1. TARGET AUTHOR/ARTICLE
Arbib, M. A. From monkey-like action recognition to human language: An evolutionary framework for
neurolinguistics
2. WORD COUNT:
Abstract: 76
Commentary: 909
References: 271
Total: 1256
3. COMMENTARY TITLE: Mirror, Mirror, in the Brain: (Why, Are, If, Is, How, Could, What, etc. … )?
4.
AUTHOR INFORMATION:
Dr. Fred H. Previc
Northrop Grumman Information Technology
4241 Woodock Dr. Ste. B100
San Antonio TX 78228
210-487-2919
Abstract
Arbib has proposed that “mirror” neurons in the ventrolateral prefrontal cortex of monkeys (F5) may, because of their responsiveness to both perception and production of the same action, be critical to complex imitation skills and a homologue of Broca’s area in humans. While there are many commendable aspects to the mirror theory, it has not convincingly demonstrated that the cortical networks responsible for complex imitation are either necessary or even sufficient for the acquisition of language.
Commentary
The “mirror theory” (MT) is a welcome departure from many language-evolution theories in that it posits that the evolution of human language evolved from a more fundamental cognitive capability and was partly influenced by nongenetic/cultural influences. The MT rightly points to the need for complex imitation in the learning of language, although this is certainly a skill required of other advanced cognitive outputs. And, it further fuels the controversy over what exactly Broca’s area does in the brain—e.g., is it the site of speech, the site of sophisticated grammar (Grodzinsky, 2000), a cross-modal hierarchical motor programming center (Greenfield, 1991), a key part of a working memory network (Aboitiz & Garcia, 1997), or a center for complex imitation (the MT)? Despite all of this, the following represent some difficult questions that must be asked of the MT before it can be widely accepted by the neuroscientific community.
1. Why would an area like F5, supposedly devoted to integrating peripersonal visual inputs (Fogassi et al., 2001), be crucial for the establishment of a function (language) that is used primarily as a means of communicating over large distances or about distant space and time?
2. Why are the regions of posterior parietal cortex that form the major connections with F5 (e.g., AIP, area 7b) lumped in with area TPT in the monkey and stretched into becoming a homologue or extension of Wernicke’s area in humans, when 1) these areas are functionally dissimilar to Wernicke’s area (i.e., they have, in contrast to the latter, very few auditory inputs); 2) lesions to them do not produce aphasia; and 3) the homologous parietal areas in humans are apparently located even more dorsally than those in the monkey (Rapoport, 1990), precisely because of the expansion of the language functions in the temporal-parietal regions?
3. Are not the proposed connections between AIP and 7B, on the one hand, and the inferotemporal cortex, on the other, difficult to reconcile with the data of Cavada and Goldman-Rakic (1989), who showed in the monkey very little connectivity between 7B and IT along with little overlap in their prefrontal projections?
4. If complex, symbolic manual imitation was the primordial scaffolding for human language, supposedly dating back to Homo Erectus according to the MT, why does most evidence (see McBrearty & Brooks, 2001) point to the fact that all other advanced manual activities (e.g., tool-making, art, beads, etc.) that would presumably require use of icons and/or complex imitation were confined to the last 100K (or less) years of evolution, or long after anatomically modern human emerged?
5. Why do blind individuals learn language so well, since their culturally mediated linguistic competence could presumably not make use of protolinguistic manual imitation skills? Or, for that matter, why do dolphins show evidence of good communication capabilities, since they have vision but no hands?
6. Is Broca’s area really all that critical for speech, since 1) it isn’t lateralized at birth and 2) can be removed in infancy due to surgical hemispherectomy or by virtue of infantile hydrocephalus without any major linguistic (or even imitation) deficits (see Previc, 1999)?
7. How similar are left-hemispheric language activations in spoken and native signed language, which should be closely linked according to the MT? (Although there is fundamental overlap between the representations of speech in normals and signing in deaf individuals, both the laterality and the involvement of Wernicke’s area may be altered when native signers of good hearing are tested (MacSweeney et al., 2000), thereby suggesting that some putative similarities between normal speech and deaf signing may be due more to the re-organization of visual and tactile modalities into area 22 rather than to a primordial linguistic capability of this area.)
8. Could not the dual involvement of Broca’s area in signing and speech reflect its role in other higher-order cognitive factors—e.g., hierarchical programming of oral and manual outputs (Greenfield, 1991) or working memory (Aboitiz & Garcia, 1997)—or merely that it is homologous to a structure (F5) that processes both manual and inputs?
9. Since a striking aspect of all language is its lateralization to the left hemisphere in most humans, what is the mechanism whereby the development of complex visuo-manual imitation (as well as speech, on which it supposedly depends) presides in the left hemisphere? (While Arbib claims that language lateralization was beyond the scope of his paper, one could argue that the issue of laterality is of such paramount importance to all language theories that it must be considered early on in the development of such theories.)
The issue of what came first—manual or spoken language—has been a contentious topic among theorists of language evolution, but it is clear that humans are highly inventive when it comes to language, having generated languages comprised of speech sounds, manual signs, tactile signals, tones, visual icons, clicks, whistles, and probably other signals as well. Disabled humans can use the eyes for communication, and our species undoubtedly could have generated sophisticated pedi-languages if we were freed from using our feet for postural control and locomotion. I believe that something more fundamental occurred during human evolution—an intellectual leap that was neurochemically (dopaminergically) mediated, modality-nonspecific, not reliant on a particular brain size, shape, or developing brain area, and not necessarily even genetically mediated (Previc, 1999, 2002). The MT points to a possibly fundamental linguistic skill (complex imitation) but has not necessarily shown why the proposed neural circuitry for that skill is equally crucial to language.
References
Aboitiz, F.,
& Garcia, V. R. (1997). The evolutionary origin of the language areas
in the human brain. A neuroanatomical perspective. Brain Research Brain Research Reviews, 25, 381-296.
Cavada, C., & Goldman-Rakic, P. S. (1989). Posterior parietal cortex in rhesus monkey: II. Evidence for segregated corticocortical networks linking sensory and limbic areas with the frontal lobe. Journal of Comparative Neurology, 287, 422-445.
Fogassi, L.,
Gallese, V., Buccino, G., Craighero, L., Fadiga, L., & Rizzolatti, G. (2001). Cortical mechanism for the visual
guidance of hand grasping movements in the monkey: A reversible inactivation
study. Brain, 124, 571-586.
Greenfield, P. M. (1991). Language, tools and brain: The ontogeny and phylogeny of hierarchically organized sequential behavior. Behavioral and Brain Sciences, 14, 531-595.
Grodzinsky, Y. (2000). The neurology of syntax: language use without Broca's area. Behavioral and Brain Science, 23, 1-21.
McBrearty, S., & Brooks, A. S. (2000). The revolution that wasn’t: A new interpretation of the origin of modern human behavior. Journal of Human Evolution, 39, 453-563.
MacSweeney,
M., Woll, B., Campbell, R., McGuire, P. K., David, A. S., Williams, S. C.,
Suckling, J., Calvert, G. A., & Brammer, M. J. (2002). Neural systems underlying British Sign
Language and audio-visual English processing in native users. Brain, 125,
1583-1593.
Previc, F. H. (1999). Dopamine and the origins of human intelligence. Brain and Cognition, 41, 299-350.
Previc, F. H. (2002). Thyroid hormone production in chimpanzees and humans: Implications for the origins of human intelligence. American Journal of Physical Anthropology, 118, 402-403.
Rapoport. S. I. (1990). Integrated phylogeny of the primate brain, with special reference to humans and their diseases. Brain Research Brain Research Reviews, 15, 267-294.