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DOI: 10.1055/s-0031-1285902
Changes in Excitability of the Human Motor Cortex Face Area by Observing Speech
Veränderungen in der Erregbarkeit des menschlichen Motorkortex Gesichtsareals während SprachbeobachtungPublication History
Publication Date:
05 December 2011 (online)
Introduction
Language is the most important communicative tool with substantial evolution in the process of human phylogenetic development. Language processing in humans occurs in a distributed network of brain areas including the superior temporal gyrus which functionally links with the posteroinferofrontal area (including Broca’s area) and the dorsolateral premotor area. This network forms a sensory-motor transformation pathway to map speech perception onto speech production processes [1] [2], which has strong overlap with the putative mirror neuron system (MNS). The MNS is considered to play an important role in unifying action perception and motor execution. The theory of perception-execution matching predicts that observation of motor action should lead to an increase of excitability in the primary motor cortex (M1) representations involved in the observed action. Indeed, motor evoked potential (MEP) amplitude in hand muscles increases during observation of hand and arm movements [3] [4], and MEP amplitude of facial muscles involved in speech production increases when observing speech-related lip movements [5] [6], or even when listening to speech [6] [7]. Furthermore, recent studies also provided evidence for a role of inhibitory mechanisms to prevent overt motor activation during action observation [8] [9].
In this study, we investigated mechanisms of the putative human MNS related to speech perception using focal transcranial magnetic stimulation (TMS) focusing on effector and task specificity and correlation with task difficulty. Effector and task specific inhibitory control mechanisms were also investigated.