1. Reading electric minds: How blood reveals the spark Michelle Rigozzi Integrating the evoked response potential (ERP) with the functional magnetic resonance imaging blood oxygen level dependent (fMRI BOLD) response

2. In the beginning… Stimulus Neurons fire Oxygen deficiency. Increase in dHb Blood rushes in Oxygen excess. dHb drops

4. ER P Evoked response potential  reads neuronal activity Advantage: –High temporal resolution

5. fMRI BOLD Functional magnetic resonance imaging Blood oxygen level dependent  reads dHb levels Advantage: High spatial resolution

6. What we know Yet we are still to uncover…

7. …the gap Is one really just a slow version of the other? How is the underlying neuronal activity (ERP) manifested through the haemodynamic BOLD response? New insights for future models?

8. Super models Robinson & Rennie – neuronal model –P. A. Robinson, C.J. Rennie et al., 2002. Neurophysical Modeling of Brain Dynamics. Phys. Rev. E. Friston – haemodynamic model –Friston, K.J., 2003. Dynamic Causal Modelling. NeuroImage 0.

10. Real sparky Friston Robinson & Rennie Neuronal networks Electrical Response (Activity) input BOLD

11. ∫ing models…

12. Testing, testing… General behaviour, reliability and limits of equations ERP v BOLD response when changing: –Overall amplitude of a biphasic ERP –ERP peak ratio –Width of ERP

13. Changing ERP amplitude Fix peak ratio ERP = BOLD Hypothesis

15. Changing ERP peak ratios Vary height of 2 nd peak Hypothesis: –Area of ERP  BOLD

17. Changing ERP width Amplitude same, width stretched Hypothesis: ERP = BOLD

18. Log-log Linear-linear

19. What the future holds… We now know: –The peak amplitudes are linearly related –BOLD reflects integral of ERP –Linearity is lost once stimulation lengthens Shape of ERP is critical – The relationship still has much to reveal!

20. Got you thinking?