Introducing the special topic “The when and why of sensorimotor processes in conceptual knowledge and abstract concepts”

A fundamental question of cognitive neuroscience concerns therole of sensory and motor information in representing the con-ceptual knowledge in the brain. Indeed, the extent to whichconceptual representations are held to be grounded in sen-sory and motor systems has yielded different hypotheses as tohow conceptual knowledge is organized. On the one hand, theembodied hypothesis promotes the idea that conceptual repre-sentations are modality-dependent and built from sensory andmotor experiences, that is by re-enacting sensorimotor memo-ries acquired through experience (Barsalou, 1999; Pulvermulleret al., 1999; Barsalou et al., 2003; Gallese and Lakoff, 2005). Thus, recognizing objects, actions and words is accomplished byre-enacting sensorimotor memories that have been previouslyacquired (this is also called motor simulation). On the oppositeextreme, the disembodied hypothesis holds that conceptual rep-resentations are abstract (symbolic) and modality-independent(amodal),separatedfromsensorimotorinformation,e.g.,(Fodor,1983; Caramazzaet al., 1990; Tyler and Moss, 2001). To reconcilethese two extreme views, the grounding by interaction hypoth-esis proposes that what we know about words, for instance, ismeant to beneﬁt from the contribution of both abstract contentand sensory and motor systems (Mahon and Caramazza, 2008;Bedny and Caramazza,2011). From the beginning, neuropsychological and neuroimagingstudies contributed to this debate with the necessary evidence toconstrainhypothesesabouttheroleofsensoryandmotorsystemsin understanding objects, actions and words. The three theoreti-cal accounts reviewed above generate different predictions as tothe involvement of such systems in these cognitive operations.For the embodied hypothesis, the involvement of sensorimotorsystems appears to be a fundamental, however, how the brainimplements abstractconcepts andsymbolic operationsisstill noteasily explained within the embodied account. According to thedisembodied hypothesis the involvement of mental simulation isancillary, whereas the grounding by interaction hypothesis spec-iﬁes its dependency upon the contextual factors. Even thoughboth the disembodied hypothesis and grounding by interactionhypothesis agree on concepts being stored in an abstract way,a direct demonstration that this is actually the case is seldomdocumented. A related aspect that still requires more theoreticaland empirical effort concerns the role of implicit motor imageryin understanding words. In fact, despite the growing evidence,results are contradictory: motor activity has been observed notonly for action-related verbs but also for imaginable concretewords that are not grounded in sensorimotor experience.In order to promote the development of the neuroscien-tiﬁc investigation and discussion on how conceptual knowledgeis represented, this Frontiers Research Topic aimed at bringingtogether contributions from researchers whose interests focuson the action-related and abstract concepts processing. We col-lected both reviews and original research articles in which theauthors used neuropsychology, behavioral methods, electromyo-graphyrecordings,event-related potentials, fMRIexperiments onpatientsandhealthycontrols,andreversiblevirtuallesions.Takentogether these contributions strongly indicate that the role of thesensorimotor context is neither automatic nor a necessary one.Inastudyinwhichtheneuropsychologicalapproachwasused,Gvion and Friedmann (2013) presented the intriguing case ofpatientNissimwithalesionoftheleftoccipitallobewhoseabilityto retrieve and understand words with visual and sensory char-acteristics, such as ball, spoon, carrot (and proper names) wasdependent on the item imageability. The patient showed severedifﬁculties in retrieving and understanding imageable words,while with abstract and complex items he was perfect. Nissim’sability to retrieve gestures for objects and pictures he saw wasmuch better than his retrieval of the names of the same objects.Kemmerer et al. (2013) studied 10 patients with Parkinson’s dis-ease who performed a semantic judgment task including actionand non-action related verbs both while they were ON and OFFmedicationasaccuratelyasagroupof10healthycontrols.Garceaet al. (2013) studied patient AA with a left fronto-parietal lesionand hemiplegia who presented a dissociation between action andobjectknowledge,withanimpairmentinobject-associatedactionproductionandinhisconceptualknowledgeaboutactions, whilehis knowledge of objects was largely preserved. Maieron et al.(2013), combining neuropsychological and fMRI-PPI connectiv-ity data, failed to ﬁnd an effect of neurosurgical lesions in theprimarymotor cortex (M1)ontheabilitytonameactionverbsaswell as a functional coupling between M1 and functional nodesof the linguistic network during verb generation for both con-trols and patients. Crutch et al. (2013) used a new approach,i.e., the abstract cognitive feature (ACF), to examine semanticrelatedness of abstract words and to obtain ratings of the con-tribution of different cognitive systems (e.g., sensation, action,emotionmorality,space,time,socialinteraction)toabstractcon-cepts.Themappingwastested andconﬁrmedbystudying patient