dromes, cognitive systems are partially dissociable by learning effects. The coordination view is compatible with those contra- dictory findings, since it does not assume a necessary and sufficient motor involvement in language but a dynamic coordination in interaction with diverse brain regions and cognitive systems. Limitations The necessity of the contribution of the motor process for sentence comprehension remains to be established. Evidence for the effects of the motor system on comprehension is supported by present research but is not a sufficient argument for the radical embodiment of language. Rather, these results only provide evidence of multiple brain areas that are systematically involved in understanding, suggesting a blending of motor-semantic interac- tions. Studies of causal implication of the motor system in ACE are required as well as more specific semantic effects in the motor system. Future work would assess ACE in semantic and motor pathologies in order to highlight more precise and detailed effects of motor-language network impairments. For example, it could be expected that patients with Early Parkinson’s Disease (ePD, a disease that mainly affects subcortical motor structures) and also patients with early Amyotrophic Lateral Sclerosis (eALS, a disease affecting both upper and lower motor neurons in the motor cortex of the brain) would present remarkable deficits in action-sentence compatibility tasks. Moreover, direct comparisons between both pathologies would allow the exploration of the relevance of different areas in action-language comprehension. It can be expected that deficits in eALS probably would be larger than those in ePD, suggesting in that case that cortical areas are more relevant than motor subcortical areas for motor-language interaction. The complete balance between categories regarding prototypi- cality was problematic in the current design. During the sentence construction process, we found that many verbs with CH carried hand-shape specificity more inherently in their semantics without the contextual restriction (e.g., the verb to wield or to hammer does not require the direct object to comprehend the CH of the action). In contrast, we found that many actions that required OH implied verbs with intrinsic semantic that promoted less accentuation of the specific hand-shape. Thus, contextual restriction must be higher to denote OH than to denote CH: by itself, a verb such as to show does not necessarily imply OH. One can show an object in the house (sentence with no specific hand-shape involved) and show the gypsy your hand so she can read it (sentence with OH involved). In both groups and within the two categories, the ACE was found and therefore, language-induced motor effects were likely modulated by the whole sentence (when information was integrated). However, weather the compatibility effect was incremented by the lexical level of the critical verbs or from the complete sentence event remains unclear. Future work will investigate differences between action-sentence context and verb-inherent semantics regarding the modulation of language-induced motor effects. Another restriction of this study is that it does not directly show that motor activation is evoked during ‘‘normal’’ language comprehension without an action needing to be performed. Responses were required to obtain motor ERPs in our design. Nevertheless, further designs without explicit responses could compare the current results of peripheral activity in hand muscle activation (motor) and an N400-like component (semantic). Another possible caveat is that in the present design, we were not able to determine the early stage of MRP known as Bereitschaftspotential. Nevertheless, the inter-individual variability for this component is extreme to the point that it may be absent in Neural Signatures of ACE a number of participants [100,130,131]. Also, because our paradigm did not have the 2 s inter-stimuli windows needed for the early Bereitschaftspotential [100], it was not possible to observe this component. Finally, to elicit this component in the classic form, participants are required to move irregularly, not repetitively and not too fast [100], features absent in this design. Future experiments can be designed for the study of Bereitschaft- spotential that can address the possible ACE modulation of this component. Conclusion Within the motor-language debate, our study is the first to report brain markers of bidirectional impact between language comprehension and motor process. We account for a genuine and online interaction by combining ACE and ERP regarding the motor-to-semantics direction in addition to the previously studied semantics-to-motor direction. Since previous studies have investigated only general aspects of motor action such as the effectors or direction of motion [10], we report neural markers of the motor-language relation at a subtle aspect of the action (hand-shape). Our results showed the robustness of ACE in low imagery processes. Motor aspects were not relevant to the task, therefore the compatibility effect appeared to be automatic and independent from cognitive control (e.g., attention). An N400-like effect was found, indicating that the incongruence of the motor process interferes with sentence comprehension in a semantic fashion. Larger amplitudes of MP and RAP in the compatible condition suggest that semantic priming facilitates motor performance. Thus, our results evidenced, by comparing sentence processing and motor response ERPs, the interplay between action-sentence processing and motor processes (see related studies, reviewed in [132]). Together, three of the explored ERPs suggest that sentence and motor information are integrated in a bidirectional way. Supporting Information Stimuli S1 Sentences lists. Found at: doi:10.1371/journal.pone.0011751.s001 (0.06 DOC) Methods S1 Stimuli validation. Found at: doi:10.1371/journal.pone.0011751.s002 (0.03 DOC) Methods S2 Selection of electrode position. Found at: doi:10.1371/journal.pone.0011751.s003 (0.02 DOC) MB MB MB Table S1 N400-Like stimulus content 6 group interaction. Rel- evant comparisons are in bold. A significant effect of stimulus content was observed (F(2, 48) = 17.8; p,0.001). Post hoc anal- ysis (MS = 1.207; df = 48) evidenced that NS were less nega- tive (M = 0.014 mV, SD = 0.44) compared with OHS (M = 21.69 mV, SD = 0.61; p,0.001) and CHS (M = 21.38 mV, SD = 0.66; p,0.001). No difference between OHS and CHS was found (p = 0.58). However, an interaction effect between stimulus content 6 group was found (F(2, 48) = 48.31, p,0.001). Post hoc comparisons (MS = 1.21; df = 71.99) showed that the compatible stimuli in each group (OHS in the OHG and CHS in the CHG) were statistically different in terms of N400-like amplitudes. In brief, this last effect mirrored the category 6 group effect reported in the Results section. Found at: doi:10.1371/journal.pone.0011751.s004 (0.03 MB DOC) PLoS ONE | www.plosone.org 11 July 2010 | Volume 5 | Issue 7 | e11751