Exploring And Training Spatial Reasoning Via Eye Movements: Implications On Performance

This dissertation sought to determine if eye movements could serve as an indicator of success in spatial reasoning, and if eye movements associated with successful completion could be applied to strategically improve spatial reasoning. Using the line images of Shepard and Metzler, an electronic test of mental rotations ability (EMRT) was designed. Two versions of the test were created, allowing for both a timed (6 seconds per question) and untimed testing environment. Four experiments were designed and completed to relate mental rotation ability (MRA) scores from the EMRT, to patterns in chrononumeric and visual salience data. In each experiment, participants completed the EMRT under a different protocol. These protocols included an untimed EMRT, a timed EMRT, a within-participant crossover study where participants completed both the timed, and untimed EMRT in series, and a training crossover study where low MRA participants completed the timed EMRT in both a guided and unguided environment. In the untimed experiment, individuals of high and low MRA were asked to complete the EMRT while their eye movements were observed. As no time limit was imposed, the results allowed for observations based on MRA alone, and served to demonstrate and how individuals of different skill level differ in terms of eye movement. In the following experiment, the addition of a time limit to the EMRT revealed how individuals of high and low MRA perform when under a time restriction. The results of the Timed experiment confirmed differences between the high and low MRA group in terms of eye movements, and attention to salient regions of test images. In the third experiment, the addition of a time limit was further explored through a crossover design. By adding a time limit to an MRT, the ability of individuals to solve spatial problems is impaired, and is manifest in eye movements. Data derived from the Crossover Experiment suggested that salience-based metrics might serve to distinguish between groups of MRA, and that time restrictions may influence both participant accuracy, and identification of visually salient elements. The results from the first three experiments were then applied in the Guidance Experiment to confirm the role that visual salience plays in the context of spatial problem solving. By mapping the apprehension patterns of successful high MRA individuals onto the EMRT, low MRA individuals could be guided to salient areas on the timed EMRT. The results revealed that the application of visual guidance is an effective mechanism for MRA training. This research attends to a previously unaddressed niche in eye-movement and spatial ability training literature. As a result, it may serve as a foundation to cultivate methods of honing and improving spatial skills in the general population

Refractoriness within the semantic system: investigations on the access and the content of semantic memory

The starting purpose of this project was to investigate some issues related to the mechanisms underlying the efficient access to concepts within the semantic memory systems. These issues were mainly related to the role of refractoriness in explaining the comprehension deficits underlying semantic access. The insights derived from this first approach were then used to formulate and test hypotheses about the organization of the contents of the semantic system itself. The first part of the thesis presents an investigation of the semantic abilities of an unselected case-series of patients affected by tumours to either the left or right temporal lobes in order to detect possible semantic access difficulties. Semantic access deficits are typically attributed to the semantic system becoming temporarily refractory to repeated activation. Previous investigations on the topic were mainly based on single case reports, mainly on stroke patients. The rare examples of group studies suggested moreover the possibility that the syndrome might not be functionally unitary. The tasks used in the study were two word-to-picture matching tasks aimed to control for the typical variables held to be able to distinguish semantic access from degradation syndromes (consistency of access, semantic relatedness, word frequency, presentation rate and serial position). In the group of tumour patients tested access deficits were consistently found in patients with high grade tumours in the left posterior superior temporal lobe. However, the patients were overall only weakly affected by the typical temporal factors (presentation rate and serial position) characterizing an access syndrome as refractory. The pattern of deficit, together with the localization data, suggested that the deficit described is qualitatively different from typical semantic access syndromes and possibly caused by the disconnection of posterior temporal lexical input areas from the semantic system. In the second study we tried to answer the question whether semantic access deficits are caused by the co-occurrence of two causes (refractoriness and a lexicalsemantic disconnection) or whether the presence of refractoriness in itself is sufficient to induce all the behavioural effects described in access syndromes. A second aim of the study was moreover to investigate the precise locus of refractory behaviour, since refractory effects have also been reported in naming tasks in which the possibility exists that the interference might be located at a post-semantic lexical stage of processing. To address these issues a series of three behavioural experiments on healthy subjects was conducted. The tasks used were speeded versions of the same word-to picture matching tasks used in the previous study. A speeded paradigm was adopted in order to induce a mild refractory state also in healthy participants. The results showed that it was possible to induce, in the group of subjects tested, a performance similar to that of refractory semantic access patients. Since no post-semantic stage of processing is assumed to be necessary to perform these tasks it was argued that refractoriness arises due to interference occurring between representations within the semantic system itself. In the second part of the project, the finding that refractoriness arises due to interference involving semantic representations themselves, was used to investigate issues related to the organization of the content within the semantic memory. In particular, a second series of behavioural experiments was performed to investigate whether the way an object is manipulated is indeed a feature that defines manipulable objects at a semantic level. The tasks used were speeded word-to-picture matching tasks similar to those previously described. A significantly greater interference was found in the recognition of objects sharing similar manipulation than in the recognition of objects sharing only visual similarity. Moreover the repeated presentation of objects with similar manipulation created a \u2018negative\u2019 serial position effect (with error increasing over presentations), while the repeated presentation of objects sharing only visual similarity created an opposite \u2018positive\u2019 serial position effect (learning). The role of manipulability in the semantic representation of manipulable objects was further investigated in the last study of this work. In a second unselected group of brain tumour patients the ability to name living things and artifacts was investigated. Artifacts were manipulable objects, varying in the degree of their manipulability. Results from both behavioural and Voxel-based Lesion Symptom Mapping (VLSM) analyses showed that the only patients showing a selective deficit in naming artifacts (particularly highly manipulable objects) were patients with lesions in the posterior middle and superior portions of the left temporal lobe, an area lying within the basin of those regions involved in processing object-directed actions and previously linked to the processing of manipulable objects in a wide range of studies. The results of these last two studies support \u2018property-based networks\u2019 accounts of semantic knowledge rather than \u2018undifferentiated network\u2019 accounts. Overall this series of studies represents an attempt to better understand the mechanisms that underlie the access to semantic representations and, indirectly, the structure of representations stored within semantic networks. The insights obtained about the mechanisms of access to stored semantic representations were used as a tool to investigate the structures of the same semantic representations. A combination of different approaches was used (from behavioural speeded interference paradigms on healthy subjects, to neuropsychological case series investigations, as well as Voxel-based Lesion Symptom Mapping technique), to \u2018cross-validate\u2019 the results obtained at any level of analysis

