In aphasia literature, it has been considered that a speech repetition defect represents the main constituent of conduction aphasia. Conduction aphasia has frequently been interpreted as a language impairment due to lesions of the arcuate fasciculus (AF) that disconnect receptive language areas from expressive ones. Modern neuroradiological studies suggest that the AF connects posterior receptive areas with premotor/motor areas, and not with Broca's area. Some clinical and neurophysiological findings challenge the role of the AF in language transferring. Unusual cases of inter-hemispheric dissociation of language lateralization (e.g. Broca's area in the left, and Wernicke's area in the right hemisphere) have been reported without evident repetition defects; electrocortical studies have found that the AF not only transmits information from temporal to frontal areas, but also in the opposite direction; transferring of speech information from the temporal to the frontal lobe utilizes two different streams and conduction aphasia can be found in cases of cortical damage without subcortical extension. Taken altogether, these findings may suggest that the AF is not required for repetition although could have a subsidiary role in it. A new language network model is proposed, emphasizing that the AF connects posterior brain areas with Broca's area via a relay station in the premotor/motor areas.

The interest in understanding how language is "localized" in the brain has existed for centuries. Departing from seven meta-analytic studies of functional magnetic resonance imaging activity during the performance of different language activities, it is proposed here that there are two different language networks in the brain: first, a language reception/understanding system, including a "core Wernicke's area" involved in word recognition (BA21, BA22, BA41, and BA42), and a fringe or peripheral area ("extended Wernicke's area:" BA20, BA37, BA38, BA39, and BA40) involved in language associations (associating words with other information); second, a language production system ("Broca's complex:" BA44, BA45, and also BA46, BA47, partially BA6-mainly its mesial supplementary motor area-and extending toward the basal ganglia and the thalamus). This paper additionally proposes that the insula (BA13) plays a certain coordinating role in interconnecting these two brain language systems.

We are proposing that, in the future, tests included in psychological and neuropsychological batteries should fulfil the following criteria. (1) Have a large enough normative database (“normative criterion”). Performance of subjects of different ages and different educational levels, including illiterates, should be well established. Normative data from different countries and cultural contexts should be available. (2) Know the effects of brain damage on different characteristics on the test (“clinical criterion”). (3) Know how the brain is activated when the test is performed (“experimental criterion”). (4) Know how this test correlates with other cognitive tests (“psychometric criterion”). Few contemporary tests fulfil all these criteria. A notable exception is Semantic Verbal Fluency test using the category ANIMALS. This test requires the generation of words corresponding to a specific semantic category, such as animals, fruits, vegetables, etc. Typically, the number of correct words produced in 1 minute is counted. Semantic verbal fluency taps lexical knowledge and semantic memory organization. Using regional cerebral blood flow measures, it has been reported that both frontal and temporal activation are observed while performing this test. Optimal fluency performance involves generating words within a subcategory and, when a subcategory is exhausted, switching to a new subcategory. Although different semantic categories have been used in this test, ANIMALS is the most frequent due to some significant advantages: (1) it is a clear enough semantic category across languages and cultures; (2) it is a relatively easy semantic category with only minor differences among people living in different countries, different educational systems, or belonging to different generations; and (3) it is an easy‐to‐administer, short, and common test included in different neuropsychological test batteries. It is concluded that obtaining similar information for other cognitive tests represents a huge research endeavour for psychology and neuropsychology during the 21st century.

The field of the neurobiology of language is experiencing a paradigm shift in which the predominant Broca-Wernicke-Geschwind language model is being revised in favor of models that acknowledge that language is processed within a distributed cortical and subcortical system. While it is important to identify the brain regions that are part of this system, it is equally important to establish the anatomical connectivity supporting their functional interactions. The most promising framework moving forward is one in which language is processed via two interacting "streams"--a dorsal and ventral stream--anchored by long association fiber pathways, namely the superior longitudinal fasciculus/arcuate fasciculus, uncinate fasciculus, inferior longitudinal fasciculus, inferior fronto-occipital fasciculus, and two less well-established pathways, the middle longitudinal fasciculus and extreme capsule. In this article, we review the most up-to-date literature on the anatomical connectivity and function of these pathways. We also review and emphasize the importance of the often overlooked cortico-subcortical connectivity for speech via the "motor stream" and associated fiber systems, including a recently identified cortical association tract, the frontal aslant tract. These pathways anchor the distributed cortical and subcortical systems that implement speech and language in the human brain.

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