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Open Access Publications from the University of California

Scholarly Works (2 results)

  • Thesis
  • Peer Reviewed
UCLA Electronic Theses and Dissertations (2015)

How the brain represents space is a long-standing question, whose answer is most likely to be found within the hippocampal formation. There, spatially selective neurons called place cells provide strong evidence that they are able to form relations between elements of the environment and map the position of the animal with respect to them. These cells are modulated by multiple inputs, and their activity patterns both at the neuronal and population change appropriate to the available sensory and motor information. However, the degree of their contributions and the mechanism behind their integration are unclear.

The goal of this thesis is to determine the contribution of these different afferent signals by manipulating the spatial information provided by them in order to shed light on the mechanisms of multisensory integration in the hippocampus. This is difficult, if not impossible, to realize in real world (RW) experiments but virtual reality (VR) has become a popular tool that can be used to achieve this dissociation. In this thesis VR environments are used to manipulate the spatially relevant information provided by visual and locomotion cues and hence determine their contributions to the hippocampal spatial map.

The results described show that distal visual cues alone are insufficient to generate spatially selective activity, but are sufficient to generate activity that is selective to the head-direction of the animal. Additionally, traditionally described spatially selective activity in the form of place fields is not necessary in order to perform a spatial navigation task.

  • 4 supplemental videos
Cover page: Multisensory Representations of Space in Hippocampal CA1
  • Article
  • Peer Reviewed
UCLA Previously Published Works (2021)
Three major pillars of hippocampal function are spatial navigation1, Hebbian synaptic plasticity2 and spatial selectivity3. The hippocampus is also implicated in episodic memory4, but the precise link between these four functions is missing. Here we report the multiplexed selectivity of dorsal CA1 neurons while rats performed a virtual navigation task using only distal visual cues5, similar to the standard water maze test of spatial memory1. Neural responses primarily encoded path distance from the start point and the head angle of rats, with a weak allocentric spatial component similar to that in primates but substantially weaker than in rodents in the real world. Often, the same cells multiplexed and encoded path distance, angle and allocentric position in a sequence, thus encoding a journey-specific episode. The strength of neural activity and tuning strongly correlated with performance, with a temporal relationship indicating neural responses influencing behaviour and vice versa. Consistent with computational models of associative and causal Hebbian learning6,7, neural responses showed increasing clustering8 and became better predictors of behaviourally relevant variables, with the average neurometric curves exceeding and converging to psychometric curves. Thus, hippocampal neurons multiplex and exhibit highly plastic, task- and experience-dependent tuning to path-centric and allocentric variables to form episodic sequences supporting navigation.
    Cover page: Linking hippocampal multiplexed tuning, Hebbian plasticity and navigation
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