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This thesis explores the role of path integration on the firing of hippocampal place cells and medial entorhinal grid cells. Grid cells fire at equidistant locations in an environment, indicating that they keep track of the distance and direction an animal has moved in an environment. One class of model of path integration uses a continuous attractor network to update position information. The first part of this thesis showed that such a network can generate a "look-ahead" of neural activity that sweeps through the positions just visited and about to be visited, on the short time scale that is observed<italic>in vivo</italic>. Adding intrinsic currents to the neurons in the network model allowed this look-ahead to recur every theta cycle, and generate grid fields of a size comparable to data. Grid cells are a major input the hippocampus, and are hypothesized to be the source of the place specificity of place cells. When an animal explores an open environment, place cells are active in a particular location regardless of the direction in which the animal travels through it. While performing a specific task, such as visiting specific locations in the environment in sequence, however, most place cells are active only in one direction. The second part of this thesis studied the development of this directionality. It was determined that upon the initial appearance of place fields in a novel environment, place cells fired in all directions, supporting the hypothesis that the path integration is the primary determinant of place specificity. The directionality of place fields developed gradually, possibly as a result of learning. Ideas about how this directionality could develop are explored.

In the study of navigation, frequently it is assumed that navigation is accomplished using either an allocentric strategy based on a cognitive map, or an egocentric strategy based on stimulus response associations. Further, it is frequently assumed that individual navigators, or even entire genders, are only capable of navigating by one strategy or the other. The present study investigated whether individuals or genders were limited to a particular navigational strategy and whether both strategies might be learned or used at the same time. In the present study, undergraduate students were tested in a virtual Morris water maze that was modified to allow successful and efficient navigation using either an allocentric or an egocentric strategy. Learning trials on which the participants had to learn the location of the platform were alternated with probe trials on which participants would show which strategy they were using. At the end of testing, participants were given a series of tests to determine what knowledge they had acquired and which strategies they were capable of using. Results indicated that: a) most people preferred to navigate egocentrically in this maze, but some preferred to navigate allocentrically, b) people tended to use an egocentrically strategy first, but it was not a necessary step to learning to navigate allocentrically, c) people were better at their preferred strategy, d) people learned information about their non-preferred strategy, and e) those who preferred to navigate egocentrically could nevertheless learn to navigate allocentrically. Surprisingly, all of these results were true for both men and women, although women tended to prefer egocentric navigation at a higher rate than men, and men outperformed women when forced to navigate allocentrically. These results suggest it may be too simple to think of navigators as being capable of only a single navigational strategy or of learning only one strategy at a time. / Graduate

Stress is known to impair spatial navigation in rat models of declarative memory, and declarative memory in humans, but the effects on spatial navigation in humans are unclear. At least four models have been proposed to account for the cognitive effects of stress, based on the two different physiological stress response systems (the sympathetic-adrenal-medullary (SAM) and the hypothalamic-pituitary-adrenal (HPA) systems) and the effects of these responses on the hippocampus and (sometimes) other subcortical structures. In this dissertation, I examined the effects of an acute (experimental) stressor on human spatial navigation in three variations of virtual Morris water mazes designed to dissociate between hippocampus-dependent (allocentric) and hippocampus-independent (egocentric) forms of navigation. Results were considered in the light of all 4 models. Experiment 1 used a dual-strategy Morris water maze to test whether acute stress influences navigational strategy selection and whether this effect is mediated by the activation of the HPA or the SAM system. Surprisingly, stress increased hippocampus-based strategy selection, and did so in the presence of SAM but not HPA activation. Experiment 2 used new dual-strategy and place mazes to examine the effects of acute stress on both strategy selection and allocentric navigational performance. It also attempted to contrast the effects of stress at a short delay, which would favour mediation by the SAM system, and a longer, 30 minute delay (from stressor onset), which would favour mediation by the HPA system. Contrary to expectations, results revealed no effect of stress when tested immediately and sex-dependent impairments of performance (in females) and allocentric strategy selection (in males) at the delay. Experiment 3 used the same mazes as Experiment 2, plus a new cue maze to examine the effects of acute stress on strategy selection and both allocentric and egocentric navigational performance after a 30 minute delay. Results confirmed that stress reduces allocentric strategy selection and impairs allocentric performance, but also has sex-dependent effects on egocentric performance: in females, stress enhanced navigation (as expected) but in males, stress impaired it. None of the 4 models provided a good explanation for these results, suggesting that current accounts of the cognitive effects of stress may be inadequate. / Graduate

