Factor structure of paediatric timed motor examination and its relationship with IQ

Aim: Brain systems supporting higher cognitive and motor control develop in a parallel manner, dependent on functional integrity and maturation of related regions, suggesting neighbouring neural circuitry. Concurrent examination of motor and cognitive control can provide a window into neurological development. However, identification of performance-based measures that do not correlate with IQ has been a challenge. Method: Timed motor performance from the Physical and Neurological Examination of Subtle Signs and IQ were analysed in 136 children aged 6 to 16 (mean age 10y 2.6mo, SD 2y 6.4mo; 98 female, 38 male) attending an outpatient neuropsychology clinic and 136 right-handed comparison individuals aged 6 to 16 (mean age 10y 3.1mo, SD 2y 6.1mo; 98 female, 38 male). Timed activities - three repetitive movements (toe tapping, hand patting, finger tapping) and three sequenced movements (heel-toe tap, hand pronate/supinate, finger sequencing) each performed on the right and left - were included in exploratory factor analyses. Results: Among comparison individuals, factor analysis yielded two factors - repetitive and sequenced movements - with the sequenced factor significantly predictive of Verbal IQ (VIQ) (ΔR²=0.018, p=0.019), but not the repetitive factor (ΔR²=0.004, p=0.39). Factor analysis within the clinical group yielded two similar factors (repetitive and sequenced), both significantly predictive of VIQ, (ΔR²=0.028, p=0.015; ΔR²=0.046, p=0.002 respectively). Interpretation: Among typical children, repetitive timed tasks may be independent of IQ; however, sequenced tasks share more variance, implying shared neural substrates. Among neurologically vulnerable populations, however, both sequenced and repetitive movements covary with IQ, suggesting that repetitive speed is more indicative of underlying neurological integrity.