Neurosurgery was a unique opportunity to study cortical function intraoperatively also in humans and to obtain important data almost as side effect during the intervention. At the beginning more of 20th century the neurophysiologist and later Nobel laureate Charles Scott Sherrington (1857�C1952) performed experiments to delineate the motor and the sensory cortex [16]. His map in opposition to previous studies was only a narrow strip on both sides of the Rolandic sulcus [17]. In 1900, Sherrington while working in Liverpool was attended during his experiments for 3 weeks by the promising young American neurosurgeon Harvey Cushing (1869�C1939) who was on his educational journey leading him through many important European medical centres.

Back home in Baltimore, Cushing applied the cortical stimulation technique on humans during neurosurgical interventions and published a map of sensory cortex in 1908 [18, 19]. Cortical stimulation had also practical implications in neurosurgery and became increasingly important during epilepsy surgery. Fedor Krause (1857�C1937), the pioneer of the German neurosurgery, and the neurologist and neurosurgeon Otfrid Foerster (1873�C1941) from Breslau, Germany, used the cortical electric stimulation to localize intraoperatively the epileptic foci by provoking an aura or a typical epileptic fit [20�C22]. This electrical stimulation was superior to focus localization based merely on anatomical landmarks. The knowledge of the localization of the eloquent cortical areas had also a very practical consequence for neurosurgery.

At the end of the 19th century, two Swiss professors of surgery Rudolf Ulrich Kr?nlein (1847�C1910) [23, 24] in Zurich and Theodor Kocher (1841�C1917) [25, 26] in Bern developed independently a method to localize the underneath situated central sulcus and the Sylvian fissure on the scalp. Kr?nlein used for this a construction of two parallel horizontal and three vertical supporting lines which were based on external bony landmarks (Figure 2) [23]. These lines allowed defining and localizing the position and extension of the central sulcus on the scalp or on the sagittal X-ray image. These supporting lines and the lines representing the central sulcus and the Sylvian fissure in form of ribbons could be also pulled over the head. They marked on the scalp the position of these intracranial structures [24].

The device was called craniometer. In contrast to Kr?nlein, Kocher’s craniometer was based on cadaver studies and consisted of elastic ribbons Drug_discovery which were arranged and fixed on the head in a way that the ribbons were just beyond the central sulcus. The elasticity of this craniometer had the advantage that the ribbons preserved their relative position independently of the size of the head. Kocher already described this method in 1892 in his book Lessons in Operative Surgery [25, 26].