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August 21, 2021 10:00 am

Cuttlefish Remember the What, When, and Where of Meals -- Even Into Old Age

According to a new paper published in the Proceedings of the Royal Society B, cuttlefish appear able to recall the time and place of their meals -- and their capability doesn't decrease as they get older. Ars Technica reports: This latest study focuses on whether cuttlefish have some form of episodic memory -- the ability to recall unique past events with context about what happened, where it happened, and when it happened. Human beings develop this capability around age 4, and our episodic memory declines as we advance into old age. That's in contrast to "semantic memory," our ability to recall general learned knowledge without the context of space and time. Semantic learning in humans has been shown to remain relatively intact with advancing age. Cuttlefish lack a hippocampus, but they do have their own distinctive brain structure and organization, complete with a vertical lobe that shows similarities to the connectivity and function of the human hippocampus -- i.e., learning and memory. Past studies have shown that cuttlefish are sufficiently future-oriented that they can optimize foraging behavior and can remember details of what, where, and when from past forages -- hallmarks of episodic-like memory -- adjusting their strategy in response to changing prey conditions. But does that ability remain constant with age? [Co-author Alexandra Schnell of the University of Cambridge] et al. developed a series of semantic and episodic memory tests for cuttlefish to explore that question. The relatively short life span of cuttlefish (about two years) makes them an excellent candidate for this research. For the experiments, Schnell and her colleagues used 24 common cuttlefish, half of which were young (between 10-12 months old) and half of which were old (22-24 months, apparently the equivalent of a human's 90 years). All had been reared from eggs at the Marine Biological Laboratory and were kept in individual tanks. The team first trained the cuttlefish to respond to visual cues (the waving of black and white flags) by marking specific locations in their respective tanks. As in Schnell's prior work on delayed gratification, the cuttlefish could choose their preferred prey -- in this case, either live grass shrimp or a piece of prawn meat of equal size. Over the next four weeks, the cuttlefish were taught that these two types of prey were available at specific locations (marked by the waving of the flags) after delays of either one hour (for the prawn meat) or three hours (for the preferred grass shrimp). The two feeding locations were unique for each day in order to ensure that the cuttlefish weren't merely learning a pattern. Surprisingly, Schnell et al. found that all the cuttlefish, regardless of age, were able to note which type of prey appeared first at each flagged location and were able to use that observation to figure out where to find their preferred prey at each subsequent feeding. Earlier this year, researchers found that cuttlefish could pass a cephalopod version of the famous Stanford marshmallow test: waiting a bit for their preferred prey rather than settling for a less desirable prey. "Cuttlefish also performed better in a subsequent learning test -- the first time such a link between self-control and intelligence has been found in a non-mammalian species," adds Ars.

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