Thesis (Ph.D.)--Boston University / Research in rodents and computational modeling work suggest a critical role for the hippocampus in representing overlapping memories. This thesis tested predictions that the hippocampus is important in humans for remembering overlapping spatial events, and that flexible navigation of spatial routes is supported by key prefrontal and striatal structures operating in conjunction with the hippocampus. The three experiments described in this dissertation used functional magnetic resonance imaging (fMRI) in healthy young people to examine brain activity during context-dependent navigation of virtual maze environments. Experiment 1 tested whether humans recruit the hippocampus and orbitofrontal cortex to successfully retrieve well-learned overlapping spatial routes. Participants navigated familiar virtual maze environments during fMRI scanning. Brain activity for flexible retrieval of overlapping spatial memories was contrasted with activity for retrieval of distinct non-overlapping memories. Results demonstrate the hippocampus is more strongly recruited for planning and retrieval of overlapping routes than non-overlapping routes, and the orbitofrontal cortex is recruited specifically for context-dependent navigational decisions. Experiment 2 examined whether the hippocampus, orbitofrontal cortex, and striatum interact cooperatively to support flexible navigation of overlapping routes. Using a functional connectivity analysis of fMRI data, we compared interactions between these structures during virtual navigation of overlapping and non-overlapping mazes. Results demonstrate the hippocampus interacts with the caudate more strongly for navigating overlapping than non-overlapping routes. Both structures cooperate with the orbitofrontal cortex specifically during context-dependent decision points, suggesting the orbitofrontal cortex mediates translation of contextual information into the flexible selection of behavior. Experiment 3 examined whether the hippocampus and caudate contribute to forming context-dependent memories. fMRI activity for learning new virtual mazes which overlap with familiar routes was compared with activity for learning completely distinct routes. Results demonstrate both the hippocampus and caudate are preferentially recruited for learning mazes which overlap with existing route memories. Furthermore, both areas update their responses to familiar route memories which become context-dependent, suggesting complementary roles in both learning and updating overlapping representations. Together, these studies demonstrate that navigational decisions based on overlapping representations rely on a network incorporating hippocampal function with the evaluation and selection of behavior in the prefrontal cortex and striatum.

Recent research demonstrates that new verbal memories are retained better if learning is followed by a brief period of wakeful rest. This effect is hypothesised to be the result of wakeful rest providing a state that is conducive for early-stage cellular consolidation (i.e. strengthening of specific memory traces) by protecting this process from interfering sensory input and associated encoding. The aims of this PhD project were to (i) examine whether the benefit of wakeful rest extends to the retention of complex spatial memories, and (ii) explore the effects of different cognitive states on memory consolidation. In order to address the first aim, three virtual reality spatial memory experiments were conducted. In young and older adults, wakeful rest not only enhanced the retention of complex spatial memories, but it also promoted the systems-level integration of spatial memories into accurate cognitive maps, a function, hitherto, assumed to be specific to sleep (Chapters 2-4). Pilot work also tentatively suggested that wakeful rest enhances the retention of complex spatial memories (i.e. a recently travelled route) in patients with amnestic Mild Cognitive Impairment (Chapter 4). In order to address the second aim, five experiments were run in young adults. The first experiment directly compared the effects of wakeful rest and sleep, two states that are positively associated with consolidation. Wakeful rest enhanced the retention of a list of known words, whereas a similar-length period of sleep enhanced the acquisition of novel linguistic constraints (Chapter 5). The final four experiments revealed that, similar to continuous external sensory input, internally generated autobiographical thinking activities (recalling the past and imagining the future) interfere with consolidation (Chapter 6). Together, the findings reported in this thesis reveal that wakeful rest promotes the strengthening (cellular consolidation) and wider integration (systems consolidation) of basic and complex declarative memories, and that this effect is contingent on a reduction in external sensory input as well as rich autobiographical thought.

