An assemblage of movement sensitive neurons that may participate in object tracking and the directional tunning of the escape response to visual stimuli in crabs

VIOLETA MEDAN, DAMIAN OLIVA, DANIEL TOMSIC

Vancouver, Canada

Congreso; Eighth International Congress of Neuroethology.; 2007

International Sosciety of Neuroethology

Semiterrestrial crabs are higly visual animals that react to dangerous moving stimuli with conspicuous escape responses. In the absece of a nearby shelter the crab directs its course sthaigth away from the potential predator. However, because the crab´s prefered running mode is sideways, any time the stimulus change its position the course of the escape is adjusted. In fact, there is a visual control system that enable crabs to track predators, which implies a rotational mechanism using continuous feedback that turns the crab so that the stimulus is kept at 90° to the body axis (Land and Layne, 1995). The neural bases of the system for object tracking are however completely unknown. From a series of behavioral, anatomical and electrophysiological studies in the crab Chasmagnathus we found a class of large projecting neurons from the lobula, named M1 neurons, that seems to play a key role in the behavior elicited by visual danger stimuli (Oliva et al., 2007). There are 14 M1 neurons in each lobula, whose dendritic threes are regularly distributed along the retinotopic mosaic (Starker et al. 2005). Here we present results obtained by in vivo intracellular recordings followed by dye inyections, which allowed us to establish the correspondence between the anatomical position of M1 units within the lobula and their receptive field location. The experiments also shown that these neurons have a preference for horizontal instead of vertical object motion. These, jointly with other results (see the poster from Oliva et al.), suggest that the system of M1 neurons is suitably matched to play a central role in tracking a predator movements and, hence, in adjusting the direction of the escape.