# Measurements and modeling of the hemodynamic response function in human cerebral cortex

> **NIH NIH R56** · BAYLOR COLLEGE OF MEDICINE · 2021 · $759,261

## Abstract

Summary
Brief periods of neural activity trigger a mixture of vascular and metabolic responses with somewhat
stereotypical dynamics. This hemodynamic response function (HRF) is heavily used in functional magnetic
resonance imaging (fMRI). While the HRF is usually assumed to be spatially invariant, detailed measurements
show that its dynamics exhibit significant temporal variability; such variability confounds standard linear
analysis of fMRI measurements. Nonetheless, the variability likely reflects changing interactions between blood
flow and oxygen metabolism that could provide critically useful information about brain function. Thus, it is of
strong interest to better understand the physics and physiology of the HRF.
 We developed and validated the Arterial Impulse Model (AIM) that combines a novel flow description with
compartmental, 1D, convection-diffusion oxygen transport. We propose further development and validation of
the model, coupled with detailed investigation of the HRF. Experimentally, we use multi-sensory stimulus
protocols to evoke the HRF broadly across the brain, and evaluate the responses using high-resolution arterial
spin labeling and fMRI to examine the character and variability of these responses across the brain. We will
expand our model to explain the biomechanical basis of this HRF variability in a far richer framework than
previous models, with the potential to transform fMRI from a rough neural correlate to a quantitative
measurement of cerebral blood flow and metabolism. We will also develop a clinical application of our whole-
brain HRF methods to evaluate early Alzheimer’s Disease (AD) or Mild Cognitive Impairment. Our simple,
hour-long fMRI evaluation has strong potential to provide a prospective biomarker of AD pathology.

## Key facts

- **NIH application ID:** 10419668
- **Project number:** 2R56NS095933-05A1
- **Recipient organization:** BAYLOR COLLEGE OF MEDICINE
- **Principal Investigator:** DAVID B RESS
- **Activity code:** R56 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $759,261
- **Award type:** 2
- **Project period:** 2016-05-15 → 2024-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10419668

## Citation

> US National Institutes of Health, RePORTER application 10419668, Measurements and modeling of the hemodynamic response function in human cerebral cortex (2R56NS095933-05A1). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10419668. Licensed CC0.

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