# C-fiber-related brain responses evoked by laser heat pulses applied to the back

## TL;DR

This study identifies an effective laser stimulation protocol to reliably detect brain responses related to C-fiber activation in the back.

## Contribution

A reliable stimulation protocol using laser heat pulse trains is proposed for studying C-fiber-related brain responses.

## Key findings

- Laser pulse trains at 0.67 Hz elicited C-fiber responses in 86.7% of participants.
- C-fiber responses occurred between 500 and 1500 ms post-stimulus, aligning with second pain perception.
- The protocol enables temporal summation of second pain and detection in most individuals.

## Abstract

The aim of the present study was to examine C-fiber-related brain responses evoked by laser heat stimuli applied to the lumbar area, and to determine the stimulation protocol that produces the most reliable responses. Thirty healthy volunteers completed the study. Combinations of different stimuli (single pulses or trains of three pulses) with different pulse durations (7 or 14 ms) were used to compare C-fiber-related brain responses between protocols. The four protocols elicited comparable C-fiber-related brain responses to laser heat pulses. However, pulse trains of 7 ms pulses at 0.67 Hz elicited C-LEPs in the greatest proportion of participants (86.7 %). C-LEPs occurred within a 500 ms to 1500 ms post-stimulus time window, consistent with the perception associated with C-fiber activation. These results provide novel data on C-fiber-related brain responses to painful stimuli and a reliable stimulation protocol for future studies on low back pain.

•Laser pulse trains applied to the back produce temporal summation of second pain.•These stimuli also allow the detection of C-fiber brain responses in most individuals.•This provides a reliable stimulation protocol for future studies on low back pain.

Laser pulse trains applied to the back produce temporal summation of second pain.

These stimuli also allow the detection of C-fiber brain responses in most individuals.

This provides a reliable stimulation protocol for future studies on low back pain.