fMRI: Biological Basis and Experiment Design Lecture 13: BOLD

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fMRI Biological Basis and Experiment
DesignLecture 13 BOLD

• Neurons per voxel
• Neural signaling
• Neural/vascular link?
• HRF
• linearity

1 light year 5,913,000,000,000 miles?
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BOLD relies on T2-weighted images
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Predicting BOLD signal in a single voxel
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Neural activity input local computation
output
astrocyte
Excitatory neuron
Inhibitory neuron
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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.
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Predicting BOLD signal, Part I neural activity

• Stimulus
• Input
• Local computation
• Output__________________
• Total

Molecules of ATP
time (ms)
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BOLD signal, Part II Hemodynamic response

• Total Neural Activity
• Oxygen extraction fraction
• CBF
• CBV_______________
• BOLD

Molecules of ATP
time (ms)
time (sec)
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Cannonical HIRF
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Key assumptions of convolution model

• Linearity
• Homogeneity
• Additivity
• Superposition
• Shift-invariance no refractory period

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Modeling BOLD with convolution