Aphasia, apraxia and the evolution of the language-ready brain

Abstract

Background: The Mirror System Hypothesis offers the mirror system for grasping (i.e., neural mechanisms active for both execution and observation of grasping) as a neural ''missing link'' between the brains of our non-human ancestors of 20 million years ago and the modern human language-ready brain, stressing the importance of manual gesture in the evolution of mechanisms supporting language. Aims: To assess the view that neural mechanisms for both praxis and language share an evolutionary relationship to the ancestral mirror system for grasping. Main Contribution: The praxis system receives a new analysis based on the attempt to link human praxis to computational models of execution and observation of grasping in the macaque as well as the analysis of parallels between language and praxis. Conclusions: The conceptual analysis presented here may prove insightful for clinicians seeking to relate and differentiate aphasia and apraxia.

Articulatory capacity of Neanderthals, a very recent and human-like fossil hominin

“…Lieberman [29] listed other fossil skulls that were morphologically similar to either the La Chapelleaux-Saints Neanderthal or to the MH configuration, indicating that in each case the phonetic potential was expected to match that of the relevant comparator. 1 As more direct supporting evidence for his reconstruction, and having previously proposed that the Neanderthal styloid process (as also in human newborns) is characteristically less vertically aligned than in adult humans reflecting the more superior position of the point of insertion of the Neanderthal stylohyoid muscle, in a subsequent paper, Lieberman [29] also proposed that if the mandibular facets at the origin of the anterior digastric, insertion of the posterior digastric, and origin of the geniohyoid muscles are angled to minimize sheer stress, then the human adult chin could be seen as an adaptation to the lowered position of the hyoid (since it enables these facets to be more inferiorly oriented); in Neanderthals as in human newborns, however, these facet orientations are consistent with a horizontal alignment of these muscles-again implying a more superiorly positioned hyoid. Lieberman, therefore, argued that selection on VT anatomy for stable and complex speech output had occurred among early MHs, but not among Neanderthals.…”

“…Numerous attempts have been made to reconstruct the evolutionary trajectory leading to human language. In one recent example, Arbib [1,2] has proposed a 'mirror system' model in which the language system evolves from complex imitation of manual praxis (involving the capacity for social learning of longer sequences of novel and hierarchically organized actions), via a manual protosign stage (involving pantomime gestures by the signaller, with conventionalized gestures to disambiguate the meaning of these pantomimes), to a protolanguage stage in which vocal gestures accompany and 'invade' the communicative domain of these manual gestures. The last stage (fully grammatical linguistic structure) may then have been reached by cumulative cultural evolution (and not by genetic adaptation: [3,4]).…”

A neuropsychological perspective on the link between language and praxis in modern humans

“…Independently from the potential involvement of a mirror neuron system, the relationship between praxis, gesture and language has to be further examined on the basis of recent neuropsychological data [39]. The lateralization to the left hemisphere seems to be the key phenomenon for evolution of both language and complex action systems in humans.…”

Towards a Computational Comparative Neuroprimatology: Framing the language-ready brain

“…My action-oriented view is that the signifieds are realized in the brain as schemas of a human acting in (or abstracted from) its world -and that the linkage between signifiers and signifieds is many-to-one, competitive and contextual, so that appropriate words to express a schema may vary from occasion to occasion, in part because of the context (assemblage) in which the schema instance is currently embedded. The resulting framework is shown in Figure 13 (Arbib, 2006 similarly lift words to more complex utterances via the use of constructions. We may see the models of Section 4.2 and 4.3 as two attempts to fill in many details missing in Figure 14; steps toward a synthesis and a brief discussion the challenges such a synthesis poses will then follow in Section 5.…”

“…Our next partial view comes from Arbib (2006Arbib ( , 2010) -the latter is titled "Mirror System Activity for Action and Language is Embedded in the…”