Summary of frontal projections to thalamic nuclei associated with language. Three-dimensional reconstruction of the left hemisphere of the rhesus monkey cortex, which was rendered semi-transparent to show frontal neurons in layers 5 and 6 that project to MD (red) or to VA/VL (green). The projection zones include prefrontal areas (in front of the arcuate sulcus), as well as premotor areas situated behind the upper and lower limbs of the arcuate sulcus (as). Abbreviations: as, arcuate sulcus; cs, central sulcus; MD, mediodorsal nucleus; ps, principal sulcus; VA, ventral anterior nucleus; VL, ventrolateral nucleus.