The brain is a stimulus-based system, it depends on outside sources for stimulation to grow and form connections. The more a brain cell is stimulated the more it will increase in size and strength.
Other than oxygen and nutrient supply 3 factors influence brain growth. They are; frequency of stimulation, duration of stimulation and intensity of stimulation. The only constant source of stimulation is gravity, other stimuli like light, sound, taste etc. comes and goes.
When humans evolved to stand on two legs, we also significantly increased the stimulation to our brains. Balancing on two legs involves a postural sway forward and back as well as side to side. This sway and balancing in multiple planes involve constant loading and unloading of movement receptors in muscles and joints which continuously talk to our brains. Walking upright therefore significantly contributed to the superior growth of the human brain through evolution.
Movement receptors are not evenly distributed throughout the body. The greatest concentration of receptors in human muscles and joints are found along the spine.
Walking upright and increased density of movement receptors in the spine has magnified the frequency, duration, and intensity of stimulation to the human brain.
In fact, it has been estimated that as much as 90% of the sensory stimulation to the human brain is generated by the spine.
So, keep your spine moving well as it is at the very core of human neurology.