Mario Wiesendanger

Role of the corpus callosum in bimanual coordination: a comparison of patients with congenital and acquired callosal damage

The objective of the study was to investigate temporal control in patients with congenital as compared to acquired pathology of the corpus callosum during two different bimanual paradigms: (i) a drawer‐opening task during which one hand opened a drawer while the other hand reached and grasped a small object, and (ii) rhythmical circling movements that were executed according to the in‐phase or antiphase mode. Synchronization values revealed that patients with acquired callosal dysfunction generally showed optimal behaviour during the goal‐directed and familiar drawer‐opening task but demonstrated strong tendencies towards desynchronization during circling movements, which became most apparent for antiphase coordination. Whereas one patient with callosal agenesis showed a similar performance, the other acallosal patients performed both activities successfully. These observations indicate that patients with congenital absence of the corpus callosum can make use of compensatory mechanisms for allowing temporal synchronization during bimanual movements whereas patients with acquired callosal dysfunction are severely hampered when the task places significant demands on the control processes. The data also underline that the ability of callosal patients to precisely time events in coordinated actions depend on the task constraints.

Time structure of a goal-directed bimanual skill and its dependence on task constraints.

The aim of the study was to elucidate the underlying principles of bimanual coordination and to establish quantitative coordination criteria. Healthy human subjects were instructed to open a loaded drawer with the left hand and to grasp, lift and reinsert with the right hand a small peg in the drawer recess. This bimanual goal-oriented task was executed promptly and consistently after a few trials. The temporal structure of the individual limb actions was assessed for computing interlimb synchronization and temporal correlation. In all subjects, both hands were well synchronized at the goal with high intermanual correlation in reaching the goal (event times of drawer opening and grasping the peg). This temporal goal-invariance was independent of movement speed and of the highly variable timing of the individual hands and persisted when subjects were blindfolded. Unilateral loading of the pulling hand and cutaneous anesthesia of the left index finger and thumb used for grasping the drawer handle significantly increased the pull-phase. This slowing of the left hand was matched by an adaptive delay of the right non-disturbed hand, thus preserving goal invariance. As a working hypothesis, we propose that multimodal sensory signals generated in the leading arm be transmitted centrally to re-parameterize the non-disturbed arm.

Grip-load force coordination in cerebellar patients

Abstract The study examined the anticipatory grip force modulations to load force changes during a drawer-opening task. An impact force was induced by a mechanical stop which abruptly arrested movement of the pulling hand. In performing this task, normal subjects generated a typical grip force profile characterized by an initial force impulse related to drawer movement onset, followed by a ramp-like grip force increase prior to the impending load perturbation. Finally, a reactive response was triggered by the impact. In patients with bilateral cerebellar dysfunction, the drawer-opening task was performed with an alternative control strategy. During pulling, grip force was increased to a high (overestimated) default level. The latter suggests that cerebellar patients were unable to adjust and to scale precisely the grip force according to the load force. In addition, the latency between impact and reactive activity was prolonged in the patients, suggesting an impaired cerebellar transmission of the long-latency responses. In conclusion, these data demonstrate the involvement of cerebellar circuits in both proactive and reactive mechanisms in view of predictable load perturbations during manipulative behavior.

Are There Unifying Structures in the Brain Responsible for Interlimb Coordination

Publisher Summary This chapter discusses the problem of whether specific cortical areas are responsible for temporal and spatial coupling of both hands when they are engaged in purposeful cooperative manipulations, as is so often the case in the natural movement repertoire of primates. Many human skills are performed with the cooperation of both hands. A closer investigation, including a quantitative analysis of the temporospatial structure of the bilateral movement sequences, of such interesting cases remains to be done. More complex disturbances of bimanual performances have also been described in cases of medial frontal lesions, including the supplementary motor area. In multiarticulate limb movements and in speech articulation, it is found that despite a large trial-by-trial temporal and spatial variability of individual movement components, goal achievement is characterized by a remarkable spatial and temporal invariance.

Disturbed sensorimotor processing during control of precision grip in patients with writer's cramp

The aim of the study was to investigate force regulation in patients with writers cramp when performing a drawer‐opening task using the precision grip. Experimental conditions included intervening load pulses and vibratory manipulations for examining grip force responses to sensory disturbances. The data revealed that grip force was increased in patients with writers cramp compared with normal subjects, with a stronger modulation in the symptomatic compared with the asymptomatic hand. This denotes a change in force scaling capabilities and most notably for the preferred hand used in manipulative activities. Vibratory stimulation of the extrinsic hand/finger muscles resulted in an increased grip force of both hands in the patients with writers cramp. The latter was not observed in normal subjects and supports a bilateral dysfunction in sensorimotor integration resulting from focal dystonia. In conclusion, the disturbed regulation of the precision grip during a drawer‐opening task is illustrative for the inability of patients with writers cramp to efficiently control the force output during manipulative activities.

