The experiment reported here adopted a design that required subjects to process identical visual stimuli while performing different tasks: an action perception task, and two ‘linguistic’ tasks, a phonological task and a conceptual task. With this experimental design, it is possible to test whether the overt linguistic processing of observed object-oriented action recruits cortical areas not engaged by action perception, and/or activates fronto-parietal action perception areas to a higher degree. Both results would support the hypothesis of some independence of linguistic processing of visual stimuli with respect to fronto-parietal areas concerned with action perception. However, we did not find any area specifically activated during the two linguistic tasks, and we did not find any area with higher activity during the linguistic tasks. We argue that these results are more readily compatible with the hypothesis that language –as far as linguistic processing of visual stimuli is concerned, at the very least – evolved by co-opting fronto-parietal systems concerned with action perception, a process known as exaptation.
Although previous studies have reported shared activation for action (or action observation) and language 
- activations typically interpreted in support of the embodied semantics framework 
- those previous studies could not comment on differential activations between action and language, since their stimuli widely differed between action and language tasks. Thus, the main novel finding of our study is that linguistic processing of visual stimuli related to actions occurs within a subset of fronto-parietal areas concerned with action perception.
It could be argued that action perception entails automatic linguistic processing, and that the left inferior frontal areas not differentially activated during action perception and the linguistic tasks are indeed exclusively linguistic in nature. While this argument is logically correct, it is unlikely to be true. Indeed, our data show that the inferior frontal cortex also has higher activity during action perception (Vd-Perc) compared to object perception (Pict-Perc), two tasks ostensibly very similar with regard to possible automatic linguistic processing, but dissimilar with regard to action perception itself. Thus, the deflationary explanation that invokes automatic linguistic processing in left inferior frontal cortex in all tasks does not easily account for all experimental results presented here. Furthermore, a virtual lesion study using repetitive TMS has shown that a transient disruption of neural activity in the left (and right) inferior frontal cortex results in imitation deficits, but not in more general visuo-motor deficits 
. This result can hardly be reconciled with a purely linguistic property of left inferior frontal cortex.
It could also be argued that the increased signal in fronto-parietal areas is only due to the increased attentional demands of the action perception task, given the increased RT for this task. It should be noted, however, that the increase in reaction time for this task was very small in relation to the overall duration of each task block during scanning. Therefore, we consider it unlikely that the difference in reaction time across tasks was of substantial influence on the fMRI activations. Moreover, the “attention” argument cannot account for the lack of increased signal in the left inferior frontal cortex during action perception, compared to the linguistic tasks. The selectivity of the effect argues against a non specific attention effect.
Our design also allowed us to compare activity during action perception and during perception of static pictures that comprised all the visual elements of the action stimuli. Thus, this comparison reveals brain activity that is quite specific to action observation, rather than to the complex visual elements that invariably go together with observed actions. This comparison in our experiment shows robust bilateral activation in fronto-parietal areas, revealing that this large network is indeed specifically concerned with action perception. Thus, the result of our specific contrast support the ‘mirror neuron’ interpretation of the vast number of previously published papers showing similar fronto-parietal activations in a variety of experimental conditions 
Fronto-parietal areas concerned with action perception are bilateral, whereas our linguistic tasks recruited exclusively left hemisphere areas. This shift from bilateral activity for action perception to a predominantly left lateralized language system may have been favored by a lateralization, in humans, of ‘mirroring’ responses to action sounds, as shown by single pulse TMS 
and fMRI 
To conclude, when visual stimuli concerning object-oriented actions are processed perceptually, they activate a large bilateral fronto-parietal network. When the same stimuli are processed linguistically, they activate only a subset of this network and no additional areas. This pattern of activity supports the evolutionary hypothesis that neural mechanisms for language in humans co-opted phylogenetically older fronto-parietal neurons concerned with action perception, such as mirror neurons in macaques.