Experience-Dependent, Layer-Specific Development of Divergent Thalamocortical Connectivity.

Area of Science:

• Neuroscience
• Developmental Neuroscience
• Sensory Systems

Background:

• Thalamocortical (TC) axons are the primary input to the primary sensory cortex.
• TC axons predominantly synapse in layer 4, but also target layer 6.
• Developmental processes governing TC input to layer 6 are less understood than those for layer 4.

Purpose of the Study:

• To investigate the developmental trajectory of TC inputs to layer 6 compared to layer 4.
• To elucidate the role of experience and synaptic plasticity in shaping these inputs during early postnatal development.

Main Methods:

• Comparative analysis of TC synapse strength and distribution in layers 4 and 6 of the primary sensory cortex in neonates and during the first postnatal week.
• Assessment of experience-dependent synaptic changes and the capacity for long-term potentiation (LTP) in both layers.

Main Results:

• In neonates, TC input strength to layer 6 is comparable to that of layer 4.
• During the first postnatal week, layer 4 inputs undergo experience-dependent strengthening, characterized by increased axon branching and connectivity divergence.
• Synapses in layer 4, but not layer 6, exhibit LTP, correlating with the observed strengthening.

Conclusions:

• Experience-driven LTP plays a critical role in stabilizing and strengthening TC synapses specifically in layer 4.
• This process leads to a greater divergence of connectivity in layer 4 compared to layer 6.
• Transient TC synapses are selectively stabilized in layer 4 through experience, enhancing its functional role over layer 6.