Head Direction Information Research Articles

Directing place representation in the hippocampus.

Theoretical models of rodent navigation consider location information and directional heading to be essential. Indeed, the existence of location-selective 'place cells' and orientation-selective 'head direction cells' is well documented. Different models suggest different forms of interaction between information about location and heading direction. However, until recently, there were no clear empirical data that could be used to distinguish the different models in terms of the nature of the integration of location and directional heading information. Recently, Leutgeb et al. provided evidence that head direction and place signals coexist within the CA1 region of hippocampus, and that the head direction signals are likely to be generated by a subpopulation of interneurons. This finding opens up new possibilities for clarifying current models and for developing biologically plausible theories of synaptic interactions between location and head direction codes. In this paper, we first present the issue concerning the nature of the interaction between location and head direction signals, followed by a selective review of place and head direction cell research. The finding of Leutgeb et al. is then summarized, and its implications for current models are discussed. Finally, a view is presented that considers place fields to be a product not only of (external and internal) sensory input, but also of non-spatial variables such as motivation and responses. The finding of Leutgeb et al. and many earlier anatomical studies suggest that hippocampal head direction, motivation and response information may be represented by the interneuron population. Thus, these factors may have strong impact on the location codes of hippocampal pyramidal neurons. Their influence may further define the behavioral context of the current spatial environment.

Convergence of head direction and place information in the CA1 region of hippocampus

The hippocampus has long been considered critical for spatial learning and navigation. Recent theoretical models of the rodent and primate hippocampus consider spatial processing a special case of a more general memory function. These non-spatial theories of hippocampus differ from navigational theories with respect to the role of self-motion representations. The present study presents evidence for a new cell type in the CA1 area of the rat hippocampus that codes for directional heading independent of location information (i.e. the angular component of self-motion). These hippocampal head direction cells are controlled by external and idiothetic cues in a similar way as head direction cells in other brain areas and hippocampal place cells. Convergent head direction information and location information may be an essential component of a neural system that monitors behavioral sequences during navigation. Conflicts between internally generated and external cues have previously been shown to result in new hippocampal place representations, suggesting that head direction information may participate in synaptic interactions when new location codes are formed. Combined hippocampal representations of self-motion and external cues may therefore contribute to path integration as well as spatial memory processing.