Bert Steenbergen

Activity limitation in hemiplegic cerebral palsy: evidence for disorders in motor planning

Review of the definition of cerebral palsy (CP) has focused on disorders of movement and posture development that cause activity limitations. Recent research provides new insights into CP, showing that activity limitation in individuals with hemiplegic CP is not exclusively caused by disorders related to movement execution, but is also related to the planning of movements. In this review article, converging evidence is presented suggesting that, in addition to movement execution impairments, impairments in movement planning may also limit the performance of activities of daily living. Evidence from studies of fingertip-force planning and anticipatory planning in object manipulation tasks is discussed.

Anticipatory planning deficits and task context effects in hemiparetic cerebral palsy

Individuals with hemiparetic cerebral palsy (HCP) display deviant motor output, predominantly on one side of the body. The question pursued here is whether HCP participants have the ability to anticipate the forthcoming perceptual-motor demands of the goal of an action sequence. Such anticipatory planning was necessary to successfully perform the tasks that were studied. In experiment I, HCP participants had to grasp a hexagonal knob with their unimpaired hand by choosing one of five possible grasping patterns (free choice) and consequently rotate it 60°, 120°, or 180° clockwise or counterclockwise. HCP participants showed a large amount of task failures that were persistent throughout the task. These findings suggest a deficit in anticipatory planning. No such task failures were observed for the control group. In addition, the instructed degree of rotation had less effect on the selected grasping pattern for the HCP participants than for the controls. In experiment II, we investigated if HCP participants are prone to use context information that is directly available in the task, instead of planning the forthcoming perceptual-motor demands. To that aim, an arrow was inserted at one of the sides of the hexagon in a position that had no relevance for the action to be planned and executed. The location of this arrow significantly affected the grip selected in the HCP participants, but not in controls. Overall, the results suggest an anticipatory planning deficit in HCP participants that may be caused by an impairment at the motor imagery level. Consequently, as an alternative strategy, performance in HCP participants was predominantly based on information directly available in the task context.

Mental rotation task of hands: differential influence number of rotational axes.

Various studies on the hand laterality judgment task, using complex sets of stimuli, have shown that the judgments during this task are dependent on bodily constraints. More specific, these studies showed that reaction times are dependent on the participant’s posture or differ for hand pictures rotated away or toward the mid-sagittal plane (i.e., lateral or medial rotation, respectively). These findings point to the use of a cognitive embodied process referred to as motor imagery. We hypothesize that the number of axes of rotation of the displayed stimuli during the task is a critical factor for showing engagement in a mental rotation task, with an increased number of rotational axes leading to a facilitation of motor imagery. To test this hypothesis, we used a hand laterality judgment paradigm in which we manipulated the difficulty of the task via the manipulation of the number of rotational axes of the shown stimuli. Our results showed increased influence of bodily constraints for increasing number of axes of rotation. More specifically, for the stimulus set containing stimuli rotated over a single axis, no influence of biomechanical constraints was present. The stimulus sets containing stimuli rotated over more than one axes of rotation did induce the use of motor imagery, as a clear influence of bodily constraints on the reaction times was found. These findings extend and refine previous findings on motor imagery as our results show that engagement in motor imagery critically depends on the used number of axes of rotation of the stimulus set.

Compromised motor control in children with DCD: A deficit in the internal model - a systematic review

A viable hypothesis to explain the compromised motor ability of children with Developmental Coordination Disorder (DCD) suggests a fundamental deficit in their ability to utilize internal models for motor control. Dysfunction in this mode of control is thought to compromise their motor learning capabilities. The aim of this systematic review is to examine the available evidence for the internal modeling deficit (IMD) hypothesis. A systematic review using five databases identified 48 relevant articles. These studies were categorized according to the effector system involved in the evaluation of motor control and were evaluated for methodological quality. In most papers, DSM-IV-TR criteria for the classification of DCD were not completely fulfilled and possible attentional problems not accounted for. Results showed compromised control of overt and covert eye movements, dynamic postural control, manual control for tasks that vary in complexity, and for motor imagery of manual and whole-body postures. Importantly, this review shows support for general hypothesis that deficits of predictive control manifest in DCD across effector systems.

Action planning in typically and atypically developing children (unilateral cerebral palsy)

In the present study, we investigated the development of action planning in children with unilateral Cerebral Palsy (CP, aged 3-6 years, n=24) and an age matched control group. To investigate action planning, participants performed a sequential movement task. They had to grasp an object (a wooden play sword) and place the sword in a hole in a wooden block. Our main dependent variable was the grip type that participants used, i.e., did they adapt their initial grip choice such that they would reach a comfortable posture at the end of the action? This end-state comfort effect has been abundantly shown in research on action planning, and is taken as evidence for anticipatory planning. The first aim of the study was to investigate the development of action planning in the unilateral CP group and the control group. Our hypothesis was that action planning improves with age in the control group, but not in the unilateral CP group. The results showed that planning was impaired in the unilateral CP group compared with the control group. Consistent with our hypothesis, we found an age effect in the control group, but not in the unilateral CP group. In the control group 5 and 6 years olds showed more anticipatory planning compared with the 3 and 4 years olds. The second aim of this study was to examine whether an intervention for children with unilateral CP (i.e., constrained induced movement therapy combined with bimanual training) affected action planning. The children with unilateral CP were therefore measured on the experimental task before and after an 8-week intervention period. The results showed that planning improved after the intervention. This finding suggests that action planning ability in young children with unilateral CP may be sensitive to improvement. These findings are discussed within the context of typical and atypical development of action planning and further guidelines for intervention in children with unilateral CP are given.

