Motor function

The use of MA has been associated with impairments in motor function. Motor function refers to several forms of movement, including automatic repetitive actions such as

walking, running, reflex actions, semi-voluntary actions such as sneezing, and voluntarily actions such as picking up something or throwing something (Bradshaw & Mattingly, 1995). Fine motor skills require the coordination of small muscle groups involved in small

movements, such as writing or drawing. Gross motor skills refer to large movements, where coordination of large muscle groups is required, such as running or kicking a ball. Motor development is fundamental to a child’s development. Proper motor development is a foundational skill for a child’s school readiness (Pienaar, Barhorst, & Twisk, 2013). Despite evidence that MA causes a decrease in motor skills in abusers, very little is known about the impact that MA has on the motor function of PME children (Chang et al., 2009).

The sensory system provides us with the means of perceiving the world, whereas the motor system, in turn, provides us with the means of acting on the world. The control of sensory systems largely occurs within the posterior regions of the brain, while cortical control of movement occurs largely in the anterior regions in interaction with motor regions of the brain. Sensory-perceptual information is processed in primary processing areas and integrated by secondary and higher order cortices. Actions are determined by the information coming from sensory associated areas, such as the parietal lobes and subcortical structures, which includes the cerebellum and the basal ganglia (Zillmer et al., 2008).

A longitudinal study by Cernerud et al. (1996) followed 65 (36 girls; 29 boys) PME children in Sweden from birth up to the age of 14 years in an attempt to examine the long- term effects of PME on the development of a child. Between the ages of 14 and 15 years old, information about their growth and school achievements was collected. This data was

compared to the means of unexposed children born in the same year of the exposed group to determine whether PME children performed worse overall. They found that PME children experienced difficulty in motor development and struggled with physical activities (Cernerud

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et al., 1996). Despite the extensive data that was collected from this Swedish study one should consider a few absent key methodological aspects that limit the strengths of the study's outcomes. For example, the study did not include a control group, neither did it consider the presence of confounding drug exposure, such as tobacco and alcohol.

The Infant Development, Environment, and Lifestyle (IDEAL) study is the largest longitudinal study on the effect of PME on neurobehavioral outcomes. The IDEAL study (LaGasse et al. 2011), recruited participants, between the ages of 0-36 months, from the USA and New Zealand (NZ). The USA had a total of 379 participants (183 PME and 196

unexposed) and NZ had a total of 180 participants (85 PME and 95 unexposed) for the study. The NICU Neurobehaviour Scale (NNNS) was used to examine motor function in infants. All participants were measured within five days of birth. They found that PME infants

experienced low tone, under arousal, poorer quality in movement and increased stress. Their findings suggest that PME does effect motor development (LaGasse et al., 2011).

The IDEAL study also examined the effect of PME on cognitive and motor development in children between the ages of 1-3 years. Smith et al. (2011) suggested that motor development during the infancy stage is associated with visual perceptual and spatial skills. Since visual perceptual processing may be negatively affected by PME, PME children might be at risk for experiencing difficulties when it comes to tasks that requires the

coordination of movement (Smith et al., 2011). The authors found that PME children displayed poorer fine motor development compared to unexposed children at the age of one year old, with the poorest performance observed in those children who were exposed to heavy MA use prenatally. However, at the age of 3 they found that both high- and low-dose groups experienced similar levels of motor function that was not different compared to controls (Kiblawi et al., 2013). From these results the authors concluded that PME has

modest motor effects at the age of 1 year, which are mostly resolved by the time the child reaches the age of 3 (Smith et al., 2011). The results of this study prove inconsistent with the results of neuroimaging studies on the effect of PME on motor development. For instance, a study by Chang et al. (2009) found significant impaired motor development in PME children at the age of 4 years (Chang et al., 2009).

A study by Wouldes et al. (2014) also contradicts the findings of Smith et al. (2011) by finding similar results as Chang et al. (2009). The authors conducted their study on 210 participants (103 PME; 107 unexposed) from NZ. All children were assessed on the Bayley Scales of Infant Development, second Edition (BSID-II) at the ages of 1, 2 or 3 years to measure their cognitive and motor performance. Children were also assessed with the Peabody Development Motor Scale, second Edition (PDMS-2) at the ages of 1 and 3 to measure their gross and fine motor performance. They found that PME children experienced poorer fine and gross motor development when compared to unexposed children (Wouldes et al., 2014). It has been shown that children experiencing difficulty with motor coordination also experience difficulty with visual-motor coordination (Pienaar et al., 2013).