Speaker
Description
A fundamental property of neurons in the primary visual cortex is their preference for orientation of edges that is invariant under contrast changes.
We designed a synthetic hybrid neural circuit to study the emergence of orientation selectivity under different thalamo-cortical connection schemes. To this end, a computational model of the retino-thalamic pathway was combined with an in-vitro model of cortical input layer 4. The latter was either a primary culture of cortical neurons or an acute brain slice of primary visual cortex. The two stages were interfaced optogenetically by expression of channelrhodopsin in the neurons of the in-vitro circuit and holographic stimulation. Neural activity was then monitored electrophysiologically with multielectrode arrays.
We then implemented a classical feed-forward connectome and found that neurons reliably reproduced the orientation selectivity defined by the input as long as cortical hypercolumns were large enough. Strength of selectivity did not increase further beyond the typical hypercolumn size observed across different species.
When the thalamocortical input was retinotopic but unselective for orientation, we measured orientation selective responses in the cortical activity that we reasoned had to be generated intrinsically by the target network. We tested the effect of different contrast levels on this tuning and found that the orientation selectivity can change for individual neurons but is stable on the population level.
In summary, we showed that contrast-invariant orientation preference can emerge from unspecific thalamic input in a simplified cortex model.
