Optode placement is central to fNIRS data quality. Reliable optode-scalp contact can be affected by hair density, curl pattern, hairstyle, head shape, scalp sensitivity, participant comfort, and hardware fit.
This stage focuses on practical, participant-centered approaches to optode placement and data collection.
What this stage covers
- Standardized placement frameworks, such as 10-20 or ROI-based layouts
- Balancing anatomical consistency with signal quality
- Documenting placement adjustments
- Using multiple cap sizes or adaptable configurations
- Gentle, hair-aware preparation strategies
- Parting and sectioning hair while minimizing disruption
- Clearing hair from beneath optodes before increasing pressure
- Checking comfort throughout setup and recording
- Explaining each step and involving participants in the process
- Respecting cultural considerations, including head coverings and preferences about physical contact
- Adjusting procedures for infants, children, clinical groups, and other specific populations
Current resources
- “Towards more inclusive fNIRS research: Best practices for participants with afro-textured hair,” NIRx webinar presented by Abria Simmons, University of Maryland College Park, and Gavkhar Abdurokhmonava, University of Maryland.
- “Signal Optimization with Long Hair, Types 1 and 2, High-Density fNIRS Array” prepared by Jessica Anderson and Laura Carlton, Boston University, demonstrates a method for signal optimization with long hair, shown with an open-webbed high-density fNIRS headcap design. Starting from the top/front of the head, the researcher uses a tool to thread the hair through the headcap, reducing the amount of hair between the scalp and optodes to improve signal clarity.
- “Signal Optimization with Braided Hair, Types 3 and 4, Sparse fNIRS Array” prepared by Jessica Anderson and De’Ja Rogers, Boston University, demonstrates a method for signal optimization with installed braids, shown with an open-webbed sparse-array fNIRS headcap design. The researcher gently pulls braids through the headcap close to the braid base to reduce hair volume between the scalp and cap, allowing optodes to sit nearer the scalp.
- “Removing an fNIRS Headcap with Long Hair” prepared by Jessica Anderson and Laura Carlton, Boston University, accompanies the long-hair signal optimization demonstration. It shows an approach for unthreading long hair from the fNIRS headcap after data collection, prioritizing hair preservation and participant comfort. The researcher uses the parting end of a comb, or their hand, to unthread hair in the opposite order in which it was threaded, with frequent verbal check-ins to maintain comfort.
Suggested additions
We welcome hair-handling demonstrations, optode-placement protocols, setup checklists, comfort-monitoring scripts, participant-facing setup instructions, examples of documenting placement adjustments, and videos showing practical fNIRS setup across different hair types and hairstyles.
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