Secondary Somatosensory Cortex Is Required for Learning but Not Execution of a Tactile Discrimination

TL;DR

The study shows that the secondary somatosensory cortex is needed for learning a tactile task in mice but not for performing it once learned.

Contribution

The study reveals a specific role for S2 in tactile learning, distinct from S1 and not required for task execution.

Findings

S2 is essential for learning tactile discrimination but not for executing it after learning.

Inhibiting S2 during learning prevents task acquisition in naive mice.

S2 is not required for olfactory discrimination, highlighting its tactile-specific role.

Abstract

The relationship between primary (S1) and secondary (S2) somatosensory cortex is not well understood, and the role of S2 in somatosensory function is not well defined. To test the role of S2 and its interplay with S1 in learning a texture discrimination, we reversibly inhibited primary (S1) and/or secondary somatosensory cortex (S2) bilaterally using DREADDs and measured the effect on the ability of mice to learn a whisker‐dependent tactile discrimination. Freely moving mice foraged in an arena that contained two bowls, one of which contained a buried food reward. The bowls could only be distinguished by the texture on the outer surface. DREADD‐mediated inhibition suppressed sensory responses and disrupted network activity in the cortical area in which DREADDs were expressed. We found that both S1 and S2 were critical for learning the tactile discrimination. Tactile learning in naive mice required normal S2 function during the learning phase but not during the post‐training consolidation phase of approximately 6 h. Furthermore, S2 was only required during learning. Once expert levels of discrimination had been attained, S2 was not required for execution of the learned discrimination. The role of S2 was confined to tactile learning and was not required for olfactory discrimination. Our findings suggest that S1 and S2 interact when learning a new tactile discrimination, but the learned skill eventually becomes independent of S2.

The relationship between primary somatosensory cortex (S1) and secondary somatosensory cortex (S2) during learning is not clear. Here, we show that when confronted with a texture discrimination using the whiskers, S2 is required during learning but not after learning. Left: The mouse learns that it can find a hidden food reward in one of two pots that are only distinguishable by their surface texture in the dark. Right: Learning is rapid, taking 72 trials spaced over 2–3 days (left hand graph, blue line), but only if S2 is normally active. Inhibition of S2 using DREADDs prevents learning in a naive mouse (red line). However, once the discrimination is learned, inactivating S2 has no effect on performance (right hand graph).

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