Orientation of the opposition axis in mentally simulated grasping

Five normal subjects were tested in a simulated grasping task. A cylindrical container filled with water was placed on the center of a horizontal monitor screen. Subjects used a precision grip formed by the thumb and index finger of their right hand. After a preliminary run during which the container was present, it was replaced by an image of the upper surface of the cylinder appearing on the horizontal computer screen on which the real cylinder was placed during the preliminary run. In each trial the image was marked with two contact points which defined an opposition axis in various orientations with respect to the frontal plane. The subjects’ task consisted, once shown a stimulus, of judging as quickly as possible whether the previously experienced action of grasping the container full of water and pouring the water out would be easy, difficult or impossible with the fingers placed according to the opposition axis indicated on the circle. Response times were found to be longer for the grasps judged to be more difficult due to the orientation and position of the opposition axis. In a control experiment, three subjects actually performed the grasps with different orientations and positions of the opposition axis. The effects of these parameters on response time followed the same trends as during simulated movements. This result shows that simulated hand movements take into account the same biomechanical limitations as actually performed movements

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 (Floël et al., 2003; Hauk & Pulvermüller, 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)

Prehension movements in a patient (AC) with posterior parietal cortex damage and posterior callosal section

Prehension movements of the right hand were recorded in a right-handed man (AC), with an injury to the left posterior parietal cortex (PPC) and with a section of the left half of the splenium. The kinematic analysis of AC’s grasping movements in direct and perturbed con- ditions was compared to that of Wve control subjects. A novel eVect in prehension was revealed—a hemispace eVect—in healthy controls only. Movements to the left hemispace were faster, longer, and with a smaller grasp aperture; perturbation of both object position and distance resulted in the attenuation of the direction eVect on movement time and the time to velocity peak, with a reverse pattern in the time to maximum grip aperture. Nevertheless, the correlation between transport velocity amplitude and grasp aperture remained stable in both perturbed and non-perturbed movements, reXecting the coordination between reaching and grasping in control subjects. In contrast, transport and grasp, as well as their coordination in both direct and perturbed conditions, were negatively aVected by the PPC and sple- nium lesion in AC, suggesting that transport and grasp rely on two functionally identiWable subsystems

Action relevance in linguistic context drives word-induced motor activity

Many neurocognitive studies on the role of motor structures in action-language processing have implicitly adopted a “dictionary-like” framework within which lexical meaning is constructed on the basis of an invariant set of semantic features. The debate has thus been centered on the question of whether motor activation is an integral part of the lexical semantics (embodied theories) or the result of a post-lexical construction of a situation model (disembodied theories). However, research in psycholinguistics show that lexical semantic processing and context-dependent meaning construction are narrowly integrated. An understanding of the role of motor structures in action-language processing might thus be better achieved by focusing on the linguistic contexts under which such structures are recruited. Here, we therefore analyzed online modulations of grip force while subjects listened to target words embedded in different linguistic contexts. When the target word was a hand action verb and when the sentence focused on that action (John signs the contract) an early increase of grip force was observed. No comparable increase was detected when the same word occurred in a context that shifted the focus toward the agent's mental state (John wants to sign the contract). There mere presence of an action word is thus not sufficient to trigger motor activation. Moreover, when the linguistic context set up a strong expectation for a hand action, a grip force increase was observed even when the tested word was a pseudo-verb. The presence of a known action word is thus not required to trigger motor activation. Importantly, however, the same linguistic contexts that sufficed to trigger motor activation with pseudo-verbs failed to trigger motor activation when the target words were verbs with no motor action reference. Context is thus not by itself sufficient to supersede an “incompatible” word meaning. We argue that motor structure activation is part of a dynamic process that integrates the lexical meaning potential of a term and the context in the online construction of a situation model, which is a crucial process for fluent and efficient online language comprehension

Grip Force Reveals the Context Sensitivity of Language-Induced Motor Activity during “Action Words

Studies demonstrating the involvement of motor brain structures in language processing typically focus on \ud time windows beyond the latencies of lexical-semantic access. Consequently, such studies remain inconclusive regarding whether motor brain structures are recruited directly in language processing or through post-linguistic conceptual imagery. In the present study, we introduce a grip-force sensor that allows online measurements of language-induced motor activity during sentence listening. We use this tool to investigate whether language-induced motor activity remains constant or is modulated in negative, as opposed to affirmative, linguistic contexts. Our findings demonstrate that this simple experimental paradigm can be used to study the online crosstalk between language and the motor systems in an ecological and economical manner. Our data further confirm that the motor brain structures that can be called upon during action word processing are not mandatorily involved; the crosstalk is asymmetrically\ud governed by the linguistic context and not vice versa

Grasp It Loudly! Supporting Actions with Semantically Congruent Spoken Action Words

Evidence for cross-talk between motor and language brain structures has accumulated over the past several years. However, while a significant amount of research has focused on the interaction between language perception and action, little attention has been paid to the potential impact of language production on overt motor behaviour

Functional connectivity during real vs imagined visuomotor tasks: an EEG study.

International audienceIt is proposed that real and imagined movements activate identical neural networks. Cortical oscillatory activity is proposed as a mechanism through which distributed neuronal networks may bind into coherent ensembles and coupling of oscillators is used as a tool to investigate modulations of cortical connectivity. The aim of the present study was to test the hypothesis that, although the same brain network is involved in both real and imagined movements, the functional connectivity within the network differs. To do so, we measured interregional coupling, quantified using coherence between scalp EEG electrodes, during different periods of a prehension task during real and imagined movements. The results demonstrated a different pattern of coupling in the beta frequency range between electrodes overlying occipital and motor cortices during executed and imagined movements. These findings are consistent with the hypothesis that the neural networks during real and imagined movements are not identical

Visuo-motor learning with combination of different rates of motor imagery and physical practice.

International audienceSports psychology suggests that mental rehearsal facilitates physical practice in athletes and clinical rehabilitation attempts to use mental rehearsal to restore motor function in hemiplegic patients. Our aim was to examine whether mental rehearsal is equivalent to physical learning, and to determine the optimal proportions of real execution and rehearsal. Subjects were asked to grasp an object and insert it into an adapted slot. One group (G0) practiced the task only by physical execution (240 trials); three groups imagined performing the task in different rates of trials (25%, G25; 50%, G50; 75%, G75), and physically executed movements for the remaining trials; a fourth, control group imagined a visual rotation task in 75% of the trials and then performed the same motor task as the others groups. Movement time (MT) was compared for the first and last physical trials, together with other key trials, across groups. All groups learned, suggesting that mental rehearsal is equivalent to physical motor learning. More importantly, when subjects rehearsed the task for large numbers of trials (G50 and G75), the MT of the first executed trial was significantly shorter than the first executed trial in the physical group (G0), indicating that mental practice is better than no practice at all. Comparison of the first executed trial in G25, G50 and G75 with the corresponding trials in G0 (61, 121 and 181 trials), showed equivalence between mental and physical practice. At the end of training, the performance was much better with high rates of mental practice (G50/G75) compared to physical practice alone (G0), especially when the task was difficult. These findings confirm that mental rehearsal can be beneficial for motor learning and suggest that imagery might be used to supplement or partly replace physical practice in clinical rehabilitation