Kids with high pain tolerance

My son has a high pain tolerance and never cries. He's being treated for this, with attachment and bonding therapy and sensory integration therapy. Children with high pain tolerance could have been severely neglected, and not touched much as infants. I'm not saying this is the case, but it was with our son. He was in an orphanage for nearly two years, from the age of 5 months to 2 and a half years old. I'm told the reason that he does not cry is because, when he did.... no one came, no one comforted, so he learned not to ask for comfort.