Mechanisms of Navigation in Fiddler Crabs: An Analysis of Allocentric and Egocentric Contributions

Navigation in biological systems is a complex task-set that involves learning processes and may include constructing representations of features of their environment. Across the animal kingdom, different learning mechanisms have evolved to similar spatial problems. The extent to which mechanisms are conserved across taxa are an important research area that can guide our understanding of the cognitive dimensions of navigation. Recent studies of mammals, birds, and arthropods has found that these animals often attend to multiple forms of sensory cues, and to either integrate the solutions generated by these cues, or at times prefer one form of cue over another. This dissertation examines the fiddler crab (Uca pugilator), a burrow-homing arthropod whose ecology and behavior engender evolutionary pressures that favor spatial memory to determine which these kinds of multi-modal integrative processes are at they employ. Previous field studies give indications of complexity beyond simple route reversal methods. U. pugilator are a species that share and likely resemble a basal ancestor to the insect taxa that have proved fruitful to the study of navigation. The results of this dissertation suggest that the ability to employ and integrate solutions from multiple navigational mechanisms is evolutionarily old and conserved across a wide range of taxa. Four experiments are presented that employ a place learning paradigm to examine the roles of externally (allocentric) and internally (egocentric) generated sensory cues in the construction of fiddler crab navigational strategies. Three of these experiments provide evidence for a preexisting taxis in these animals that dictates they approach certain visual stimuli, and two of these experiments provide evidence of an allocentrically informed associative process in navigating fiddler crabs, a finding not before seen in a laboratory study of these animals. Taken together the results of this dissertation suggest that fiddler crabs possess some form of cognitive representation of the external world, which is informed by multiple sensory modalities, and extends beyond response learning and path integration

Eye movements in the wild : Oculomotor control, gaze behavior & frames of reference

Understanding the brain's capacity to encode complex visual information from a scene and to transform it into a coherent perception of 3D space and into well-coordinated motor commands are among the outstanding questions in the study of integrative brain function. Eye movement methodologies have allowed us to begin addressing these questions in increasingly naturalistic tasks, where eye and body movements are ubiquitous and, therefore, the applicability of most traditional neuroscience methods restricted. This review explores foundational issues in (1) how oculomotor and motor control in lab experiments extrapolates into more complex settings and (2) how real-world gaze behavior in turn decomposes into more elementary eye movement patterns. We review the received typology of oculomotor patterns in laboratory tasks, and how they map onto naturalistic gaze behavior (or not). We discuss the multiple coordinate systems needed to represent visual gaze strategies, how the choice of reference frame affects the description of eye movements, and the related but conceptually distinct issue of coordinate transformations between internal representations within the brain.Peer reviewe

Anchoring The Cognitive Map To The Visual World

To interact rapidly and effectively with the environment, the mammalian brain needs a representation of the spatial layout of the external world (or a “cognitive map”). A person might need to know where she is standing to find her way home, for instance, or might need to know where she is looking to reach for her out-of-sight keys. For many behaviors, however, simply possessing a map is not enough; in order for a map to be useful in a dynamic world, it must be anchored to stable environmental cues. The goal of the present research is to address this spatial anchoring problem in two different domains: navigation and vision. In the first part of the thesis, which comprises Chapters 1-3, we examine how navigators use perceptual information to re-anchor their cognitive map after becoming lost, a process known as spatial reorientation. Using a novel behavioral paradigm with rodents, in Chapter 2 we show that the cognitive map is reoriented by dissociable inputs for identifying where one is and recovering which way one is facing. The findings presented in Chapter 2 also highlight the importance of environmental boundaries, such as the walls of a room, for anchoring the cognitive map. We thus predicted that there might exist a brain region that is selectively involved in boundary perception during navigation. Accordingly, in Chapter 3, we combine transcranial magnetic stimulation and virtual-reality navigation to reveal the existence of such a boundary perception region in humans. In the second part of this thesis, Chapter 4, we explore whether the same mechanisms that support the cognitive map of navigational space also mediate a map of visual space (i.e., where one is looking). Using functional magnetic resonance imaging and eye tracking, we show that human entorhinal cortex supports a map-like representation of visual space that obeys the same principles of boundary-anchoring previously observed in rodent maps of navigational space. Together, this research elucidates how mental maps are anchored to the world, thus allowing the mammalian brain to form durable spatial representations across body and eye movements

Cortico-spinal modularity in the parieto-frontal system: a new perspective on action control

: Classical neurophysiology suggests that the motor cortex (MI) has a unique role in action control. In contrast, this review presents evidence for multiple parieto-frontal spinal command modules that can bypass MI. Five observations support this modular perspective: (i) the statistics of cortical connectivity demonstrate functionally-related clusters of cortical areas, defining functional modules in the premotor, cingulate, and parietal cortices; (ii) different corticospinal pathways originate from the above areas, each with a distinct range of conduction velocities; (iii) the activation time of each module varies depending on task, and different modules can be activated simultaneously; (iv) a modular architecture with direct motor output is faster and less metabolically expensive than an architecture that relies on MI, given the slow connections between MI and other cortical areas; (v) lesions of the areas composing parieto-frontal modules have different effects from lesions of MI. Here we provide examples of six cortico-spinal modules and functions they subserve: module 1) arm reaching, tool use and object construction; module 2) spatial navigation and locomotion; module 3) grasping and observation of hand and mouth actions; module 4) action initiation, motor sequences, time encoding; module 5) conditional motor association and learning, action plan switching and action inhibition; module 6) planning defensive actions. These modules can serve as a library of tools to be recombined when faced with novel tasks, and MI might serve as a recombinatory hub. In conclusion, the availability of locally-stored information and multiple outflow paths supports the physiological plausibility of the proposed modular perspective

