Bistability in Ephaptic Coupling as a Possible Memory Element Explored through a Colloid Interptation of Stereocilia Bistability

Abstract

When the processes of neurons are in close proximity they effectively couple to each other in a process termed Ephaptic coupling. This coupling occurs without the membranes touching when the space between them is some tens of nanometers. If the intra-membrane spacing has a mechanical bistability, which moves the membranes closer and further apart, the Ephaptic coupling will be turned on and off allowing one neuron to read, or not read the content of the other. This paper explores the possibilities of bistable ephaptic memory element by a study of an analogous system that operates at a much larger scale, the Stereocilia of the hair cell. Published measurement of hair cell Stereocilia force/displacement function shows both a negative slope region in the displacement function and tendency to express bistability. We show here how this negative slope region can arise through the exigency of colloid forces. An explanation of Colloid Theory, presented in a graphic form, shows how a colloid force function can be modified to match the measured hair cell cilia force function. The colloid force function is modified by a limiting function resulting from Stereocilia side links, structural details that tie together the hair cell Stereocilia clusters. Understanding how a limited, simple behavior such as Stereocilia bistability functions may point to a more general understanding of how bistability may underlie other areas of living organisms such as memory and computation.