fMRI: Biological Basis and Experiment Design Lecture 2

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fMRI Biological Basis and Experiment
DesignLecture 2

• Pretest results
• Neural architecture
• Programming assignment

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Pretest results
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The brain uses 20 of consumed glucose in adults
50 in children.
Pediatric patient (with fungal infection of liver)
Adult (showing scar tissue following hernia
repair)
18-FDG PET images from Abouzied et al. (2005). J.
Nuc. Med. Tech. 33(3)145
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Neuronsbased on Ch. 3, Zigmund et al.
Fundamentals of Neuroscience
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An example of cortical architecture/circuit

1. Thalamic afferent
2. Cortical efferent
3. Cortico-cortical eff.
4. Thalamic afferent
5. Cortico-thalamic eff.

http//137.222.110.150/calnet/mcortex/page2.htm
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Layers cortical and vascularfrom Fonta
Imbert, Vascularization in the primate visual
cortex during development. Cer. Cortex
12199-211brown cytochrome oxidase (neurons)
blue alkaline phosphatase (endothelial cells)
neurons
blood vessels
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Basic neuron behavior

• Dendriditic input
• Integration
• Propagation
• Synapse

EPSPs
Action potentials
(neurtransmitter concentration in synaptic cleft)
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Neuron types (neocortex)

• Pyramidal output cells
• location
• Layer II and III cells are small, with restricted
  dendritic trees and axonal collaterals to
  neighboring cortical domains
• Layer III and V are medium-to-large with more
  extensive dendritic trees and long
  corticocortical cxns
• Layer VI exhibit greater morphologic variability
  and extend to corticothalamic
• Size giant p. neurons can have dendritic arbors
  2mm across
• Spiny stellate excitatory interneurons (only
  other spiny neuron, aside from pyramidal)
• Location IV, mostly in primary sensory
  intrinsic axonal targets with radial
  organization link IV with III, V, and VI
• Size small dendritic arbor contained w/in
  layer
• Basket, chandelier and double bouquet inhibitory
  interneurons (regulate pyramidal cell function)
• Locations
• Basket III and V Chandelier III (can shut down
  pyramidal)
• ... "Clutch" cell driven by thalamus and
  targets spiny stellate interneurons

Images taken from http//huanglab.cshl.edu/gallery
.html, www.albany.edu/neuron/summer/
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Neuroglia

• Oligodendrocytes make myelin (Schwann cells in
  the peripheral nervous system)
• Astrocytes
• Connected by gap junctions intracellular
  calcium waves
• Contribute to angiogenesis
• Source of extracellular matrix proteins and
  adhesion molecules
• Source of growth factors
• Housekeeping at synaptic clefts (glutamate
  cycling)
• Microglia CNS immune response

Images taken from www.cytochemistry.net/.../membra
ne_intro.htm and www.bergleslab.com/research.html

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images from Nedergaard et al, New Roles for
Astorcytes , Trends in Neuroscience 26(10523
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Cortical computation
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Roll call (per mm3, in V1)

• Excitatory neurons .8 x 40,000 32,000
• Pyramidal cells dominate throughout
• Stellate interneurons in input layers
• Inhibitory interneurons .2 x 40,000 8,000
• Basket, chandelier, ...
• Glia (most of which are astrocytes) 38,000
• Endothelial cells ???

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Energy budget

• Dendriditic input EPSP
• Restore membrane potential
• Integration EPSP
• Restore membrane potential
• Propagation
• (in unmyelinated axons)
• Restore membrane potential
• Synapse glutamate cycling and presynaptic Ca
• Restore membrane potential

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Energy budgets
Lennie (2003) The Cost of Cortical Computation,
Current Biology 13493. Attwell and Laughlin
(2001) An energy budget for signaling in the
grey matter of the brain, J. Cer. Blood Flow
Metab. 211133.