Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, 1998. / Includes bibliographical references (p. 19-20). / Normal subjects adapt quickly to the displacing effects of prism goggles. A measure of this adaptation comes from the negative aftereffects in reaching that subjects show after the prism goggles are removed. Neural circuitry within the cerebellar cortex has been implicated as the site of plasticity for visuomotor adaptation. An opportunity to test a 15-year-old boy, A.C., with near complete cerebellar agenesis allowed us to determine whether cerebellar structures are critical for prism adaptation to occur. A.C. was tested on two separate occasions, twice using his left hand, and once using his right hand. He wore prism goggles while pointing to a vertical line at each of nine target locations in baseline, exposure, and postexposure conditions. The position of his finger was recorded after each response. In the exposure condition, the goggles were adjusted to 11" displacement to the right when A.C. pointed with his left hand, and to the left when he pointed with his right hand. He received visual feedback only in the exposure condition. His results were compared to those of 20 normal control subjects (NCS). Independent measures of performance and adaptation were calculated for left- and right-handed pointing by each subject. A.C. showed greater variablity in pointing with his right (nonpreferred) hand compared to his left hand and compared to NCS. An ordinal ranking indicated that his adaptation scores did not differ significantly from those of the NCS for either the left (p = 0.30 ) or right hand (p = 0.22). While these results do not disprove the theory that the cerebellum plays a role in normal adaptation, it does indicate that neural structures outside the cerebellum are sufficient to allow adaptation to occur. / by Regina A. Rendon. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, February 2007. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references (leaves 139-142). / A fundamental question in neuroscience is how sensory information is represented in the brain. In particular, what principles guide the spatial organization of neurons with regard to their receptive field properties, and how is this organization established mechanistically? The visual cortex serves as a model area to address these questions, but whether general principles can explain the layouts of cortical maps, such as those of visual space and of specific response features, remains unresolved. We find that in primary visual cortex of ferret, the layout of each map is inter-dependent with that of the others. First, we find a strong anisotropy in the visual map, such that receptive field positions change more rapidly along one axis of cortex; and importantly, along the axis where visual space changes rapidly, the feature maps of orientation, ocular dominance, and spatial frequency change slowly. Second, orientation, ocular dominance, and spatial frequency maps have local spatial relationships with each other: in areas of cortex where one feature changes rapidly, the other features change more slowly. Each of these relationships are well-explained by a dimension-reduction model of cortex. / (cont.) This suggests that the constraints which drive map formation in the model, continuity (representing each feature smoothly across cortex) and coverage uniformity (representing each feature combination to an equal extent), may play a central role in determining the functional organization of visual cortex. To explore the mechanisms giving rise to the map relationships, we alter the expression of one feature map early in development and measure the impact on the layouts of the remaining maps. We find that alteration of the ocular dominance map, due to neonatal monocular enucleation, does not prevent the formation of the orientation and spatial frequency maps, but it does alter their spatial relationships. The highest gradient regions of the spatial frequency map have a stronger tendency to avoid high gradient orientation regions, and the contours of the two maps have a greater tendency to cross orthogonally. The results are consistent with the predictions of a dimension-reduction model for removing a feature map, suggesting that as a result of altered input patterns, the cortex can rearrange over the time scale of development according to a dimension-reduction strategy. / by Brandon J. Farley. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, 1994. / Includes bibliographical references (leaves 185-194). / by Sergey Avrutin. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, 1993. / Includes bibliographical references. / by Miles G. Cunningham. / Ph.D.

Thesis (S.M. in Computational Neuroscience)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, 2002. / Includes bibliographical references (p. 75-80). / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / This thesis describes a representation for objects and scenes that is stable against variations in image intensity caused by illumination changes and tolerant to image degradations such as sensor noise. The representation, called a ratio-template, uses low-resolution ordinal contrast relationships as its matching primitives. The choice of these primitives was inspired not only by considerations of computational simplicity and robustness, but also by current knowledge of the early stages of visual processing in the primate brain. The resulting representation is biologically plausible, although there is currently no evidence to suggest that the representation is actually used by the primate visual system. Constructed manually at first, the ratio-template can be learned automatically from a set of examples. Two applications--face detection and scene indexing--are described. The ratio-template achieves detection rates higher than 90% and can process a 320×280 pixel image in 2.6 seconds at multiple scales. / by Keith John Thoresz. / S.M.in Computational Neuroscience

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, 2005. / Includes bibliographical references (p. 75-78). / How do people think about things they can never see or touch? The ability to invent and reason about domains such as time, ideas, or mathematics is uniquely human, and is arguably the hallmark of human sophistication. Yet, how people mentally represent these abstract domains has remained one of the great mysteries of the mind. This dissertation explores a potential solution: perhaps the mind recruits old structures for new uses. Perhaps sensory and motor representations that result from physical interactions with the world (e.g., representations of physical space) are recycled to support our thinking about abstract phenomena. This hypothesis is motivated, in part, by patterns observed in language: in order to talk about abstract things, speakers often recruit metaphors from more concrete or perceptually rich domains. For example, English speakers often talk about time using spatial language (e.g., a long vacation; a short meeting). Cognitive