Parallelized Egocentric Fields for Autonomous Navigation

In this paper, we propose a general framework for local path-planning and steering that can be easily extended to perform high-level behaviors. Our framework is based on the concept of affordances: the possible ways an agent can interact with its environment. Each agent perceives the environment through a set of vector and scalar fields that are represented in the agent’s local space. This egocentric property allows us to efficiently compute a local space-time plan and has better parallel scalability than a global fields approach. We then use these perception fields to compute a fitness measure for every possible action, defined as an affordance field. The action that has the optimal value in the affordance field is the agent’s steering decision. We propose an extension to a linear space-time prediction model for dynamic collision avoidance and present our parallelization results on multicore systems. We analyze and evaluate our framework using a comprehensive suite of test cases provided in SteerBench and demonstrate autonomous virtual pedestrians that perform steering and path planning in unknown environments along with the emergence of high-level responses to never seen before situations

Perception and Orientation in Minimally Invasive Surgery

During the last two decades, we have seen a revolution in the way that we perform abdominal surgery with increased reliance on minimally invasive techniques. This paradigm shift has come at a rapid pace, with laparoscopic surgery now representing the gold standard for many surgical procedures and further minimisation of invasiveness being seen with the recent clinical introduction of novel techniques such as single-incision laparoscopic surgery and natural orifice translumenal endoscopic surgery. Despite the obvious benefits conferred on the patient in terms of morbidity, length of hospital stay and post-operative pain, this paradigm shift comes at a significantly higher demand on the surgeon, in terms of both perception and manual dexterity. The issues involved include degradation of sensory input to the operator compared to conventional open surgery owing to a loss of three-dimensional vision through the use of the two-dimensional operative interface, and decreased haptic feedback from the instruments. These changes have led to a much higher cognitive load on the surgeon and a greater risk of operator disorientation leading to potential surgical errors. This thesis represents a detailed investigation of disorientation in minimally invasive surgery. In this thesis, eye tracking methodology is identified as the method of choice for evaluating behavioural patterns during orientation. An analysis framework is proposed to profile orientation behaviour using eye tracking data validated in a laboratory model. This framework is used to characterise and quantify successful orientation strategies at critical stages of laparoscopic cholecystectomy and furthermore use these strategies to prove that focused teaching of this behaviour in novices can significantly increase performance in this task. Orientation strategies are then characterised for common clinical scenarios in natural orifice translumenal endoscopic surgery and the concept of image saliency is introduced to further investigate the importance of specific visual cues associated with effective orientation. Profiling of behavioural patterns is related to performance in orientation and implications on education and construction of smart surgical robots are drawn. Finally, a method for potentially decreasing operator disorientation is investigated in the form of endoscopic horizon stabilization in a simulated operative model for transgastric surgery. The major original contributions of this thesis include: Validation of a profiling methodology/framework to characterise orientation behaviour Identification of high performance orientation strategies in specific clinical scenarios including laparoscopic cholecystectomy and natural orifice translumenal endoscopic surgery Evaluation of the efficacy of teaching orientation strategies Evaluation of automatic endoscopic horizon stabilization in natural orifice translumenal endoscopic surgery The impact of the results presented in this thesis, as well as the potential for further high impact research is discussed in the context of both eye tracking as an evaluation tool in minimally invasive surgery as well as implementation of means to combat operator disorientation in a surgical platform. The work also provides further insight into the practical implementation of computer-assistance and technological innovation in future flexible access surgical platforms

A Tale of Two Direction Codes in Rat Retrosplenial Cortex: Uncovering the Neural Basis of Spatial Orientation in Complex Space

Head direction (HD) cells only become active whenever a rat faces one direction and stay inactive when it faces others, producing a unimodal activity distribution. Working together in a network, HD cells are considered the neural basis supporting a sense of direction. The retrosplenial cortex (RSC) is part of the HD circuit and contains neurons that express multiple spatial signals, including a pattern of bipolar directional tuning – as recently reported in rats exploring a rotationally symmetric two-compartment space. This suggests an unexplored mechanism of the neural compass. In this thesis, I investigated whether the association between the two-way firing symmetry and twofold environment symmetry reveals a general environment symmetry-encoding property of these RSC neurons. I recorded RSC neurons in environments having onefold, twofold and fourfold symmetry. The current study showed that RSC HD cells maintained a consistent global signal, whereas other RSC directional cells showed multi-fold symmetric firing patterns that reflected environment symmetry, not just globally (across all sub-compartments) but also locally (within each sub-compartment). The analyses also showed that the pattern was independent of egocentric boundary vector coding but represented an allocentric spatial code. It means that these RSC cells use environmental cues to organise multiple singular tuning curves which sometimes are combined to form a multidirectional pattern, likely via an interaction with the global HD signal. Thus, both local and global environment symmetry are encoded by local firing patterns in subspaces. This interestingly suggests cognitive mapping and abstraction of space beyond immediate perceptual bounds in RSC. The data generated from this study provides important insights for modelling of direction computation. Taken together, I discuss how having two types of direction codes in RSC may help us to orient more accurately and flexibly in complex and ambiguous space