Unravelling developmental disregard in children with unilateral cerebral palsy by measuring event-related potentials during a simple and complex task

Abstract

Background: In a subset of children with unilateral Cerebral Palsy (CP) a discrepancy between capacity and performance of the affected upper limb can be observed. This discrepancy is known as Developmental Disregard (DD). Though the phenomenon of DD has been well documented, its underlying cause is still under debate. DD has originally been explained based on principles of operant conditioning. Alternatively, it has been proposed that DD results from a diminished automaticity of movements, resulting in an increased cognitive load when using the affected hand. To investigate the amount of involved cognitive load we studied Event-Related Potentials (ERPs) preceding task-related motor responses during a single-hand capacity and a dual-hand performance task. It was hypothesised that children with DD show alterations related to long-latency ERP components when selecting a response with the affected upper limb, reflecting increased cognitive load in order to generate an adequate response and especially so within the dual-hand task.

Methods: Fifteen children with unilateral CP participated in the study. One of the participants was excluded due to major visual impairments. Seven of the remaining participants displayed DD. The other seven children served as a control group. All participants performed two versions of a cue-target paradigm, a single-hand capacity and a dual-hand performance task. The ERP components linked to target presentation were inspected: the mid-latency P2 component and the consecutive long-latency N2b component.

Results: In the dual-hand performance task children with DD showed an enhancement in mean amplitude of the long-latency N2b component when selecting a response with their affected hand. No differences were found regarding the amplitude of the mid-latency P2 component. No differences were observed regarding the single-hand capacity task. The control group did not display any differences in ERPs linked to target evaluation processes between both hands.

Conclusion: These electrophysiological findings show that DD is associated with increased cognitive load when movements are prepared with the affected hand during a dual-hand performance task. These findings confirm behavioural observations, advance our insights on the neural substrate of DD and have implications for therapy.

Figure 1

Stimuli of cue-target paradigm. Schematic of the cue-target paradigm shown on the left side of the screen. For presentation on the right side, the smiley figures were mirrored horizontally.

Figure 2

Mean absolute amplitude with SEM for the N2b (330 - 380) component following target evaluation at FCz. Differences between sides of target presentation (NA = non-affected; A = affected) are depicted for children with unilateral CP without indications of DD (control) and children with unilateral CP and DD (DD). The significant difference between the movement preparations of both hands for the DD group is indicated by the asterisk.

Figure 3

Grand averaged ERP waveforms following target stimuli. Grand averaged ERP waveforms elicited by target stimuli in children with unilateral CP without indications of DD (Grand Averages: control group) and children with unilateral CP and DD (Grand averages: DD group) in response to movement selection of the affected hand (dashed line) compared to the non-affected hand (solid line). For calculation of these grand averages all 14 participants (DD: N = 7; control: N = 7) were included. Highlighted temporal windows indicate N1, P2, and N2b components. The significant difference for the DD group between the movement preparations of both hands is indicated by the asterisk.