The majority of neurons in primary visual cortex are tuned for stimulus orientation, but the factors that account for the range of orientation selectivities exhibited by cortical neurons remain unclear. To address this issue, we used in vivo 2-photon calcium imaging to characterize the orientation tuning and spatial arrangement of synaptic inputs to the dendritic spines of individual pyramidal neurons in layer 2/3 of ferret visual cortex. The summed synaptic input to individual neurons reliably predicted the neuron’s orientation preference, but did not account for differences in orientation selectivity among neurons. These differences reflected a robust input-output nonlinearity that could not be explained by spike threshold alone, and was strongly correlated with the spatial clustering of co-tuned synaptic inputs within the dendritic field. Dendritic branches with more co-tuned synaptic clusters exhibited greater rates of local dendritic calcium events supporting a prominent role for functional clustering of synaptic inputs in dendritic nonlinearities that shape orientation selectivity.

The principles governing the functional organization and development of long-range network interactions in the neocortex remain poorly understood. Using in vivo wide-field and 2-photon calcium imaging of spontaneous activity patterns in mature ferret visual cortex, we find widespread modular correlation patterns that accurately predict the local structure of visually-evoked orientation columns several millimeters away. Longitudinal imaging demonstrates that long-range spontaneous correlations are present early in cortical development prior to the elaboration of horizontal connections, and predict mature network structure. Silencing feed-forward drive through retinal or thalamic blockade does not eliminate early long-range correlated activity, suggesting a cortical origin. Circuit models containing only local, but heterogeneous, connections are sufficient to generate long-range correlated activity by confining activity patterns to a low-dimensional subspace via multi-synaptic short-range interactions. These results suggest that local connections in early cortical circuits can generate structured long-range network correlations that guide the formation of visually-evoked distributed functional networks.

AbstructA formal approach is presented of ordering the time scales of the dominant fluxes of material in an estuary and then accordingly choosing the spatial and temporal resolution of the sampling program. In this way bounds can be derived for the internal turnover times, boundary exchange rates, and import or export fluxes of a particular substance purely from measurements of the standing stock values in the estuary water. Application of this methodology to an experiment in the Duplin River, Georgia, showed that if the effects of the water motion and mixing are extracted from the variation of a biological component, then the variability of the residual can be successfully interpreted. For a typical summer condition it was shown that ammonium was cycled rapidly within the marsh water, its distribution was very patchy, and only its decomposition products left the marsh; that the refractory dissolved organic carbon (DOC) component was steadily exported by longitudinal mixing while labile DOC was rapidly recycled in the water; that silicate was produced in large amounts in the marsh and exported by longitudinal mixing; that particulate organic carbon (POC) concentrations were almost completely determined by the turbulence intensity in the water; and that compared to this internal cycling, export was of minor significance.bution 398 of the University of Georgia Marine Institute.

Across sensory areas, neural microcircuits consolidate diverse streams of information into unified, representations of the external world. In the carnivore visual cortex, where eye-specific inputs converge, it has been posited that a single, shared columnar representation of orientation develops independent of sensory experience. In this study, in vivo calcium imaging with columnar and cellular resolution reveals a strikingly different developmental process in ferret visual cortex, starting with an early developmental period in which contralateral, ipsilateral or binocular stimulation each yield distinct well-organized representations of orientation that are misaligned at the columnar and cellular scale. Experience-dependent processes drive the reorganization of these three representations towards a single binocularly-aligned representation resembling the early binocular representation through concerted shifts in the preferred orientation of individual neurons. Thus, contrary to previous findings, a unified binocular representation of orientation results from an experience-dependent process that aligns the activity patterns of three distinct neural representations..

Summary The spatial arrangement of luminance increments (ON) and decrements (OFF) falling on the retina provides a wealth of information used by central visual pathways to construct coherent representations of visual scenes. But how the polarity of luminance change is represented in the activity of cortical circuits remains unclear. Using wide-field epifluorescence and two-photon imaging we demonstrate a robust modular representation of luminance polarity (ON or OFF) in the superficial layers of ferret primary visual cortex. Polarity-specific domains are found with both uniform changes in luminance and single light/dark edges, and include neurons selective for orientation and direction of motion. The integration of orientation and polarity preference is evident in the selectivity and discrimination capabilities of most layer 2/3 neurons. We conclude that polarity selectivity is an integral feature of layer 2/3 neurons, ensuring that the distinction between light and dark stimuli is available for further processing in downstream extrastriate areas.