Updating headings in 3D navigation

This study investigated to what extent humans can encode spatial relations between different surfaces (i.e., floor, walls, and ceiling) in a three-dimensional (3D) space and extend their headings on the floor to other surfaces when locomoting to walls (pitch 90°) and the ceiling (pitch 180°). In immersive virtual reality environments, participants first learned a layout of objects on the ground. They then navigated to testing planes: south (or north) walls facing Up, or the ceiling via walls facing North (or South). Participants locomoted to the walls with pitch rotations indicated by visual and idiothetic cues (Experiment 1) and only by visual cues (Experiment 2) and to the ceiling with visual pitch rotations only (Experiment 3). Using the memory of objects’ locations, they either reproduced the object layout on the testing plane or did a Judgements of Relative Direction (JRD) task (“imagine standing at object A, facing B, point to C”) with imagined headings of south and north on the ground. The results showed that participants who locomoted onto the wall with idiothetic cues showed a better performance in JRD for an imagined heading from which their physical heading was extended (e.g., imagined heading of North at the north wall). In addition, the participants who reproduced the layout of objects on the ceiling from a perspective extended from the ground also showed a sensorimotor alignment effect predicted by an extended heading. These results indicate that humans encode spatial relations between different surfaces and extend headings via pitch rotations three-dimensionally, especially with idiothetic cues.

Passive Transport Disrupts Directional Path Integration by Rat Head Direction Cells

A subset of neurons in the rat limbic system encodes head direction (HD) by selectively discharging when the rat points its head in a preferred direction in the horizontal plane. The preferred firing direction is sensitive to the location of landmark cues, as well as idiothetic or self-motion cues (i.e., vestibular, motor efference copy, proprioception, and optic flow). Previous studies have shown that the preferred firing direction remains relatively stable (average shift ± 18°) after the rat walks from a familiar environment into a novel one, suggesting that without familiar landmarks, the preferred firing direction can be maintained using idiothetic cues, a process called directional path integration. This study repeated this experiment and manipulated the idiothetic cues available to the rat as it moved between the familiar and novel environment. Motor efference copy/proprioceptive cues were disrupted by passively transporting the animal between the familiar and novel environment. Darkening the room as the animal moved to the novel environment eliminated optic flow cues. HD cell preferred firing directions shifted in the novel environment by an average of 30° after locomotion from the familiar environment with the room lights off; by an average of 70° after passive transport from the familiar environment with the room lights on; and by an average of 67° after passive transport with the room lights off. These findings are consistent with the view that motor efference copy/proprioception cues are important for maintaining the preferred firing direction of HD cells under conditions requiring path integration.

Interactions Between Idiothetic Cues and External Landmarks in the Control of Place Cells and Head Direction Cells

Knierim, James J., Hemant S. Kudrimoti, and Bruce L. McNaughton. Interactions between idiothetic cues and external landmarks in the control of place cells and head direction cells. J. Neurophysiol. 80: 425–446, 1998. Two types of neurons in the rat brain have been proposed to participate in spatial learning and navigation: place cells, which fire selectively in specific locations of an environment and which may constitute key elements of cognitive maps, and head direction cells, which fire selectively when the rat's head is pointed in a specific direction and which may serve as an internal compass to orient the cognitive map. The spatially and directionally selective properties of these cells arise from a complex interaction between input from external landmarks and from idiothetic cues; however, the exact nature of this interaction is poorly understood. To address this issue, directional information from visual landmarks was placed in direct conflict with directional information from idiothetic cues. When the mismatch between the two sources of information was small (45°), the visual landmarks had robust control over the firing properties of place cells; when the mismatch was larger, however, the firing fields of the place cells were altered radically, and the hippocampus formed a new representation of the environment. Similarly, the visual cues had control over the firing properties of head direction cells when the mismatch was small (45°), but the idiothetic input usually predominated over the visual landmarks when the mismatch was larger. Under some conditions, when the visual landmarks predominated after a large mismatch, there was always a delay before the visual cues exerted their control over head direction cells. These results support recent models proposing that prewired intrinsic connections enable idiothetic cues to serve as the primary drive on place cells and head direction cells, whereas modifiable extrinsic connections mediate a learned, secondary influence of visual landmarks.