Take a look at our recent work in Neuron Neuron examining the contribution of early thalamic inputs onto L1 interneurons in the establishment of top-down connectivity in V1 cortex authors.elsevier.com/a/1dgve3BtfGzk…

1. Work from many labs have suggested that activity in the early postnatal cortex is initially dominated by bottom-up signals. The cortex only later develops recurrent activity following the establishment of functional connectivity between primary and associative cortical areas.

The question we wanted to address was whether there is a link between early bottom-up activity and the later establishment of top-down connectivity.

2. To investigate this, we focused on L1 interneurons (INs) in V1, since most cortico-cortical projections primarily terminate in this layer.

3. Using monosynaptic rabies tracing from NDNF INs, we found that early in development, dLGN inputs are predominant, whereas inputs from the ACC and RSP are comparatively weaker. This trend shifts in the adult.

4. We found that projections from the dLGN preferentially target Neurogliaform cells (NGF) in L1 and a fraction of the projections to L1 are shared with those in L4.

5. Using optogenetics and patch clamp recording from L1 IN subtypes in brain slices, we found that ACC projections strengthen across development, whereas bottom-up inputs get slightly weakened.

Moreover, sensory deprivation or selective removal of dLGN inputs to L1 INs prevented the strengthening of ACC projections, but not those from the RSP.

6. Conversely, premature chemogenetic activation of ACC caused strengthening of these top-down inputs onto L1 NGF cells, and this was dependent on activity from the thalamus.

7. Conclusion: Proper establishment of top-down connectivity in the visual cortex depends critically on bottom-up inputs from the thalamus during postnatal development.

This work would not have been possible without the invaluable contribution of all co-authors Shuhan Huang Marian Fernandez Spurti Vemuri Gabrielle Pouchelon rudylab Gord Fishell and Twitterless Mia, Yanjie, Qing and Rob.