Episodic-like memory is preserved with age in cuttlefish.

Alexandra K Schnell,Nicola S Clayton,Roger T Hanlon,Christelle Jozet-Alves

doi:10.1098/rspb.2021.1052

Abstract

Episodic memory, remembering past experiences based on unique what–where–when components, declines during ageing in humans, as does episodic-like memory in non-human mammals. By contrast, semantic memory, remembering learnt knowledge without recalling unique what–where–when features, remains relatively intact with advancing age. The age-related decline in episodic memory likely stems from the deteriorating function of the hippocampus in the brain. Whether episodic memory can deteriorate with age in species that lack a hippocampus is unknown. Cuttlefish are molluscs that lack a hippocampus. We test both semantic-like and episodic-like memory in sub-adults and aged-adults nearing senescence (n = 6 per cohort). In the semantic-like memory task, cuttlefish had to learn that the location of a food resource was dependent on the time of day. Performance, measured as proportion of correct trials, was comparable across age groups. In the episodic-like memory task, cuttlefish had to solve a foraging task by retrieving what–where–when information about a past event with unique spatio-temporal features. In this task, performance was comparable across age groups; however, aged-adults reached the success criterion (8/10 correct choices in consecutive trials) significantly faster than sub-adults. Contrary to other animals, episodic-like memory is preserved in aged cuttlefish, suggesting that memory deterioration is delayed in this species.

Highlights

Episodic memory is the ability to remember unique past events [1]
The idea that episodic recall requires autonoetic consciousness represents an intractable barrier for demonstrating episodic memory in animals, since conscious experience cannot be evaluated in non-verbal subjects in the absence of agreed behavioural markers of non-linguistic consciousness [19]
In the semantic-like memory task, cuttlefish were able to learn the location of a rewarded food resource in response to the time of day

Summary

Introduction

Episodic memory is the ability to remember unique past events [1]. This type of memory receives and stores information about the context in which an event occurred including what happened, where and when. Episodic memory develops around the age of 4 [2,3,4,5,6] and declines with advancing age [7,8,9,10,11] This type of memory differs from another form of recollection, namely semantic memory, which is the ability to recall general knowledge acquired through learning without retrieving unique spatio-temporal features about the learning context. In the episodic-like memory task subjects were required to recall a specific memory that was unique to each test day These tasks were chosen to investigate whether, like humans, only episodic information deteriorates with age while semantic information stays relatively intact

Methods

Results

Findings

Discussion