1. 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?

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

3. Predicting BOLD signal in a single voxel

4. Neural activity = input + local computation + output Cortico-cortical cxns Intrinsic cxns Thalamic input: spikes Output: spikes 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 time (ms) Molecules of ATP

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