Anticipatory postural adjustments in children with hemiplegia and diplegia

Anticipatory postural adjustments (APAs) play an important role in the performance of many activities requiring the maintenance of standing posture. However, little is known about how or if children with cerebral palsy (CP) generate APAs. Two groups of children with CP (hemiplegia and diplegia) and a group of children with typical motor development performed arm flexion and extension movements while standing on a force platform. Electromyographic activity of six trunk and leg muscles and displacement of center of pressure (COP) were recorded. Children with CP were able to generate anticipatory postural adjustments, produce directionally specific APAs and COP displacements similar to those described in adults and typically developing children. However, children with diplegia were unable to generate APAs of the same magnitude as children with typical development and hemiplegia and had higher baseline muscle activity prior to movement. In children with diplegia, COP was posteriorly displaced and peak acceleration was smaller during bilateral extension compared to children with hemiplegia. The outcomes of the study highlight the role of APAs in control of posture of children with CP and point out the similarities and differences in anticipatory control in children with diplegia and hemiplegia. These differences may foster ideas for treatment strategies to enhance APAs in children with CP

Movement-related potentials (MRPs) were affected by the predictability of the imperative release cue.

<p>A. Grand average movement-related potentials derived from control trials at each of the nine EEG electrodes for both the PREDICT (black) and REACT (red) conditions. The cartoon to the right shows the locations of the electrodes on the scalp. B. Average integrated EEG calculated over 100 ms time bins at 8 time points centered on −4500, −2500, −1500, −1000, −500, −250, −100, 0 ms. Differences between conditions were significant (p<0.007) at all time points except at baseline (−4500 ms). C. Average slope of the movement-related potentials over three time intervals. The slopes were significantly different between conditions during movement preparation but not baseline (PRE) (p<0.007).</p

Summary of the stimulus timing conditions and muscle activation patterns.

<p>A load release task was tested using two cueing conditions: PREDICT and REACT. A. Summary of the timing of the cues and presentation of the startle stimuli. For the PREDICT condition, subjects were presented with a warning tone 3500 ms prior to an imperative cue release tone. Subjects were trained to release the load within 1 simple reaction time in 50% of trials. For the REACT condition, there was no warning cue and the release tone was presented randomly between 4–12 s. For both conditions, a 40 ms, 124 dB startling acoustic stimulus (SAS) was presented in 22% of all trials at 7 time points over the preparation interval. B. Average rectified EMG data from a single subject showing responses in the biceps brachii (BB) and extensor digitorum communis (EDC) muscles during the PREDICT and REACT conditions. EMG responses were time-locked to the onset of activity in the EDC muscle (0 ms).</p

Summary of the effects of a startling acoustic stimulus (SAS) on the timing of movement release.

<p>Reaction times relative to the onset of the SAS were sorted into 20 ms bins. The histograms show the percentage of trials within each reaction time bin for both the PREDICT (open rectangles) and REACT (filled rectangles) tasks. The vertical black arrows show the timing of the imperative release tone. The vertical dashed line is drawn at reaction time of 100 ms. The percentage of trials with reaction times less than 100 ms is shown to the right of the histogram distributions. Note that fast reaction times were common for the PREDICT condition when the SAS was presented 250 ms or less before the imperative cue.</p

Movement-related oscillations were affected by the predictability of the imperative release cue.

<p>The upper plots show the grand average time-frequency spectrograms at the C3 electrode overlying the contralateral sensorimotor region for the PREDICT (A) and REACT (B) conditions. Magnitudes have been normalized to the power over the pre-warning cue interval (−5 to −4.25 s). Note the marked suppression of oscillations in the alpha band (8–12 Hz) immediately following the warning cue and in the beta-band (15–30 Hz) during the 1500 ms time period immediately preceding the onset of wrist extensor (EDC) muscle activity (0 ms) for the PREDICT task. In contrast, the suppression of MRCOs occurred immediately prior to EMG onset for the REACT task and was confined to the beta-band. Plots C and D show the results of the statistical analysis of the normalized time-frequency spectrograms at the C3 electrode for the PREDICT (C) and REACT (D) conditions. Significant (p<0.05) increases (red) and decreases (blue) in MRCOs relative to baseline activity are shown.</p