Hex Maze: A new virtual maze able to track acquisition and usage of three navigation strategies

L-DOPA enhances neural direction signals in younger and older adults

Previous studies indicate a role of dopamine in spatial navigation. Although neural representations of direction are an important aspect of spatial cognition, it is not well understood whether dopamine directly affects these representations, or only impacts other aspects of spatial brain function. Moreover, both dopamine and spatial cognition decline sharply during age, raising the question which effect dopamine has on directional signals in the brain of older adults. To investigate these questions, we used a double-blind cross-over L-DOPA/Placebo intervention design in which 43 younger and 37 older adults navigated in a virtual spatial environment while undergoing functional magnetic resonance imaging (fMRI). We studied the effect of L-DOPA, a dopamine precursor, on fMRI activation patterns that encode spatial walking directions that have previously been shown to lose specificity with age. This was done in predefined regions of interest, including the early visual cortex, retrosplenial cortex, and hippocampus. Classification of brain activation patterns associated with different walking directions was improved across all regions following L-DOPA administration, suggesting that dopamine broadly enhances neural representations of direction. No evidence for differences between regions was found. In the hippocampus these results were found in both age groups, while in the retrosplenial cortex they were only observed in younger adults. Taken together, our study provides evidence for a link between dopamine and the specificity of neural responses during spatial navigation. SIGNIFICANCE STATEMENT: The sense of direction is an important aspect of spatial navigation, and neural representations of direction can be found throughout a large network of space-related brain regions. But what influences how well these representations track someone's true direction? Using a double-blind cross-over L-DOPA/Placebo intervention design, we find causal evidence that the neurotransmitter dopamine impacts the fidelity of direction selective neural representations in the human hippocampus and retrosplenial cortex. Interestingly, the effect of L-DOPA was either equally present or even smaller in older adults, despite the well-known age related decline of dopamine. These results provide novel insights into how dopamine shapes the neural representations that underlie spatial navigation.

London taxi drivers: A review of neurocognitive studies and an exploration of how they build their cognitive map of London

Licensed London taxi drivers have been found to show changes in the gray matter density of their hippocampus over the course of training and decades of navigation in London (UK). This has been linked to their learning and using of the "Knowledge of London," the names and layout of over 26,000 streets and thousands of points of interest in London. Here we review past behavioral and neuroimaging studies of London taxi drivers, covering the structural differences in hippocampal gray matter density and brain dynamics associated with navigating London. We examine the process by which they learn the layout of London, detailing the key learning steps: systematic study of maps, travel on selected overlapping routes, the mental visualization of places and the optimal use of subgoals. Our analysis provides the first map of the street network covered by the routes used to learn the network, allowing insight into where there are gaps in this network. The methods described could be widely applied to aid spatial learning in the general population and may provide insights for artificial intelligence systems to efficiently learn new environments.

Methylene blue and photobiomodulation recover cognitive impairment in hepatic encephalopathy through different effects on cytochrome c-oxidase

Mitochondrial dysfunction plays a central role in hepatic encephalopathy (HE), due to changes in enzyme cytochrome c-oxidase (CCO), causing a decline in brain metabolism. We used an HE animal model and applied intracranial administration of methylene blue (MB) and transcranial photobiomodulation (PBM), both targeting CCO, to determine their differential effects on recovering cognition. Five groups of rats were used: sham-operated group + saline (SHAM + SAL, n = 6), hepatic encephalopathy + SAL (HE + SAL, n = 7), SHAM + methylene blue (SHAM + MB, n = 7), HE + MB (n = 7), HE + PBM (n = 7). PBM animals were exposed transcranially to 670 +/- 10 nm LED light at a dose of 9 J/cm2 once a day for 7 days, and the MB and SAL groups were injected with 2.2 μg/0.5 μL in the accumbens. Cognitive dysfunction was evaluated on a striatal stimulus-response task using the Morris water maze. Our results showed cognitive improvement in the HE group when treated with MB. This improvement was accompanied by a decrease in CCO activity in the prefrontal cortex, dorsal striatum, and dorsal hippocampus. When comparing MB and PBM, we found that, although both treatments effectively improved the HE-memory deficit, there was a differential effect on CCO. A general decrease in CCO activity was found in the prefrontal and entorhinal cortices, dorsal striatum, and hippocampus when PBM, compared to MB, was applied. Our results suggest that mitochondrial dysfunction and brain metabolic decline in HE might involve CCO alteration and can be improved by administering MB and PBM.

