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fMRI: Biological Basis and Experiment Design Lecture 13: BOLD

fMRI: Biological Basis and Experiment Design Lecture 13: BOLD. Neurons per voxel Neural signaling Neural/vascular link? HRF linearity. 1 light year = 5,913,000,000,000 miles?. Signal is low where T 2 * is short. Signal will increase where blood flow increases.

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fMRI: Biological Basis and Experiment Design Lecture 13: BOLD

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  1. 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?

  2. Signal is low where T2* is short. Signal will increase where blood flow increases. BOLD relies on T2*-weighted images

  3. Predicting BOLD signal in a single voxel

  4. Cortico-cortical cxns Intrinsic cxns Output: spikes Thalamic input: spikes Neural activity = input + local computation + output astrocyte Excitatory neuron Inhibitory neuron

  5. 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.

  6. Predicting BOLD signal, Part I: neural activity • Stimulus • Input • Local computation • Output__________________ • Total Molecules of ATP time (ms)

  7. BOLD signal, Part II: Hemodynamic response • Total Neural Activity • Oxygen extraction fraction • CBF • CBV_______________ • BOLD Molecules of ATP time (ms) time (sec)

  8. Cannonical HIRF

  9. Key assumptions of convolution model • Linearity: Homogeneity+ Additivity= Superposition • Shift-invariance: no refractory period

  10. Modeling BOLD with convolution

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