Jennifer Randerath

Different left brain regions are essential for grasping a tool compared with its subsequent use

Tool use engages a left hemispheric network including frontal, temporal and parietal regions. Patients with left brain lesions (LBD patients) exhibit deficits when demonstrating use of a single tool (apraxia). When attempting to use a tool, some apraxic patients show errors in the preceding grasping movement. Forty-two LBD patients and 18 healthy controls grasped individual tools and demonstrated their typical use. For patients with a tool use impairment (22), lesion analysis revealed a large area of overlap in the left hemisphere, mainly in the supramarginal gyrus (SMG). For patients with erroneous grasping (12), the lesion overlay showed overlaps in the left frontal and parietal cortices, especially in the inferior frontal gyrus (IFG) and the angular gyrus (ANG). However, contrasting lesions associated with impaired grasping versus tool use impairments reveal little overlap, limited to the inferior parietal cortex. Presumably the left IFG is involved in selection processes in the context of tool use, such as choosing a functional or non-functional grasping movement depending on the task and the online information about the tools structure and orientation. The ANG might provide this grasp related information, which is relevant for the specific action. The contribution of the SMG to tool use involves more general principals, such as integrating online and learned tool use information into the action plan for the use movement.

Tool use without a tool: kinematic characteristics of pantomiming as compared to actual use and the effect of brain damage

Movement goals and task mechanics differ substantially between actual tool use and corresponding pantomimes. In addition, apraxia seems to be more severe during pantomime than during actual tool use. Comparisons of these two modes of action execution using quantitative methods of movement analyses are rare. In the present study, repetitive scooping movements with a ladle from a bowl into a plate were recorded and movement kinematics was analyzed. Brain-damaged patients using their ipsilesional hand and healthy control subjects were tested in three conditions: pantomime, demonstration with the tool only, and actual use in the normal context. Analysis of the hand trajectories during the transport component revealed clear differences between the tasks, such as slower actual use and moderate deficits in patients with left brain damage (LBD). LBD patients were particularly impaired in the scooping component: LBD patients with apraxia exhibited reduced hand rotation at the bowl and the plate. The deficit was most obvious during pantomime but actual use was also affected, and reduced hand rotation was consistent across conditions as indicated by strong pair-wise correlations between task conditions. In healthy control subjects, correlations between movement parameters were most evident between the pantomime and demonstration conditions but weak in correlation pairs involving actual use. From these findings and published neuroimaging evidence, we conclude that for a specific tool-use action, common motor schemas are activated but are adjusted and modified according to the actual task constraints and demands. An apraxic LBD individual can show a deficit across all three action conditions, but the severity can differ substantially between conditions.

From pantomime to actual use: How affordances can facilitate actual tool-use

The main goal of the study was to investigate whether the presence of affordances, such as physical properties of given objects and resulting movement constraints, induce a performance increase in actual tool-use compared to demonstrating it with only the tool or pantomiming it without the tool and recipient object. In the present study the perception of affordances was manipulated by omission or supply of contextual information. The three execution modes - pantomiming, demonstration and actual use, - were investigated concerning the actions hammering and scooping in 25 patients with left unilateral brain damage and 10 healthy controls. The content of the movement, the grip formation, the direction and the location of the movement were evaluated with video-analysis. The results show that the pantomime condition is most prone to errors. The information given by the tool and the recipient object in the actual use task seems to facilitate especially scooping - the more complex tool-use action. A factor analysis and the high correlation between performance-scores show that the three execution modes of both actions have a major common factor. One possible joint commonality of the execution modes could be the nature of an action related working memory component, which is responsible for the recall and the integration of semantic information into a movement-plan. Additional analyses with a smaller group revealed a second factor, that might depict the online processing of spatial relationships of the hand, the tool and the recipient objects. The results indicate that performance improvement can be achieved by providing perceptual cues and reducing the degrees of freedom for the required action. It is concluded that manipulating affordances in a tool use context should be taken into consideration for future investigation of therapeutic approaches.

