Small-volume effect enables the spine robust, sensitive and efficient information transfer

TL;DR

This paper demonstrates that the small-volume effect in neuronal spines enhances robustness, sensitivity, and efficiency of calcium-based information transfer by leveraging intrinsic noise, explaining why spines are so small.

Contribution

The study reveals that small-volume effects enable robust, sensitive, and efficient information transfer in neuronal spines, a mechanism not present in larger cell volumes.

Findings

Intrinsic noise surpasses extrinsic noise in spines, ensuring robustness.

Stochastic facilitation enhances sensitivity to weak inputs.

Volume-dependent transfer improves efficiency per input.

Abstract

Why is the spine of a neuron so small that only small numbers of molecules can exist and reactions inevitably become stochastic? Despite such noisy conditions, we previously showed that the spine exhibits robust, sensitive and efficient features of information transfer using probability of Ca$^{2+}$ increase; however, their mechanisms remains unknown. Here we show that the small-volume effect enables robust, sensitive and efficient information transfer in the spine volume, but not in the cell volume. In the spine volume, intrinsic noise in reactions becomes larger than extrinsic noise of input, making robust information transfer against input fluctuation. Stochastic facilitation of Ca$^{2+}$ increase occurs in the spine volume, making higher sensitivity to lower intensity of input. Volume-dependency of information transfer enables efficient information transfer per input in the spine volume. Thus, we propose that the small-volume effect is the functional reasons why the spine has to be so small.