The Royal College of Obstetricians and Gynecologists released an updated report on fetal awareneess with a focus on pain (summary here, pdf of full report here, hat tip: Parableman). Its key conclusion is that there is no fetal pain prior to 24 weeks of gestation. This is because “connections from the periphery to the cortex are not intact before 24 weeks” and “most neuroscientists believe that the cortex is necessary for pain perception.”
The conclusion is broadly similar to the JAMA report from 2005 (see my post here; another post on this topic was here), except that the emphasis is on the 24 week point (which is when cortical connections begin to form) as opposed to the 29-30 week stage emphasized by JAMA which is when cortical functioning is relatively complete. Reading between the lines, I suspect the increasing numbers of surviving premature infants in the 24 -30 week range (and the empathy they engender if you come in contact with them) has encouraged this change in emphasis.
On the other hand, the UK study adds a section which concludes (from studies of unborn lambs) that fetuses are unlikely to feel much even later in gestation, due to their not being in a state of full wakefulness. The in utero environment is compared to a state of sedation. I don’t think is a very compelling aspect of the report: nothing increases awareness like trauma to one’s body.
Like my comments in earlier posts, I think this sort of interpretion of the data suffer from a sort of “cortical chauvinism”. As the report details, nerves form and pathways develop to the spinal cord, brain stem, and thalamus at various points from 8 to 18 weeks. I also think the role of the cortical subplate is intriguing. This structure, which develops at 12-13 weeks and disappears after 32-34 weeks, starts to receive connections from the thalamus between 12 and 18 weeks – this is kind of a primitive precursor to the cortex. And it is known that much earlier than 24 weeks the fetus both withdraws from a needle and launches a stress response.
Fetuses without fully developed brains certainly don’t feel pain the way we do, but this doesn’t mean there cannot be analogue of pain experience worthy of consideration. For many reasons I don’t believe experience is an all-or-nothing phenomenon, and I think we need to give the benefit of the doubt when considering the experiential status of fetuses (as well as animals) who don’t fully share our brain structure.