Hotspots of dendritic spine turnover facilitate clustered spine addition and learning and memory.

Modeling studies suggest that clustered structural plasticity of dendritic spines is an efficient mechanism of information storage in cortical circuits. However, why new clustered spines occur in specific locations and how their formation relates to learning and memory (L&M) remain unclear. Using in vivo two-photon microscopy, we track spine dynamics in retrosplenial cortex before, during, and after two forms of episodic-like learning and find that spine turnover before learning predicts future L&M performance, as well as the localization and rates of spine clustering. Consistent with the idea that these measures are causally related, a genetic manipulation that enhances spine turnover also enhances both L&M and spine clustering. Biophysically inspired modeling suggests turnover increases clustering, network sparsity, and memory capacity. These results support a hotspot model where spine turnover is the driver for localization of clustered spine formation, which serves to modulate network function, thus influencing storage capacity and L&M

EEG-Based Mental States Identification

In this thesis, we focus on the identification of mental states described according to the definition of awareness and wakefulness. Using algorithmic methods, we show that it is possible to differentiate between two brain states based on the brain electrical activity collected by EEG. We begin by explaining the overall theoretical framework which enabled us to develop the detection of brain states. It starts with data acquisition. Following that, we analyse the pre-processing of the data before the extraction of features. Finally, we go on to statistically evaluate the results. In order to achieve this task, we propose four experiments. We will first focus on exploring different brain states for patients in Intensive Care Unit (ICU) such as coma and quasi-brain-death states. To distinguish these states, we use a signal processing method based on the EEG signal phase. A phase synchrony index based on Shannon entropy was used to separate the two states. Statistical validation revealed a significant difference between the two via delta-alpha and theta-alpha frequency couplings. Next, we studied the neuronal mechanisms which is used to understand consciousness. We did that by using dipole modelling. This method was applied to local-global experiment and the paradigm of auditory deviance with two hierarchical levels. A modulation of this experiment is generated by a sedative Propofol to study the effect on conscious states. This experiment was analysed in greater detail using the Imaging Method to do the source localisation. We analysed three different time-windows. The first window corresponds to the local effect during the initial response of the brain. We assume that this input is related to auditory areas and activates the temporal lobe. The second window is at the interface between the local effect and the global effect. In here we are especially interested in the interaction between these two effects during the second window. Finally, the third window will enable us to study the overall effect. We hypothesize a global activation of neural networks corresponding to consciousness as described by the global workspace theory. The third experiment focused on brain states high-level athletes experience during a cognitive task. Two different groups of cyclists, endurances and sprinters, were asked to do a Stroop task for 30 minutes. We studied the influence of the task and the potential differences in brain activity between the two groups. We found through the frequency analysis that the brain activity between the two groups can be distinguished, but was not modified by the cognitive task. Finally, we studied the influence of the sensorimotor loop on the brain. A physical task was applied, consisting in lifting a weight with two measurements, where the lifting arm can also be in fatigued state. Using sources reconstruction from EEG, we studied the impact of weight-lifting and the physical fatigue upon neuronal activities and the neuronal origins of these effects. We found that only weight has an effect, whereas fatigue effect is not significant. We conclude with a discussion of the mechanisms of consciousness analysed via algorithmic methods and some future work for the possibility to distinguish better between different cognitive states

Preserved neural dynamics across animals performing similar behaviour

Animals of the same species exhibit similar behaviours that are advantageously adapted to their body and environment. These behaviours are shaped at the species level by selection pressures over evolutionary timescales. Yet, it remains unclear how these common behavioural adaptations emerge from the idiosyncratic neural circuitry of each individual. The overall organization of neural circuits is preserved across individuals1 because of their common evolutionarily specified developmental programme2-4. Such organization at the circuit level may constrain neural activity5-8, leading to low-dimensional latent dynamics across the neural population9-11. Accordingly, here we suggested that the shared circuit-level constraints within a species would lead to suitably preserved latent dynamics across individuals. We analysed recordings of neural populations from monkey and mouse motor cortex to demonstrate that neural dynamics in individuals from the same species are surprisingly preserved when they perform similar behaviour. Neural population dynamics were also preserved when animals consciously planned future movements without overt behaviour12 and enabled the decoding of planned and ongoing movement across different individuals. Furthermore, we found that preserved neural dynamics extend beyond cortical regions to the dorsal striatum, an evolutionarily older structure13,14. Finally, we used neural network models to demonstrate that behavioural similarity is necessary but not sufficient for this preservation. We posit that these emergent dynamics result from evolutionary constraints on brain development and thus reflect fundamental properties of the neural basis of behaviour