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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)
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)
Any analysis of plastic reorganization at a neuronal locus needs a veridical measure of changes in the functional output--that is, spiking responses of the neurons in question. In a study of the effect of retinal lesions on adult primary visual cortex (V1), Smirnakis et al. propose that there is no cortical reorganization. Their results are based, however,(More)
A. Das contribution is estimated to lie between 5% and 28% intracortical excitatory and inhibitory connections provide the rest. Other models were therefore proposed for orientation selectivity, with intracortical connections playing a more significant role. These models started A recent report by David Ferster and colleagues (1996) with the assumption that(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)
Adult visual cortex undergoes substantial functional change as a result of alterations in visual experience. Binocular retinal lesions lead to a reorganization of the visuotopic map in primary visual cortex. Associated with this change is a strengthening of an existing plexus of long-range horizontal connections by sprouting of axon collaterals and(More)