Department of Electrical
and Computer Engineering

Research in Vibrissae and Inner Ear Hair Bundle Hydrodynamics

The purpose of this research is to understand the relationship between the morphology of sensor hairs and their functionality.

Fig. 1 Rat vibrissae

The goals of this research are to further our understanding of the mechanics of sensor hairs, and to develop acoustic sensors based upon the mechanics of these sensor hairs. The motion of fluid surrounding them stimulates sensor hairs, and their motion leads to a neural signal that is interpreted by an organism's central nervous system. Sensor hairs are found in hearing organs, lateral line organs of fish and amphibians, and in spiders, crickets and cockroaches; and these hairs are used to detect sound-induced or mechanically induced motion of the fluid surrounding the hairs. The sensor hair system in crickets and spiders has been shown to be far superior to most man-made devices (such as microphones and anemometers); only laser anemometers have shown to have comparable sensitivity (Kamper and Kleindeist 1990). Sensor hairs are also found in vestibular organs, to detect fluid motion caused by head movements in order to maintain postural equilibrium.

Vibrissae or whiskers are also types of sensor hairs, and for certain organisms, these play a vital role in detecting disturbances in their surrounding fluid, which could be air or water. Pinnipeds like seals use their vibrissae to track water waves as small as a micron in amplitude left in the wake of their prey (Dehnhardt et al. 2001). Manatees have vibrissae over their whole bodies, analogous to a lateral line system, with which they detect changes in water motion caused by mechanical or sound stimuli (Reep et al. 2002).

Significant progress has been made to understanding the mechanics of sensor hairs in the inner ear (Freeman and Weiss 1990a; Freeman and Weiss 1990b; Freeman and Weiss 1990c; Freeman and Weiss 1990d; Shatz 2000; Aranyosi 2002; Shatz 2004), as well as in the mechanics of the sensor hairs found in crickets, spiders and cockroaches (Shimozawa 1984; Barth et al. 1993; Humphrey et al. 1993; Shimozawa et al. 1998a; Shimozawa et al. 1998b). These sensor hairs have been shown to be frequency selective; each sensor hair has been shown to have a frequency or range of frequencies to which it responds best. Shorter hairs have been shown to respond best to higher frequencies while longer hairs respond best to lower frequencies.

Vibrissae have also been shown to be frequency selective (Hartmann et al. 2003; Neimark et al. 2003) and a preliminary effort has been made to model the mechanics of rat vibrissae. A thin elastic beam model has been used to predict a rat vibrissa's resonant frequencies, but did not account for the effects of the fluid motion surrounding the vibrissae or for the mechanics of the follicle.

Understanding the mechanics of sensor hairs is vital to understanding how environmental stimuli are processed neurally, and would be extremely beneficial in developing highly sensitive acoustic detectors.