# Measuring Communication between Brain Regions

James Kent

Dr. Michelle Voss

Health, Brain, and Congition Lab

## Overview

• How do we measure brain activity?
• How do we model brain activity?
• How do we know the model works?

## Blood Oxygen Level Dependent (BOLD) Response

Ogawa, S., Lee, T. M., Kay, A. R., & Tank, D. W. (1990).

How do we measure brain activity?

## Hemodynamic Response Function (HRF)

How do we model brain activity?

## The Brain during a Task

How do we model brain activity?

## Condition A (Orange)

How do we model brain activity?

## Condition A (Orange)

How do we model brain activity?

## Condition B (Blurple)

How do we model brain activity?

## Condition B (Blurple)

How do we model brain activity?

## Beta Series Correlations

• Brain Regions Conditionally Correlated
• Activated vs Activated Together

How do we model brain activity?

## But Data are Noisy

How do we model brain activity?

## And Trials Occur Close Together

How do we model brain activity?

## LSA

(least squares all)

• Computationally Cheap
• Works when intertrial interval is long

## LSS

(least squares separate)

• Computationally Expensive
• Works regardless of inter trial interval

## Estimate Activation (Betas) of Individual Trials

How do we model brain activity?

# How Can We Tell If Our Estimations are Accurate?

## Simulations!

1. Assign the ground truth beta series correlation (e.g., 0.2, 0.4, etc.)
2. Create data with the assigned correlation.
3. Vary the inter trial interval/number of trials.
4. Insert noise into the data.
5. Calculate beta series correlation on the simulated data.
6. Compare the ground truth with the observed correlations.

How do we know the model works?

## Validity of Correlations

Inter Trial Interval

Number of Trials

## Power to detect Differences

Inter Trial Interval

Number of Trials

# Conclusions

## Future/Current Directions

• Simulated vs. Real Data
• Find Real Effect Sizes
• Spatial Organization of Correlations

## Aknowledgments

Health, Brain, and Cognition Lab

• Matt Sodoma

NIH Funding: 5R01AG055500

Thesis Committee

• Dr. Michelle Voss
• Dr. Jatin Vaidya
• Dr. Vince Magnotta
• Dr. Jan Wessel
• Dr. Eliot Hazeltine

Florida International University

Talyor Salo (implemented LSA)

## Questions?

`Slides: slides.com/jameskent/2019-seminar`
`Simulations: github.com/jdkent/betaSeriesSimulations`
`HRF App: bit.ly/hrf_viz`
`Beta Series App: bit.ly/beta_series`

Come to Hacky Hour!

uihackyhour.github.io

Come to the Neuroimaging Workgroup:

github.com/NeuroimagingUIowa/monthlyMeetingMinutes

By James Kent

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