One of the things that integration of primitive reflexes and a mature brainstem does is to help develop muscle tone and postural stability.
Not only is muscle tone and postural stability very important in order to develop eye stability and ocular reflexes, but it is critical for the creation of brain waves within the thalamus.
The VA and VL nuclei in the thalamus are the motor nuclei and are the ones that primarily dictate the firing rate of the non-specific nucleus, the part of the thalamus where consciousness resides. So the nuclei that have the greatest effect on the brain is related to motor input to the cerebellum and basal ganglia, especially from postural muscles. Stronger postural muscles yield stronger brain wave oscillation.
Stability must first be developed in a non-gravitational position, then sitting, then standing, then moving. Imbalances and asymmetry of muscle tone is directly related to brain maturity and balance as well as both bottom up and top down regulation.
Note, back muscles should be 30% stronger than the abdomen, thus focus should be on developing back strength.