Neurobiology of Speech and Language. Proceedings of the 2nd International Workshop
Proceedings of the 2nd International Workshop Organised by the Laboratory of Behavioural Neurodynamics, Saint Petersburg State University September, 2018. Edited by Olga Shcherbakova, Yury Shtyrov Saint Petersburg, Russia
Previous research showed that under uncertainty (when we are not sure about what the correct answer is) in informal contexts such as chatting with friends, we tend to provide any retrieved information indiscriminately. However, in more formal contexts, like a job interview, we apply a more conservative threshold and balance reporting some information while withholding other answers as a way to provide some information while keeping the accuracy high, if possible. The left medial prefrontal cortex (lmPFC) was suggested as one of the areas linked with self-referential processing in metacognitive decisions. In the present research, we used repetitive transcranial magnetic stimulation (rTMS) to assess the involvement of the lmPFC in two different types of social contexts: formal and informal. Three groups of participants were exposed for 15 minutes to an offline 1-Hz rTMS stimulation of either: (1) lmPFC, (2) control site (rmPFC) or (3) sham (placebo stimulation). Afterwards, participants answered difficult general knowledge questions and rated their confidence in the correctness of their answers. Finally, they decided if they would report or withhold those answers in a formal (job interview) and in informal (chatting with friends) contexts. There were significantly more reported than withheld answers in the informal context for all three groups. However, in the formal context, there were more withheld than reported answers in the lmPFC group, with no differences in the other two groups. No differences in confidence ratings between groups were found. These results suggest a selective involvement of the lmPFC in self-monitoring in formal contexts; its inhibition seems to highlight the need of accuracy in our answers in a job interview over the socially more acceptable behaviour of always providing an answer when asked.
Intensive speech therapy was shown to lead to plastic changes reflected by lexical mismatch negativity (MMN) responses in aphasic patients (Mohr et al., 2016). Since many studies point to the role of the right hemisphere (RH) in aphasia recovery, noninvasive brain stimulation techniques (TMS, tDCS; Shah et al. 2013) usually target RH to facilitate this process. However, individual variance in stimulation-induced neural changes and resulting therapy outcomes are not understood. Here, 14 patients with chronic non-fluent mild-to-moderate aphasia caused by a left middle-cerebral artery stroke underwent Intensive Language-Action Therapy (ILAT, Pulvermüller, 2008) combined with anodal tDCS over the left IFG. To assess speech comprehension mechanisms, lexical MMN paradigm (120 deviant words vs. 487 standard pseudowords) was applied in MEG, before and after therapy for patients and once for a group of 10 controls. To improve the SNR of the responses, we applied a noise bootstrapping procedure with individual noise level computation. We found that the average power of the MMN response in the LH was significantly higher in the patients comparing to the healthy controls (p=0.01). Moreover, the variance of the MMN power increased significantly in the patient group after the treatment. This increase correlated with the behavioural improvements measured as a change of accuracy in a verb generation task (p=0.002). These changes were also associated with clinical improvements in speech comprehension measured by Russian Aphasia Test: scores in a sentence repetition subtest significantly increased after therapy (p = 0.035). No effects were found for the RH. Our results point to the compensatory role of the left hemisphere in the chronic stage of aphasia. They also highlight the role of individual variability in recovery of the language function, suggesting considerable individual differences in the recovery potential. The study continues to investigate these effects in larger samples.