Coding for time and space

18th Dec 2020

‘Neurophysiological coding of space and time in the hippocampus, entorhinal cortex, and retrosplenial cortex’, is a recent article published in the British Neuroscience Association (BNA) journal, Brain and Neuroscience Advances, where authors, Andrew Alexander et al. (2020), review the coding for time and space.

This article examines the coding for space and time in the hippocampus and associated cortical structures, with a focus on how experiences occurring in similar locations, but with varying sensory or contextual information, can be disambiguated. 

Neurophysiological recordings were made in behaving rodents to demonstrate neuronal response properties that may code space and time for episodic memory and goal-directed behaviour.

What is episodic memory?

Episodic memory is for events that occur at a specific place and at a specific time (Eichenbaum et al., 1999; Tulving, 1984). It includes the concept of mental time travel, in which episodic memory ‘produces many snapshots whose orderly succession can create the mnemonic illusion of the flow of past time’ (Tulving, 1984).

Later, models of the full spatiotemporal trajectory of an episodic memory (Hasselmo, 2009, 2012) argued that a full account of episodic memory should also include coding of the viewpoint or heading direction of a person perceiving a particular event (Conway, 2009), the speed of movement of that agent (Hasselmo, 2009, 2012), the movement of objects in the event (Hasselmo et al., 2010), and coding of context for disambiguation of memories (Hasselmo, 2009; Hasselmo and Eichenbaum, 2005).

To put that in context, consider an individual person or animal freely moving through an environment and encountering other agents or objects. This requires coding not only of where the agent was, and the relative time that an event occurred, but also requires more detailed information to encode memory of all elements of the episode, such as the direction the agent was facing, the speed it was moving at, the locations of objects or barriers relative to the agent, and the context of prior or future actions by the agent.

Time and space coding

The authors firstly surveyed single neuron and ensemble coding mechanisms by which episodic memories occurring in the same place can be separated in the temporal domain.

They then reviewed modes by which cortical areas, such as the medial entorhinal cortex, can support episodic encoding by providing the spatial framework upon which memories can be laid.

Finally, they synthesized recent work reporting coding of sensory features in the environment relative to the animal itself, which may be critical for integrating ‘point-of-view’ sensory or spatial information into the spatiotemporal structure of episodic memories formed by the hippocampus and medial entorhinal cortex.   

Click here to read the full article

About Brain and Neuroscience Advances  

Brain and Neuroscience Advances is a peer-reviewed, open-access journal, which publishes high quality translational and clinical articles from all neuroscience disciplines; including molecular, cellular, systems, behavioural and cognitive investigations.

The journal welcomes submissions in basic, translational and/or clinical neuroscience. Research papers should present novel, empirical results that are expected to be of interest to a broad spectrum of neuroscientists working in the laboratory, field or clinic. 

Brain and Neuroscience Advances is now indexed in PubMed Central.

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