Grasp With Hand and Mouth: A Kinematic Study on Healthy Subjects

Abstract

Neurons involved in grasp preparation with hand and mouth were previously recorded in the premotor cortex of monkey. The aim of the present kinematic study was to determine whether a unique planning underlies the act of grasping with hand and mouth in humans as well. In a set of four experiments, healthy subjects reached and grasped with the hand an object of different size while opening the mouth (experiments 1 and 3), or extending the other forearm (experiment 4), or the fingers of the other hand (experiment 5). In a subsequent set of three experiments, subjects grasped an object of different size with the mouth, while opening the fingers of the right hand (experiments 6-8). The initial kinematics of mouth and finger opening, but not of forearm extension, was affected by the size of the grasped object congruently with the size effect on initial grasp kinematics. This effect was due neither to visual presentation of the object, without the successive grasp motor act (experiment 2) nor to synchronism between finger and mouth opening (experiments 3, 7, and 8). In experiment 9 subjects grasped with the right hand an object of different size while pronouncing a syllable printed on the target. Mouth opening and sound production were affected by the grasped object size. The results of the present study are discussed according to the notion that in an action each motor act is prepared before the beginning of the motor sequence. Double grasp preparation can be used for successive motor acts on the same object as, for example, grasping food with the hand and ingesting it after bringing it to the mouth. We speculate that the circuits involved in double grasp preparation might have been the neural substrate where hand motor patterns used as primitive communication signs were transferred to mouth articulation system. This is in accordance with the hypothesis that Broca's area derives phylogenetically from the monkey premotor area where hand movements are controlled.

Does dysfunction of the mirror neuron system contribute to symptoms in amyotrophic lateral sclerosis?

“…Concurrent contraction of other facial muscles not directly involved in articulation was not observed during these acts (Higginbotham et al , 2008). This observation mimics the hand-mouth activity in non-human primates and prelinguistic infants, and the influence of grasping on labial articulation in adult humans (Gentilucci et al , 2001). It also supports the idea that there is a transition from gestural to verbal, articulate communication systems.…”

Slip of the tongue: Implications for evolution and language development

“…The motor coupling is believed to occur due to shared neural resources for hand actions (Iacoboni et al, 1998) and actual or internal speech (Hinke et al, 2003) and is further supported by behavioral evidence demonstrating selective disruption of speech syllables when the hands are required to perform non-congruent articulations (Gentilucci et al, 2001). However, tongue protrusions were also reported during the Story Recall task that had no manual motor requirement.…”

“…For example, chimpanzees generated sympathetic mouth movements significantly more often during tasks requiring fine motor manipulation compared with tasks requiring gross motor actions (Waters & Fouts, 2002). In humans, Gentilucci, Benuzzi, Gangitano, and Grimaldi (2001) demonstrated that the pronunciation of a syllable could be selectively disrupted when producing a simultaneous grasping action for target objects of a non-congruent size to that of the mouth vocalization. The finding suggests that the fine motor articulation required for grasping is processed similarly by both hand and mouth in humans, thus they tend to complement each other.…”

Mirror neurons and the social nature of language: The neural exploitation hypothesis

“…Several works by Gentilucci and colleagues (Gentilucci, 2003;Gentilucci, Benuzzi, Gangitano, & Grimaldi, 2001, Gentilucci, Santunione, Roy, & Stefanini, 2004aGentilucci, Stefanini, Roy, & Santunione, 2004b) have shown a close relationship between speech production and the execution/observation of arm and hand gestures. In one of these studies, Gentilucci et al (2004a) showed that the execution/observation of the action of bringing an object to the mouth activates a mouth articulation posture likely related to food manipulation, which selectively influences speech production.…”