Damage to the parietal lobe impairs bimanual coordination.

Moving the upper limbs at a common tempo according to a mirror or parallel mode represents elementary coordination dynamics. Previously, the role of the medial wall areas have been emphasized for successful production of these bimanual patterns. The involvement of the parietal lobe is less clear despite its importance for the representation of motor skill and sensorimotor integration. The objective of this study was to investigate temporal control in patients with parietal pathology when performing isofrequency configurations. As compared to control subjects, these patients showed desynchronization of movement trajectories that was most apparent during parallel patterns. These observations suggest the significant role of the parietal lobe for bimanual coordination which becomes increasingly relevant as a function of task complexity.

The quest to understand bimanual coordination.

Many skillful manipulations engage both hands for goal achievement. Whereas the goal is planned consciously and achieved quasi-invariantly, the articulators are mobilized automatically, but in a flexible manner (Lashleys principle of motor equivalence). In brain disorders affecting hand functions, adaptive mechanisms are mobilized to improve goal achievement. Thus, chronic cerebellar patients were found to initiate a bimanual drawer task with marked intermanual desynchronization as compared to control subjects. This was partly compensated for, however, by adjusting the kinematics as the individual limbs move toward the goal, thereby improving the initial desynchronization. Adaptive strategies rarely correct deficits completely, however. Bimanual movement patterns, either in-phase or anti-phase are relatively stable in healthy human subjects, whereas brain pathology may preferentially impair the anti-phase pattern. This is the case in patients with acquired pathology of the corpus callosum, thereby suggesting that this structure is important for maintaining temporally independent limb and hand movements.

Role of the Cerebellum in Tuning Anticipatory and Reactive Grip Force Responses

The aim of our study was to determine if load perturbations that could destabilize grasp control are adequately controlled by cerebellar patients. We examined patients with unilateral cerebellar lesions who had largely recovered from their initial symptoms and compared grip force regulation for the affected and unaffected hand during a drawer-opening task. Two experimental paradigms were included: (1) a brief load perturbation during a self-stopped drawer pull and (2) a loading impact when the drawer was pulled out to the mechanical stop. The results showed that when a self-stopped movement was perturbed during its trajectory, anticipatory grip force increase was smaller for the affected than for the unaffected hand, illustrating a disturbed gain control due to cerebellar dysfunction. When the mechanical stop arrested the movement, the amount of grip force did not differ significantly between the affected and unaffected side; however, both hands used different control strategies. Whereas the unaffected hand anticipated the load perturbation by a ramp-like increase of grip force toward the impending impact, the affected hand increased grip force at movement onset to a default level and maintained this value until the task was ended. In addition, the latency between impact and reactive peak in grip force was prolonged for the affected hand, suggesting a delayed cerebellar transmission of reactive responses. In conclusion, these findings demonstrate that the cerebellum is involved in anticipatory and reactive mechanisms dealing with load perturbations during goal-directed behavior.

Experimental evidence for the existence of a proprioceptive transcortical loop.

Publisher Summary There is a powerful, rapid and somatotopically organized projection system, originating in stretch receptors, to the cerebral cortex, including the motor fields. The descending output cells of the motor cortex may include in their command signal an “error signal” (provided by the muscle spindles). There are behavioral data, which show that if an otherwise intact motor cortex is deprived of its somatosensory input, the motor control, especially of hand manipulations, is strikingly disturbed. These findings are a great challenge and warrant further studies on the nature of the transcortical loop, especially with respect to adaptive mechanisms. This chapter discusses the main electro-anatomical evidence for the existence of a transcortical loop, and then discusses its possible functional significance. It provides grounds that the transcortical loop is bound to provide some of the myotatic response, but that it is difficult to conceive the extent of this contribution and its functional meaning. It further suggests that the transcortical loop may play a more meaningful role as an adaptive controller engaged in non-reflex changes of motor commands imposed by the environment in a predictable situation.

Dissociation of grip/load-force coupling during a bimanual manipulative assignment

Abstract. The aim of the present study was to examine interlimb interactions of grasping forces during a bimanual manipulative assignment that required the execution of a drawer-opening task with the left hand and an object-holding task with the right hand. Compared with the unimanual performance, the grip/load-force ratio of the object-holding task was shifted towards that of the simultaneously executed drawer-opening task. This shows that force parameterization of the dynamic activity interacted with that of the static activity. That the increased force ratio only involved modification of grip force, while load force was held constant, indicates a disruption of the commonly observed co-variation of both forces during a manipulative action. These data are consistent with the notion that the coordinative constraint between grip and load force is a flexible parameter.