Circuit-specific and neuronal subcellular-wide E-I balance in cortical pyramidal cells

Area of Science:

• Neuroscience
• Computational Neuroscience
• Circuit Neuroscience

Background:

• Neuronal circuits rely on a balance between excitatory and inhibitory synaptic transmission (E-I balance) for proper function.
• Understanding the specificity and variability of E-I balance across different brain regions and neuronal compartments is crucial for deciphering neural computation.

Purpose of the Study:

• To investigate the neuronal and compartmental E-I balance in pyramidal cells across various cortical and paleocortical brain regions.
• To determine the specific contributions of somatostatin (SOM)- and parvalbumin (PV)-containing interneurons to E-I balance in a layer-specific manner.

Main Methods:

• Utilized ChR2-assisted circuit mapping (CRACM) to analyze E-I balance in pyramidal cells.
• Employed chemogenetics to selectively silence SOM- and PV-interneurons.
• Optogenetically activated long-range M1 inputs to assess their impact on E-I ratios.

Main Results:

• Demonstrated significant differences in E-I ratios across pyramidal cells in various brain regions.
• Showed that distinct inputs on the same neurons, or the same inputs on different targets, yield varying E/I ratios.
• Revealed layer-specific contributions of PV and SOM interneurons to E-I balance in the somatosensory cortex (S1).

Conclusions:

• Established both universal subcellular-wide E-I balance and high specificity of E-I ratios across diverse circuits (visual, somatosensory, piriform, hippocampal).
• Hypothesized that unique glutamatergic innervation of interneurons underlies the observed specificity of E-I balance.
• Concluded that this dichotomy of specificity and generalization provides a foundation for understanding neuronal computation in health and disease.