At the interface between action verbs and grip force

Action verbs and motor actions activate similar cortical brain areas (Price et al., 1994; Grafton et al., 1998). An increasing number of studies reveal that the sensorimotor components of word meaning activate cortical regions overlapping with the neural systems involved in the perception and execution of actions described by the words. For example, processing verbally presented actions activates corresponding sectors of the motor system, depending on the effector (face, hand or foot) used in the listened-to action (Floel et al., 2003; Hauk & Pulvermuller, 2004; Buccino et al., 2005). Moreover, in sign language there is a close semantic relationship between the gestures and the function of the object expressed, suggesting that transmodal processes are implicated in pragmatic representations. These studies and numerous observations strongly suggest that the brain areas subtending object-oriented actions are closely related to the brain areas involved with language (e.g., Gentilucci & Dalla Volta, 2008). Recently, Boulanger et al. (2006) showed that verbs related to manual action could perturb reaching movements. Since reaching and grasping are intimately linked (Jeannerod & Biguer, 1981; Frak et al., 2006) manual action verbs could also alter aspects of grasp, such as prehension force. Reaching is a process with a recognized bi-hemispheric activity involving the proximal musculature. Thus, the influence of language on grasp is a highly pertinent subject of study: action with the preferred hand is under control by left cerebral areas, as is the case with language. A novel approach examining the relationship between language and prehension force is presented using a tactile sensing paradigm. Using their preferred hand, subjects seized and held with a precision grasp a 300 g cylinder with an integrated force sensor. With eyes closed and arm extended, subjects listened to words related or not related to a manual action. There was an increase in grasp force when subjects heard words related to manual action only. This increase began at about 100 ms following word presentation, peaked at 300-400 ms and fell abruptly after 400 ms, signalling a possible inhibition of the motor simulation of the action evoked by the words. These observations reveal the intimate relationship that exists between language and prehension force and show that it is possible to elucidate online new aspects of sensorimotor interaction. They also reveal that there is a continuum between lexical access and motor simulation. Figure 1 shows the grand average of normalized grasp force amplitude of action words (AT) and non-action words (NAT) when they are targets. A paired t-test was done on the data defining both curves. The gray part of the graph, starting at 260 msec and ending at 430 msec, shows where there’s a significative difference (p<0.05).