2003 |
Das, Aniruddha |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Tuning For Complex Visual Stimuli in V1 @ Columbia University Health Sciences
DESCRIPTION (provided by applicant): The long-term goal of this work is to understand the neural mechanisms of visual form perception. The current project aims to study the processing of modestly complex visual stimuli such as smooth contours, junctions and texture boundaries in primary visual cortex (V1). Recent evidence suggests that V1 is much more than just a bank of filters that passively extracts the simplest elements (e.g. short oriented line segments) from all visual input, as was earlier believed. Rather, the elemental components of complex stimuli interact strongly with each other to give V1 responses that could differ dramatically from the responses to the individual components. The current project is intended to test the hypothesis that such complex visual processing can be predicted from the columnar architecture and intrinsic circuitry of VI. In particular, it is proposed that cortical columns tuned to elemental components of a complex stimulus (e.g. line segments at particular retinotopic positions, orientations, color contrast etc.) facilitate and inhibit each other in predictable ways through intrinsic V1 circuitry to generate tuning for the composite whole. Further, that the complex tuning of any given V1 neuron can be predicted from its geographical position on cortex relative to columns activated by the complex stimulus in question. This hypothesis will be tested by studying the V1 processing for different families of complex stimuli including smooth contours, junctions and texture boundaries that are perceptually important for scene segmentation. A combination of optical imaging and electrode recordings in alert monkey V1 will be used for this study. Optical imaging will allow for mapping the cortical positions of neurons responding to each complex stimulus and its individual components. Electrode recordings and cross correlations, guided by optical images, will be used to measure the intracortical interactions between the same groups of neurons. The complex tuning computed on the basis of these interactions can then be compared with the measured values and thus test our hypothesis. The proposed combination of optical imaging and electrode recording will make it possible to elucidate the geometry of cortical mechanisms underlying V1 tuning, a goal that is not reachable through electrode recordings alone. The results of this study will provide a broad framework for understanding the cortical processing of complex visual stimuli, an essential step for clinical applications including the design of visual prostheses for the blind.
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1 |
2004 — 2006 |
Das, Aniruddha |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
The Tuning For Complex Visual Stimuli in V1 @ Columbia University Health Sciences
DESCRIPTION (provided by applicant): The long-term goal of this work is to understand the neural mechanisms of visual form perception. The current project aims to study the processing of modestly complex visual stimuli such as smooth contours, junctions and texture boundaries in primary visual cortex (V1). Recent evidence suggests that V1 is much more than just a bank of filters that passively extracts the simplest elements (e.g. short oriented line segments) from all visual input, as was earlier believed. Rather, the elemental components of complex stimuli interact strongly with each other to give V1 responses that could differ dramatically from the responses to the individual components. The current project is intended to test the hypothesis that such complex visual processing can be predicted from the columnar architecture and intrinsic circuitry of VI. In particular, it is proposed that cortical columns tuned to elemental components of a complex stimulus (e.g. line segments at particular retinotopic positions, orientations, color contrast etc.) facilitate and inhibit each other in predictable ways through intrinsic V1 circuitry to generate tuning for the composite whole. Further, that the complex tuning of any given V1 neuron can be predicted from its geographical position on cortex relative to columns activated by the complex stimulus in question. This hypothesis will be tested by studying the V1 processing for different families of complex stimuli including smooth contours, junctions and texture boundaries that are perceptually important for scene segmentation. A combination of optical imaging and electrode recordings in alert monkey V1 will be used for this study. Optical imaging will allow for mapping the cortical positions of neurons responding to each complex stimulus and its individual components. Electrode recordings and cross correlations, guided by optical images, will be used to measure the intracortical interactions between the same groups of neurons. The complex tuning computed on the basis of these interactions can then be compared with the measured values and thus test our hypothesis. The proposed combination of optical imaging and electrode recording will make it possible to elucidate the geometry of cortical mechanisms underlying V1 tuning, a goal that is not reachable through electrode recordings alone. The results of this study will provide a broad framework for understanding the cortical processing of complex visual stimuli, an essential step for clinical applications including the design of visual prostheses for the blind.
