Navigation & Memory

 

History

  • Our ability to navigate and what the underlying neural substrates enabling this function has been an area of considerable research within the field of cognitive neuroscience.

  • Early work with rodents by Tolman led to the observation of their ability to find shorter, more direct routes to a goal within a maze, which could not be explained by simple stimulus-response mechanisms. This led to the coining of the term ‘cognitive map’ —a theory that the brain builds and holds a unified representation of our spatial environment to aid memory and flexible navigation strategies.

Neural Evidence

  • Rodent studies are an important way of providing insight into the more precise aspects of the neural systems underlying spatial navigation

  • Initial neural evidence in support of the cognitive map theory can be attributed to John O’Keefe for the Nobel Prize winning discovery of ‘place cells’ within the hippocampus (a subcortical structure in our brain). These cells have shown to fire when in particular locations of an environment and have been proposed to be the neural underpinnings for a spatial map within the brain.

  • Other cells that support the cognitive map theory have also been discovered in the surrounding hippocampal regions:

    • Grid cells in the medial entorhinal cortex fire in a repeating hexagonal pattern that tiles the floor of the environment, these have been suggested to provide a metric for distance.

    • Head-direction cells, found in several cortical and subcortical structures fire when the head is at a particular orientation within the navigational plane, they fire independent of location.

    • Border cells in the entorhinal cortex and boundary cells in the subiculum, fire when at particular distances from borders within the environment.

    • All of these groups of cells provide the neural evidence for a spatial navigation system within the brain.


  • Recent human-studies have also shown that the hippocampus is an important structure for cognitive-map based navigation in humans.

  • Hippocampal activity has been associated with the use of cognitive-map based strategies during navigation tasks, with its activity being a predictor of task accuracy.

  • The size of the hippocampus is also a good predictor of the ability of acquiring new cognitive maps.

  • The hippocampus has also been shown to support map-like spatial codes, with buildings that are physically closer in an environment being represented more closely within the hippocampus than ones further away — much like a map.

Memory

  • Past neuro-psychological cases have implicated the hippocampus as an important structure for memory, particularly our general declarative memory (this consists of our memory of facts and past-experiences/events that can be consciously retrieved).

  • Lesion studies have shown that damage to the hippocampus profoundly impairs our spatial memory and navigation ability.

  • Due to the spatial nature of ‘place cell’ activity, it has been recently proposed that the hippocampal spatial map may play a role in the organisation of our memories:

    • The first idea is that this function is achieved through place cell activity, which uses physical space as a framework for associating our episodic memories (memories of past-experiences/events) together to aid retrieval of them.

    • The second is that the hippocampus may serve as a ‘memory map’, organising where our memories are stored in the brain, acting as a biological index.

  • This area of neuroscience is still being constantly reviewed, however, what is clear is that the hippocampus serves an important function in both our navigation and memory processing, with place and memory being inextricably linked.


 
Josh Artus