Solving a mental rotation task in congenital hemiparesis: Motor imagery versus visual imagery

A recent study showed that motor imagery was compromised after right congenital hemiparesis. In that study, posture of the displayed stimuli and the actual posture of the hand making the response were incongruent. Ample evidence exists that such an incongruency may negatively influence laterality judgements in a mental rotation task. In the present study, three participant groups (controls, left hemiparesis, right hemiparesis [all n=11]) performed a mental rotation task in which posture of the displayed hand and the responding hand were congruent. A small amount of errors were made and linear relations between reaction times and rotation angles of the stimuli were found for all groups, suggesting intact motor imagery. However, reaction times for the participants with hemiparesis were consistently slower compared to controls and no asymmetry in responding between the affected and less-affected hand was found, suggesting a visual imagery strategy. Collectively, these results suggest that the ability to mentally rotate stimuli is still intact in right hemiparesis. The results are discussed in relation to two strategies that may have been used to solve the task: visual imagery and motor imagery.

Motor imagery training in hemiplegic cerebral palsy: a potentially useful therapeutic tool for rehabilitation

Converging evidence indicates that motor deficits in cerebral palsy (CP) are related not only to problems with execution, but also to impaired motor planning. Current rehabilitation mainly focuses on alleviating compromised motor execution. Motor imagery is a promising method of training the more ‘cognitive’ aspects of motor behaviour, and may, therefore, be effective in facilitating motor planning in patients with CP. In this review first we present the specific motor planning problems in CP followed by a discussion of motor imagery and its use in clinical practice. Second, we present the steps to be taken before motor imagery can be used for rehabilitation of upper limb functioning in CP. Motor imagery training has been shown to be a useful addition to existing rehabilitation protocols for poststroke rehabilitation. No such study has been conducted in CP. The age at which children can reliably use motor imagery, as well as the specific way in which motor imagery training needs to be implemented, must be researched before motor imagery training can be employed in children with CP. Based on the positive results for poststroke rehabilitation, and in light of the motor problems in CP, motor imagery training may be a valuable additional tool for rehabilitation in CP.

Impaired motor imagery in right hemiparetic cerebral palsy

It is generally assumed that movements of a part of the body (e.g., hands) are simulated in motor imagery (MI) tasks. This is evidenced by a linear increase in reaction time as a function of the angular rotation of the stimulus. Under the assumption that MI plays a critical role for anticipatory motor planning, which is known to be impaired in individuals with right hemiparetic cerebral palsy (right HCP; left congenital brain damage), but to a lesser extent in individuals with left HCP, we hypothesized that MI is impaired in the participants with right HCP. In the present study, 8 participants with right and 11 participants with left congenital brain damage and 9 neurologically healthy controls were presented with two MI tasks to study this supposed relation between hemispheric processes and behaviour. Participants were instructed to make a laterality judgment on the basis of displayed pictures of hands (either holding a hammer or not) presented in different orientations. For both the control group and the left HCP group, a linear increase in reaction time as a function of angle of rotation was found. Interestingly, no such relationship was observed for the right HCP group, suggesting a disorder in MI for these participants. Collectively, these findings provide new insights into the cause of the anticipatory planning deficits in right HCP individuals.

Implicit and explicit learning: Applications from basic research to sports for individuals with impaired movement dynamics

Purpose. Motor skills can be learned in an explicit or an implicit manner. Explicit learning places high demands on working memory capacity, but engagement of working memory is largely circumvented when skills are learned implicitly. We propose that individuals with impaired movement dynamics may benefit from implicit learning methods when acquiring sports-related motor skills. Method. We discuss converging evidence that individuals with cerebral palsy and children born prematurely have compromised working memory capacity. This may in part explain the difficulties they encounter when learning motor and other skills. We also review tentative evidence that older people, whose movement dynamics deteriorate, can implicitly learn sports-related motor skills and that this results in more durable performance gains than explicit learning. Results. Individuals with altered movement dynamics and compromised working memory can benefit from implicit motor learning. Conclusion. We conclude with an appeal for more extensive evaluation of the merits of implicit motor learning in individuals with impaired movement dynamics.

The timing of prehensile movements in subjects with cerebral palsy

In this study, a paradigm is presented for the assessment of manual dexterity in subjects With cerebral palsy (CP) that divides the prehensile action into a ‘time‐to‐contact’ phase and a ‘time‐in‐contact’ phase. Two experiments were performed that determined the effect of object weight on the timing of both phases for the impaired hand and non‐impaired hand of subjects with spastic hemiparesis (N = 14). In the first experiment, subjects had to reach for and lift a tube at their own preferred speed. The results showed that the prehensile deficit of the impaired limb is to a large degree manifested by a longer time spent in contact with the object before it was lifted. The time‐in‐contact phase was decreased after repeated lifts, suggesting that subjects with CP can control and modify force output in advance based on weight information from preceding lifts. In the second experiment speed of movement execution was stressed to examine whether the observed timing pattern of the first experiment is characteristic of prehensile movements of the paretic arm or represents a movement strategy adapted to the disorder. The results of the second experiment showed that subjects could comply with the instruction by reducing the absolute duration of both phases of the prehensile movement. Furthermore, the anticipation effects were eliminated to a large degree. In both experiments the time‐in‐contact phase was longer for the impaired limb. These results indicate a pathological constant in the time‐in‐contact phase for the impaired limb. This assumption is discussed in relation to the application of grip and lift forces during this phase. It is concluded that the paradigm is well suited for use in a practical setting as a simple and broad clinical test to assess the prehensile decrements of subjects with CP.