Cardiovascular component of the context signal memory in the crab Chasmagnathus.

Research on diverse models of memory in vertebrates demonstrates that behavioral, autonomic and endocrine responses occur together during fear conditioning. With invertebrates, no similar studies have been performed despite the extensive study of fear memory paradigms, as the context signal memory (CSM) of the crab Chasmagnathus granulatus, usually assessed by a behavioral parameter. Here, we study the crab's CSM, considering both the behavioral response and the concomitant neuroautonomic adjustments resulting in a heart rate alteration. Results show that upon the first presentation of the visual danger stimulus, a heart arrest followed by bradycardia is triggered together with a conspicuous escape response. The latter declines throughout training, while heart arrests become sporadic and bradycardia tends to deepen along the session. At test, 24 h after training, the outcome clearly contrasts with that shown at training, namely, stimulus presentation in the same context induces lower escape, no heart arrests and quick suppression of bradycardia. These results support the view that the same memory process brings about the changes in both responses. High escape, heart arrest and bradycardia are considered three parameters of the unconditioned response while minor escape, no heart arrests and bradycardia attenuation are three parameters of the learned response.