Introduction

Cortical mapping during surgical craniotomy in awake and cooperative patients was introduced almost a century ago, at the beginning of the twentieth century, but was rarely used until relatively recently, when the development of MRI-guided neuronavigational and MRI-based functional and anatomical mapping techniques made the accuracy of the functional localization afforded by cortical mapping more relevant. Modern neuroimaging provides morphological, metabolic, and functional measurements that may guide and refine surgical treatment. Functional MRI (fMRI) and MR tractography can establish the relationship between the margin of the lesion and the surrounding functionally viable brain tissue. Therefore, increasingly, accurate estimates of procedural risks and prognosis are potentially available to the neurosurgeon before surgery.

Mapping brain function

Historical review

The observation that a focal brain lesion may cause a behavioral or motor deficit was alluded to in an Egyptian papyrus that has been dated to roughly 2500 BC It is possible that Imhotep, a military surgeon at the time of the pyramids, was the author of this detailed clinical report on 27 cases with head injury.[1] It was at the time of the Alexandria Medical School in the third century BC that Erofilo from Calcedonia (Turkey), an early anatomist, suggested that the brain harbors motor, sensory, and cognitive functions. However, at the time of the Roman Empire, Claudio Galen (129–201 AD) thought that the three main mental functions (motor, sensory, and thought/memory) were localized in the cerebral ventricles, not in the brain tissue. Abu Ali Ibn Abdallah Ibn Sina (980–1037), also known as Avicenna, spread Galen’s theories throughout the Arab world. Avicenna also believed that the three main functions were localized in the ventricles. The movement of fluid from one ventricle to the next was hypothesized to mediate the transfer from one function to another: imagination was localized in the lateral ventricles, rational thinking in the third ventricle, and memory in the fourth ventricle. It was Costanzo Varolio (1543–1575) who advanced the notion that the brain parenchyma itself subserves higher cognitive functions. Thomas Willis (1621–1675), the English anatomist and surgeon, localized memory to the cortical gray matter, imagination in the white matter, perception and movement in the striatum, and involuntary actions to the cerebellum and brainstem.