Extending the Mirror System Hypothesis: Homologies, Comparative
Neurobiology and Brain Imaging

Michael A. Arbib 

University of Southern California, Los Angeles, CA 90089-2520, USA

arbib@pollux.usc.edu 

Arbib and Bota (2003) used two hypotheses on the evolution of brain
mechanisms of language, that of Aboitiz & García (1997) and the Mirror
System Hypothesis of Rizzolatti & Arbib (1998), to ground the search for
homologies between different cortical areas in macaque and human.  The
data they used were focused primarily on information concerning the
anatomy of brain regions and the connections between them.  The present
paper builds on this work by updating the analysis of homologies to more
fully relate functional analysis of the monkey brain (neurophysiology of
the behaving animal) to functional analysis of the human brain (starting
with behaviors shared with monkeys and progressing to studies of
imitation and language). 

Aboitiz and García assume that the human brain evolved (in part) to
support language.  They offer an essentially retrospective theory.  They
look at features of the human brain, seek homologous areas of the
macaque brain, note what has changed (some areas enlarge, some
connections are strengthened) and then suggest how these changes could
support a lexicon of spoken words and a syntax to bind them into
sentences. 

By contrast, Rizzolatti and Arbib offer more of a prospective theory. 
They start from an analysis of the monkey’s capabilities, especially the
fact that species-specific vocalizations have their cortical outpost in
the anterior cingulate but that a different area, involved in hand
movements, is homologous to Broca’s area.  The Arbib (2002) version
assumes that the human brain evolved (in part) to support protosign and
protospeech, with the richness of human languages being a
“post-biological accumulation of inventions”, and offers hypotheses on
how intermediate stages from the mirror system for grasping led via
imitation and protosign to protospeech.  However, Rizzolatti and Arbib
are relatively silent on the phonological loop and other working memory
systems whose emphasis is an important feature of the Aboitiz and
García. 

On this basis, we will present a new conceptual model of neurolinguistic
processing, incorporating lessons from the work of Aboitiz and García
(and other authors) to address a number of shortcomings of the original
Mirror System Hypothesis. 

Note to reviewers: This talk will not be "yet another" exposition of the
Mirror System Hypothesis but will rather review key data to ground the
most comprehensive model that has been developed within this tradition
to date, taking us "Beyond the Mirror". 

References:

Aboitiz, F., and García V., R., 1997, The evolutionary origin of the
language areas in the human brain.  A neuroanatomical perspective Brain
Research Reviews 25: 381-396

Arbib, M.A., 2002, The Mirror System, Imitation, and the Evolution of
Language, in Imitation in Animals and Artifacts, (Chrystopher Nehaniv
and Kerstin Dautenhahn, Editors), The MIT Press, pp.  229 - 280. 

Arbib, M.A., and Bota, M., 2003, Language Evolution: Neural Homologies
and Neuroinformatics, Neural Networks (in press). 

Rizzolatti, G, and Arbib, M.A., 1998, Language Within Our Grasp, Trends
in Neurosciences, 21(5):188-194.