# Presentation: 721099

## Slide 1

## HDR varies across regions

- HDR varies across *regions*
- (plumbing or neuronal?)

## Can FMR adaptation be at least partially due to hemodynamics?

## Slide 4

## Slide 5

## Slide 6

## Slide 7

## Slide 8

## Slide 9

## Slide 10

## A. S. Tuan, R. M. Birn, P. A. Bandettini, G. M. Boynton, Differential MEG and fMRI responses to visual stimulation onset rate  (in preparation) 

- R.M. Birn, P. A. Bandettini, The effect of stimulus duty cycle and "off" duration on BOLD response linearity. *NeuroImage*, **27**, 70-82 (2005)

- R. M. Birn, Z. Saad, P. A. Bandettini, Spatial heterogeneity of the nonlinear dynamics in the fMRI BOLD response. *NeuroImage*, **14**: 817-826, (2001).

## Increases: linearity

**Logothetis et al. (2001) Nature, 412, 150-157.**

**P. A. Bandettini et al, (2001) Nature Neuroscience, 4:  864-866.**

*R.M. Birn, et al. Neuroimage 14, 817-26, 2001*

## Nonlinearity – visual task

*R.M. Birn, et al. Neuroimage 14, 817-26, 2001*

**Notes:**
The nonlinearity clearly shows some variation across space, as illustrated for one slice.  The amplitude of a response in this pixel was only about 3 times larger than a linear model at 250ms, whereas it was about 7 times as large in a different voxel. 
These differences can also be seen in the response time courses at each of the stimulus durations.  The nonlinearity map, however, does not appear similar to maps of magnitude or latency.

## Nonlinearity – motor task

- 2

- 4

- 6

- 8

- 0

- 1

- 2

- 3

- 4

- 5

- Stimulus Duration

- f (SD)

- 2

- 4

- 6

- 8

- 0

- 1

- 2

- 3

- 4

- 5

- Stimulus Duration

- f (SD)

- nonlinearity

- 20

- 40

- 0

- 5

- 10

- 15

- 20

- 25

*R.M. Birn, et al. Neuroimage 14, 817-26, 2001*

**Notes:**
In the SMA, the response for a 500ms period of finger tapping was approximately 8 times as large as a linear prediction, whereas in the primary motor area, it was only 3 times as large.  This is also seen in the signal time courses, where responses in the SMA at 500ms to 4000ms periods of finger tapping have very similar responses.

## Reproducibility

- Nonlinearity2

- Nonlinearity1

- Nonlinearity2

- Nonlinearity1

*Visual task*

*Motor task*

- Experiment 1

- Experiment 2

- Experiment 1

- Experiment 2

*R.M. Birn, et al. Neuroimage 14, 817-26, 2001*

## Estimated neuronal input

- Estimated Neuronal Activity

*Contrast Reversing Checkerboard*

## Estimated neuronal input

- time(s)

- Estimated Neuronal Activity

*Static Grating*

## Decreases: linearity

- R.M. Birn, P. A. Bandettini. *NeuroImage*,

## Slide 19

## Increases: duty cycle

- R.M. Birn, P. A. Bandettini, The effect of stimulus duty cycle and "off" duration on BOLD response linearity. *NeuroImage*, **27**, 70-82 (2005)

## Model – Neuronal effects

- adaptation

- OFF response

- refractory period

## Refractory effect

- ISI

## Simulation results – Neuronal effects

- Adaptation

- Adaptation + refractory

- Adaptation + refractory + OFF response

- Linear

- 1

- 1

- 1

- 2

- 1

## Slide 24

## Slide 25

## Slide 26

## 11026–11031  PNAS  September 26, 2000 vol. 97  no. 20

**11026–11031 ** PNAS  **September 26, 2000** vol. 97  no. 20

## BOLD response amplitude and linearity

- 0

- 5

- 10

- 15

- 20

- -6

- -4

- -2

- 0

- Stimulus OFF Duration (s)

- % Signal Change

- 0

- 5

- 10

- 15

- 20

- 0

- 0.5

- 1

- 1.5

- Stimulus OFF duration (s)

- Relative Amplitude
- (measured / linear)

*linear*

*linear*

*measured*

*measured*

*Amplitude*

*Linearity*

- to different stimulus OFF periods

## BOLD response to different stimulus duty cycles

## Nonlinearity of oxygen extraction, E(f)

- Flow

- E(f) / E0

- Small flow increase

- Small flow decrease

- 0.8

- 1

- 1.2

- 1.4

- 1.6

- 1.8

- 2

- 2.2

- 2.4

- 0.4

- 0.6

- 0.8

- 1

- 1.2

- 1.4

*Linear prediction*

*Actual change*

*Linear prediction*

*Actual change*

## Estimate Neuronal Input from BOLD fMRI

- stimulus  duration

- 0.5 s

- 1 s

- 2 s

- 20 s

- measured response

- estimated
- neuronal input

*Contrast-reversing Checkerboard*

*R.M. Birn, et al. Proc ISMRM 2002*

## BOLD response to neuronal transients

- Neurons
- responding
- to change

- Population
- response

*Stimulus*

- Steady-state neurons

- Stimulus Duration

- BOLD Response
-  amplitude

**a** = initial slope

**b** = final slope

**a**

**b**

## CR-Checkerboard vs. Static Grating

- 0

- 1

- 2

- 3

- 4

- 5

- 0

- 5

- 10

- Stimulus Duration (s)

- Amplitude (%)

*Contrast-Reversing*
*Checkerboard*

*Static*
*Grating*

## Balloon Model Parameters

## “on” Linearity

- “on” Linearity

## “off” linearity

- “off” linearity

## Duty Cycle

## Neuronal effects to explain duty cycle effects

## Different stimulus “OFF” periods

- Stimulus
- timing

- BOLD
- Response

- Signal

- 2 s

- 3 s

- 4 s

- 8 s

- 16 s

*Brief stimulus OFF periods produce smaller decreases than expected*

*R.M. Birn, et al. Proc. ISMRM, 2001.*

## Varying “ON” and “OFF” periods

*Rapid event-related design with varying ISI*

- 25% ON

- 50% ON

- 75% ON

-  8% ON

*R.M. Birn, et al. Proc. OHBM 2001.*

## Varying “ON” and “OFF” periods

*Estimated *
*Impulse Response*

*Predicted Responses *
*to 20 s stimulation *

*R.M. Birn, et al. Proc. OHBM 2001.*