A language-related coactivation of hand motor cortex on the left hemisphere

Introduction: Manual gestures are believed to denote an early step during the evolution of language preceding vocalisation. According to this theory development of the so-called mirror neuron system which is active in the brain during observation and execution of an action was a necessary prerequisite of the emergence of human communication. If so, cortical systems for dominant hand use and language may be closely connected.Using functional magnetíc resonance imaging, the present study tested whether there are functional interaction between the cortical systems for planning and execution of hand movements and linguistic processing.

Methods: Fourteen right-handed subjects were examined during performance of articulation, overt reading, fingertapping of right or left hand and the combination of artication or reading with fingertapping. The hypothesis was that language processing modulates the excitability of the dorsal premotor cortex of the dominant hemisphere whereas articulation without language does not.

Results: We found a language-specific enhancement of activity of a distinct region of the left dorsal premotor cortex which is part of the mirror neuron system and mediates planning of right hand movements. Fingertapping of dominant or nondominant hand both facilitated activity in this region and left primary hand motor cortex.

Conclusion: We demonstrated a functional coactivation of dorsal premotor cortex of the dominant hemisphere during linguistic processing. The close interaction between cortical representation of hand movements and language may be of interest for aphasia rehabilitation. This results support the hypothesis on the common evolutionary development of language and right-handedness through gesture.