CROSSED THALAMOCORTICAL AND CORTICO-THALAMIC PROJECTIONS IN ADULT MICE

The crossed thalamo-cortical and cortico-thalamic connections of the m ouse are drawn using the tracer wheat germ agglutinin-horseradish pero xidase. After injections in the frontal cortex of the right hemisphere cells labeled retrogradely and axons labeled anterogradely are observ ed in the thalamus ipsilateral and contralateral to the cortical injec tions. The retrograde and anterograde labeling in the contralateral th alamus is less intense than ipsilaterally and involves the mediodorsal , ventral medial, central medial, and paracentral nuclei. Crossed fron to-thalamic axons reach more lateral regions than those containing con tralateral thalamo-frontal neurons. Our results demonstrate that the t halamo-cortical system of mice has a bilateral component. The function al significance of this pathway and analogies with crossed thalamo-cor tical connections in other species are discussed.