CONICET | Buscador de Institutos y Recursos Humanos

In the crab Chasmagnathus, a visual danger stimulus (VDS) elicits animal escape, which declines after a few presentations and remains reduced to that stimulus for several days. The behavioral change entails an association between the VDS (signal) and the contextual environment, in such a way that memory is expressed only if the animal is tested in the same context of the training. The paradigm is known as contest-signal memory (CSM). By performing in vivo intracellular recordings we have shown that movement detector neurons (MDNs) from the lobula of the crab modify their response to the VDS during learning. The modifications strikingly correlate with the rate of acquisition and with the memory retention 24 hs after training. Throughout those experiments, the neuronal changes were assessed by testing the animal in the training environment. Here we explored whether the neuronal changes could be still observed when the animal is tested 24 hs later in a context different from the training one. Results show that contextual changes do not affect the learning-induced changes of MDNs. With some caveats, this means that the changes occurring in MDNs may only account for the signal component of the CSM, whereas the contextual component and the process of association between the two component would occur somewhere else. In addition, we evaluated whether MDNs are capable of reflecting translation invariance, i.e., the ability of the animal to recognize an object regardless of the visual region from where it had been learned. Results show that MDNs can readily generalize the stimulus to new retinal positions. Thus, MDNs reflect the crabs ability to recognize the VDS with independence of its retinal position. We discuss our results in connection with studies in flies and bees, which suggest that stimulus cues and contextual information are processed by separate neural circuits.