The striatum is a critical component of the brain that controls motor, reward, and executive function. This ancient and phylogenetically conserved structure forms a central hub where rapid instinctive, reflexive movements and behaviors in response to sensory stimulation or the retrieval of emotional memory intersect with slower planned motor movements and rational behaviors. This review emphasizes two distinct pathways that begin in the thalamus and converge in the striatum to differentially affect movements, behaviors, and decision making. The convergence of excitatory glutamatergic activity from the thalamus and cortex, along with dopamine release in response to novel stimulation, provide the basis for motor learning, reward seeking, and habit formation. We outline how the rules derived through research on neural pathways may enhance the predictability of reflexive actions and rational responses studied in behavioral economics.

Phasic dopamine (DA) transmission encodes the value of reward-predictive stimuli and influences both learning and decision-making. Altered DA signaling is associated with psychiatric conditions characterized by risky choices such as pathological gambling. These observations highlight the importance of understanding how DA neuron activity is modulated. While excitatory drive onto DA neurons is critical for generating phasic DA responses, emerging evidence suggests that inhibitory signaling also modulates these responses. To address the functional importance of inhibitory signaling in DA neurons, we generated mice lacking the beta 3 subunit of the GABA(A) receptor specifically in DA neurons (beta 3-KO mice) and examined their behavior in tasks that assessed appetitive learning, aversive learning, and risk preference. DA neurons in midbrain slices from beta 3-KO mice exhibited attenuated GABA-evoked IPSCs. Furthermore, electrical stimulation of excitatory afferents to DA neurons elicited more DA release in the nucleus accumbens of beta 3-KO mice as measured by fast-scan cyclic voltammetry. beta 3-KO mice were more active than controls when given morphine, which correlated with potential compensatory upregulation of GABAergic tone onto DA neurons. beta 3-KO mice learned faster in two food-reinforced learning paradigms, but extinguished their learned behavior normally. Enhanced learning was specific for appetitive tasks, as aversive learning was unaffected in beta 3-KO mice. Finally, we found that beta 3-KO mice had enhanced risk preference in a probabilistic selection task that required mice to choose between a small certain reward and a larger uncertain reward. Collectively, these findings identify a selective role for GABA(A) signaling in DA neurons in appetitive learning and decision-making.

This paper raises some questions about Biggar’s accounts of the just cause and proportionality criteria for a just war. With respect to just cause, it argues that Biggar is committed to a broader range of justifications for war than one might think. Regarding proportionality, it claims that his account thereof invites reflection on the morality of conscription, and, more important still, given the book’s main aim—to refute Christian pacifism—in fact should lead him to embrace pacifism.