Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, 1996. / Includes bibliographical references (leaves 129-131). / by Janine Dale Mendola. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, 2004. / Includes bibliographical references (p. 155-160). / One of the fundamental issues in cognitive science is the problem of grounding concepts in the perceptual world. In this thesis, I present a computational theory for how spatial relations are grounded in the perceptual world. Three constraints are critical to this theory: abstractness, groundedness and flexibility all of which need to be satisfied in order to explain the structure of spatial concepts. I then show how a formal framework, based on the mathematical notions of category theory can be used to model the grounding problem. The key computational ideas are that of minimal mapping and derivations. A minimal mapping of two categories, A and B, is the "smallest' category, C, that contains A and B. A derivation is a sequence of categories that follow a minimal mapping rule. Derivations and minimal mappings are used to model three domains - the semantics of prepositions, the structure of a toy "Jigsaw World" and the semantics of generic terms and quantifiers. In each case, I show how the computational theory gives rise to insights that are not available upon a purely empirical analysis. In particular, the derivational account shows the importance of stable, non-accidental features and of multiple scales in spatial cognition. / by Rajesh Kasturirangan. / Ph.D.

Thesis: Ph. D. in Neuroscience, Massachusetts Institute of Technology, Department of Brain and Cognitive Sciences, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 113-119). / While the mechanisms preserving genomic integrity are well defined in proliferating cells, corresponding pathways in postmitotic neurons remain poorly understood. In this report, I characterize the functions of two lysine deacetylases, SIRT1 and HDAC1, in the neuronal response to DNA double strand breaks (DSBs). Both SIRT1 and HDAC1 were previously shown to promote neuronal survival in a mouse model of neurodegeneration in which the appearance of DSBs precedes other neurotoxic symptoms. Here I show for the first time the recruitment of both SIRT1 and HDAC1 to sites of DNA DSBs in neurons, where they work cooperatively to coordinate DSB signaling and DNA repair. SIRT1 physically binds HDAC1 and this interaction is strengthened upon DNA damage. I demonstrate that SIRT1 deacetylates HDAC1 at a critical lysine residue, K432, and stimulates its enzymatic activity. Moreover, HDAC1 mutants that mimic a constitutively acetylated state render neurons more susceptible to DNA damaging agents, and pharmacological SIRT1 activators that promote HDAC1 deacetylation also mitigate neuronal loss in a mouse model of neurodegeneration. I propose that the interaction between SIRT1 and HDAC1 constitutes an essential step in the DNA damage response that could be exploited to enhance neuronal survival in various neurodegenerative diseases. / by Matthew Milnes Dobbin. / Ph. D. in Neuroscience

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, 1999. / Includes bibliographical references (leaves 73-75). / by Ranxiao Wang. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, 2001. / Includes bibliographical references. / Relative motion information is required for solving many complex visual tasks, such as depth perception by motion parallax and motion-induced figure/ground segmentation. However, little is known about the neural substrate for relative motion. To explore the neural mechanisms underlying relative motion, we recorded single unit responses to relative motion in macaque VI and V2. We found that a substantial portion of V1 (62.2%) and V2 (70%) neurons respond to relative motion inputs. These neurons usually show V-shaped tuning curves to relative motion, with minimum response at zero relative motion. They respond predominantly to relative motion rather than to absolute motion. The relative ratio of target velocity to background velocity, rather than the absolute amplitude of either target/background velocity or the difference of the two determines neural responses. In area VI, relative-motion-defined boundaries matching a cell's preferred orientation evoke excitatory responses in a relative motion sensitive neuron. However, the responses are not strong enough to make such a neuron selective to the orientation of the relative-motion-defined boundaries. Relative motion sensitive neurons may participate in segregating objects from a moving background as well as preprocessing complex motion patterns. / (cont.) Utilizing a new random-dot stereogram, we tested further if these relative motion sensitive neurons contribute to the processing of motion parallax, as suggested by Nakayama and Loomis (1974). Several factors, i.e., the symmetric V shaped tuning to relative motion, the lack of neurons tuned to the degree of differential motion and the lack of correlation between disparity and relative motion tuning, indicate that those neurons are unlikely to process motion parallax directly. To summarize, we confirm the existence of relative motion sensitive neurons in macaque VI and V2. Although these neurons are not directly involved in processing motion parallax, they facilitate other motion processing such as figure/ground segmentation and motion discontinuity detection. / by An Cao. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, 2005. / Includes bibliographical references. / In the world, objects and settings tend to co-occur. Cars usually appear on streets with other vehicles, not in kitchens next to refrigerators. The present studies provide evidence that the semantic consistency of an object and its setting is available in a glimpse and affects perception. Objects are perceived more accurately in typical rather than atypical settings and when they appear with related objects regardless of the setting. Backgrounds are perceived more accurately when they contain plausible rather than unlikely foreground objects. Objects and scenes are processed interactively, not in isolation. / by Jodi L. Davenport. