**7. All together**

Recent developments in brain imaging techniques include brain *tractography* with MRI, which has been promptly used to study human language. Brain tactography can be achieved through *diffusion tensor* and *diffusion spectrum* techniques. The main difference between the two of them depends on the deterministic vs. probabilistic approaches used to analyze the movement of water molecules within the main tracts substantiating cortico-cortical connections (de Schotten et al., 2011). It must be noted here, however, that the novelty and the relative scarcity of studies approaching language with this technique may explain certain inconsistencies between studies (for an extensive review, see Friederici, 2009).

Although it is well known after Karl Wernicke, the relevance for human language of the *arquate fasciculus* (AF) connecting Broca's and Wernicke's areas appears largely strengthened by tractographic techniques. The data also stress the relevance for language processing of other fascicles connecting anterior and posterior brain areas. A detailed description of all these connections is also emerging.

One of the first studies applying tractography to approach language was developed by Catani et al. (2005). These authors reported a direct strong connection between Broca's and Wernicke's areas through the FA, but given the fact that the areas actually connected covered a wider territory than the classical Broca's and Wernicke's areas (though, as shown earlier, the precise limits for these two areas may vary depending on the author), Catani and colleagues suggested to call them Broca's and Wernicke's *territories*, respectively. Their results also revealed the existence of two additional but indirect pathways connecting Broca's and Wernicke's territories. One would run laterally, consisting of an anterior segment connecting Broca's territory and the inferior parietal cortex. The other would be a posterior segment connecting the inferior parietal cortex with Wernicke's territory. Given the apparent relevance of these two indirect segments, and the fact that the inferior parietal cortex appears the main meeting point for these indirect connections, Catani et al. (2005) suggested to call this region the *Geschwind's territory*, in the memory of Norman Geschwind, who already proposed a relevant role of the inferior parietal cortex in language. This region largely overlaps with semantic areas involved in word and discourse processing, as we have seen.

The AF seems to have evolved substantially in the human brain from tiny tracts connecting the IFG with the posterior part of BA 22 and the inferior parietal regions, already present in the macaque brain. These connections appear more robust and abundant in the chimpanzee, thereafter reaching the plainest robustness of the human brain (Rilling et al., 2008). Actually, one of the main differences between the human and the chimpanzee brains in this regard is the notable expansion of the posterior ramifications of the AF, which spread not only to involve Wernicke's area and surrounding parietal regions, but also posterior portions of the MTG. The development of these connections, occurring particularly and noticeably within the left hemisphere, seem to have played a critical role in the evolution of human language.

Interestingly, two other tracts connecting anterior and posterior regions seem relevant in language processing. One is the superior longitudinal fasciculus (SLF), connecting Broca's area (particularly, BA 44) with the posterior temporal lobe, namely in the STG and the MTG and also involving portions of BA 40. As this tract runs parallel to the AF, several authors (e.g., Rilling et al., 2008) consider both as representing together a functional unit called the *dorsal stream*. The other connection is more primitive; part of it is actually the most developed fronto-temporal connection in the macaque brain and conveys the ventral portion of the extreme capsule and the uncinate fasciculus. Through these connections, the IFG is connected with the anterior and posterior STG (Frey et al., 2008; Rilling et al., 2008), and it is indeed possible that at least part of this *ventral stream* is preferentially used in simpler grammar such as finite-state, relatively accessible to other non-human primates (Friederici et al., 2006).

Finally, there are evidences for an additional number of connections importantly involved in language, most of them located locally within the IFG and the STG (Friederici, 2009).
