Navigational Strategies and Their Neural Correlates

Investigating boundary-geometry use by whip spiders (Phrynus marginemaculatus) during goal-directed navigation

Previous studies have shown that whip spiders (Amblypygi) can use a variety of cues to navigate to and recognize a home refuge. The current study aimed to determine whether whip spiders were capable of using the boundary geometry of an experimental space (geometric information) to guide goal-directed navigation and to investigate any preferential use of geometric or feature (visual) information. Animals were first trained to find a goal location situated in one corner of a rectangular arena (geometric information) fronting a dark-green-colored wall, which created a brightness contrast with the other three white walls (feature information). Various probe trials were then implemented to determine cue use. It was found that animals were capable of directing their choice behavior towards geometrically correct corners at a rate significantly higher than chance, even when the feature cue was removed. By contrast, choice behavior dropped to random chance when geometric information was removed (test in a square arena) and only feature information remained. Choice behavior was also reduced to chance when geometric and feature information were set in conflict (by moving the feature cue to one of the longer walls in the rectangular arena). The data thus suggest that whip spiders are capable of using geometric information to guide goal-directed navigation and that geometric information is preferred over feature guidance, although a feature cue may set the context for activating geometry-guided navigation. Experimental design limitations and future directions are discussed.

An Automated Visual Psychophysics Method to Measure Visual Function in Swine Preclinical Animal Model

Purpose

The aim of this study was to develop and validate a test to assess visual function in pigs using the visual psychophysics contrast sensitivity function.

Methods

We utilized a touchscreen along with a pellet reward dispenser to train three Göttingen pigs on a visual psychophysics test and determined their contrast sensitivity function. Images with different contrast resolutions were used as visual stimuli and presented against a control image in a two-choice test. Following animals' acclimatization and the first phase of training, the system was arranged such that animals could self-run multiple consecutive trials without human intervention.

Results

All animals were trained within a week and remembered the task with 1 day of reinforcement when tested 1 month after the last visual assessment. All trained animals performed well during the trial with minimal screen side bias, especially at contrast threshold above 40%.

Conclusions

Göttingen pigs are trainable for a visual psychophysics test and able to self-run the trial without human intervention.

Translational Relevance

Contrast sensitivity is one of the key parameters to assess visual function in humans. The possibility of measuring the same parameters in a large animal model allows for a better translation and understanding of drug safety and efficacy in preclinical ophthalmology.

Acute stress impairs visual path integration

Acute stress exerts substantial effects on episodic memory, which are often mediated by glucocorticoids, the end-product of the hypothalamic-pituitary-adrenal axis. Surprisingly little is known, however, about the influence of acute stress on human spatial navigation. One specific navigational strategy is path integration, which is linked to the medial entorhinal cortex, a region harboring glucocorticoid receptors and thus susceptible for stress effects. Here, we investigated effects of acute stress on path integration performance using a virtual homing task. We divided a sample of healthy young male participants into a stress group (nstress = 32) and a control group (ncontrol = 34). The stress group underwent the socially evaluated cold-pressor test, while the control group underwent a non-stressful control procedure. Stress induction was confirmed via physiological and subjective markers, including an increase of salivary cortisol concentrations. We applied linear mixed models to investigate the effect of acute stress on path integration depending on task difficulty and the presence or absence of spatial cues. These analyses revealed that stress impaired path integration especially in trials with high difficulty and led to greater decline of performance upon removal of spatial cues. Stress-induced deficits were strongly related to impaired distance estimation, and to a lesser extent to compromised rotation estimation. These behavioral findings are in accordance with the hypothesis that acute stress impairs path integration processes, potentially by affecting the entorhinal grid cell system. More generally, the current data suggests acute stress to impair cognitive functions mediated by medial temporal lobe regions outside the hippocampus.

Computational cross-species views of the hippocampal formation

The discovery of place cells and head direction cells in the hippocampal formation of freely foraging rodents has led to an emphasis of its role in encoding allocentric spatial relationships. In contrast, studies in head-fixed primates have additionally found representations of spatial views. We review recent experiments in freely moving monkeys that expand upon these findings and show that postural variables such as eye/head movements strongly influence neural activity in the hippocampal formation, suggesting that the function of the hippocampus depends on where the animal looks. We interpret these results in the light of recent studies in humans performing challenging navigation tasks which suggest that depending on the context, eye/head movements serve one of two roles-gathering information about the structure of the environment (active sensing) or externalizing the contents of internal beliefs/deliberation (embodied cognition). These findings prompt future experimental investigations into the information carried by signals flowing between the hippocampal formation and the brain regions controlling postural variables, and constitute a basis for updating computational theories of the hippocampal system to accommodate the influence of eye/head movements.

Chronic stress is associated with specific path integration deficits

Repeated exposure to stress (chronic stress) can cause excess levels of circulating cortisol and has detrimental influences on various cognitive functions including long-term memory and navigation. However, it remains an open question whether chronic stress affects path integration, a navigational strategy that presumably relies on the functioning of grid cells in the medial entorhinal cortex. The entorhinal cortex is a brain region in the medial temporal lobe, which contains multiple cell types involved in spatial navigation (and episodic memory), and a high number of corticosteroid receptors, predisposing it as a potential target of cortisol effects. Here, our goal was to investigate the association between chronic stress and path integration performance. We assessed chronic stress via hair cortisol concentration (physiological measure) and the Perceived Stress Questionnaire (subjective measure) in 52 female participants aged 22-65 years. Path integration was measured using a virtual homing task. Linear mixed models revealed selective impairments associated with chronic stress that depended on error type and environmental features. When focusing on distance estimations in the path integration task, we observed a significant relationship to hair cortisol concentrations indicating impaired path integration particularly during trials with higher difficulty in participants with high hair cortisol concentrations. This relationship especially emerged in the absence of spatial cues (a boundary or a landmark), and particularly in participants who reported high levels of subjectively experienced chronic stress. The findings are in line with the hypothesis that chronic stress compromises path integration, possibly via an effect on the entorhinal grid cell system.

Using your nose to find your way: Ethological comparisons between human and non-human species

Olfaction is arguably the least valued among our sensory systems, and its significance for human behavior is often neglected. Spatial navigation represents no exception to the rule: humans are often characterized as purely visual navigators, a view that undermines the contribution of olfactory cues. Accordingly, research investigating whether and how humans use olfaction to navigate space is rare. In comparison, research on olfactory navigation in non-human species is abundant, and identifies behavioral strategies along with neural mechanisms characterizing the use of olfactory cues during spatial tasks. Using an ethological approach, our review draws from studies on olfactory navigation across species to describe the adaptation of strategies under the influence of selective pressure. Mammals interact with spatial environments by abstracting multisensory information into cognitive maps. We thus argue that olfactory cues, alongside inputs from other sensory modalities, play a crucial role in spatial navigation for mammalian species, including humans; that is, odors constitute one of the many building blocks in the formation of cognitive maps.