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. 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

Neurons based on Ch. 3, Zigmund et al. Fundamentals of Neuroscience

An example of cortical architecture/circuit 1.Thalamic afferent 2.Cortical efferent 3.Cortico-cortical eff. 4.Thalamic afferent 5.Cortico-thalamic eff.

Layers: cortical and vascular from Fonta & Imbert, Vascularization in the primate visual cortex during development. Cer. Cortex 12: brown = cytochrome oxidase (neurons); blue = alkaline phosphatase (endothelial cells) neurons blood vessels

Basic neuron behavior Dendriditic input Integration Propagation Synapse (neurtransmitter concentration in 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

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 and

images from Nedergaard et al, “New Roles for Astorcytes …”, Trends in Neuroscience 26(10:523

Cortical computation Cortico-cortical cxns Intrinsic cxns Thalamic input: spikes Output: 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.