Twenty newborn infants were housed in a special facility. They had caregivers who would go in to feed them, bathe them and change their diapers, but they would do nothing else. The caregivers had been instructed not to look at or touch the babies more than was necessary, and they never spoke to them. All their physical needs were attended to scrupulously, however. The environment was kept sterile; the babies were never ill.
The experiment was halted after four months. At least half of the babies had died at that point, at least two more died even after being rescued and brought into a more normal environment. There was no physiological cause for the babies' deaths; they were all physically very healthy. Before each baby died, there was a period where they would stop verbalizing and trying to engage their caregivers, and just stop moving, never cry or change expression. Death would follow shortly. The babies who had "given up" before being rescued died in the same manner, even though they had been removed from the experimental conditions.
The conclusion was that nurturing is actually a very vital need in humans.