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 (with substantial randomness) Heispheres -> Lobes -> Sulci & Gyri Sulci and Gyri are all named but somewhat variable across individuals

Structural Anatomy Brodmann Areas defined by cytoarchitecture map of variations in cellular morphology

Connectivity Anatomists are 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 (e.g. dextran) follow axons to where they are going 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!

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! Which is more useful?

Structural and Functional Imaging This is a Functional MRI Image !?

Structural and Functional Imaging This is a structural MRI image (an “anatomical” image)

Structural and Functional Imaging What you really want is both images co-registered

Structural and Functional Imaging What you really want is both images co-registered Why? What’s wrong with the functional image alone?

Structural and Functional Imaging Functional images tend to be lower resolution and fail to convey spatial information Pixels

Structural and Functional Imaging Structural images have finer (smaller) pixels Pixels

Structural and Functional Imaging Brain scans (CAT, PET, MRI, fMRI) are all made up of pixels (stands for picture elements) Pixels

Structural and Functional Imaging “Slices” are assembled into “volumes” Pixels

Structural and Functional Imaging Volumes are composed of “volume elements” or voxels Voxels

Structural and Functional Imaging Another thing you want: the ability to tell other people where something is “the activity was centered on voxel #653” will not work in a scientific journal

Structural and Functional Imaging MRI anatomical spaces Talairach Space: Based on detailed analysis of one elderly woman Talairach & Tournoux (1988) Montreal Neurological Institute Template (MNI) based on average of 152 different brains, each normalized to Talairach space advantage: gyri and sulci are more representative disadvantage: it’s blurry MNI “Representative Brain” the one brain from the 152 in the MNI Template set that is most like the average advantage: it’s not blurry disadvantage: it’s still just one brain

Structural and Functional Imaging Reasons for normalizing to standard stereotaxic space (templates) two levels: within-subject and between-subjects

Structural and Functional Imaging Within-Subject Reasons: structural and functional volumes may not be coregistered due to movement distortion results can be described in standard coordinates data across sessions can be averaged

Structural and Functional Imaging Between-Subject Reasons: Volumes will not match because of variability across individuals results can be described in standard coordinates data across participants can be averaged

Preprocessing of Structural and Functional Images Normalizing images to fit a standard template (e.g. Talairach) Define Coordinate System using easily recognizable landmarks Origin in the Anterior Commissure y-axis connects AC and PC x-axis perpendicular interhemispheric plane and through AC z-axis perpendicular to x and y

The Talairach Coordinate System PC AC

The Talairach Coordinate System AC - PC line defines y-axis +y

The Talairach Coordinate System -x x-axis perpendicular to interhemispheric plane +x +y

The Talairach Coordinate System +z -y -x z-axis perpendicular to x-y plane +x -z +y

Next time: Cortical Flattening