New research suggests that infants that are late developing certain motor skills, such as pulling themselves to a standing position, may face challenges in later cognitive development, but more research needs to be done before any clinical recommendations can be made.
Motor skill milestones are often used to assess overall development in premature or developmentally disabled infants. In children with developmental disabilities, delayed motor milestones are viewed as important prodromal symptoms of more severe impairments and possible intellectual disabilities, according to the report. There is little research, however, exploring the age at which motor skills are developed and later cognitive performance in children without developmental problems.
Infants in the United States typically sit without support around age 6 months, and may stand with support. By 9 months, infants usually can pull themselves to a standing position and crawl. They begin to walk alone or take a few unassisted steps around age 12 months with full-blown walking occurring around 18 months, according to the Centers for Disease Control and Prevention.
In this study, researchers evaluated children born between 2008 and 2010 to better understand the connection between motor milestones and later development of cognitive skills. The study was performed using data from 599 children—314 singletons, 259 twins, and 26 triplets—participating in the Upstate KIDS study.
Demographics of the study participants were 50% boys, 52.4% singletons, and 59.6% that attended daycare in the first year of life. Almost half (44.6%) of the mothers received fertility treatments, and 85.8% were non-Hispanic white.
Mothers were asked to report on major milestones at 4, 8, 12, 18, and 24 months of age. A follow-up assessment of the child’s development was performed at 4 years in a clinical setting using the Battelle Developmental Inventory, Second Edition.
Maternal reporting covered milestones including sitting with support, standing with assistance, crawling on hands and knees, walking with assistance, standing alone, and walking alone.
In the 4-year clinical assessment, children were evaluated on personal/social, adaptive, motor, communication, and cognitive skills using a 3-point scale.
The research team found that children who began standing later had more cognitive challenges as they aged. Associations between motor milestones and later cognitive development were primarily observed in relation to the age when the children crawled and when they stood without assistance.
“In the Upstate KIDS study, the age a child first stood was a significant predictor of later cognition. This finding is consistent with previous investigations in older cohorts that highlight the influence of the speed of development during infancy on later cognition,” the researchers note. “One speculative explanation for this finding is that early establishment of connection loops between cortical and subcortical circuits in the brain may have a favorable influence on the early development of motor function as well as cognitive abilities in an older age.”
The majority of the infants enrolled in the study were able to pull themselves to a standing position by roughly 9 months of age, but those that reached that milestone later—at about 11 months of age—scored significantly lower, about 22% behind their peers, on later cognitive and adaptive skill tests.
Researchers stressed that although later motor development was associated with lower cognitive scores later in life, the scores were not low enough to signal impairment. They note that earlier studies also made connections between earlier motor skill development and better memory and cognitive processing later in life.
One weakness of the study, perhaps, is the lack of diversity among the participants. The 599 children included in the analysis were older; had higher socioeconomic status; had parents with higher levels of education; were more often conceived using fertility treatment; and had increased access to private insurance. Children from more diverse backgrounds were excluded because their parents did not participate in the follow-up clinic visit, or no milestone data was submitted, according to the report.
“These results imply that the importance of normal progression of infant motor development to subsequent developmental status may not be limited to children with developmental disabilities. Rather, within the normal range, achieving a gross motor milestone earlier than peers may have favorable effects on adaptive skills and cognitive performance in childhood,” the authors state. “Clinically, our findings suggest age of achieving motor milestones in infancy may be an important basis for various aspects of later child development.”
The researchers found no associations, however, among twins participating in the study.
More research is needed to fully explore the underlying mechanisms that explain the association between motor development and cognitive function, the report states. It is theorized that the function in the basal ganglia, which controls motor function, has an effect on the development of frontal lobes, which control cognitive function. The study showed no connection with functions associated with other parts of the brain, such as personal, social, or communication skills.
Edwina Yeung, PhD, an investigator at the Eunice Kennedy Shriver National Institute of Child Health and Human Development in Bethesda, Maryland, and co-author of the report, says the findings are, at this point, not substantive enough to make recommendations for clinical practice. Pediatricians and parents are advised not to jump to conclusions about cognitive development based on the ages at which motor milestones are achieved.