Brain networks underlying tactile softness perception: A functional magnetic resonance imaging study

Area of Science:

• Neuroscience
• Sensory Perception
• Haptics

Background:

• Humans perceive object properties via touch, categorized into macro-spatial (shape, orientation) and material (roughness, softness, temperature).
• Previous research indicates distinct neural networks for material properties like roughness and temperature compared to macro-spatial properties.
• The neural basis for processing tactually perceived softness magnitude remains largely unexplored.

Purpose of the Study:

• To investigate the involvement of the parietal operculum and insula in the neural representation of tactually perceived softness magnitude.
• To determine if the brain regions processing other material properties are also engaged in softness perception.
• To map the brain activity associated with estimating perceived softness magnitude.

Main Methods:

• Functional magnetic resonance imaging (fMRI) was employed with 56 healthy participants.
• Participants used their right middle finger to estimate perceived softness magnitude of stimuli with identical shapes but varying compliances.
• Stimulus force was manipulated across two levels, and both mass-univariate and multivariate analyses were conducted.

Main Results:

• Activity in the parietal operculum, insula, and medial prefrontal cortex correlated positively with perceived softness magnitude, independent of applied force.
• Enhanced activity in the ventral striatum was observed in the high-force condition compared to the low-force condition.
• Multivariate pattern analysis identified the parietal operculum/insula, postcentral gyrus, posterior parietal lobule, and middle occipital gyrus as key regions for softness representation.

Conclusions:

• The findings indicate that a distributed network of brain regions, crucially including the parietal operculum and insula, is involved in representing perceived softness.
• This suggests that the neural processing of softness magnitude shares common pathways with other tactile material properties.
• The study contributes to understanding the neural mechanisms underlying haptic perception of material properties.