Wilson, JJ; (2016) Behavioural and electrophysiological investigations of three-dimensional navigation. Doctoral thesis , (UCL) University College London.

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Abstract

The world through which animals navigate is complex and three-dimensional, yet the majority of studies of navigation have been conducted in two-dimensional planar environments. The aim of this thesis, therefore, was to test whether animals are able to represent three-dimensional space, and if so, to determine the manner in which this space is represented in the brain. Behavioural and electrophysiological techniques were employed to answer these questions. In the first set of experiments, the ability of mice to complete working and reference memory tasks on a three-dimensional radial arm maze was compared with their ability on a two-dimensional analogue of the three-dimensional maze. The findings showed an equally good level of working memory in two and three-dimensional mazes, but reduced reference memory in the three-dimensional maze. These results suggest an intact representation of three-dimensional space over short time scales, but impairment in the formation, retention and/or recall of these representations over longer timescales. The second study, using electrophysiological techniques, tested the manner in which the brain represents orientation in three-dimensional environments. A three-dimensional apparatus was developed to test whether head direction (HD) cells encode orientation in a planar, multi-planar or volumetric manner. Head direction cells, which are known to be responsive to spatial orientation in 2D environments, were recorded as rats climbed between different vertical walls on cuboidal climbing apparatus. The findings showed that the HD cell system represents orientation in a multi-planar manner, in which the animal’s plane of locomotion and the position of that plane relative to the azimuth inform the firing direction of HD cells. It will be argued in this thesis that the HD system is optimised to allow animals to translate their representation of orientation from vertical planes back to the horizontal plane without the accumulation of heading errors. Together, the findings presented in this thesis suggest that rodent use a multi-planar reference frame to aid navigation in complex three-dimensional environments.

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