Youth with Cerebral Palsy Display Abnormal Somatosensory Cortical Activity During a Haptic Exploration Task

Abstract

There are numerous clinical reports that youth with cerebral palsy (CP) have proprioceptive, stereognosis and tactile discrimination deficits. The growing consensus is that the altered perceptions in this population are attributable to aberrant somatosensory cortical activity seen during stimulus processing. It has been inferred from these results that youth with CP likely do not adequately process ongoing sensory feedback during motor performance. However, this conjecture has not been tested. Herein, we address this knowledge gap using magnetoencephalographic (MEG) brain imaging by applying electrical stimulation to the median nerve of youth with CP (N = 15, Age = 15.8 ± 0.83 yrs, Males = 12, MACS levels I-III) and neurotypical (NT) controls (N = 18, Age = 14.1 ± 2.4 yrs, Males = 9) while at rest (i.e., passive) and during a haptic exploration task. The results illustrated that the somatosensory cortical activity was reduced in the group with CP compared to controls during the passive and haptic conditions. Furthermore, the strength of the somatosensory cortical responses during the passive condition were positively associated with the strength of somatosensory cortical responses during the haptic condition (r = 0.75, P = 0.004). This indicates that the aberrant somatosensory cortical responses seen in youth with CP during rest are a good predictor of the extent of somatosensory cortical dysfunction during the performance of motor actions. These data provide novel evidence that aberrations in somatosensory cortical function in youth with CP likely contribute to the difficulties in sensorimotor integration and the ability to effectively plan and execute motor actions.

Keywords: MEG; hand; motor; sensorimotor integration; sensory feedback.

Figure 1.

Depiction of the haptic condition where the youth is seated with their head in the MEG and moving the ball within the fingers of the left hand. Note that the electrical stimulator is positioned proximal to the wrist and near the left median nerve.

Figure 2:

Brain images averaged within group for neurotypical (NT) controls and persons with cerebral palsy (CP), separated by condition and side of stimulation. In each panel, neural data for stimulation of the right hand is shown on the left and stimulation of the left hand is shown on the right. A.) Brain images averaged across NT controls on the left and right side during the haptic condition (top) and passive condition (bottom) B.) Brain images averaged across persons with CP on the left and right side during the haptic condition (top) and passive condition (bottom). Note that the image scale bars are different across the respective images. This was done to enable the anatomical location of the peak response to be accurately visualized in each map. Hence, the magnitude of the scale bars should be used when interpreting if the neural responses were weaker or stronger per condition, side, and group. See text for further explanation.

Figure 3.

A.) Somatosensory cortical activity in the neurotypical (NT) controls and the youth with cerebral palsy (CP) averaged across the two conditions. For illustration purposes, persons with stimulation on the left side are shown. Note that the image scale bars are different across the respective images. This was done to highlight the precise anatomical location of the neural responses. Hence, the magnitude of the scale bars should be used when interpreting if the source activity was weaker or stronger across groups. B.) Neural time course representing the somatosensory cortical activity averaged across all NT controls (red) and youth with CP (dark blue). The green box denotes the time window analyzed (28 – 168 ms), with the stimulation onset being at time zero, represented by a vertical black line. Note that time series were extracted from individual peaks. C.) Box and whisker plot representing the difference in somatosensory cortical activity between the youth with CP and NT controls. The box represents the median, 25^th and 75^th percentiles, and the whiskers represent the 5^th and 95^th percentile. As depicted, the youth with CP had a much weaker response (P = 0.014). D.) The somatosensory cortical activity from the haptic and passive conditions averaged across all participants. For illustration purposes, persons with stimulation on the left side are shown. Note that the image scale bars are different across the respective images. This was done to highlight the precise anatomical location of the neural responses. Hence, the magnitude of the scale bars should be used when interpreting if the source activity was weaker or stronger across conditions. E.) Neural time course representing the somatosensory cortical activity averaged by condition across all participants, with the haptic data shown in dark blue and the passive data shown in red. The green box denotes the time window analyzed, and the stimulation onset is at time zero, represented by a vertical black line. F.) Box and whisker plot representing the difference in somatosensory cortical activity between the haptic and passive conditions. The box represents the median, 25^th and 75^th percentiles, and the whiskers represent the 5^th and 95^th percentile. As depicted, the somatosensory cortical activity evoked during the passive condition was much stronger than the cortical activity evoked during haptic condition (P < 0.001).

Figure 4.

Scatterplots depicting the relationship between the strength of somatosensory cortical responses during the haptic condition (y-axis) and the passive condition (x-axis) in persons with cerebral palsy (CP) (left) and neurotypical (NT) controls (right). The respective scatter plots show that the individuals who had weaker somatosensory cortical activity during the passive condition also tended to have weaker cortical activity during the haptic condition (P’s < 0.05).