Brain Struct Funct (2008) 212:443–463 three-dimensional coordinates of the fct and ft determined in the present study allow placing RFL to selectively interrupt one or the other tract, as shown in Figs. 12 and 14. The most commonly used surgical approach for PD is to target the subthalamic nucleus with DBS. In the last few years, increasing evidence for more effectiveness of the stimulation sites at the dorsal border of the STh, rather than within the nucleus, has been reported (Voges et al. 2002; McIntyre et al. 2004; Zonenshayn et al. 2004; Breit et al. 2006; Godinho et al. 2006; Miocinovic et al. 2006; Butson et al. 2007). This indicates that the effect is at least partially due to involvement of the ﬁbres from the ﬂ (or H2 ﬁeld of Forel) coursing over the dorsal border of the nucleus, on their way to join the al to ﬁnally form the ft. Similar evi- dence for the importance of the ﬁbres in DBS efﬁcacy was proposed by Benabid and col. (Benabid et al. 1996) using DBS of the VLp (or VIM) against tremor. They suggest that at the frequency most optimal for tremor suppression, the ﬁbres (probably from the fct), rather than the thalamic cells, are affected. All these observations point to the fact that in the near future, the ﬁbre tracts may well regain importance for the surgical treatment of motor disorders. Acknowledgments We thank V. Streit for her skilful histological work, S. Kolias and M. Wyss for post-mortem MR scanning; and A. Aguzzi and H.-P. Lipp for providing autopsy material. This study was supported by the Swiss National Science Foundation (grants No. 31- 47238.96, 31-54179.98; 31-68248.02). Open Access This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which per- mits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited. 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