Phd in PHD PROGRAM IN BEHAVIORAL NEUROSCIENCE

Thesis title: A new tool to assess spatial orientation abilities and its usage in clinical populations

One of the fundamental skills in daily activity is recognizing one's position in the space, getting around obstacles along the way and moving around in the environment while maintaining a sense of direction. Spatial navigation is a highly complex process in which the integrated activity of different cognitive processes and a wide neural network allows the processing of several metrics and sensory information derived from the environment to build internal representations of space that will be used to guide navigational behavior. Lesions in one or more nodes of this network may result in topographical disorientation, with different phenomenological characteristics, therefore it is necessary to use adequate tools that allow the evaluation of this ability, both clinically and experimentally. This thesis aims to propose a new tool to evaluate spatial navigation abilities by testing its use in clinical populations. In the first study, I will present a computerized test battery reflecting the complexity of the real-life navigational environment, hereafter called Laboratory Based Setting (LBS); LBS is aimed at testing the possible dissociation between different navigational strategies. Indeed, it is composed of four subtests tapping landmark, route and survey environmental knowledge and a landmark ordering task. To verify the battery effectiveness, I compared the performance of a group of healthy subjects in each subtest of the LBS battery with that of equivalent tasks performed in an ecological setting. The results show an association between all subtests except the route knowledge task, probably due to the impossibility of replicating the vestibular clues acquired during navigation in an ecological environment in a laboratory base setting. However, when running this subtest, optical flow is guaranteed, and this alone may elicit the illusion of motion needed to gain route knowledge. A shorter version of the LBS battery was then proposed and tested. The results show that LBS reliability is guaranteed also in this version. Subsequently, I used the short version of LBS to test navigational skills in patients with acquired brain injury. In study two, I compared the performance of a control group with stroke patients, who were grouped into three subgroups: patients with a left lesion, patients with a right lesion affected by neglect and patients with a right lesion without neglect. The results show that patients with neglect perform worse in route knowledge on the third attempt, landmark knowledge, and survey knowledge but not in route knowledge on the second attempt and the landmark ordering task, probably due to deficits in path integration and working memory typical in these patients. Subsequently, a subtraction analysis in each spatial knowledge acquisition process showed that all stroke patients present the probability of exhibiting a lesion in the same cluster of areas known to be engaged during the egocentric and allocentric spatial representation. In study three, I compared the performance of a control group with that of a group of patients with traumatic brain injury. The results show that the performance of these patients differs from the controls in the acquisition of landmark and survey knowledge. Although performance does not differ in the route knowledge, patients take longer to achieve this kind of knowledge, using a response-based strategy to acquire environmental information similarly to the elderly and they use a compensatory strategy to acquire environmental knowledge. The results of this study also show that in these patients there is a relationship between attention, memory and executive function domains and the acquisition of spatial knowledge. Overall, the results of this thesis offer a new tool for the study and evaluation of topographical orientation, demonstrating its effectiveness in both normal and pathological populations. Furthermore, the experimental evidence described in this work offers a new perspective on the specific functioning of the brain networks involved in the acquisition of environmental knowledge and the complex mechanisms involved.