Smith et al. in Nature Communications, 12, 5121, (2021) provided evidence to challenge the simple dichotomy that learning of actions and expression of habitual behaviors are processed separately in dorsomedial (DMS) and dorsolateral striatum (DLS) by demonstrating that D2 receptor-expressing medium spiny neurons (D2-MSNs) in anterior DLS could modulate newly learned action, except for its involvement in the expression of habitual actions. Here we review recent advances and introduce a valuable addition to the traditional hypothesis by taking into account the common ligand of D1 and D2 neurons, dopamine.
Keywords Behavior systems • Operant conditioning • HabitIt has long been proposed that learning of actions and expression of habitual behaviors are processed separately in dorsomedial (DMS) and dorsolateral striatum (DLS), respectively. Within this conceptual framework, it is further hypothesized that activity in the direct pathway could play a role in initiating actions while activation of the striatal indirect pathway might be responsible for the termination of movements. However, recent studies challenge this simple dichotomy by demonstrating that DMS and DLS coordinate with each other and that heterogeneous activities simultaneously exist in direct and indirect pathways.
To study the different mechanisms of understanding figurative language in a speaker’s native language (L1) and their second language (L2), this study investigated how scientific metaphors in Chinese (L1) and English (L2) are electrophysiologically processed via event-related potential experimentation. Compared with the metaphors from daily life or in literary works, scientific metaphors tend to involve both a more complicated context structure and a distinct knowledge-inferencing process. During the N400 time window (300–500 ms), English scientific metaphors elicited more negative N400s than Chinese ones at the parietal region. In the late positive component (LPC) time window (550–800 ms), English scientific metaphors elicited less positive LPCs than Chinese ones at the parietal region, and larger late negativities encompassing smaller areas of the brain. The findings might indicate that for late unbalanced bilingual speakers, L2 scientific metaphor comprehension requires more effort in information retrieval or access to the non-literal route. Altogether, the possible findings are that non-native and non-dominant language processing involves decreased automaticity of cognitive mechanisms, and decreased sensitivity to the levels of conventionality of metaphoric meanings.
Our previous study found that, in a triadic experiment, helplessness exhibited in mice in the loss of control over stress (LOC) group in response to aversive events was more prominent than that seen in the yoked (Yoked) group of mice. However, the mechanisms responsible for such phenomena are poorly understood. Increasing evidence has demonstrated that 5-hydroxytryptamine (5-HT) plays a critical role in emotional behaviours. Therefore, we hypothesized that the serotonergic system might mediate depression induced by the loss of control over stress. Our results showed that the activity level of 5-HT neurons of mice in the LOC group was significantly higher than that of mice in the Yoked and Control groups. Additionally, optogenetic inhibition of 5-HT neuron projections from the dorsal raphe nucleus (DRN) to the ventral hippocampus (VH) significantly reduced escape latency and freezing time, improved escape defect behaviour of mice in the LOC/Yoked group, and downregulated the expression of DRN 5-HT1A autoreceptor (DRN 5-HT1AR) of mice in the LOC group. These results provide compelling evidence that the sensitization of dorsal raphe 5-HT neurons mediates depression in a mouse model of loss of control over stress.
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