Tactile foveation in the star-nosed mole

Abstract

Star-nosed moles have a specialized somatosensory system with 22 mechanosensory appendages surrounding the nostrils. A pair of appendages (the 11th pair on the ventral midline) acts as the tactile fovea and is used for detailed investigations. Here we used a high speed video camera to document movements of the star while moles searched for small prey items. Mole foraging behavior was very fast; the star, which is just over a centimeter in diameter, was touched to different areas of the environment approximately 13 times per second. This suggests that a mole foraging without interruption could potentially investigate 46,000 cm2 of surface area per hour. In 100% of 526 trials in which prey was identified and eaten, star-nosed moles made rapid, saccadic movements of the star to investigate the contacted prey with the foveal appendages. The movements of the star were similar to visual saccades in other species. Maximum velocity of the star during saccades was approximately 40 cm/s, and most saccades were between 30 and 60 ms in duration. As in the primate visual system, small corrective saccades were often needed to accurately foveate. We quantified the number of contacts different appendages made with prey items of various sizes during each encounter and compared this distribution to a previously proposed simulation of star movements during prey encounters. The behavior pattern and the simulation produced similar distributions of contact between the appendages and prey, and both distributions were closely correlated with the degree of cortical magnification of the appendage representations in primary somatosensory cortex (S1).