Neural oscillations and a nascent corticohippocampal theory of reference

The ability to use words to refer to the world is vital to the communicative power of human language. In particular, the anaphoric use of words to refer to previously mentioned concepts (antecedents) allows dialogue to be coherent and meaningful. Psycholinguistic theory posits that anaphor comprehension involves reactivating a memory representation of the antecedent. Whereas this implies the involvement of recognition memory, or the mnemonic sub-routines by which people distinguish old from new, the neural processes for reference resolution are largely unknown. Here, we report time-frequency analysis of four EEG experiments to reveal the increased coupling of functional neural systems associated with referentially coherent expressions compared to referentially problematic expressions. Despite varying in modality, language, and type of referential expression, all experiments showed larger gamma-band power for referentially coherent expressions compared to referentially problematic expressions. Beamformer analysis in high-density Experiment 4 localised the gamma-band increase to posterior parietal cortex around 400-600 ms after anaphor-onset and to frontaltemporal cortex around 500-1000 ms. We argue that the observed gamma-band power increases reflect successful referential binding and resolution, which links incoming information to antecedents through an interaction between the brain’s recognition memory networks and frontal-temporal language network. We integrate these findings with previous results from patient and neuroimaging studies, and we outline a nascent cortico-hippocampal theory of reference

Antidepressant-like properties of Antiaris toxicaria aqueous extract

Background: Depression is a global burden whose therapy is plagued with inconsistent efficacy. Hence, the need for the discovery of newer therapies.Methods: In this study, Antiaris toxicaria extract (200, 400 and 800 mg/kg, p.o.), was evaluated for antidepressant activity using behavioral tests battery particularly the forced swim test (FST) and tail suspension test (TST). In order to investigate its mechanism of action, animals groups were pretreated with α-methyldopa (α-MD), para-chlorophenylalanine (PCPA), reserpine, D-serine and 5-hydroxytryptophan.Results: It increased the mobility periods and decreased immobility periods significantly in both the FST and the TST when compared to the control group. But the TST showed more promising effect than the FST. Pre-treatment with α-MD reversed the antidepressant property of A. toxicaria aqueous extract as did PCPA, reserpine and reserpine combined with α-MD. The extract increased the number of head twitches produced by 5-hydroxytryptophan confirming the involvement of serotonin in the antidepressant property and inhibited carbachol-induced contractions on the isolated rat uterus, which was non-competitively antagonized by propranolol.Treatment with D-serine produced no significant increase in the immobility time produced by the extract at the doses studied. This excludes the involvement of N-methyl-d-aspartate in the possible mechanisms of action.Conclusion: A. toxicaria possesses antidepressant-like action in rodents

On predicting form and meaning in a second language

We used event-related potentials (ERP) to investigate whether Spanish−English bilinguals preactivate form and meaning of predictable words. Participants read high-cloze sentence contexts (e.g., “The student is going to the library to borrow a . . .”), followed by the predictable word (book), a word that was form-related (hook) or semantically related (page) to the predictable word, or an unrelated word (sofa). Word stimulus onset synchrony (SOA) was 500 ms (Experiment 1) or 700 ms (Experiment 2). In both experiments, all nonpredictable words elicited classic N400 effects. Form-related and unrelated words elicited similar N400 effects. Semantically related words elicited smaller N400s than unrelated words, which however, did not depend on cloze value of the predictable word. Thus, we found no N400 evidence for preactivation of form or meaning at either SOA, unlike native-speaker results (Ito, Corley et al., 2016). However, non-native speakers did show the post-N400 posterior positivity (LPC effect) for form-related words like native speakers, but only at the slower SOA. This LPC effect increased gradually with cloze value of the predictable word. We do not interpret this effect as necessarily demonstrating prediction, but rather as evincing combined effects of top-down activation (contextual meaning) and bottom-up activation (form similarity) that result in activation of unseen words that fit the context well, thereby leading to an interpretation conflict reflected in the LPC. Although there was no evidence that non-native speakers preactivate form or meaning, non-native speakers nonetheless appear to use bottom-up and top-down information to constrain incremental interpretation much like native speakers do