Brain Advance Access originally published online on May 14, 2009
Brain 2009 132(7):1980-1988; doi:10.1093/brain/awp118
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Encoding of human action in Broca's area
1 DSBTA, Section of Human Physiology, University of Ferrara, Ferrara, Italy 2 Department of Neuroscience Rehabilitation, Hospital and University of Ferrara, Ferrara, Italy 3 Institute of Cognitive Science, CNRS, Lyon, France 4 INSERM-ERM 207 Motricité Plasticité, Université de Bourgogne, Dijon, France 5 Italian Institute of Technology (IIT), Genova, Italy
Correspondence to: Prof. Luciano Fadiga, DSBTA, Section of Human Physiology, University of Ferrara, Via Fossato di Mortara 17/19, 44100 Ferrara, Italy E-mail: luciano.fadiga{at}unife.it
Broca's area has been considered, for over a century, as the brain centre responsible for speech production. Modern neuroimaging and neuropsychological evidence have suggested a wider functional role is played by this area. In addition to the evidence that it is involved in syntactical analysis, mathematical calculation and music processing, it has recently been shown that Broca's area may play some role in language comprehension and, more generally, in understanding actions of other individuals. As shown by functional magnetic resonance imaging, Broca's area is one of the cortical areas activated by hand/mouth action observation and it has been proposed that it may form a crucial node of a human mirror-neuron system. If, on the one hand, neuroimaging studies use a correlational approach which cannot offer a final proof for such claims, available neuropsychological data fail to offer a conclusive demonstration for two main reasons: (i) they use tasks taxing both language and action systems; and (ii) they rarely consider the possibility that Broca's aphasics may also be affected by some form of apraxia. We administered a novel action comprehension test—with almost no linguistic requirements—on selected frontal aphasic patients lacking apraxic symptoms. Patients, as well as matched controls, were shown short movies of human actions or of physical events. Their task consisted of ordering, in a temporal sequence, four pictures taken from each movie and randomly presented on the computer screen. Patient's performance showed a specific dissociation in their ability to re-order pictures of human actions (impaired) with respect to physical events (spared). Our study provides a demonstration that frontal aphasics, not affected by apraxia, are specifically impaired in their capability to correctly encode observed human actions.
Key Words: Broca's area; action recognition; mirror-neuron system; frontal aphasia; motor syntax
Abbreviations: IFG, inferior frontal gyrus; LST, Language sequencing task; MRI, magnetic resonance imaging; RT, reaction time; TT, trial time
Received November 12, 2008. Revised January 29, 2009. Accepted March 30, 2009.