Tool use kinematics across different modes of execution. Implications for action representation and apraxia

Studying the characteristics of movements performed under different action conditions may foster the understanding of disturbed tool use in apraxia and may enhance the knowledge about the links between states of action representations. We registered hand and arm movements during a hammering action executed under three task conditions: pantomime, demonstration with the hammer only, and actual execution with hammer and nail. Various movement parameters were calculated to characterize the kinematic aspects of the hammering movements. An apraxia score that reflects conceptual errors was derived from video-evaluation of pantomiming. Twenty-three patients with left brain damage (LBD), 10 patients with right brain damage (RBD), and 19 control subjects were tested. Patients performed with the non-paretic ipsilesional hand. Four apraxic LBD patients failed to perform the task due to severe conceptual errors. The remaining LBD patients frequently produced movements that were slower, shorter, and less vertical than those of control subjects in all task conditions. Lesion analyses for the LBD patients suggested that inferior frontal areas were particularly responsible for impaired performance. RBD patients performed normally in most kinematic task aspects. Although the conditions differed characteristically in geometry and kinematics, correlations of performance measures indicated that individual patterns in patients as well as in control subjects were stable across the conditions. Performance stability across conditions and the overlapping neural network both support the concept of a general action prototype that is adapted flexibly to environmental constraints. Findings in patients show that LBD can affect the execution of an actual hammering action also in the absence of conceptual errors. It remains to be shown however whether conceptual errors and abnormalities of movement kinematics have a common cause or are two independent manifestations of damage to the motor-dominant brain.

Anticipatory scaling of grip forces when lifting objects of everyday life

The ability to predict and anticipate the mechanical demands of the environment promotes smooth and skillful motor actions. Thus, the finger forces produced to grasp and lift an object are scaled to the physical properties such as weight. While grip force scaling is well established for neutral objects, only few studies analyzed objects known from daily routine and none studied grip forces. In the present study, eleven healthy subjects each lifted twelve objects of everyday life that encompassed a wide range of weights. The finger pads were covered with force sensors that enabled the measurement of grip force. A scale registered load forces. In a control experiment, the objects were wrapped into paper to prevent recognition by the subjects. Data from the first lift of each object confirmed that object weight was anticipated by adequately scaled forces. The maximum grip force rate during the force increase phase emerged as the most reliable measure to verify that weight was actually predicted and to characterize the precision of this prediction, while other force measures were scaled to object weight also when object identity was not known. Variability and linearity of the grip force–weight relationship improved for time points reached after liftoff, suggesting that sensory information refined the force adjustment. The same mechanism seemed to be involved with unrecognizable objects, though a lower precision was reached. Repeated lifting of the same object within a second and third presentation block did not improve the precision of the grip force scaling. Either practice was too variable or the motor system does not prioritize the optimization of the internal representation when objects are highly familiar.

Are tool properties always processed automatically? The role of tool use context and task complexity

Previous work with healthy adults supports the idea that perception of the orientation of a tools handle may automatically activate cognitive components for grasping and use. An important source of evidence for this automatic activation view comes from studies showing interference when automatically activated action representations are inconsistent with the behaviors demanded by a task (e.g., Tucker and Ellis, 1998). Here, we evaluated whether such effects occur in a grip selection task in which responses were chosen based on a learned rule (Rule task) versus anticipatory planning (Plan task). Participants were asked to pantomime grasping horizontally presented objects with handles. In the Rule task, a color cue indicated on which side of the tools handle the thumb had to be placed. In the Plan task, participants had to choose the most comfortable way to grasp and rotate the object into a specific end-position. Across three experiments we found evidence of interference on grip selection exclusively during the Rule task, and only when it was preceded by a prime task that involved tool use. These findings suggest that prior activation of cognitive components through use of tools can be effective over time and interferes with grip selection based on use of a pre-learned rule. Absence of interference effects during the plan task, even when preceded by the Use task, suggest that engagement of similar mechanisms during active planning overwrites this automatic activation of previously effective components. Possible cognitive and neural mechanisms are discussed.

