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.