Memory recognition elicits autonomic-like responses in crayfish.

Organisms achieve homeostasis by making compensatory adjustments in response to changes in their internal and external environments. Such adjustments can be observed, for example, in variations of heart and respiratory rates triggered by different disturbances. In invertebrates, evidence of the existence of an autonomic nervous system structure has not been found. Even so, these animals show physiological responses - changes in cardiorespiratory activity (autonomic-like responses) - that maintain internal stability. In crustaceans, studies have found changes in both behavioural response and heart rate during memory processes. In the crayfish Procambarus clarkii, recognition memory has been behaviourally described when triads of these invertebrates interact under laboratory conditions and establish a hierarchical order (a dominant animal and two submissives). The main purpose of this work was to characterize the cardiorespiratory autonomic-like responses of P. clarkii during a 5-day recognition memory protocol. Our findings indicate significant differences in cardiorespiratory activity between day 1 (start of the memory protocol) and day 5 (when recognition memory is consolidated). Notably, there are differences based on hierarchy status, suggesting that the physiological response to recognition differs between dominant and submissive animals. This indicates that the retrieval of long-term recognition memory may lead to changes in autonomic-like responses.