Specificity and non-specificity of synaptic connections within mammalian visual cortex.

It is clear from reviewing the findings of our own studies and those of others that the cerebral cortex has combined two very different strategies of organisation. Firstly it has a strictly defined genetically determined substrate of specific neurons classes, specific rules for which kinds of cells interconnect, a laminar architecture where efferent and afferent relays and interlaminar links are predetermined. But, as well, a second strategy allows great developmental lability in the precise spatial patterns of intralaminar circuits of the excitatory neurons and in the actual weights of excitatory and inhibitory synapses that are contributed to each neuron.

The spatial extent over which neurons in macaque striate cortex pool visual signals.

We recorded activity of single units in macaque monkey primary visual cortex (V1) to define the retinotopic extent of the visual inputs that drive or modulate V1 neuron responses in parafoveal and peripheral (calcarine) cortex. We used high-contrast drifting grating stimuli to define the extent of the area over which responses summate and the extent of the receptive-field surround. We found responses of most V1 cells to summate over 1 deg, with a suppressive surround typically twice that in diameter, though for some cells (even in parafoveal V1) surrounds exceeded 13 deg in diameter.

Anatomical substrates for functional columns in macaque monkey primary visual cortex.

In this review we re-examine the concept of a cortical column in macaque primary visual cortex, and consider to what extent a functionally defined column reflects any sort of anatomical entity that subdivides cortical territory. Functional studies have shown that columns relating to different response properties are mapped in cortex at different spatial scales. We suggest that these properties first emerge in mid-layer 4C through a combination of thalamic afferent inputs and local intracortical circuitry, and are then transferred to other layers in a columnar fashion, via interlaminar relays, where additional processing occurs.

Circuits for local and global signal integration in primary visual cortex.

Contrast-dependent changes in spatial summation and contextual modulation of primary visual cortex (V1) neuron responses to stimulation of their receptive field reveal long-distance integration of visual signals within V1, well beyond the classical receptive field (cRF) of single neurons. To identify the cortical circuits mediating these long-distance computations, we have used a combination of anatomical and physiological recording methods to determine the spatial scale and retinotopic logic of intra-areal V1 horizontal connections and inter-areal feedback connections to V1. We have then compared the spatial scales of these connectional systems to the spatial dimensions of the cRF, spatial summation field (SF), and modulatory surround field of macaque V1 neurons.

Anatomical origins of the classical receptive field and modulatory surround field of single neurons in macaque visual cortical area V1.

From the analyses of our own and others' anatomical and physiological data for the macaque visual system, we arrive at a conclusion that three pathways can provide the V1 neuron with access to information from the visual field and affect its response. First, direct thalamic input can determine the size of the initial activating RF at high contrast. Second, lateral connections can enlarge the RF at low contrast by pooling information from larger regions of cortex that are otherwise ineffective when high contrast thalamic input is driving the cortical neuron.

Early phase II trial of human rotavirus vaccine candidate RV3.

A naturally attenuated, human neonatal strain, rotavirus vaccine candidate RV3, was tested in a limited phase II randomized double-blind controlled trial. Doses of 1 ml, containing placebo or 6.5 x 10(5) fluorescent cell forming units (fcfu) of virus in AGMK cells, were given at 3, 5 and 7 months of age.