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1 |
2009 — 2014 |
Das, Aniruddha |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Anticipatory Hemodynamic Signals in Primary Visual Cortex @ Columbia University Health Sciences
Description (provided by applicant): Our long-term goal is to understand the neural mechanisms of visual processing early in the cortical pathway. To this end we record from rhesus macaque visual cortex using a combination of intrinsic-signal optical imaging and electrophysiology while the animals are engaged in visual form processing tasks. The goal of the current project is two-fold. We propose to study a novel stimulus-independent anticipatory haemodynamic signal that we observed earlier in alert macaque V1 (primary visual cortex). Through this process we also propose to better understand the physiological basis of neuroimaging signals including fMRI. This project derives from our recent discovery that haemodynamic signals in alert monkey V1 have two distinct components. One component is predictable by visual input and associated V1 neuronal activity. The other component - of comparable strength - is a hitherto unknown haemodynamic signal marking task anticipation. It reflects an arterial pumping mechanism bringing fresh blood to cortex in anticipation of predicted visual events. Electrode recordings conducted simultaneously with the optical imaging showed that this novel haemodynamic signal is not driven by local V1 neuronal activity, in dramatic contrast to visually evoked responses obtained from the same recording sites. We hypothesize that the anticipatory stimulus-independent haemodynamic signal is a mechanism of predictive arousal. We propose to test this hypothesis by characterizing the anticipatory and visually evoked signals, and their interaction, and asking if the anticipatory signal can modulate visually evoked responses and behavior. Our finding of the novel haemodynamic signal also challenges current understandings of neuroimaging signals, notably functional magnetic resonance imaging (fMRI), the most commonly used tool for human neuroimaging. Through the course of this project we will investigate the links between neuroimaging signals and electrophysiology in the alert macaque in a variety of visual perceptual tasks. This will be an unparalleled opportunity to gain new insights into fMRI in an animal model that is the closest possible to the human. Our novel findings were obtained as a result of a new imaging technique developed in our laboratory, continuous dual-wavelength intrinsic-signal optical imaging, combined with electrode recordings, in alert behaving macaques. For the imaging, one wavelength is absorbed preferentially in oxygenated haemoglobin, thus monitoring blood oxygenation;the other wavelength, absorbed equally in oxygenated and deoxygenated haemoglobin, measures blood volume. The simultaneous electrode recordings give an electrophysiological measure of the underlying neuronal activity. The continuous recording allows us to distinguish between ongoing signals and stimulus-evoked responses. This technique will form the basis of the current project, giving a unique combination of tools to answer the questions at hand. PUBLIC HEALTH RELEVANCE This project has two significant implications for public health. We propose to characterize a novel mechanism of brain arousal, thus shedding new light on processes of attention or alertness and their disorders (attention deficit disorder etc.). Further, our work challenges the current understanding of functional magnetic resonance imaging (fMRI), the most commonly used means of studying the human brain in clinical or scientific settings, and will therefore have major implications for the correct interpretation of this critically important medical tool.
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1 |
2016 — 2019 |
Das, Aniruddha |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Endogenous Neural Activity: Neurophysiology, Optical Imaging, Fmri, and Behavior. @ Columbia University Health Sciences
? DESCRIPTION (provided by applicant): We have recently identified a type of neural activity that reflects the subject's engagement in a task. This task- related activity, which we have measured using both intrinsic-signal optical imaging and functional magnetic resonance imaging, is independent of external visual stimuli and is, instead, linked to internal brain states such as arousal and endogenous attention. Here, we propose a series of experiments that test several hypotheses about task-related brain activity, using a wide range of neurophysiological methods. Aim 1 will test whether hemodynamic activity (measured with optical imaging or with fMRI) can be separated into a linear sum of neurally distinct stimulus-evoked and task-related components. Aim 2 will test whether the task-related component is widespread but possibly a function of task modality (e.g. visual vs. auditory) and not spatially global. Aim 3 will test whether the task-related component reflects the degree of engagement (a form of arousal or attention) and is thus a function of reward, difficulty and timing. The endogenous processes that we propose to investigate are implicated a variety of neurological and psychiatric disorders. For example, individuals with ADHD demonstrate a wide variety of attentional deficits, but their most pronounced deficits are related to sustained attention, i.e., maintaining a steady level of performance on an infrequent task over a prolonged period of time. It is likely that the task-related component that we are proposing to study is related to sustained attention, and knowledge gained from the proposed experiments may provide insights into ADHD and related disorders.
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