Reliable EEG responses to the selective activation of C-fibre afferentsusing a temperature-controlled infrared laser stimulator in conjunctionwith an adaptive staircase algorithm
(2013) PAIN® — Vol. 154, n° 9, p. 1578-1587 (2013)
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- Brain responses to the activation of C-fibres are obtained only if the co-activation of Ad-fibres is avoided. Methods to activate C-fibres selectively have been proposed, but are unreliable or difficult to implement. Here, we propose an approach combining a new laser stimulator to generate constant-temperature heat pulses with an adaptive paradigm to maintain stimulus temperature above the threshold of C-fibres but below that of Ad-fibres, and examine whether this approach can be used to record reliable C-fibre laserevoked brain potentials. Brief CO2 laser stimuli were delivered to the hand and foot dorsum of 10 healthy subjects. The stimuli were generated using a closed-loop control of laser power by an online monitoring of target skin temperature. The adaptive algorithm, using reaction times to distinguish between late detections indicating selective activation of unmyelinated C-fibres and early detections indicating coactivation of myelinated Ad-fibres, allowed increasing the likelihood of selectively activating C-fibres. Reliable individual-level electroencephalogram (EEG) responses were identified, both in the time domain (hand: N2: 704 ± 179 ms, P2: 984 ± 149 ms; foot: N2: 1314 ± 171 ms, P2: 1716 ± 171 ms) and the timefrequency (TF) domain. Using a control dataset in which no stimuli were delivered, a Receiver Operating Characteristics analysis showed that the magnitude of the phase-locked EEG response corresponding to the N2-P2, objectively quantified in the TF domain, discriminated between absence vs presence of C-fibre responses with a high sensitivity (hand: 85%, foot: 80%) and specificity (hand: 90%, foot: 75%). This approach could thus be particularly useful for the diagnostic workup of small-fibre neuropathies and neuropathic pain.
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Jankovski, A., Plaghki, L., & Mouraux, A. (2013). Reliable EEG responses to the selective activation of C-fibre afferentsusing a temperature-controlled infrared laser stimulator in conjunctionwith an adaptive staircase algorithm. PAIN®, 154(9), 1578-1587. https://doi.org/10.1016/j.pain.2013.04.032 (Original work published 2013)