From Morphology to Computation: How Synaptic Organization Shapes Place Fields in CA1 Pyramidal Neurons.

Area of Science:

• Neuroscience
• Computational Neuroscience
• Synaptic Plasticity

Background:

• Feature selectivity in neurons, particularly place selectivity in hippocampal CA1 pyramidal neurons (PNs), is critical for spatial navigation.
• The role of excitatory (E) and inhibitory (I) synaptic distributions in developing place specificity in CA1 PNs is not well understood.
• Behavioral time scale plasticity (BTSP), involving dendritic spikes, is thought to contribute to place field formation.

Purpose of the Study:

• To investigate the impact of excitatory and inhibitory synaptic distributions on place selectivity in individual CA1 PNs.
• To determine how the spatial organization of synapses influences neuronal output and feature tuning.
• To elucidate the interplay between synaptic input patterns and postsynaptic organization in dictating neuronal function.

Main Methods:

• Performed full synaptic reconstructions from individual CA1 PNs in the mouse hippocampus.
• Quantified the number of excitatory (E) and inhibitory (I) synapses per neuron.
• Utilized computational modeling to simulate the effects of different synaptic distributions on spatial tuning.

Main Results:

• CA1 PNs receive approximately 10,000-15,000 E synapses and 900-1,400 I synapses.
• Spatial tuning is maintained when E synapses are co-tuned and spatially clustered.
• Randomized E synapse distributions disrupt spatial tuning, with varying effects in apical versus basal dendritic domains.

Conclusions:

• The spatial organization and clustering of excitatory synapses significantly impact place selectivity in CA1 PNs.
• Synaptic clustering plays a differential role in spatial tuning across distinct dendritic compartments.
• Neuronal output is determined by a complex interaction between presynaptic input patterns and the spatial arrangement of postsynaptic targets.