Ludwig Lichtheim (1845−1928) and his representation of the language network from his 1885 Brain paper.

Johann Christian Reil (1759−1813) and his description of the arcuate fibres from his 1812 Archiv für die Physiologie paper.

Distribution of the pattern of lateralization of the long segment in the normal population and between genders (mod. from Catani et al., 2007).

Topological and hodological approaches in clinico-anatomical correlation studies. In the upper row an example of a lesion overlap study for clinico-anatomical correlation is represented where four patients present with similar neurological deficits and their respective brain images are overlapped in order to identify a common anatomical substrate. Here we want to highlight that the conclusion that one may draw from this type of studies depends on the hypothesis that is tested and the general framework adopted. (A) A strict topological approach considers brain functions as localized in specific cortical regions. Within this framework the critical area for the same neurological deficit manifested by a group of stroke patients (four in the example, where each area, from 1 to 4, represents the extension of the lesion for each patient) is located at the cortical region of maximum lesion overlap (region b in the example). (B) The hodological (network) approach to brain–behaviour correlation includes a consideration of brain pathways that pass through the damaged area. Within this framework, the neurological deficit could also be attributed to a disconnection between a and c because all lesions affect the same a to c pathway at different levels (red circle). Note that A and B represent the same experiment (i.e. same patients and image analysis), however the conclusions are opposite due to the different approach. (C) Image of the brain of Broca's aphasic patient showing a lesion to the inferior frontal cortex. Broca, who worked within a topological framework, considered that his patient's speech deficit was the consequence of the cortical lesion in the inferior frontal lobe. (D) Sagittal MRI image (mod. from Dronkers et al., 2007) of the same brain shown in (C). Clearly the lesion extends into the white matter of the arcuate (red arrows) of the left hemisphere. If Broca had worked within a hodological framework and performed dissections of his patient's brain it is probable that he would have attributed the speech deficit to a lesion of the arcuate fasciculus.

Carl Wernicke (1848−1905) and his representation of the language network from his 1874 MD thesis.

Norman Geschwind (1926−1984) and his representation of the language network from his 1970 Science paper.

Tractography reconstruction of the arcuate fasciculus. Numbers indicate the cortical projections of the segments: 1, superior temporal lobe; 2, middle temporal lobe; 3, inferior frontal and precentral gyrus; 4, middle frontal and precentral gyrus; 5, supramarginal gyrus; 6, angular gyrus (mod. from Catani et al., 2005).

Tractography reconstruction of the ventral pathways of the left hemisphere.

Tractography reconstruction of the white matter pathways involved in the most frequent neurodegenerative disorders, some of which affect language function.