Somatosensory evoked potentials, indexing lateral inhibition, are modulated according to the mode of perceptual processing: comparing or combining multi-digit tactile motion

Abstract

Many perceptual studies focus on the brain's capacity to discriminate between stimuli. However, our normal experience of the world also involves integrating multiple stimuli into a single perceptual event. Neural circuit mechanisms such as lateral inhibition are believed to enhance local differences between sensory inputs from nearby regions of the receptor surface. However, this mechanism would seem dysfunctional when sensory inputs need to be combined rather than contrasted. Here, we investigated whether the brain can strategically regulate the strength of suppressive interactions that underlie lateral inhibition between finger representations in human somatosensory processing. To do this, we compared sensory processing between conditions that required either comparing or combining information. We delivered two simultaneous tactile motion trajectories to index and middle fingertips of the right hand. Participants had to either compare the directions of the two stimuli, or to combine them to form their average direction. To reveal preparatory tuning of somatosensory cortex, we used an established event-related potential design to measure the interaction between cortical representations evoked by digital nerve shocks immediately before each tactile stimulus. Consistent with previous studies, we found a clear suppressive interaction between cortical activations when participants were preparing to compare the tactile motion directions. Importantly, this suppressive interaction was significantly reduced when participants had to combine the same stimuli. These findings suggest that the brain can strategically switch between a comparative and a combinative mode of somatosensory processing, according to the perceptual goal, by preparatorily adjusting the strength of a process akin to lateral inhibition.

Sensory and cognitive factors affecting multi-digit touch: a perceptual and modeling study

“…In addition, Walsh et al (2016) also failed to observe somatotopic distance effects during unimanual aggregation of intensity-based tactile signals. This is also consistent with our previous findings (Arslanova et al, 2020) showing that suppressive interactions between digits may be reduced when participants try to estimate average directions, as opposed to direction discrepancies. Thus, somatotopic effects might have been attenuated in our averaging conditions.…”

“…Thus, multi-digit tactile motion integration remains poorly understood. In a previous study (Arslanova et al, 2020), we found evidence for a neural mechanism that promotes multi-digit tactile integration by modulating the degree of suppressive interactions between stimulated digit representations. Here, we sought to characterise two aspects of this integration process - sensory-integration performance and sensory weighting among digits - and examined whether the latter aspect was based on natural statistics of tactile motion stimuli.…”