Social Modulation during Songbird Courtship Potentiates Midbrain Dopaminergic Neurons

Synaptic transmission onto dopaminergic neurons of the mammalian ventral tegmental area (VTA) can be potentiated by acute or chronic exposure to addictive drugs. Because rewarding behavior, such as social affiliation, can activate the same neural circuitry as addictive drugs, we tested whether the intense social interaction of songbird courtship may also potentiate VTA synaptic function. We recorded glutamatergic synaptic currents from VTA of male zebra finches who had experienced distinct social and behavioral conditions during the previous hour. The level of synaptic transmission to VTA neurons, as assayed by the ratio of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) to N-methyl-D-aspartic acid (NMDA) glutamate receptor mediated synaptic currents, was increased after males sang to females, and also after they saw females without singing, but not after they sang while alone. Potentiation after female exposure alone did not appear to result from stress, as it was not blocked by inhibition of glucocorticoid receptors. This potentiation was restricted to synapses of dopaminergic projection neurons, and appeared to be expressed postsynaptically. This study supports a model in which VTA dopaminergic neurons are more strongly activated during singing used for courtship than during non-courtship singing, and thus can provide social context-dependent modulation to forebrain areas. More generally, these results demonstrate that an intense social encounter can trigger the same pathways of neuronal plasticity as addictive drugs

Drug addiction and criminal responsibility

Recent studies reveal some of the neurophysiological mechanisms involved in drug addiction. This prompts some theorists to claim that drug addiction diminishes responsibility. Stephen Morse however rejects this claim. Morse argues that these studies show that drug addiction involves neither compulsion, coercion, nor irrationality. He also adds that addicted people are responsible for becoming addicted and for failing to take measures to manage their addiction. After summarizing relevant neuroscience of addiction literature, this chapter engages critically with Morse to argue that a subgroup of addicted people does meet plausible criteria for compulsion, coercion, or irrationality; that few addicted people are fully responsible for becoming addicted; and that some addicted people can be at least partly excused for failing to manage their addiction. Pickard and Lacey’s “responsibility without blame” approach is also suggested as a fruitful basis for future work in this field.19 page(s