Anatomical Connections of Primate Mediodorsal and Motor Thalamic Nuclei with the Cortex.

Non-sensory thalamic nuclei interact with the cortex through thalamocortical and cortico-basal ganglia-thalamocortical loops. Reciprocal connections between the mediodorsal thalamus (MD) and the prefrontal cortex are particularly important in cognition, while the reciprocal connections of the ventromedial (VM), ventral anterior (VA), and ventrolateral (VL) thalamus with the prefrontal and motor cortex are necessary for sensorimotor information processing. However, limited and often oversimplified understanding of the connectivity of the MD, VA, and VL nuclei in primates have hampered development of accurate models that explain their contribution to cognitive and sensorimotor functions.

Prelimbic cortical targets of ventromedial thalamic projections include inhibitory interneurons and corticostriatal pyramidal neurons in the rat.

Ventromedial thalamic axons innervate cortical layer I and make contacts onto the apical dendritic tuft of pyramidal neurons. Optical stimulation of ventromedial thalamic axon terminals in prefrontal cortical areas in mouse brain slices evokes responses in corticocortical, corticothalamic and layer I inhibitory interneurons. Using anterograde tracing techniques and immunohistochemistry in male Sprague-Dawley rats, we provide anatomical evidence that ventromedial thalamic axon terminals in prelimbic cortex make contacts onto pyramidal neurons and, in particular, onto corticostriatal neurons as well as layer I inhibitory interneurons.

Thalamic afferents to prefrontal cortices from ventral motor nuclei in decision-making.

The focus of this literature review is on the three interacting brain areas that participate in decision-making: basal ganglia, ventral motor thalamic nuclei, and medial prefrontal cortex, with an emphasis on the participation of the ventromedial and ventral anterior motor thalamic nuclei in prefrontal cortical function. Apart from a defining input from the mediodorsal thalamus, the prefrontal cortex receives inputs from ventral motor thalamic nuclei that combine to mediate typical prefrontal functions such as associative learning, action selection, and decision-making. Motor, somatosensory and medial prefrontal cortices are mainly contacted in layer 1 by the ventral motor thalamic nuclei and in layer 3 by thalamocortical input from mediodorsal thalamus.