Neurons in rat orbitofrontal cortex and medial prefrontal cortex exhibit distinct responses in reward and strategy-update in a risk-based decision-making task.

The orbitofrontal cortex (OFC) and the medial prefrontal cortex (mPFC) are known to participate in risk-based decision-making. However, whether neuronal activities of these two brain regions play similar or differential roles during different stages of risk-based decision-making process remains unknown. Here we conducted multi-channel in vivo recordings in the OFC and mPFC simultaneously when rats were performing a gambling task. Rats were trained to update strategy as the task was shifted in two stages. Behavioral testing suggests that rats exhibited different risk preferences and response latencies to food rewards during stage-1 and stage-2. Indeed, the firing patterns and numbers of non-specific neurons and nosepoking-predicting neurons were similar in OFC and mPFC. However, there were no reward-expecting neurons and significantly more reward-excitatory neurons (fired as rats received rewards) in the mPFC. Further analyses suggested that nosepoking-predicting neurons may encode the overall value of reward and strategy, whereas reward-expecting neurons show more intensive firing to a big food reward in the OFC. Nosepoking-predicting neurons in mPFC showed no correlation with decision-making strategy updating, whereas the response of reward-excitatory neurons in mPFC, which were barely observed in OFC, were inhibited during nosepoking, but were enhanced in the post-nosepoking period. These findings indicate that neurons in the OFC and mPFC exhibit distinct responses in decision-making process during reward consumption and strategy updating. Specifically, OFC encodes the overall value of a choice and is thus important for learning and strategy updating, whereas mPFC plays a key role in monitoring and execution of a strategy.

Respectfulness-processing revisited: An ERP study of Chinese sentence reading.

In Mandarin Chinese, an important manifestation of respectfulness is the use of different forms of second-person pronouns. Jiang et al. (2013) examined the event-related potential (ERP) correlates of processing respectful and plain pronouns in Chinese. However, this study suffered from a few methodological limitations, which restricted both the reliability and functional interpretations of the study's findings. In the present study, we resolved these limitations and further investigated the neurocognitive mechanisms of processing the respectfulness of pronouns. In the present study, participants read 160 critical Chinese sentences with a second-person pronoun (ni or nin) that was either consistent or inconsistent with its prior sentence context in terms of respectfulness, as well as 240 filler sentences. Unlike the previous study that reported a 300-500 ms negative response (N400) for both types of inconsistent pronouns, a sustained positive response for Nin inconsistent and a sustained negativity response for Ni inconsistent in the late time window, the present study found an N400 response and late sustained negativity for Nin inconsistent, but not for Ni inconsistent. Furthermore, the cluster-based permutation showed a significant negative cluster for Nin inconsistent, extending from 432-622 ms. We related this negative response for Nin inconsistent with recent accounts of the N400 and late negativity. Finally, the absence of the ERP effect for the Ni condition was linked to the role of the pragmatic property of Ni.