Compartmentation and Connectivity of the Thalamus: fMRI “Resting State” and DWI Examinations

DFG Project

Figure 1. Segmentation of thalamic substructures and the major cortical projections areas of five dominant clusters in males.
Figure 2. Segmentation of thalamic substructures using rsfMRI and their major structural and functional cortical pro-jections.

The human thalamus is in terms of its internal parcellation, its connectivity pat-terns, the functioning of its circuitry, and its relationship to the cerebral cortex, still partly a terra incognita. Almost all information processing in cortex strongly depends on the thalamic interactions. Therefore, the knowledge of thalamic connections and interconnections is es-sential to understand cortical functions. Although changes in the thalamus play a prominent role in the functionally defined pathophysiology of psychiatric and neurodegenerative diseas-es, its internal structures are mostly identified and delineated based on anatomical cytoarchi-tectonic postmortem atlases. The objective of our study is to examine the subdivisions of the thalamus and determine its cortical connectivity pattern by the use of resting state fMRI (rsfMRI), and diffusion weighted imaging (DWI). DTI: To assess stable anatomical features of the human thalamus, an unbiased DTI parcella-tion approach was used to segment thalamic structures with similar spatial orientation. We determined localization, size and individual variations of 21 thalamic clusters in a group of 63 healthy human subjects (32 males/31 females). The laterality differences accounted for ±6 % and gender differences for ±4 % of the thalamic volume. Consecutively, five stable clusters in the anterior, medial, lateral and posterior thalamus were selected, which were common to 90 % of all subjects and contained at least 10 voxels. These clusters could be assigned to the anteroventral nucleus (AN) group, the mediodorsal (MD) nucleus, the medial pulvinar (PuM), and the lateral nuclei group (see. Figure 1). The corresponding cortical targets were determined using fiber tractography (Kumar et al., 2014).

rsfMRI: We used resting state-fMRI to investigate the functional anatomy of the thalamus by applying an Independent Component Analysis (ICA) to delineate thalamic substructures into stable and reproducible parcels for the left and right thalamus. We determined 15 functionally distinct thalamic parcels, which differed in laterality and size but exhibited a correspondence with 18 cytoarchitectonally-defined nuclei. We characterized their structural connectivity in determining DTI based cortical fiber pathways and found selected projections to different cor-tical areas. In contrast, the functional connections of these parcels were not confined to cer-tain cortical areas or lobes (see Figure 2). We, finally evaluated cortical projections and found a particular cortical pattern for each parcel, which partly exhibited a correspondence with the thalamo-cortical connectivity maps of the mouse (Kumar et al., 2017).

References

  1. Kumar, V., Mang, S., Grodd, W., 2014. Direct diffusion-based parcellation of the human thalamus. Brain Struct. Funct. 220, 1619–1635. doi:10.1007/s00429-014-0748-2
  2. Kumar, V.J., van Oort, E., Scheffler, K., Beckmann, C.F., Grodd, W., 2017. Functional anatomy of the human thalamus at rest. NeuroImage 147, 678–691. doi:10.1016/j.neuroimage. 2016.12.071

DFG Project
GR 833/11-1
Compartmentation and Connectivity of the Thalamus: fMRI “Resting State” and DWI Examinations PI: W. Grodd
Funding: 269.458 Euro for 3 years

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