Jonas T. Kaplan

There is evidence that the right hemisphere is involved in processing self-related stimuli. Previous brain imaging research has found a network of right-lateralized brain regions that preferentially respond to seeing one's own face rather than a familiar other. Given that the self is an abstract multimodal concept, we tested whether these brain regions would also discriminate the sound of one's own voice compared to a friend's voice. Participants were shown photographs of their own face and friend's face, and also listened to recordings of their own voice and a friend's voice during fMRI scanning. Consistent with previous studies, seeing one's own face activated regions in the inferior frontal gyrus (IFG), inferior parietal lobe and inferior occipital cortex in the right hemisphere. In addition, listening to one's voice also showed increased activity in the right IFG. These data suggest that the right IFG is concerned with processing self-related stimuli across multiple sensory modalities and that it may contribute to an abstract self-representation.

We used functional magnetic resonance imaging (fMRI) to investigate the neural systems responding to the sight and to the sound of an action. Subjects saw a video of paper tearing in silence (V), heard the sound of paper tearing (A), and saw and heard the action simultaneously (A + V). Compared to a non-action control stimulus, we found that hearing action sounds (A) activated the anterior inferior frontal gyrus and middle frontal gyrus in addition to primary auditory cortex. The anterior inferior frontal gyrus, which is known to be activated by environmental sounds, also seems to be involved in recognizing actions by sound. Consistent with previous research, seeing an action video (V) compared with seeing a non-action video activated the premotor cortex, intraparietal cortex, and the pars opercularis of the inferior frontal gyrus. An A + V facilitation effect was found in the ventral premotor cortex on the border of areas 44, 6, 3a, and 3b for the action stimuli but not for the control stimuli. This region may be involved in integrating multimodal information about actions. These data provide evidence that the ventral premotor cortex may provide an action representation that abstracts across both agency (self and other) and sensory modality (hearing and seeing). This function may be an important precursor of language functions.

We have previously shown that a right inferior frontal mirror neuron area for grasping responds differently to observed grasping actions embedded in contexts that suggest different intentions, such as drinking and cleaning (Iacoboni, Molnar-Szakacs, Gallese, Buccino, Mazziotta, & Rizzolatti, 2005 Iacoboni, M. , Molnar-Szakacs, I. , Gallese, V. , Buccino, G. , Mazziotta, J. C. and Rizzolatti, G. 2005. Grasping the intentions of others with one's own mirror neuron system. PLoS Biology, 3(3): e79 [Crossref], [PubMed], [Web of Science ®] [Google Scholar] ). Information about intentions, however, may be conveyed also by the grasping action itself: for instance, people typically drink by grasping the handle of a cup with a precision grip. In this fMRI experiment, subjects watched precision grips and whole-hand prehensions embedded in a drinking or an eating context. Indeed, in the right inferior frontal mirror neuron area there was higher activity for observed precision grips in the drinking context. Signal changes in the right inferior frontal mirror neuron area were also significantly correlated with scores on Empathic Concern subscale of the Interpersonal Reactivity Index, a measure of emotional empathy. These data suggest that human mirror neuron areas use both contextual and grasping type information to predict the intentions of others. They also suggest that mirror neuron activity is strongly linked to social competence.

We believe that an account of the role of mirror neurons in language evolution should involve a greater emphasis on the auditory properties of these neurons. Mirror neurons in premotor cortex which respond to the visual and auditory consequences of actions allow for a modality-independent and agent-independent coding of actions, which may have been important for the emergence of language.