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, February 2011. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references. / Inhibitory interneurons are thought to play a crucial role in several features of neocortical processing, including dynamics on the timescale of milliseconds. Their anatomical and physiological characteristics are diverse, suggesting that different types regulate distinct aspects of neocortical dynamics. Interneurons expressing parvalbumin (PV) and somatostatin (SOM) form two non-overlapping populations. Here, I describe computational, correlational (neurophysiological) and causal (optogenetic) studies testing the role of PV and SOM neurons in dynamic regulation of sensory processing. First, by combining extra- and intracellular recordings with optogenetic and sensory stimulation and pharmacology, we have shown that PV cells play a key role in the generation of neocortical gamma oscillations, confirming the predictions of prior theoretical and correlative studies. Following this experimental study, we used a biophysically plausible model, simulating thousands of neurons, to explore mechanisms by which these gamma oscillations shape sensory responses, and how such transformations impact signal relay to downstream neocortical areas. We found that the local increase in spike synchrony of sensory-driven responses, which occurs without decreasing spike rate, can be explained by pre- and post-stimulus inhibition acting on pyramidal and PV cells. This transformation led to increased activity downstream, constituting an increase in gain between the two regions. This putative benefit of PV-mediated inhibition for signal transmission is only realized if the strength and timing of inhibition in the downstream area is matched to the upstream source. Second, we tested the hypothesis that SOM cells impact a distinct form of dynamics, sensory adaptation, using intracellular recordings, optogenetics and sensory stimulation. In resting neocortex, we found that SOM cell activation generated inhibition in pyramidal neurons that matched that seen in in-vitro studies. Optical SOM cell activation also transformed sensory-driven responses, decreasing evoked activity. In adapted responses, optical SOM cell inactivation relieved the impact of sustained sensory input, leading to increased membrane potential and spike rate. In contrast, SOM cell inactivation had minimal impact on sensory responses in a non-adapted neocortex, supporting the prediction that this class of interneurons is only recruited when the network is in an activated state. These findings present a previously unappreciated mechanism controlling sensory adaptation. / by Ulf Knoblich. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, 1995. / Includes bibliographical references (p. 83-89). / by Thomas M. Brashers-Krug. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, 1997. / Includes bibliographical references. / by Alessandra Angelucci. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 117-122). / This thesis aims to elucidate shared mechanisms between retrieval in sentence processing and memory retrieval processes in nonlinguistic domains using an individual differences approach. Prior research in individual differences in sentence processing has provided conflicting evidence as to whether the same memory mechanisms operate in linguistic processing, potentially a quite specialized cognitive domain, and in other, more general areas of cognition (Just & Carpenter, 1992; Caplan & Waters, 1999). This question has been primarily addressed from the point of view of capacity-based theories of working memory (Baddeley, 1986). Under these theories, verbal working memory is either comprised of multiple components including separate components for syntactic and non-syntactic verbal processing, or is dependent on a unitary pool of resources shared across all verbal domains. However, recent memory research has suggested that the capacity-theory architecture may be incorrect. Instead of a three-part memory system composed of focal attention, working memory, and long-term memory, a better model of the memory system may be bipartite, comprising focal attention and long-term memory. In the bipartite theory, working memory is viewed as a set of mechanisms mediating between these two stores, and accurately describes empirical data (McElree, 2006). If the latter hypothesis is correct, then it follows that the bipartite system underlying sentence processing should rely on the same set of working memory mechanisms as in general memory processes. In particular, a number of empirical studies have shown that both general memory and sentence processing are subject to interference from contextually-relevant intervening elements. Such interference is thought to occur at retrieval (as opposed to encoding) both for general memory tasks (e.g., retrieving items from a list) and in sentence processing (e.g., retrieving elements in long-distance syntactic dependencies). However, no systematic attempts have been made to investigate whether this interference results from the same processing limitations. In Study 1, performance on a battery of memory and cognitive tasks is compared to performance on sentence processing tasks. One of the sentence processing tasks correlated with multiple measures likely to rely on general memory mechanisms involved in resolution of retrieval interference. However, low internal reliability of the language tasks in the first study was observed. In Study 2, a series of sentence processing tasks is examined in order to determine which tasks exhibit the highest internal reliability. The results indicate that syntactic complexity manipulations presented in null (isolated) contexts exhibit highest internal reliability and are good candidates for future studies investigating individual differences in sentence processing. Suggestions for future studies investigating shared resources between sentence processing tasks and general memory mechanism are then discussed, informed by the results from these studies. / by Melissa L. Troyer. / S.M.