?Visually mediated decisions of the escape direction in the crab Chasmagnathus?

MOLINAS JULIETA; TOMSIC DANIEL

Boston

Conferencia; ?Neuroethology: Behavior, Evolution & Neurobiology" Gordon Research Conference; 2011

Gordon Research Conferences

A critical feature of evasive behaviors is the ability to localize the threatening stimulus in space and perform consequently. When no shelter is available, crabs react to a sudden approaching object by running in the direction opposite to this looming stimulus. However, when an object is coming straight from above, the information about the proper side to run becomes less certain. Using this condition, we began to investigate what kind of contextual visual information may affect the decision for the direction of escape. The study is performed by using a running simulator device located inside an arrangement of 5 computer screens (1 above and 1 on each side of the simulator). This allows us to precisely record the course of the escape response elicited by a looming stimulus in the upper screen, and to investigate how it is affected by changes in the contextual visual environment. We found that when the luminance of the four screens surrounding the crab at the horizontal level where equal, 50 % of the animals ran to the left and the other 50 % ran to the right. Upon repeated stimulus presentations each individual tended to maintain the same escape direction, indicating the existence of individual directional preferences. The directional preference, however, could be rapidly modified by pairing the chosen running side with an electrical shock, i.e. by a learning process taking place in a paradigm of operant conditioning. On the other hand, when naive animals faced visual contextual asymmetries between the horizontal screens, like differences in luminance, polarization pattern or object form, the side preferences were clearly biased. Results show that when deciding the direction for escaping in the absence of a shelter, crabs take into account the predator?s direction but also contextual visual information and previous experiences. By using in vivo intracellularly recording we have previously shown that the lobula giant neurons of the crab play a key role in the escape reaction to visual stimuli. Moreover, changes in the intensity of the escape response induced by learning were found to be supported by response changes in the LG. The behavioural results presented here give us now the possibility of exploring to what extent the decision for the escape direction takes place in these lobula giant neurons.