On redefining "sentience"

You may have noticed a rash of posts around the ScienceBlogs decrying the ARA terrorist extremists who have vowed, again, to target the children of a UCLA neuroscientist. Dario Ringach famously gave up his nonhuman primate research in 2006 because of threats against his family. His participation in last week’s dialog held at the UCLA campus apparently induced the extremist attention seekers, angry at having the momentum and PR shift to their slightly more rational co-travelers, to renew their threats. This is utterly despicable. Utterly.
This would be a great time for people who purport to be non-extremist animal rights advocates or sympathizers to do some deep soul searching. Soul searching that does not just easily write off the terrorists as a crazy fringe but asks penetrating questions about the nature of their own beliefs.
I cannot help you with this difficult work but I noticed something a little odd and new to me popping up in comment threads following the posts linked above. It has to do with the concept of sentience.

As many dependent on cannabis as have tried heroin?

A recent review paper covers animal models of adolescent drug taking, which is in and of itself an interesting read. Human adolescence tends to be a time when people first encounter psychoactive substances taken for recreational purposes. Unsurprisingly, problematic drug taking which emerges later in life often has antecedent roots in adolescent drug taking. The epidemiology goes further in identifying age-graded risk such that the earlier one starts using some drugs, the greater the chances of problematic drug use later in life.
Given the inescapable limitations human epidemiology (lack of random assignment means you cannot eliminate risk-associated variables from the genetic to the environmental) animal models are required to determine if there are neurobiological sensitivities in the adolescent brain which confer increased risk of developing dependence on a given recreational drug. This paper reviews much of the animal studies to date.

Are adolescents more vulnerable to drug addiction than adults? Evidence from animal models. Schramm-Sapyta NL, Walker QD, Caster JM, Levin ED, Kuhn CM. Psychopharmacology (Berl). 2009 Sep;206(1):1-21.

In providing the background context, Schramm-Sapyta et alia did something dear to my heart, as my readers will quickly appreciate. They created an interesting graphical depiction of the conditional probability of dependence on several drugs from the US National Survey on Drug Use and Health (NSDUH, 2007).