linguists have argued such expressions reveal that people conceptualize abstract domains like time metaphorically, in terms of space. Although linguistic evidence for this Conceptual Metaphor Theory is abundant, the necessary nonlinguistic evidence has been elusive. / (cont.) In two series of experiments, I investigated whether mental representations that result from physical experience underlie people's more abstract mental representations, using the domains of space and :!I.:e as a testbed. New experimental tools were developed in order to evaluate Conceptual Metaphor Theory as an account of the evolution and structure of abstract concepts, and to explore relations between language and nonlinguistic thought. Hypotheses about the way people represent space and time were based on patterns in metaphorical language, but were tested using simple psychophysical tasks with nonlinguistic stimuli and responses. Results of the first set of experiments showed that English speakers incorporate irrelevant spatial information into their estimates of time (but not vice versa), suggesting that people not only talk about time using spatial language, but also think about time using spatial representations. The second set of experiments showed that (a) speakers of different languages rely on different spatial metaphors for duration, (b) the dominant metaphor in participants' first languages strongly predicts their performance on nonlinguistic time estimation tasks, and (c) training participants to use new spatiotemporal metaphors in language changes the way they estimate time. / (cont.) Together, these results demonstrate that the metaphorical language people use to describe abstract phenomena provides a window on their underlying mental representations, and also shapes those representations. The structure of abstract domains such as time appears to depend, in part, on both linguistic experience and on physical experience in perception and motor action. / by Daniel J. Casasanto. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 64-70). / Axons exhibit a rich variety of behaviors, such as elongation, turning, branching, and fasciculation, all in service of the complex goal of wiring up the brain. In order to quantify these behaviors, I have developed a system for in vitro imaging of axon growth cones with time-lapse fluorescence microscopy. Image tiles are automatically captured and assembled into a mosaic image of a square millimeter region. GFP-expressing mouse cortical neurons can be imaged once every few minutes for up to weeks if phototoxicity is minimized. Looking at the data, the trajectories of axon growth cones seem to alternate between long, straight segments and sudden turns. I first rigorously test the idea that the straight segments are generated from a biased random walk by analyzing the correlation between growth cone steps in the time and frequency domain. To formalize and test the intuition that sharp turns join straight segments, I fit a hidden Markov model to time series of growth cone velocity vectors. / (cont.) The hidden state variable represents the bias direction of a biased random walk, and specifies the mean and variance of a Gaussian distribution from which velocities are drawn. Rotational symmetry is used to constrain the transition probabilities of the hidden variable, as well as the Gaussian distributions for the hidden states. Maximum likelihood estimation of the model parameters shows that the most probable behavior is to remain in the same hidden state. The second most probable behavior is to turn by about 40 degrees. Smaller angle turns are highly improbable, consistent with the idea that the axon makes sudden turns. When the same hidden Markov model was applied to artificially generated meandering trajectories, the transition probabilities were significant only for small angle turns. This novel application of stochastic models to growth cone trajectories provides a quantitative framework for testing interventions (eg. pharmacological, activity-related, etc.) that can impact axonal growth cone movement and turning. For example, manipulations that inhibit actin polymerization increase the frequency and angle of turns made by the growth cone. More generally, axon behaviors may be useful in deducing computational principles for wiring up circuits. / by Neville Espi Sanjana. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, 1991. / Includes bibliographical references (p. 329-368). / by Robert Martyn Bracewell. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, 1999. / Includes bibliographical references. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Extracellular recordings of neural activity were made in areas around and ventral to the principal sulcus of the lateral prefrontal (PF) cortex in two monkeys (macacca mulatta). Activity was assessed during the performance of three visual memory tasks. In the first task, the sensory and mnemonic receptive fields were studied, by requiring monkeys to simultaneously remember both the identity and the location of an object presented at different locations. We report that many conveyed both object and spatial information during the sensory and mnemonic period. Receptive field size was similar during the two periods (10.8 deg. during sensory, 9.3 deg. during mnemonic period). In addition, visual space contralateral to the recording site was preferentially represented. In a second task, the effect of attention on the responses of PF neurons was studied. Visual scenes were presented which contained three objects, only one of which was relevant for behavior. We report that PF neural activity selectively represented information about this relevant object, and activity was often identical to when the relevant object was presented alone. In addition, we describe the time-course of this attentional effect, and show that the relevant object captures PF activity very early, as soon as 140msec after onset of the visual scene. In a third task, the role of PF neurons in a visual-visual association task was assessed. Monkeys were presented with sample objects, and had to choose the test objects that had been associated with them during training after a short delay. The behavior of the monkeys suggested that they were using a prospective strategy to solve this task, i.e. they were recalling the associated visual information soon after sample presentation, and maintaining this in working memory. We report that many neurons showed activity consistent with prospective coding. Examination of the time course of this effect suggests that the recall took place several 100 msec after sample presentation, and that the strongest prospective effects appeared 300-500msec before test object presentation. In conclusion, across these three tasks PF neural activity selectively represented information relevant to immediate behavioral demands. / by Gregor Rainer. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, 1995. / Includes bibliographical references (leaves 46-47). / by James Davis Thomas. / M.S.