MORFOFUNCTIONAL MAPPING OF THE HUMAN ANTERIOR THALAMUS
The connectivity between the anterior part of the human thalamus (AT) and the frontal cortex is crucial for complex cognitive processes. The AT is also a major target for deep brain neurosurgery in various neurological disorders such as epilepsy, Parkinson’s disease or essential tremor. Functionally relevant nuclear segmentation is essential to understand both normal and pathological processes, however morphological division of the human AT based on inputs and cell types is still lacking. Here we used vesicular glutamate transporter 1 and 2 (vGLUT1, vGLUT2), calbindin, calretinin and parvalbumin immunostainings in consecutive sections of post-mortem human thalami to label cortical and subcortical excitatory inputs, basal ganglia afferents as well as distinct thalamic cell types. Immunostained slices were digitized with a slidescanner and analysed with ImageJ. The combination of markers clearly outlined the major nuclear divisions of the human AT albeit their extensions and input types were different from the accepted schemes. Both the arousal related midline nuclei and the anterior nuclear group involved in memory circuits occupied much larger proportions of the AT than indicated in human atlases. The rostral part of mediodorsal nucleus lacked giant vGLUT1-positive inputs but were innervated by vGLUT2 terminals. Surprisingly, afferents of the two large motor systems (cerebellar and basal ganglia) did not display complete segregation as expected. Our data indicate that segmentation of human AT based on functionally relevant markers significantly deviate from the accepted schemes. It indicates nucleus specific, complex combination of afferent systems which display both evolutionary conserved and highly derived human features.