytoarchitecture– map of variations in cellular morphology– It is probably not coincidence that Broadman areas are also

generally functionally distinct – WHY?

Connectivity

• Anatomists are also concerned with brain regions and how they are interconnected

• Interconnectedness occurs at various levels:– interneurons– cortico-cortical connections– thalamo-cortical and cortico-thalamic– afferent = “to” (e.g. sensory) and efferent = “from”

(e.g. motor)

Connectivity

• How do anatomists study connectivity?– Retrograde Tracers (e.g. horseradish peroxidase)

follow axons back to where they came from– Anterograde Tracers follow axons to where they

are going

Connectivity

• Diffusion Tensor Imaging (DTI)– MRI Technique that

traces long white matter tracts

Connectivity

• “Ascending” and “descending” projections in sensory systems– estimate: for every

ascending projection there are ten descending projections

Connectivity

• “Ascending” and “descending” projections in sensory systems– estimate: for every ascending projection there are

ten descending projections

Why would we have descending projections?

Connectivity

• It is the inter-connectivity of the brain that (probably) allows it to perform the vastly complex processes of cognition

Structural and Functional Imaging

• There are a number of well known techniques to create images of brain anatomy– CAT scan, MRI, X-Ray,

• Note however that structural and functional images are not the same thing!


• There are a number of well known techniques to create images of brain anatomy– CAT scan, MRI, X-Ray,

• Note however that structural and functional images are not the same thing!

• Which is more useful? If you could go back in time and give one of these techniques to the earliest neuroscientists, which would it be?


• This is a Functional MRI Image !?


• This is a structural MRI image (an “anatomical” image)


• What you really want is both images co-registered


• What you really want is both images co-registered

• Why? What’s wrong with the functional image alone?


• Functional images tend to be lower resolution and fail to convey spatial information

Pixels


• Structural images have finer (smaller) pixels

Pixels


• Why? What’s wrong with the functional image alone?

• More subtly: a functional image typically isn’t a picture of the brain at all! It’s a picture of something else– PET, fMRI = oxygenated blood– EEG = electric fields– MEG = magnetic fields

Documents

Deconstructing the 10% myth