Despite a large amount of information obtained during the last 50 plus years, the human thalamus still remains for the most part terra incognita. Refinement of imaging techniques has led to an impressive leap in understanding of cortical functioning in human and interaction between different parts of the cortex during performance of specific tasks. A sort of functional brain anatomy has been unfolding in front of our eyes. At the same time the thalamus, which is intricately interconnected with the entire cortex and plays a pivotal role in its functioning, has somehow faded from the attention focus. The fact that thalamic neuronal circuits, especially in the nuclei connected with the frontal lobe, are species-specific and their complexity is the highest in primates, points to evolutionary importance of this brain entity. Yet, due to its deep position in the brain, complex anatomical organization, and quite importantly, the lack of easily graspable maps to enable interpretation of imaging data, thalamus has been rarely considered in the analysis of functional circuits.
Over several decades our studies concentrated on so-called motor-related thalamic nuclei in primate and nonprimate species that process information from the basal ganglia and cerebellum before forwarding it to the neocortex. In a recent study we have also been able to outline these nuclei in the human thalamus using immunocytochemical techniques. With monoclonal antibody to isoform 65 of glutamic acid decarboxylase (GAD65) we identified the territories of three major subcortical afferents (pallidal, nigral and cerebellar) in human motor thalamus and demonstrated their extent and topographical relationships. Using these data and continuous series of Nissl-stained sagittal sections we began constructing the nuclear maps of the human thalamus within a system of coordinates used in stereotactic neurosurgery.
The work on classification and delineations of motor thalamic nuclei is completed (Ilinsky et al. 2018) whereas delineations of individual subnuclei of somatosensory complex, mediodorsal nucleus, and pulvinar are still in need of refinement. This can be done and incorporated in this database when appropriate data on the human thalamus are available. Demonstrated at this site are digitized images of Nissl-stained sections and series of color-coded maps in sagittal, coronal and horizontal planes as well as a series of sagittal MRI cuts all from the same tissue block. Recently the 3D volume was co-registered with MNI space and is available in version 2 of Lead-DBS website (www.lead-dbs.org). Feedback in form of constructive criticism, suggestions, and/or proposals is welcome.