Alexander Easton

Spatial navigation is the ability to purposefully move from one location to another. Central to many theories of navigation is the proposal that we build a ‘cognitive map’ of our external environment. We identify three conceptions of cognitive maps, from highly coherent long-term representations of space to more fragmentary representations. Reviewing the literature, we show that many navigation behaviours thought to require a cognitive map can be supported by the interaction of specific navigation strategies with minimal, fragmentary knowledge of the environment. Further, we argue that the range of navigation behaviours, strategies, individual differences, and navigational aids and systems used during navigation point toward representations that are more flexible than any of the three main conceptions of a cognitive map allow. We propose that spatial knowledge is stored in a more fragmentary manner but, critically, more complex representations are (re)constructed dynamically in the given navigational moment. The form and complexity of these constructed representations are tightly connected to the dynamic interaction between the navigator, including the strategies and aids they are using, and the environment. We link this proposal to the literature on spatially tuned neurons in the medial temporal lobes, emphasising that the heterogeneity of these functional neurons and their adaptation to changes in environmental structure and navigational goals supports our proposal that cognitive maps are dynamically (re)constructed representations. Therefore, cognitive maps are not relatively coherent, stable representations of spatial environments, but instead are dynamically and flexibly (re)constructed representations of the given navigational moment.

The Barkley Marathons is a uniquely difficult ultramarathon race held yearly in the United States. The exceptional physical demands of the race notwithstanding, its difficulty is notably amplified by its distinctive navigational challenges, including exacting environmental conditions and the prohibition of advanced navigational aids. Given the lack of research into these important navigational challenges, we conducted an exploratory qualitative study to investigate how runners navigate the race. We collected and analysed data – collating eight publicly available online race reports and conducting three interviews – from three participants who have taken part in the race. Our findings highlight how navigation is entangled with the environment, other people and task demands. In particular: the physical environment affords runners certain navigational behaviours and strategies; runners perceive landmarks and other navigational cues multimodally, dependent on various situational factors; and the, largely unwritten, rules of the race open up and close down particular navigational possibilities. Importantly, although the Barkley Marathons is a distinctive setting, we argue that this distinctiveness does not set it apart from everyday navigation. Rather, it serves to emphasise aspects and practices of navigation routinely overlooked in everyday life, precisely because we experience them so regularly and thus do not pay close attention. We conclude by discussing the conceptual and methodological consequences of this for wider navigation research. In particular, our findings support an embodied and situated approach to navigation research that embraces the dynamic and relational importance of the environment, other people and cultural knowledge systems in how we find our way.

There is substantial scientific interest in improving approaches that can enhance cognition through brain stimulation. We implemented a non-invasive focal Transcranial Ultrasound Stimulation (TUS) approach with known longer-lasting post-stimulation effects in two rhesus macaques performing a context-dependent memory-sequencing task implemented on multiple touchscreens within their home units. Consistently in both monkeys, TUS to the anterior – but not posterior – medial temporal lobe enhanced performance under stable memory-sequencing contexts. TUS to the medial prefrontal cortex, on the other hand, selectively improved performance when contexts were unstable and the monkey needed to adapt to both a change in context and temporal sequence. These findings shed new light on fronto-temporal nodes that, when perturbed, can selectively enhance cognitive performance, paving the way for further developing non-invasive approaches to improve cognitive function in humans and to study neural circuits under focal perturbation across species.

Event segmentation is a neurocognitive process bridging perception and episodic memory. To our knowledge, almost all segmentation work is framed towards humans, yet evolutionarily conserved mechanisms in event cognition exist across species. Here, we addressed segmentation in a way that is applicable to humans and non-human animals, inspired by research in rats; specifically, the fragmentation of grid-cell spatial representations following the insertion of boundaries into an environment (forming a corridor maze). Participants indicated when they felt a meaningful unit of activity ended and another began, while watching an agent traverse from a first-person perspective. A virtual corridor maze (experiment 1) and two other mazes were used (experiment 2), with participants viewing/segmenting the same stimuli twice. We found that people segmented more during turns relative to corridors, with elevated segmentation occurring in discrete moments around turns. Interestingly, we also found that boundaries of the corridor maze facilitated an increase in segmentation within and across viewings. These results suggest that segmentation can be driven by recognized repeating activity that can become more meaningful over time, highlighting an important link between event segmentation and pattern separation that is relevant to many species in their formation of episodic-(like) memory.

40 years ago, Endel Tulving published his hugely influential Elements of Episodic Memory (Oxford: Clarendon Press, 1983). For the first time, this discussed the details of episodic memory (i.e. the ability to remember personal past events), including a specific conscious experience. Ten years later, Tulving defined the ability to mentally project oneself in time to be the critical feature distinguishing episodic from semantic memory (‘What is episodic memory?’ Curr . Dir . Psychol . Sci . 2 , 67–70, doi:10.1111/1467-8721.ep10770899). In this conception, the conscious experience of episodic memory captures the experience of reliving a personal event as it was experienced in the past, while the same ability allows a potential symmetry between remembering the past, and our ability to project into an imagined future. With the recent passing of Endel Tulving, this theme issue offers an opportunity to question our understanding of mental time travel in full. This article is part of the theme issue ‘Elements of episodic memory: lessons from 40 years of research’.

Mental time travel is the projection of the mind into the past or future, and relates to experiential aspects of episodic memory, and episodic future thinking. Framing episodic memory and future thinking in this way causes a challenge when studying memory in animals, where demonstration of this mental projection is prevented by the absence of language. However, there is good evidence that non-human animals pass tests of episodic memory that are based on behavioural criteria, meaning a better understanding needs to be had of the relationship between episodic memory and mental time travel. We argue that mental time travel and episodic memory are not synonymous, and that mental time travel is neither a requirement of, nor an irrelevance to, episodic memory. Mental time travel can allow improved behavioural choices based on episodic memory, and work in all species (including humans) should include careful consideration of the behavioural outputs being measured. This article is part of the theme issue ‘Elements of episodic memory: lessons from 40 years of research’.