Background & Aims

The nociceptive system can process complex sensory information in relation to both time and space. Directional discrimination is a combined measure of how both temporal and spatial information is integrated and discriminated in the nociceptive system (Frahm et al., 2018). Directional discrimination increases with decreasing stimulation velocity and increasing stimulation intensity (Frahm et al., 2019). Perceptual learning has been shown to improve the discrimination of both stimulation intensity and spatial location in the nociceptive system (Mancini et al., 2016), but it has not been investigated for directional discrimination, which combines several sensory features. Here, it was hypothesized that perceptual learning could also improve directional discrimination in the nociceptive system. Thus, this study investigated how perceptual learning could improve directional discrimination. Both supervised (with feedback) and unsupervised (without feedback) training were compared.

Methods

To determine the directional discrimination threshold, 28 healthy subjects were stimulated at the volar forearm. The stimulus was provided using a temperature-controlled laser system allowing moveable stimulation (Rujoie et al., 2023). Stimuli were delivered in four different directions (medial, lateral, proximal and distal), five stimulation lengths were used in either direction. Stimulation intensity was 46 °C, and the laser beam was displaced at 10 mm/s. Subjects had to indicate the perceived direction of the stimulus (forced choice).
The study ran over two separate days (48 hours apart). Each day was divided into three blocks. The first block was the baseline, the second was the training block and the third was the test block. In each block, 40 stimuli were delivered (four directions, five lengths, repeated twice). In one day, subjects received supervised training in the training block and in the other day they received non-supervised training. The order of days was randomized.

Results

All subjects participated in all sessions. Following supervised training, there was a significant increase in the correctness of the discriminated directions between the baseline and test session (LMM, p < 0.05). In contrast, following unsupervised training there was no significant difference between the baseline and test sessions (LMM, p = 0.598). Furthermore, there was no significant difference in the response correctness between the baseline of the groups on day 1, but there was a significant difference in the response correctness in the baseline sessions between day 1 and 2 for those who received supervised training on day 1 (LMM, p < 0.01). In the lateral-medial direction, the directional threshold decreased following supervised training, but not after unsupervised training. In the distal-proximal direction, the threshold increased for both types of training.

Conclusions

This study showed that perceptual learning can improve directional discrimination in the nociceptive system. The increase in discrimination performance was greater following training with feedback (supervised), indicating that training with feedback has a greater modulatory effect than merely repeating the same task (unsupervised learning). Our findings also support previous literature, showing that perceptual learning is capable of modulating the discriminative performance in the nociceptive system. The current study shows that this modulation is also possible for more complex tasks, such as directional discrimination, relying on both temporal and spatial information.

References

Frahm, K. S., Mørch, C. D., & Andersen, O. K. (2018). Tempo-spatial discrimination is lower for noxious stimuli than for innocuous stimuli. PAIN, 159(2), 393–401.

Frahm, K. S., Mørch, C. D., & Andersen, O. K. (2019). Directional discrimination is better for noxious laser stimuli than for innocuous laser stimuli. European Journal of Pain, ejp.1521.

Mancini, F., Dolgevica, K., Steckelmacher, J., Haggard, P., Friston, K., & Iannetti, G. D. (2016). Perceptual learning to discriminate the intensity and spatial location of nociceptive stimuli. Scientific Reports, 6, 1–10.

Rujoie, A., Andersen, O. K., & Frahm, K. S. (2023). A novel temperature-controlled laser system to uniformly activate cutaneous thermal receptors during movable thermal stimulation. Journal of Neural Engineering, 20(1).

Presenting Author

Steffen Frahm

Poster Authors

Steffen Frahm, M.Sc., PhD

MSc BME, PhD

Integrative Neuroscience group, Center for Neuroplasticity and Pain (CNAP), Aalborg University

Lead Author

E-mail

Ahmad Rujoie

PhD

Integrative Neuroscience group, Center for Neuroplasticity and Pain (CNAP), Aalborg University

Lead Author

E-mail

Ole Kæseler Andersen

Integrative Neuroscience group, Center for Neuroplasticity and Pain (CNAP), Aalborg University

Lead Author

E-mail

André Mouraux

Institute of Neuroscience (IoNS), UCLouvain

Lead Author

E-mail

Topics

  • Mechanisms: Biological-Systems (Physiology/Anatomy)