Background & Aims

Spatial summation in thermosensation refers to the integration of multiple sensory signals across space, resulting in the perception of a unique sensation. While a relationship between stimulus size and perceived intensity may exist, it is typically characterized as sub-additive (Stevens & Marks, 1971 and 1979), meaning that the collective impact of a stimulus is less than the sum of its individual components. This observation suggests that lateral inhibition, a process in which adjacent neurons inhibit each other’s activity (Quevedo et al., 2017), may play a role in this relationship. The study aims to investigate whether spatial summation and lateral inhibition operate differently in innocuous cold and warm perception and whether these differences could constitute a key mechanism underlying illusory pain experienced in the thermal grill illusion.

Methods

We devised a perceptual decision-making task to explore the impact of spatial summation and lateral inhibition in thermosensation. In this task, thermal stimuli were applied to the volar surface of 16 participants’ forearms, with temperatures increasing or decreasing from 31°C. Participants were instructed to promptly and accurately determine whether the stimuli felt warm or cold. Following this, participants rated the intensity of their warm or cold sensations. Unbeknownst to the participants, the stimuli varied spatially in two dimensions: area size (with 5 possible areas) and distance size (comprising 2 areas with 4 possible distances). To analyze the data, we employed generalized mixed-effects models to assess response times and ratings. Additionally, we utilized a Hierarchical Drift Diffusion Model to model both response times and accuracy of the binary warm/cold choices. This approach allowed us to gain insights into the interplay of spatial factors in thermosensory perception.

Results

The impact of spatial summation was evident as participants demonstrated quicker response times to larger stimuli (beta = 0.56, CI = [0.49; 0.64], p < .05) and rated larger stimuli as more intense. This effect was more pronounced for cold compared to warm (beta = -0.19, CI = [-0.29; -0.09], p < .0001). From the evidence accumulation modeling, we observed similar drift rates for warm and cold stimuli (P(v_warm > v_cold) = 0.80). However, the interaction between stimulus quality and area size exhibited a more pronounced effect for cold stimuli compared to warm (P(v_warm > v_cold) = 0.00) indicating that spatial summation exerts a more substantial influence on the drift rate for cold stimuli when compared to warm stimuli. The effect of lateral inhibition was less consistent. The models indicated no effect of distance size for ratings, however, participants did exhibit slightly faster responses to stimuli with increasing distance size ( = -0.03, CI = [-0.05; -0.01], p < .001).

Conclusions

Our findings indicate that spatial summation operates differently in cold and warm perception, and demonstrate weak but significant lateral inhibition in innocuous thermosensation. The difference in the effect of spatial summation for warm and cold was due to a difference in the speed of evidence accumulation.r In future studies we aim to investigate the dynamics of spatial summation and lateral inhibition for different stimuli intensities and how these processes are affected by aging or in the context of nerve damage.

References

Quevedo, A.S. et al. (2017) ‘Lateral inhibition during nociceptive processing’, Pain, 158(6), pp. 1046–1052. doi:10.1097/j.pain.0000000000000876.
Stevens, J.C. and Marks, L.E. (1971) ‘Spatial summation and the dynamics of warmth sensation’, Perception & Psychophysics, 9(5), pp. 391–398. doi:10.3758/bf03210236.
Stevens, J.C. and Marks, L.E. (1979) ‘Spatial summation of Cold’, Physiology & Behavior, 22(3), pp. 541–547. doi:10.1016/0031-9384(79)90023-4.

Presenting Author

Camilla Eva Krænge

Poster Authors

Camilla Eva Kraenge

MSc

Aarhus University

Lead Author

E-mail

Malthe B. Sørensen

MD

Aarhus University

Lead Author

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Arthur Courtin

Aarhus University

Lead Author

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Jesper Ehmsen

center of functionally integrative neuroscience

Lead Author

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Micah G. Allen

Ph.d.

Center of Functionally Integrative Neuroscience, Department of Clinical Medicine, Aarhus University

Lead Author

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Francesca Fardo

Aarhus University

Lead Author

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Topics

  • Assessment and Diagnosis