The social and neurosciences are moving toward a conceptualization of the psychological construct of sense of place in relation with spatial cognition, place imageability, and meaning. To help advance progress, this dissertation proposes a conceptual framework of sense of place that includes variables of spatial navigational strategy (i.e., egocentric and allocentric) and place imageability using notions of edges, paths, landmarks, districts, nodes. Three studies using different methods tested the proposed framework. Study 1 used a questionnaire and an interview-based protocol analysis to examine whether navigational strategy associated with participants’ levels of sense of place for recalled urban neighbourhoods. Preliminary work investigating whether sense of place and spatial navigation varied with place imageability was also done using qualitative analyses. Participants used more egocentric and allocentric strategies during cognitive map navigation when sense of place was stronger compared to when they recalled places for which they felt weak or neutral levels of sense of place. Seven categories were revealed from participants’ qualitative descriptions of urban place visualizations after completing three sense of place scales (i.e., home-sense, compactness, environment, safety, vibrancy, design, and aesthetics) and differed depending on sense of place condition. Study 2 enabled participants to articulate recollections of settings for which they felt different strengths of sense of place via a cognitive mapping task. Results reinforced the notion that individuals who experience a strong level of sense of place for an urban environment also recall more of the physical features that make it imageable. Existing literature was confirmed by this study’s results that paths and landmarks are integral to urban place imageability. Study 3 gathered information about community members’ current representations of their urban neighbourhood. Results supported hypotheses based on results of Studies 1 and 2. Nodes, edges, and landmarks were found to be particularly meaningful to residents’ spatial understanding of their neighbourhood. The fact that more allocentric strategies than egocentric strategies were used in each of the three place imageability conditions (compared to non-significant differences in sense of place conditions in Study 1) highlights compelling future research questions concerning the three variables of the proposed conceptual framework of sense of place. Similar to Study 1, qualitative analyses in Study 3 revealed paths as the predominant meaningful place imageable feature noted by residents. Thematic information about the features in each area reported to have meaning for residents indicate the categories of environment, aesthetics, and design as most prevalent. As a whole, this dissertation can inform future environmental psychology research, as well as the practices of urban planners, as they consider spatial navigation and place imageable attributes in relation to the psychological construct of sense of place in urban environments. Planners and researchers alike may benefit from this dissertation as they respond to human spatial needs while facilitating a sense of attachment and identity toward, and compatibility with, city spaces. Finally, findings may assist social scientists in clarifying how sense of place develops in urban neighbourhoods, and how it is experienced over time. / Graduate

Research on the neural and cognitive basis of spatial navigation over the last 30 years has been largely guided by cognitive map theory and many of the studies have used a standardized procedure in a single task, the Morris Water Maze (MWM). Although this theory proposes that acquisition of place knowledge should be very rapid, little evidence has been provided to support this point. The present study investigates the possibility that a new procedure for measuring place knowledge in the MWM will show that place learning is faster than previously shown. In a virtual MWM with a fixed goal location, participants were given pairs of standard learning trials plus new explicit probe trials in which they were directed to go to where they found the goal on the immediately preceding trial. The distance between their estimate and the actual location was measured as “Place Error”. Results indicated that Place Errors were surprisingly small after just one learning trial and were equivalent for females and males. These findings provide new evidence for the fast learning proposed by cognitive map theory and demonstrate the value of this new method for measuring place learning. / Graduate

