World-first MRI study shows babies experience pain 'like adults' (Medical News Today)
"Dr. Slater states that their findings stand in contrast with previous understandings of infant pain. "In fact, some people have argued that babies' brains are not developed enough for them to really 'feel' pain, any reaction being just a reflex," she says. "Our study provides the first really strong evidence that this is not the case."

What Parents Need to Know About Pain in Newborns (Harvard University)
"We certainly need to avoid doing painful procedures in the first place. The policy statement does say that we should be very thoughtful and careful when it comes to choosing to do painful things to babies."

Neonatal Cortisol Response to Circumcision with Anesthesia (Clinical Pediatrics)
"Eleven male newborns were circumcised with a local dorsal penile nerve block, and 13 controls were circumcised without anesthetic. Matched pairs of pre- and postcircumcision cortisol levels in the two groups were compared. The adrenal cortisol response to surgery was not significantly reduced by the administration of lidocaine."

A Comparison of the Mogen and Gomco Clamps (Pediatrics-AAP)
"Although considerable controversy exists regarding the medical value of circumcision, the evidence is overwhelming that it is a painful procedure. Multiple studies have shown increased heart rate (HR), respiratory rate (RR), and stress hormone production, as well as decreased oxygen saturation (SaO2) during circumcision. These are all nonspecific markers associated with stress. Infants also display a specific pattern of facial expression classically associated with pain. Some studies have suggested that in addition to causing immediate pain, circumcision may have consequences that persist beyond the perioperative period."

Pain Relief for Neonatal Circumcision (Cochrane)
"Circumcision is a painful procedure frequently performed on newborn baby boys without using pain relief. Available treatments include dorsal penile nerve block (DPNB), which involves injecting anesthetic at the base of the penis. Ring block is another form of penile block."

AAP: Newborns, Especially Preemies, Experience Too Much Pain During Routine Procedures (AAP)
"Pain that newborns experience from routine medical procedures can be significant... Research suggests that repeated exposure to pain early in life can create changes in brain development and the body's stress response systems that can last into childhood.  Because of this, a new American Academy of Pediatrics policy statement recommends every health facility caring for newborns should use strategies to minimize the number of painful procedures performed..."

Infant Circumcision with Anesthesia: Does It Really Help the Pain? (Compilation) 
"A large majority of routine infant circumcisions are not performed with any anesthetic. In fact, up to 96 percent of the babies in the United States and Canada receive no anesthesia when they are circumcised, according to a report from the University of Alberta in Edmonton."

The Mystery of How Babies Experience Pain (The Conversation) "Stressed babies may not seem to respond to pain although their brain is still processing it. The phenomenon has been seen in premature babies who sometimes “tune out” and become unresponsive when they are overwhelmed. But that doesn’t mean they are not experiencing something. Importantly, this means that doctors and nurses may underestimate their pain."

Babies Remember Pain (Kindred Media) "In the last two decades, a dozen studies have reported infant reactions to circumcision. All reveal stress, manifest in the tripling and quadrupling of normal cortisol levels in the bloodstream, changes in heart rate, the oxygen content of tissues, frequency of crying, disturbances of sleep, and inability of babies to calm themselves..."