Distinct developmental principles underlie the formation of ipsilateral and contralateral whisker-related axonal patterns of layer 2/3 neurons in the barrel cortex

► Axons of cortical layer 2/3 neurons were examined using in utero electroporation. ► A whisker-related axonal pattern existed in the contralateral barrel cortex. ► Presynaptic structures were found in the axons forming the whisker-related pattern. ► Different developmental processes comprise ipsi- and contra-lateral axon formation.