Neurons in the deepest part of the neocortex alter their functions with sensory experience

The mammalian cerebral cortex consists of six layers, with distinct roles in information processing. At the bottom of the neocortex, on the boundary between the gray matter and white matter, there is a thin sheet of neurons called L6b. L6b neurons are thought to be remnants of subplate neurons that transiently form neural circuits during perinatal development and guide cortical maturation. Most subplate neurons undergo cell death, while some survive. However, the functional properties of L6b/surviving subplate neurons remain largely unknown. Taisuke Yoneda, Kenji Hayashi, and Yumiko Yoshimura at the National Institute for Physiological Sciences have found that L6b/ surviving subplate neurons in the primary visual cortex (V1) exhibit sensory responses and experience-dependent plasticity in juvenile mice. They published their findings in PNAS.

Researchers performed functional measurements of surviving subplate neurons by using two-photon Ca2+ imaging with post hoc tissue clearing and 3D immunohistochemistry of a subplate neuron marker. Most of the recorded L6b neurons expressed a subplate neuron marker and they demonstrated broadly tuned visual response properties (Figure).

Then researchers examined whether L6b neurons exhibit experience-dependent plasticity. To this end, they used ocular dominance plasticity as an experimental model. In this model, if one eye is occluded for several days during the sensitive period in juvenile animals, neurons in V1 lose their response to the deprived eye. By using chronic two-photon imaging of visual responses from the same neurons, they found that L6b neurons exhibited ocular dominance plasticity.

“We characterized the visual response properties and functional plasticity in L6b neurons in V1. The surviving subplate neurons may be involved in the experience-dependent maturation of cortical functions and information processing in the mature cortex,” Yoneda says.