What does HRF mean in UNCLASSIFIED

The Haemodynamic Response Function (HRF) is a mathematical model that describes the relationship between neural activity and changes in blood flow and oxygenation in the brain. It represents the temporal dynamics of the neurovascular coupling process, which is the physiological mechanism by which neural activity is translated into measurable changes in brain hemodynamics.

The HRF is used in functional neuroimaging techniques such as fMRI and NIRS to deconvolve the neural activity signal from the measured hemodynamic response. By convolving the estimated HRF with the measured hemodynamic signal, researchers can estimate the underlying neural activity that gave rise to the observed changes in blood flow or oxygenation.

There are various types of HRFs, each representing different aspects of the neurovascular coupling process. Common HRFs include the canonical HRF, the gamma-variate HRF, and the double-gamma HRF. The choice of HRF depends on the specific neurovascular coupling model and the experimental conditions being studied.

The HRF can be estimated using various methods, including:

• Model-based methods: These methods assume a specific shape for the HRF and estimate its parameters from the measured hemodynamic data.
• Data-driven methods: These methods use statistical techniques to directly estimate the HRF from the measured hemodynamic data without assuming a specific shape.

The HRF can be influenced by various factors, including:

• Neurophysiological factors: The type and intensity of neural activity
• Vascular factors: The properties of the cerebral vasculature, such as vessel size and density
• Physiological factors: Factors such as age, sex, and physiological state
• Experimental conditions: Factors such as scanner parameters and experimental design