Pressrelease(In Japanese only)

Establishment of precise neuronal connectivity in the mammalian neocortex relies on activity-dependent circuit reorganization during postnatal development; however, the nature of cortical activity during this period remains largely unknown.

Using two-photon calcium imaging of the mouse somatosensory cortex (barrel cortex) in vivo during the first postnatal week, we revealed that layer 4 (L4) cortical neurons within the same barrel fire synchronously in the absence of peripheral stimulation, creating a “patchwork” pattern of spontaneous activity corresponding to the barrel map. By generating transgenic mice expressing a genetically-coded calcium indicator GCaMP6s in thalamocortical axons, we showed that thalamocortical axons also demonstrated the spontaneous patchwork activity pattern. Patchwork activity was diminished by peripheral anesthesia but was mostly independent of self-generated whisker movements. The patchwork activity pattern largely disappeared during postnatal week 2, as even L4 neurons within the same barrel tended to fire asynchronously. This spontaneous L4 activity pattern has features suitable for circuit refinement in the neonatal barrel cortex.

This work was supported by JSPS KAKENHI grant numbers JP15K14322 and JP16H06143, the Takeda Science Foundation, and the Collaborative Research Project (2017-2923) of Brain Research Institute, Niigata University to H.M., and JSPS KAKENHI grant numbers JP16K14559, JP15H01454, and JP15H04263, and Grant-in Scientific Research on Innovation Areas “Dynamic Regulation of Brain Function by Scrap & Build System” (JP16H06459) from MEXT to T.I.

Figure: Novel type of spontaneous activity found in the mouse somatosensory cortex layer 4 in neonates.

(a) Five rows (A-E) of whiskers on the snout.

(b) In the barrel cortex layer 4 (L4), barrels are arranged in a one-to-one correspondence with whiskers on the snout and process tactile information derived from individual whiskers. Each barrel contains hundreds of neurons processing sensory information from the corresponding whisker. For example, the C1 barrel (arrow) processes information from the C1 whisker (arrow in (a)). Barrels are labeled with a red fluorescent protein.

(c)　Higher magnification image of the white square region in (b).

(d) Activity pattern of barrel cortex layer 4 at postnatal day 5, which looks like a “patchwork”. Each color represents a different activity event.