Dendritic Excitability and Gain Control in Recurrent Cortical Microcircuits.

Area of Science:

• Neuroscience
• Computational Neuroscience
• Cortical Circuitry

Background:

• Layer 5 thick tufted pyramidal cells (TTCs) exhibit complex electrical properties due to excitable dendrites.
• The interaction between dendritic nonlinearities and recurrent network activity in shaping cortical responses remains poorly understood.

Purpose of the Study:

• To investigate the role of dendritic nonlinearities in TTCs microcircuits during information processing.
• To elucidate how TTCs microcircuits modulate thalamocortical inputs and contribute to cortical computation.

Main Methods:

• Detailed conductance-based models of TTCs forming recurrent microcircuits were simulated.
• Network models incorporated experimentally observed interconnections and realistic background synaptic activity.

Main Results:

• TTCs microcircuits significantly amplified brief thalamocortical inputs, exhibiting cortical gain.
• This amplification was mediated by back-propagation activated N-methyl-D-aspartate (NMDA) depolarizations and dendritic calcium (Ca2+) spike firing.
• Dendritic nonlinearities linearly multiplied thalamic inputs, enhancing amplification while preserving input selectivity.

Conclusions:

• Dendritic nonlinearities are critical for regulating the gain and computational functions of TTCs microcircuits.
• TTCs microcircuits act as a major output pathway for the neocortex, with their function significantly influenced by dendritic properties.