Placebo and nocebo effects are associated with opposite responses of DA and endogenous opioid neurotransmission in a distributed network of regions. The brain areas involved in these phenomena form part of the circuit typically implicated in reward responses and motivated behavior.

Expectations, positive or negative, are modulating factors influencing behavior. They are also thought to underlie placebo effects, impacting perceptions and biological processes. Using healthy human subjects, we examined the role of the nucleus accumbens (NAC), a region centrally involved in the encoding of reward expectation, in the formation of placebo responses. Employing functional molecular imaging, activation of NAC dopamine (DA) release was observed during placebo administration and related to its anticipated effects, perception-anticipation mismatches, and placebo effect development. In additional functional MRI studies, the expectation of monetary gain increased NAC synaptic activity in a manner proportional to placebo-induced DA release, anticipated effects, perception-anticipation differentials, and actual placebo effects. Individual variations in NAC response to reward expectation accounted for 28% of the variance in the formation of placebo analgesia.

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The production of radioargon through the irradiation of CaO was performed in an in-core facility within the The University of Texas at Austin MARK II TRIGA reactor. The major radioargon isotope produced was 37 Ar via the 40 Ca(n,α) 37 Ar reaction pathway. The CaO powder was vacuumed sealed in a quartz ampoule. The sample was irradiated in a Cd-lined Al alloy canister for 2 hours at 500 kW. After the irradiation, the sample was counted using an HPGe detector five times with increasing count times. 41

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