Grip forces isolated from knowledge about object properties following a left parietal lesion

When lifting two objects with equal weight but different size, we judge the smaller object to be heavier. This size-weight illusion has been intensively tested by the recruitment of fingertip grip forces during precision lifting. Previous findings have suggested that perceptual (object size) prediction can influence sensorimotor prediction (anticipatory grip force scaling to the object size) but these predictions could be processed independently. This study investigates whether the anticipatory scaling of the grip forces according to object properties critically depends on the integrity of the posterior parietal cortex (PPC) and how a deficit may affect the perceptual size-weight illusion. Here, we report the case of a patient, F.S., with a large left temporal parietal lesion intruding into the temporal cortex and limb apraxia, who did not show anticipatory scaling of fingertip grip force to object size whereas matched controls did. However, the patients perception of the size-weight illusion was only impaired during his ipsi-lesional hand lifting. Our findings suggest that left parietal cortex may be particularly responsible for the anticipatory grip force scaling of both hands and the perceptual process of size-weight illusion involving ipsi-lesional hand motion.

Object properties and cognitive load in the formation of associative memory during precision lifting

When we manipulate familiar objects in our daily life, our grip force anticipates the physical demands right from the moment of contact with the object, indicating the existence of a memory for relevant object properties. This study explores the formation and consolidation of the memory processes that associate either familiar (size) or arbitrary object features (color) with object weight. In the general task, participants repetitively lifted two differently weighted objects (580 and 280 g) in a pseudo-random order. Forty young healthy adults participated in this study and were randomly distributed into four groups: Color Cue Single task (CCS, blue and red, 9.8(3)cm(3)), Color Cue Dual task (CCD), No Cue (NC) and Size Cue (SC, 9.8(3) and 6(3)cm(3)) group. All groups performed a repetitive precision grasp-lift task and were retested with the same protocol after a 5-min pause. The CCD group was also required to simultaneously perform a memory task during each lift of differently weighted objects coded by color. The results show that groups lifting objects with arbitrary or familiar features successfully formed the association between object weight and manipulated object features and incorporated this into grip force programming, as observed in the different scaling of grip force and grip force rate for different object weights. An arbitrary feature, i.e., color, can be sufficiently associated with object weight, however with less strength than the familiar feature of size. The simultaneous memory task impaired anticipatory force scaling during repetitive object lifting but did not jeopardize the learning process and the consolidation of the associative memory.

Size-weight illusion and anticipatory grip force scaling following unilateral cortical brain lesion

The prediction of object weight from its size is an important prerequisite of skillful object manipulation. Grip and load forces anticipate object size during early phases of lifting an object. A mismatch between predicted and actual weight when two different sized objects have the same weight results in the size-weight illusion (SWI), the small object feeling heavier. This study explores whether lateralized brain lesions in patients with or without apraxia alter the size-weight illusion and impair anticipatory finger force scaling. Twenty patients with left brain damage (LBD, 10 with apraxia, 10 without apraxia), ten patients with right brain damage (RBD), and matched control subjects lifted two different-sized boxes in alternation. All subjects experienced a similar size-weight illusion. The anticipatory force scaling of all groups was in correspondence with the size cue: higher forces and force rates were applied to the big box and lower forces and force rates to the small box during the first lifts. Within few lifts, forces were scaled to actual object weight. Despite the lack of significant differences at group level, 5 out of 20 LBD patients showed abnormal predictive scaling of grip forces. They differed from the LBD patients with normal predictive scaling by a greater incidence of posterior occipito-parietal lesions but not by a greater incidence of apraxia. The findings do not support a more general role for the motor-dominant left hemisphere, or an influence of apraxia per se, in the scaling of finger force according to object properties. However, damage in the vicinity of the parietal-occipital junction may be critical for deriving predictions of weight from size.