The somatotopic organization of the motor fibers within the posterior limb of the internal capsule (IC) in humans remains unclear. Several electrophysiological atlases created from stimulation during stereotactic neurosurgery have suggested that there is considerable overlap between representations of body parts. Overlap reported in these studies may have been due to linear scaling methods applied to the data that were unable to account for individual anatomical variability. In the current work, the authors attempted to overcome these limitations by using a nonlinear registration technique to better understand the spatial location and extent of the body-part representations in the IC.
Data were acquired during 30 cases of deep brain neurosurgery in which the IC was electrically stimulated to localize the ventrolateral nucleus for a subsequent thalamotomy or implantation of a thalamic deep brain stimulator. Motor responses from the tongue, face, arm, or leg were evoked in the IC and coded in the patient's native MR imaging space. The tagged MR images were then nonlinearly registered to a high-resolution template MR image. This work resulted in a functional electrophysiological atlas demonstrating the locations of body-part representations in the posterior limb of the IC that takes individual anatomical variability into account. To further understand the spatial location and extent of the motor responses, the electrophysiological data points were transformed into 3D probability maps that describe the likelihood of obtaining motor responses in the posterior limb of the IC.
The analyses suggest a reliable face-anterior, arm-intermediate, and leg-posterior somatotopic organization in the posterior limb of the IC with little overlap between the body-part representations.
This probabilistic atlas of functional responses evoked by stimulating the posterior limb of the IC provides better understanding of the anatomical organization of descending motor fibers, can be used for indirect intraoperative confirmation of the location of the ventrolateral thalamus, and is applicable to clinical and research MR imaging studies requiring information on spatial organization of motor fibers at the thalamic level in the human brain.
Abbreviations used in this paper: AC = anterior commissure; ANIMAL = Automated Nonlinear Image Matching and Anatomical Labeling; DBS = deep brain stimulation; IC = internal capsule; MNI = Montreal Neurological Institute; PC = posterior commissure; STN = subthalamic nucleus.
AtkinsonJDCollinsDLBertrandGPetersTMPikeGBSadikotAF: Optimal location of thalamotomy lesions for tremor associated with Parkinson disease: a probabilistic analysis based on postoperative magnetic resonance imaging and an integrated digital atlas. J Neurosurg96:854–8662002
DuerdenEGFinnisKWPetersTMSadikotAFA method for analysis of electrophysiological responses obtained from the motor fibers from the human internal capsule. EllisREPetersTM: Medical Image Computing and Computer-Assisted Intervention—MICCAI 2003: 6th International Conference, Montréal, Canada, November 2003, Proceedings, Part IIBerlin, HeidelbergSpringer-Verlag2003. 50–57
GuoTStarreveldYPPetersTMEvaluation and validation methods for intersubject nonrigid 3D image registration of the human brain. GallowayRLJrClearyKR: Medical Imaging 2005: Visualization Image-Guided Procedures and Display. Proceedings Vol 5744Bellingham, WASPIE2005. 594–603
HolodnyAIGorDMWattsRGutinPHUlugAM: Diffusion-tensor MR tractography of somatotopic organization of corticospinal tracts in the internal capsule: initial anatomic results in contradistinction to prior reports. Radiology234:649–6532005
St-JeanPSadikotAFCollinsLClondaDKasraiREvansAC: Automated atlas integration and interactive three-dimensional visualization tools for planning and guidance in functional neurosurgery. IEEE Trans Med Imaging17:672–6801998