The development of postural response patterns during reaching in healthy infants.

Reaching movements in adults are accompanied by complex postural adjustments which are controlled by spatial, temporal, and quantitative parameters. The basic postural adjustments are selected on the basis of the spatial parameter, whereas fine tuning of the pattern is guided by temporal and quantitative parameters. In specific conditions, such as during fast arm movements, postural adjustments have an anticipatory character. Recently, the development of postural adjustments during reaching was studied longitudinally in infants aged 3-18 months, placed in supine and sitting positions. The data revealed that already at 4 months, the age at which successful reaching emerges, reaching movements are accompanied by complex postural adjustments. The early postural patterns resembled the adult ones in spatial features (dorso-ventral ordering), temporal characteristics (top-down recruitment), and position dependency. With increasing age the postural patterns changed considerably, including a transient period of less extensive postural activity at 6-8 months, the age at which rolling, sitting up and crawling develops. Postural anticipation during reaching was not consistently present at any age.