Fig. 13 Spatial relationship between the fct, ft, and ﬂ. In each diagram, the x-axis represents the distance (mm) to the posterior commissure and the y-axis, the distance to the medial thalamic border. The distances were measured at three different dorsoventral levels [2 mm ventral (V2) and 1 mm ventral (V1) to intercommissural level, and intercommissural level (DV0)] of two different brains (Hb1 and Hb4) cut in the sagittal plane. For each dorsoventral level, the center of the bulk on the anteroposterior (A-P) axis was measured at medio-lateral (M- L) levels between 0 (ventricular border) and 18 mm V 2.0 V 1.0 DV 0 18 16 14 12 L10 -M 8 6 4 2 0 18 16 14 12 L 10 -M 8 6 4 2 0 18 16 14 12 L10 -M 8 6 4 2 0 A-P A-P A-P Brain Struct Funct (2008) 212:443–463 457 0 2 4 6 8 10 12 14 16 18 0 2 4 6 8 10 12 14 16 18 Case Hb1 Case Hb4 ft fct fl 0 2 4 6 8 10 12 14 16 18 0 2 4 6 8 10 12 14 16 18 18 16 14 12 L10 -M 8 6 4 2 0 18 16 14 12 L10 -M 8 6 4 2 0 18 16 14 12 L10 -M 8 6 4 2 0 A-P A-P A-P 0 2 4 6 8 10 12 14 16 18 0 2 4 6 8 10 12 14 16 18 Aufenberg et al. 2005), is a re-actualisation of earlier sur- gical experiences (Spiegel and Wycis 1954; Spiegel et al. 1963; Mundinger 1965; Bertrand et al. 1973), although with limited technical support at the time. This approach offers the advantage over thalamic RFL (as used princi- pally for tremor) to spare thalamic cells and related thalamocortical loops. Furthermore, with a relatively small lesion (*4 mm diameter), the efferents from a large pal- lidal territory (in case of the PTT in PD) and afferents to relatively large thalamic territory (in case of the CTT in ET) can be interrupted and efﬁcacy of the surgery signiﬁ- cantly improved. Risks associated with thalamic (e.g. encroachment onto internal capsule when the lateral part of the nucleus is targeted) or pallidal (with the vicinity of the optic tract and internal capsule) surgery are also prevented by accurate targeting of the subthalamic area. Methodological aspects Our results are based on histologically processed sections of the human thalamus and basal ganglia and on correla- tions with post-mortem MRI. The myelin staining served as ﬁrst basis for the identiﬁcation of the ﬁbre tracts, though with the following limitations: since the origin and terminal of the ﬁbre tracts cannot be assessed in the present material (myelin stain, in normal brains), our identiﬁcation relies on previous studies in humans, particularly those based on Marchi retrograde degeneration methods after lesions in the pallidum or cerebellar nuclei (Martinez 1961; Beck and Bignami 1968). These studies provide very valuable ana- tomical information and link to the clinic but cannot be used for stereotactic targeting. On the other hand, the most commonly used atlases of the human thalamus 123