fMRI: Biological Basis and Experiment DesignLecture 2
• Pretest results• Neural architecture• Programming
assignment
Pretest results
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
Neuronsbased on Ch. 3, Zigmund et al. Fundamentals of Neuroscience
An example of cortical architecture/circuit
http://137.222.110.150/calnet/mcortex/page2.htm
1. Thalamic afferent2. Cortical efferent3. Cortico-cortical eff.4. Thalamic afferent5. Cortico-thalamic eff.
Layers: cortical and vascularfrom 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
• Integration
• Propagation
• Synapse(neurtransmitter concentrationin synaptic cleft)
Action potentials
EPSPs
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/
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 computationCortico-cortical cxns
Intrinsic cxns
Thalamic input: spikesOutput: 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.
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