Aniruddha Das

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Two components of cortical circuits could mediate contour integration in primary visual cortex (V1): intrinsic horizontal connections and feedback from higher cortical areas. To distinguish between these, we combined functional mapping with a new technique for labeling axons, a recombinant adenovirus bearing the gene for green fluorescent protein (GFP), to(More)
The cortical 'point spread' (PS) is the area of cortex activated by a minimal visual stimulus. Here we use the PS to explore the functional role of lateral connectivity in normal cat primary visual cortex (V1) and its involvement in topographic reorganization of cortex following retinal lesions. We compared the distributions of PSs measured with optical(More)
Haemodynamic signals underlying functional brain imaging (for example, functional magnetic resonance imaging (fMRI)) are assumed to reflect metabolic demand generated by local neuronal activity, with equal increases in haemodynamic signal implying equal increases in the underlying neuronal activity. Few studies have compared neuronal and haemodynamic(More)
Cells in adult primary visual cortex are capable of integrating information over much larger portions of the visual field than was originally thought. Moreover, their receptive field properties can be altered by the context within which local features are presented and by changes in visual experience. The substrate for both spatial integration and cortical(More)
Neurons in primary visual cortex (V1) respond differently to a simple visual element presented in isolation from when it is embedded within a complex image. This difference, a specific modulation by surrounding elements in the image, is mediated by short- and long-range connections within V1 and by feedback from other areas. Here we study the role of(More)
The map of orientation columns in primary visual cortex (V1) is known to show strong local distortions, with a generally smooth progression of orientation preference across extended regions of cortex, interrupted by sharp jumps (fractures) and point singularities. The map of visual space on V1, in contrast, has been assumed to be locally smooth and(More)
In functional brain imaging there is controversy over which hemodynamic signal best represents neural activity. Intrinsic signal optical imaging (ISOI) suggests that the best signal is the early darkening observed at wavelengths absorbed preferentially by deoxyhemoglobin (HbR). It is assumed that this darkening or "initial dip" reports local conversion of(More)
1. Receptive field (RF) sizes of neurons in adult primary visual cortex are dynamic, expanding and contracting in response to alternate stimulation outside and within the RF over periods ranging from seconds to minutes. The substrate for this dynamic expansion was shown to lie in cortex, as opposed to subcortical parts of the visual pathway. The present(More)
Neuroimaging (for example, functional magnetic resonance imaging) signals are taken as a uniform proxy for local neural activity. By simultaneously recording electrode and neuroimaging (intrinsic optical imaging) signals in alert, task-engaged macaque visual cortex, we recently observed a large anticipatory trial-related neuroimaging signal that was poorly(More)
Flavoprotein fluorescence imaging (FFI) is a novel intrinsic optical signal that is steadily gaining ground as a valuable imaging tool in neuroscience research due to its closer relationship with local metabolism relative to the more commonly used hemodynamic signals. We have developed a technique for FFI imaging in the primary visual cortex (V1) of alert(More)