The art gallery maze: a novel tool to assess human navigational abilities

Humans differ widely in their ability to navigate effectively through the environment and in spatial memory skills. Navigation in the environment requires the analysis of many spatial cues, the construction of internal representations, and the use of various strategies. We present a novel tool to assess individual differences in human navigation, consisting of a virtual radial-arm maze presented as an art gallery to explore whether different sets of instructions (intentional or incidental) affect subjects' navigation performance. We furthermore tested the effect of the instructions on exploration strategies during both place learning and recall. We evaluated way-finding ability in 42 subjects, and individual differences in navigation were assessed through the analysis of navigational paths, which permitted the isolation and definition of a few strategies adopted by the incidental and intentional instructions groups. Our results showed that the intentional instruction group performed better than the other group: these subjects correctly paired each central statue and the two paintings in the adjacent arms, and they made less working and reference memory errors. Our analysis of path lengths showed that the intentional instruction group spent more time in the maze (thus being slower), specifically in the central hall, and covered more distance; the time spent in the main hall was, therefore, indicative of the quality of the following performance. Studying how environmental representations and the relative navigational strategies vary among "intentional" and "incidental" groups provides a new window into the acknowledgment of possible strategies to help subjects construct more efficient approaches in human navigation.

Passively learned spatial navigation cues evoke reinforcement learning reward signals

Since the suggestion by Tolman (1948) that both rodents and humans create cognitive maps during navigation, the specifics of how navigators learn about their environment has been mired in debate. One facet of this debate is whether or not the creation of cognitive maps - also known as allocentric navigation - involves reinforcement learning. Here, we demonstrate a role for reinforcement learning during allocentric navigation using event-related brain potentials (ERPs). In the present experiment, participants navigated in a virtual environment that allowed the use of three different navigation strategies (allocentric, egocentric-response, & egocentric-cue), in which their goal was to locate and remember a hidden platform. Following the navigation phase of the experiment, participants were shown "cue images" representative of the three navigation strategies. Specifically, we examined whether or not these passively learned strategy images elicited a reward positivity - an ERP component associated with reinforcement learning and the anterior cingulate cortex. We found that when allocentric navigators were shown previously learned cues predicting the goal location a reward positivity was elicited. The present findings demonstrate that allocentric navigational cues carry long-term value after navigation and lend support to the claim that reinforcement learning plays a role in the acquisition of allocentric navigation and thus the generation of cognitive maps.

Gender-based eye movement differences in passive indoor picture viewing: An eye-tracking study

Male and female brains have different structures, which can make genders produce various eye- movement patterns. This study presents the results of an eye tracking experiment in which we analyzed the eye movements of 25 male and 20 female participants during passive indoor picture viewing. We examined eye-movement parameters, namely fixation duration, scan path length, number of saccades, spatial density, saccade amplitude, and the ratio of total fixation duration to total saccade duration so as to investigate gender differences in eye-movement patterns while indoor picture viewing. We found significant differences in eye-movement patterns between genders. The results of eye-movement analysis also indicated that females showed more explorative gaze behavior, indicated by larger saccade amplitudes, and by longer scan paths. Furthermore, owing to shorter ratio of fixation durations to saccade duration in females as compared to male, we speculate that females inspect the images faster than males. In addition, we classified the genders into two subgroups-males and females-based on their eye-movement parameters by using a support vector machine classifier achieving an accuracy of 70%. We have come to the result males and females - with same culture - see the environment differently. Our findings have profound implications for researches employing gaze-based models.