Lecture 22 fNIR Flashcards
(32 cards)
What is fNIRS?
Functional Near-Infrared Spectroscopy (fNIRS) is a hemodynamic imaging technique using near-infrared light to measure brain activity based on changes in blood oxygenation.
What is the typical wavelength range used in fNIRS?
700–900 nanometers (in the near-infrared spectrum).
Why is near-infrared light suitable for brain imaging?
Because human skin
What molecules are key to fNIRS signal measurement?
Oxyhemoglobin and deoxyhemoglobin
What happens to blood oxygenation after neural activity?
There is an initial dip in oxygenation
What is the time course of the Hemodynamic Response Function (HRF) in fNIRS?
Peaks 4–8 seconds after neural activity; can take up to 16 seconds to return to baseline.
How is fNIRS similar to fMRI BOLD?
Both reflect the hemodynamic response to neural activity and show similar HRF profiles (initial dip and delayed peak).
How is fNIRS measured?
Using optodes—photo emitters and receivers—placed on a cap worn on the head to measure reflected NIR light.
What is the standard distance between optode emitter and receiver?
30 mm.
What path does NIR light follow in the brain?
It follows a crescent-shaped path due to scattering (modified Beer-Lambert Law).
Is there a standard optode layout for fNIRS?
No
List one advantage of fNIRS over fMRI.
It is portable
Why is fNIRS especially useful for infant research?
Infants have smaller heads and thinner skulls
Where can fNIRS be used outside the lab?
In naturalistic environments
What are some technological advantages of modern fNIRS systems?
Some can store data locally and transmit via Bluetooth.
Name one key limitation of fNIRS vs fMRI.
Lower spatial resolution due to light scatter and inability to detect deep brain activity.
What types of brain areas can fNIRS measure?
Only superficial cortical regions; not effective for sulci or deeper structures.
How does fNIRS compare to EEG/MEG in temporal resolution?
fNIRS has lower temporal resolution and poorer signal-to-noise ratio.
Why is fNIRS sensitive to extracerebral vascularization?
Because highly vascularized non-brain tissues affect the reflected light
What is one way to address extracerebral signal interference?
Use of short-channel detectors.
How is retinotopic organization validated with fNIRS?
By mapping visual field responses and confirming hemisphere-based inverted representations similar to fMRI.
What can fNIRS tell us about visual attention?
It can distinguish attention to broad areas (e.g. left vs right visual field)
Why combine fNIRS with fMRI?
To validate and localize fNIRS signals by comparing them to the high spatial resolution of fMRI BOLD responses.
In what populations is fNIRS useful over fMRI?
Infants
