Patchwork-Type Spontaneous Activity in Neonatal Barrel Cortex Layer 4 Transmitted via Thalamocortical Projections

Area of Science:

• Neuroscience
• Developmental Biology
• Systems Neuroscience

Background:

• Precise neuronal connectivity in the neocortex is established through activity-dependent circuit reorganization during postnatal development.
• The nature of cortical activity during early postnatal development is largely unknown, hindering our understanding of circuit formation.

Purpose of the Study:

• To investigate the characteristics of spontaneous neuronal activity in the neonatal mouse barrel cortex.
• To determine the role of this activity in the refinement of thalamocortical circuits.

Main Methods:

• Utilized in vivo two-photon calcium imaging of the barrel cortex in neonatal mice.
• Employed transgenic mice expressing GCaMP6s in thalamocortical axons to visualize axonal activity.
• Assessed the impact of peripheral anesthesia and whisker movements on spontaneous activity patterns.

Main Results:

• Identified a synchronous "patchwork" pattern of spontaneous activity in layer 4 (L4) neurons within the same barrel during the first postnatal week.
• Demonstrated that thalamocortical axons also exhibit this spontaneous patchwork activity pattern.
• Observed that patchwork activity diminished with peripheral anesthesia but was largely independent of whisker movements.
• Found that this pattern disappeared by the second postnatal week, with L4 neurons firing asynchronously.

Conclusions:

• Neonatal barrel cortex displays a unique, spatially organized spontaneous activity pattern (patchwork activity).
• This activity, originating from both cortical neurons and thalamocortical axons, is suitable for refining thalamocortical circuit connections.
• The transient nature of this pattern suggests a critical developmental window for circuit refinement.