Flexible navigation demands knowledge of boundaries, routes and their relationships. Within a multi-path environment, a subpopulation of subiculum neurons robustly encoded the axis of travel. The firing of axis-tuned neurons peaked bimodally, at head orientations 180° apart. Environmental manipulations showed these neurons to be anchored to environmental boundaries but to lack axis tuning in an open arena. Axis-tuned neurons thus provide a powerful mechanism for mapping relationships between routes and the larger environmental context.

No abstract

Travel constrained to paths, a common navigational context, demands knowledge of spatial relationships between routes, their components, and their positioning in the larger environment. During traversal of an environment composed of multiple interconnected paths, a subpopulation of subiculum neurons robustly encoded the animal’s current axis of travel. The firing of these axis-tuned neurons peaked bimodally at head orientations approximately 180 degrees apart. Track rotation experiments revealed that axis encoding carried the spatial reference frame of the larger environment as opposed to the track itself. However, axis-tuned activity of the same subpopulation was largely absent during unconstrained movement about a circular arena. Thus, during navigation in a path-rich environment, subpopulations of subiculum neurons encode the animal’s current axis of travel relative to environmental boundaries - providing a powerful mechanism for mapping of specific relationships between routes, route components, and the larger environment.

Fluid navigation requires constant updating of planned movements to adapt to evolving obstacles and goals. For that reason, a neural substrate for navigation demands spatial and environmental information and the ability to effect actions through efferents. The secondary motor cortex (M2) is a prime candidate for this role given its interconnectivity with association cortices that encode spatial relationships and its projection to the primary motor cortex. Here, we report that M2 neurons robustly encode both planned and current left/right turning actions across multiple turn locations in a multi-route navigational task. Comparisons within a common statistical framework reveal that M2 neurons differentiate contextual factors, including environmental position, route, action sequence, orientation, and choice availability. Despite significant modulation by environmental factors, action planning, and execution are the dominant output signals of M2 neurons. These results identify the M2 as a structure integrating spatial information toward the updating of planned movements.