Spatial navigation is essential for everyday function. It is successfully achieved by combining internally generated information – such vestibular and self-motion cues (known as path integration) – with external sources of information such as visual landmarks. These multiple sources and sensory domains are often associated with uncertainty and can provide conflicting information. The key to successful navigation is therefore how to integrate information from these internal and external sources in the best way. Healthy younger adults do this in a statistically optimal fashion by considering the perceived reliability of a cue during integration, consistent with the rules of Bayesian integration. However, the precise impact of ageing on the component senses of path integration and integration of such self-motion with external information is currently unclear. Given that impaired spatial ability is a common problem associated with ageing and is often a primary indicator of Alzheimer’s disease, this thesis asks whether age-related navigational impairments are related to fundamental deficits in the components of path integration and/or inadequate integration of spatial cues. Part 1 focussed on how ageing impacts the vestibular, kinaesthetic and visual components of path integration during linear navigation in the real world. Using path reproduction, distance estimation and depth perception tasks, I found that older adults showed no performance deficits in conditions that replicated those of everyday walking when visual and self-motion cues were present. However, they were impaired when relying on vestibular information alone. My results suggest that older adults are especially vulnerable to sensory deprivation but that weaker sensory domains can be compensated for by other sensory information, potentially by integrating different spatial cues in a Bayesian fashion: where the impact of unreliable/diminished senses can be minimised. Part 2 developed the conclusions of Part 1 by testing younger and older adults’ integration of visual landmarks and self-motion information during a simple homing task. I investigated the hypothesis that the integration of spatial information from multiple sensory domains is driven by Bayesian principles and that old age may affect the efficiency and elasticity of reliability-driven integration. Younger and older participants navigated to a previously visited location using self-motion and/or visual information. In some trials there was a conflict of information, which revealed the relative influence of self-motion and visual landmarks on behaviour. Findings revealed that both younger and older adults integrated visual and self-motion information to improve accuracy and precision, but older adults did not place as much influence on visual information as would have been optimal. This may have been the result of increased noise in the underlying spatial representations of older adults. Furthermore, older adults did not effectively re-weight visual and self-motion cues in line with the changing reliability of visual information, suggesting diminished plasticity in the underlying spatial representations. However, further development of the testing paradigm would strengthen support for these findings. Together, the findings of Part 2 suggest that increased neural noise and the suboptimal weighting of spatial cues might contribute to the common problems with navigation experienced by many older adults. This thesis provides original evidence for age-related changes to multisensory integration of spatial cues. Path integration abilities are relatively preserved when older adults navigate linear paths in the real world, despite loss of vestibular function. However, navigation is affected by old age when the task becomes more complex. Multisensory integration of spatial cues is partially preserved but it is not fully efficient. I offer evidence that the navigational impairments common to old age are related to fundamental deficits in the components of path integration, task complexity, and suboptimal integration of spatial cues. Crucially however, path integration is preserved sufficiently in older adults that they are able to navigate in small scale with relative success.

Many studies have shown a gender difference in spatial navigation ability, including a related gender difference in global metacognitive self-assessment and spatial anxiety. However, it has yet to be determined whether trial-by-trial metacognitive accuracy differs between the genders and how this may be related to gender differences in navigation performance. The goal of this research was to determine, using the Nelson and Nerens (1990) metamemory framework, if there exist gender differences in trial-by-trial metacognitive monitoring on a first-person virtual maze navigation task, and how this may be related to gender differences in navigation performance. Considering that there is a relatively pervasive stereotype that women have poor navigation stills, an additional goal of this research was to determine if the effects of stereotype could, at least partially, explain the gender difference in navigation performance, confidence, and trial-by-trial metacognitive monitoring accuracy. Many studies have shown stereotype threat and lift to influence confidence and performance between the genders on a variety of spatial cognitive tasks, but mostly on mental rotation tasks. We investigated whether this effect applied to gender differences in a spatial navigation task. In order to accomplish this, we assessed trial-by-trial metacognitive accuracy during a first-person virtual maze navigation task under three stereotype facilitation conditions where participants were told that either: 1) men outperform women on this particular task, 2) women outperform men on this particular task, or 3) the genders perform equally. Over three experiments, the results showed that men generally have more accurate metacognitive monitoring than women, especially when assessing a previous performance. Contrary to our expectations, stereotype activation had no effect on trial-by-trial metacognition, though it did have an effect on navigation performance and confidence.