Movement planning in Developmental Coordination Disorder Kate Wilmut, Maia Byrne and Anna Barnett

Action Sequences Actions are composed of a string of movements, each movement taking into account the next Internal forward modelling allows anticipation of motor consequences prior to execution (Wolpert & Kawato, 1998) Allows a spatially and temporally optimal movement (Haggard, 1998; Rosenbaum, Vaughan, Barnes, & Jorgensen, 1992)

Intended action Intended action also effects initial kinematics of the reach-to-grasp when initial demands of a reach component are identical In adults Elongated deceleration phase for a fit vs. a throw action (Marteniuk et al. 1987) Larger peak aperture and larger peak deceleration for a throwing/placing action vs. a lift action (Armbruster & Spijkers, 2006) In children 10 month-old infants: higher peak velocity when reaching to throw vs. place (Claxton, Keen, & McCarty, 2003) 4 years of age: elongated deceleration period when reaching to fit vs. reaching to throw (Chen & Yang, 2007).

Intended action IN DCD DCD: explained by a deficit in the internal modelling of movement? (Maruff et al., 1999; Smits-Engelsman et al. 2007; Williams et al., 2006). Difficulty predicting the outcome of action If so we would not expect these individuals to tailor a movement to an onward action. Aim: To consider whether children and adults with DCD tailor a movement to the onward action

Participants All reported current motor difficulties and none indicated any neurological deficit or comorbid condition that would explain their motor difficulties   Adults Children TD DCD N 18 24 Mean age 24:11 25:00 9:01 Gender ratio f:m 7:11 4:20 MABC-2 percentile All > 20th All < 5th BOT-2 percentile All < 15th ADC Childhood 6.6 All < 10 23.3 (all > 18) Adulthood 17.2 All < 40 47.6 (7 > 62)

Grasped a cylinder and: Tight place (hole x1) Loose hole (hole x2) Lift Throw A Vicon 3D motion capture system was used to track the movement of the thumb, index finger, knuckle and wrist of the dominant hand. METHOD

Results: Movement Duration DCD group showed a longer movement duration compared to the TD individuals. TD – developmental improvement DCD – no difference Effect of action type: TD group: Lift > tight place = loose place DCD group: Lift > Throw

Results: Proportion time in deceleration DCD group spent a longer proportion of MT decelerating TD – developmental improvement, DCD – no difference Effect of action type: Adults: TD: tight >loose=lift>throw DCD: tight=loose=lift>throw Children: TD: tight=loose=lift>throw DCD: no effect

Effects of action type TD adults Shortened proportion of time spent decelerating for a throw action as compared to a place or lift movement Discriminated between the tight and loose place action TD Children Shortened proportion of movement time in deceleration when throwing as compared to the other three actions No discrimination between the place action Adults with DCD Same pattern as the TD children Children with DCD Difference in the movement duration, longer for a lift vs. a throw action. No other differences.

Effects of action type Adults and children with DCD are able to concatenate actions and account for the onward action. DCD group able to use internal forward modelling, even if it is not as sophisticated as that seen in TD adults. Does it ever reach a fully mature level? Is it driven by different underlying mechanism(s)? Control of action in DCD is actually different to the typically developing population rather than simply delayed.

Movement outcome To some extent all of the groups tailored initial reach movement to the intended action Does this result in a more functional movement? For place movements: How long spent adjusting prior to placing.

Calculated % change in proportion of movement time spent decelerating from a tight place to a loose place Compared to the average adjustment time across tight and loose place trials. Movement outcome

Movement outcome Significant relationship for the TD adults, r=-0.532 p=0.023 Pp who showed a greater discrimination in deceleration period from tight to loose place showed a shorter overall adjustment time Not significant for the TD children, the adults with DCD or the children with DCD.

Functionality of movement If the children and adults with DCD are failing (even if only in some respects) to concatenate movement does this actually matter? Seems to be a functionality to predicting onward action TD adults: relationship between the degree to which they discriminated between the two place actions during the initial reach phase and the time spent adjusting

Conclusions Both adults and children with DCD seem able to use forward modelling of inverse models to anticipate movement and concatenate action. Not as sophisticated as that seen in typically developing adults. Underlying forward anticipation of action may be different, rather than simply delayed in DCD.

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