IST8AFall 2008

Introduction to the Brain

Outline of Topics

1. Imaging: postmortem and MRI

2. Brain Macro anatomy – lobes, tissues, cortex, hippocampus, amygdala, connectivity

3. Brain Micro anatomy – Neurons

4. Dynamics of brain change over time

5. Our lab: healthy normal aging vs. dementia

Studies of Brain Form and Function

• Postmortem brains

Used for precise anatomical measurements

• Living subjects (computer analysis)

Use MRI imaging to track form and function in living individuals

The Human Brain

Cerebrum and Cerebellum

-Cerebrum divided into four regions, Frontal, Parietal. Occipital, Temporal

-Highly convoluted surface with 6 layers of cells in the cortex.

Four Cerebral Lobes(viewed from midline)

MRI Images

• Magnetic Resonance Imaging• Intense magnetic and radio frequency fields• Quantum mechanics• High resolution imaging: 1. anatomical (features in fine detail)

2. functional (activations)

• Lauterbur and Mansfield – Nobel Prize 2003

Sample MRI Images

• High resolution anatomical MRI

• 3D and 2D views• Skull in place and

stripped

Axial

(horizontal)

Coronal

Whole Head MRI Slices

Sagittal Whole Head Slice

Macro Anatomy: coronal and sagittal views

GrayWhite

CSFAmygdala(one on each

side)

Hippocampus

Tissue Types

Brain Connectivity: Memory Structures

hippocampi fornix

Frontal-occipital fasciculi (axon bundles)

External view for context

An elephant never forgets: comparison of elephant and human hippocampus

Elephant hippocampi (red) Human hippocampi

Source: www.allmanlab.caltech.edu/PDFs/Hakeem2005.pdf

Brain Connectivity: Visual streams

Source: The Primary Visual Cortex, by Matthew Schmolesky, http://webvision.med.utah.edu/VisualCortex.html

Source: http://philosophy.hku.hk/courses/cogsci/media/visionstreams.jpg

Incoming

Dorsal and Ventral

Micro Anatomy: The Neuron

Components:

1. Cell body (gray matter)

2. Dendrites

3. Axon (white matter – from myelin sheathes)

Axons may be very long e.g. front to back of brain or length of spinal chord

Source: www.enchantedlearning.com

Neuron Function

Neurons are electrochemical signaling cells.

• Signals (action potentials) travel down axons to terminal boutons

• Synapse: tiny space between axonal boutons and dendrites of the next neuron

• Neurotransmitters: released across synapse by arrival of action potential.

Received by post-synaptic dendrites.

Neuron communication

Source: http://www.niaaa.nih.gov/Resources/GraphicsGallery/Neuroscience/synapse.htm

Aging and the Brain

• What anatomical differences occur between young and old?

• What about between healthy normal aging and dementia?

• What steps can be taken to minimize or prevent unhealthy changes?

Categories of Aging

Very healthy normal

Mild cognitive impairment

Alzheimer’s Disease

Brain change over 1 year:patterns of gray matter loss

Normal Alzheimer’s

Normal vs. Alzheimer’sGross feature differences

Two structures illustrated in these slides differ greatly between normal (right) and Alzheimer’s

Coronal view (from front)

Sagittal view (from side; frontal lobe to left)

Alzheimer’s Normal

Ventricles (fluid filled cavities)

Hippocampi (long-term memory). Left hippocampus in green oval.

Ventricles greatly enlarged

Hippocampi severely shrunken and surrounded by fluid (black spaces)