fMRI: Biological Basis and Experiment Design
Lecture 2
• Pretest results
• Neural architecture
• Programming
assignment
Pretest results
The brain uses 20% of consumed glucose in
adults; 50% in children.
Adult (showing scar tissue following hernia repair)
Pediatric patient (with fungal infection of liver)
18-FDG PET images from Abouzied et al. (2005). J. Nuc. Med. Tech. 33(3):145
Neurons
based on Ch. 3, Zigmund et al. Fundamentals of Neuroscience
An example of cortical architecture/circuit
1.
2.
3.
4.
5.
Thalamic afferent
Cortical efferent
Cortico-cortical eff.
Thalamic afferent
Cortico-thalamic eff.
http://137.222.110.150/calnet/mcortex/page2.htm
Layers: cortical and vascular
from Fonta & Imbert, Vascularization in the primate visual cortex during development. Cer. Cortex 12:199-211
brown = cytochrome oxidase (neurons); blue = alkaline phosphatase (endothelial cells)
neurons
blood
vessels
Basic neuron behavior
• Dendriditic input
EPSPs
• Integration
• Propagation
Action potentials
• Synapse
(neurtransmitter concentration
in synaptic cleft)
Neuron types (neocortex)
•
Pyramidal – output cells
–
location:
•
•
•
–
•
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
•
•
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
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/
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/.../membrane_intro.htm and www.bergleslab.com/research.html
images from Nedergaard et al, “New Roles for Astorcytes …”, Trends in Neuroscience 26(10:523
Cortical computation
Cortico-cortical cxns
Intrinsic cxns
Output: spikes
Thalamic input: spikes
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 = ???
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
Energy budgets
Lennie (2003) “The Cost of Cortical Computation”, Current Biology 13:493.
Attwell and Laughlin (2001) “An energy budget for signaling in the grey matter of
the brain,” J. Cer. Blood Flow & Metab. 21:1133.