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The two-point discrimination threshold depends both on the stimulation noxiousness and modality

Abstract

The two-point discrimination threshold (2PDT) has been used to investigate the integration of sensory information, especially in relation to spatial acuity. The 2PDT has been investigated for both innocuous mechanical stimuli and noxious thermal stimuli; however, previous studies used different stimulation modalities to compare innocuous and noxious stimuli. This study investigated the 2PDT in 19 healthy participants, using both thermal (laser) and mechanical stimulation modalities. Within each modality, both innocuous and noxious intensities were applied. Concurrent point stimuli were applied to the right volar forearm, with separation distances of 0–120 mm, in steps of 10 mm. 0 mm corresponds to a single point. Following each stimulus, the participants indicated the number of perceived points (1 or 2) and the perceived intensity (NRS: 0: no perception, 3: pain threshold, 10: maximum pain). The order of stimulation modality, intensity and distance was randomized. The 2PDT for innocuous and noxious mechanical stimuli was 34.7 mm and 47.1 mm, respectively. For thermal stimuli, the 2PDT was 80.5 mm for innocuous stimuli and 66.9 mm for noxious stimuli. The average NRS for thermal stimuli was 1.6 for innocuous intensities and 4.0 for noxious intensities, while for mechanical stimuli, the average NRS was 0.9 for innocuous intensities and 3.6 for noxious intensities. This study showed that the 2PDT highly depends on both stimulation modality and intensity. Within each modality, noxious intensities modulates the 2PDT differently, i.e., noxious intensities lowers the 2PDT for thermal stimuli, but increases the 2PDT for mechanical stimuli.

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Data availability

All data generated or analysed during this study are included in this published article.

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Funding

This study was funded by the Danish National Research Foundation (DNRF121).

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Authors

Contributions

KSF and SG designed the study. KSF collected the data. KSF and SG analyzed and interpreted the data. KSF drafted the manuscript. All authors read and approved the final manuscript.

Corresponding author

Correspondence to Ken Steffen Frahm.

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The experiment was approved by the local ethical committee (VN-20190005).

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None to declare.

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Communicated by Winston D Byblow.

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Frahm, K.S., Gervasio, S. The two-point discrimination threshold depends both on the stimulation noxiousness and modality. Exp Brain Res 239, 1439–1449 (2021). https://doi.org/10.1007/s00221-021-06068-x

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Keywords

  • 2-point discrimination threshold
  • Spatial acuity
  • Laser stimulation
  • Mechanical stimulation
  • Pinprick stimulation
  • Psycho-physics
  • Sensory integration