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Measurement of the levels of ozone and carbon monoxide (a tracer of anthropogenic pollution) at three surface sites on the Atlantic coast of Canada allow the estimation of the amount of ozone photochemically produced from anthropogenic precursors over North America and transported to the lower troposphere over the temperate North Atlantic Ocean. This amount(More)
In the feline visual system, neurons exhibiting sensitivity to the length of a moving contour were first observed in the cortex and described as 'hypercomplex cells'. In these cells an increase in stimulus length beyond an optimal value leads to a rapid decline in response. This decline has been attributed to an intracortical inhibitory input which may be(More)
We have compared the spatial summation characteristics of cells in the primary visual cortex with those of cells in the dorsal lateral geniculate nucleus (LGN) that provide the input to the cortex. We explored the influence of varying the diameter of a patch of grating centred over the receptive field and quantitatively determined the optimal summation(More)
Two approaches were adopted to study the pattern of connectivity between the cat visual cortex and lateral geniculate nucleus. Fourteen individual cortico-geniculate axons were labeled and reconstructed after intracellular or extracellular injection of biocytin into regions of known receptive-field position and ocular dominance preference, and the(More)
1. The lateral geniculate nucleus is the primary thalamic relay for the transfer of retinal signals to the visual cortex. Geniculate cells are heavily innervated from nonretinal sources, and these modify retinogeniculate transmission. A major ascending projection to the lateral geniculate nucleus arises from cholinergic cells in the parabrachial region of(More)
In a previous study, we have shown that the corticofugal projection to the dLGN enhances inhibitory mechanisms underlying length tuning. This suggests that the inhibitory influences deriving from the corticofugal feedback should exhibit characteristics that reflect the response properties of orientation-tuned layer VI cells. Here we report data obtained(More)
The cerebral cortex receives sensory input from the periphery by means of thalamic relay nuclei, but the flow of information goes both ways. Each cortical area sends a reciprocal projection back to the thalamus. In the visual system, the synaptic relations that govern the influence of thalamic afferents on orientation selectivity in the cortex have been(More)
Acetylcholine and acetyl-beta-methacholine were applied iontophoretically to single cells in the feline striate cortex. The directional bias of the visual response to an optimally oriented stimulus was assessed quantitatively, before and during drug application. For the great majority of the cells that were affected by the drugs, selectivity was either(More)
1. We have examined the possibility that N-methyl-D-aspartate (NMDA) receptors may be involved in the visual response of relay cells in the cat dorsal lateral geniculate nucleus (dLGN). The selective NMDA receptor antagonists D-2-amino-5-phosphonovalerate (APV) and 3-[(+/-)-2-carboxypiperazin-4-yl]-propyl-1-phosphonic acid (CPP) have been iontophoretically(More)
1. Cells in the A laminae of the dorsal lateral geniculate nucleus receive their primary innervation from either the contralateral (A) or ipsilateral (A1) eye. This paper provides evidence concerning the responses they give to visual stimulation of what is commonly regarded as the ineffective or non-dominant eye. It also examines the contribution of the(More)