Pyramidal Cell-Interneuron Circuit Architecture and Dynamics in Hippocampal Networks

Area of Science:

• Neuroscience
• Computational Neuroscience
• Systems Neuroscience

Background:

• Understanding excitatory control of inhibitory neurons in vivo is challenging due to difficulties in studying synaptic connectivity.
• Existing methods often lack the precision to infer and validate functional connections in behaving animals.

Purpose of the Study:

• To infer and validate synaptic connectivity between excitatory and inhibitory neurons in vivo.
• To elucidate how neuronal firing patterns and network structure contribute to information processing in the hippocampus.

Main Methods:

• Inferred synaptic connectivity using spike-timing analysis in behaving mice.
• Validated inferred connections using juxtacellular and optogenetic control of presynaptic neuron activity.
• Analyzed connection probability, strength, and the influence of presynaptic firing patterns.

Main Results:

• Neighboring CA1 neurons exhibited stronger connections, with superficial pyramidal cells preferentially projecting to deep interneurons.
• A small population of highly connected 'hub' neurons dominated connection probability and strength.
• Presynaptic firing frequency was decoded by postsynaptic neurons via short-term synaptic plasticity (depression and facilitation).
• Spike transmission was modulated by the postsynaptic neuron's prior spike timing.

Conclusions:

• Established a method to infer and validate in vivo synaptic connectivity, bridging anatomical structure and physiological function.
• Demonstrated that neuronal network architecture and spike timing dynamics critically shape information flow and postsynaptic responses.
• Highlighted the diversity of synaptic filters and the importance of spike timing in neuronal communication.