The Last Psychiatrist has a very interesting post on how antipsychotics function at different doses. He/she uses the metaphor of a multi-tiered fountain (filled with rum) to talk about Seroquel: you fill the top (sedation) tier of receptors before you overflow into the antipsychotic tier of receptors. I.e., Seroquel is not an antipsychotic on lower doses.
Once the top tier is filled, you cannot fill it any more, which is why people on high doses of Seroquel are not asleep 24/7 but are getting other additional effects.
I don’t have the background knowledge to evaluate this claim independently, but I thought it was interesting enough to pass on, and if I get other confirming/disconfirming info, I’ll pass that along too.