[Development of Inter-areal Association Projections in the Cerebral Cortex].

Direct projections between functional areas within the ipsilateral hemisphere (association projections) play a key role in higher cognitive functions. Deficits in these circuits are correlated with various pathological conditions including developmental disorders. We investigated the development of association projections in the mouse neocortex using single-neuron resolution imaging and observed that these were formed as interstitial collaterals that originate as buds from callosal projections of the same neurons. In this review, we describe our findings with regard to the development of association projections, together with mechanisms underlying these processes and also future perspectives in the field.