Developmental cascades
Development can be viewed as a cascade, with new behaviors building on established ones, with curiosity, motivation and experience being important driving forces.
One way to get a grip on the developmental cascade and complex interactions is to divide development of hand function into three overlapping phases with age boundaries being flexible.
The first phase lasts from birth to about 6-8 weeks when spontaneous movements predominate.
The next phase is from roughly 2-6 months where curiosity driven exploratory hand actions are supported by visual attention.
The third phase which unfolds from 6-8 months is about learning to use the hands to makes things happen and the start of goal directed actions.
Three overlapping behaviors
Another way to think about about hand function in the period from birth to 8 months is in in terms of three behaviors: general exploration, reaching and object exploration.
Together these behaviors allow alert, curious and motivated infants to explore, gather information, and learn about their bodies, objects and people in the immediate environment, and the complex relationships between them. (Lobo et al 2015)
General exploration behaviors
General exploration behaviors are the seemingly random movements infants engage in with their arms, hands and fingers and as well as with with the feet which bring the hands and feet into contact with their bodies, clothing and surrounding surfaces.
These behaviors include feeling their body and surfaces, mouthing their hands, waving their arms, and close visual attention at their hands
Embryos begin performing these exploration behaviors in utero at around 8 weeks gestation. Exploration behaviors include touching the wall of the uterus, touching their own bodies and bringing the hands to the mouth and face.
These general exploration behaviors provide opportunities for infants to gather information and learn about their own bodies and the surfaces around them.
Study of self touching
Britanny Thomas and colleagues studied infant self touching, that is contact between the hands and face, body, and surrounding surfaces from birth to 24 weeks.
In the earlier weeks, the infants mainly contacted the body using the dorsum of the hand, with a high frequency of self-contacts made with a fist, progressing to dorsum contacts with a semi-closed hand, including contacts with the back of the fingers and the side of the hand. Duration of hand-to-body contact length was brief, marked mainly by contact and release.
At 8–12 weeks, hand-to-body contacts become increasingly exploratory with increased contact duration, finger manipulation, and movement of the hand across surfaces.
By 12 weeks hand-to-body contacts were increasingly made with the palmar aspect of the hand and became more complex, often involving rotation of the hand at contact, dragging the palm or fingertips along the surface of the body, and dynamic and complex hand shaping sequences.
The role of spontaneous movements in muscle and brain development
In compiling information for this tutorial, I reviewed my library of video clips of Will. I was struck by the amount of spontaneous movements of the arms that occurred even after Will had learned to successfully reach for, grasp and manipulate toys.
This exuberance of spontaneous limb movements must serve a function. It certainly will contribute to limb muscle strength and endurance.
It also probably plays a role in experience mediated development of the cortico-spinal tract and brain connectivity.
We know that infants born preterm and those with developmental delay tend to be less active and engage in less spontaneous limb movements. The question is whether early intervention should pay attention to increasing activity levels and spontaneous movements.