Integration of the sensory inputs to place cells
Institute of Behavioural Neuroscience, Department of Psychology, UCL, London , UK
The localized firing of hippocampal place cells must somehow be determined by sensory inputs carrying information from the external world, but the exact nature of these inputs, and how they are integrated across sensory modalities and informational domains, remains poorly understood. Cue conflict experiments, in which subsets of environmental sensory cues are altered relative to others, can reveal much about how inputs are integrated, and we have used this approach to explore sensory integration in three domains: directional, linear spatial and contextual. In the directional spatial domain, it seems that static and self-motion cues compete for control, with static cues (mainly visual) predominating unless these have been experienced as unstable, in which case self-motion cues take over. In the linear spatial domain, place cells seem to use boundaries and edges to anchor their firing to the outside world, and may use self-motion cues as supporting information when direct sensory information is degraded or unavailable. In the contextual domain, cells combine information from different sensory modalities, with different cells using different subsets of the available information. The end result is a population code of “spatial context” (integrated spatial and contextual information) which, according to the results of behavioural studies, may allow flexible assignment of behaviours and/or expectations to different environmental conditions.