“There is a strong positive link between brain size and playfulness for mammals in general,” reported Neuroscientist Sergio Pellis, neuroscientist Andrew Iwaniuk and biologist John Nelson. (p33)
“Another renowned senior play researcher, Jaak Panksepp, has shown that active play selectively stimulates brain-deprived neurotrophic factor (which stimulates nerve growth) in the amygdala (where emotions get processed) and the dorsolateral prefrontal cortex (where executive decisions are processed).” (p33)
"Play seems to be a driving force helping to sculpt how the brain continues to grow and develop... Like sleep, play seems to dynamically stabilize body and social development in kids as well as sustain these qualities in adults.” (p42)
“As children, our reward for play is strong because we need it to help generate a rapidly developing brain. As adults, the brain is not developing so rapidly and the play drive may not be as strong, so we can do well enough without play in the short term. Our work or other responsibilities often demand that we set play aside. But when play is denied over the long term, our mood darkens. We lose our sense of optimism and we become anhedonic, or incapable of feeling sustained pleasure.
“There is laboratory evidence that there is a play deficit much like the well-documented sleep deficit.” (p43)