Why Isn't the Head Direction System Necessary for Direction? Lessons From the Lateral Mammillary Nuclei.

Christopher M Dillingham,Seralynne D Vann

doi:10.3389/fncir.2019.00060

Christopher M Dillingham, Seralynne D Vann

Open Access

https://doi.org/10.3389/fncir.2019.00060

Copy DOI

Journal: Frontiers in neural circuits	Publication Date: Sep 13, 2019
Citations: 19	License type: CC BY 4.0

Affiliation: Cardiff University

Abstract

Complex spatial representations in the hippocampal formation and related cortical areas require input from the head direction system. However, a recurrent finding is that behavior apparently supported by these spatial representations does not appear to require input from generative head direction regions, i.e., lateral mammillary nuclei (LMN). Spatial tasks that tax direction discrimination should be particularly sensitive to the loss of head direction information, however, this has been repeatedly shown not to be the case. A further dissociation between electrophysiological properties of the head direction system and behavior comes in the form of geometric-based navigation which is impaired following lesions to the head direction system, yet head direction cells are not normally guided by geometric cues. We explore this apparent mismatch between behavioral and electrophysiological studies and highlight future experiments that are needed to generate models that encompass both neurophysiological and behavioral findings.

Highlights

The ability to navigate through environments, and remember locations within those environments, is key to survival
The traditional hierarchical model of the head direction system involves a vestibular/vestibulomotor-derived head direction signal which ascends to the lateral mammillary nuclei (LMN) and is updated through the integration of external sensory inputs, e.g., visual information from PoSub (Yoder et al, 2015), through to ADN, PoSub and MEC
An additional example of this hierarchical increase in complexity comes from bidirectional cells in the retrosplenial cortex (RSC; Jacob et al, 2017), which can represent two sensory modalities, i.e., olfaction and vision within a given environment, or can represent a single sensory modality differently across contexts

Summary

Introduction

The ability to navigate through environments, and remember locations within those environments, is key to survival. Impairments in LMN lesion rats may be masked by animals using non-directional cues to perform the task.

Results

Conclusion