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Many every-day life situations require two or more individuals to execute actions together. Assessing brain activation during naturalistic tasks to uncover relevant processes underlying such real-life joint action situations has remained a methodological challenge. In the present study, we introduce a novel joint action paradigm that enables the assessment of brain activation during real-life joint action tasks using functional near-infrared spectroscopy (fNIRS). We monitored brain activation of participants who coordinated complex actions with a partner sitting opposite them. Participants performed table setting tasks, either alone (solo action) or in cooperation with a partner (joint action), or they observed the partner performing the task (action observation). Comparing joint action and solo action revealed stronger activation (higher [oxy-Hb]-concentration) during joint action in a number of areas. Among these were areas in the inferior parietal lobule (IPL) that additionally showed an overlap of activation during action observation and solo action. Areas with such a close link between action observation and action execution have been associated with action simulation processes. The magnitude of activation in these IPL areas also varied according to joint action type and its respective demand on action simulation. The results validate fNIRS as an imaging technique for exploring the functional correlates of interindividual action coordination in real-life settings and suggest that coordinating actions in real-life situations requires simulating the actions of the partner.

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Background/Aims: The present study investigated cortical correlates of top-down processes in visual-object working memory with multi-channel near-infrared spectroscopy. Methods: The activity of the prefrontal cortex (PFC) was investigated while performing an n-back task with sequentially presented task-relevant and task-irrelevant faces. The activation patterns in the PFC associated with working memory and interference resolution were examined in 20 healthy adults. Results: We found a bilateral enhancement of oxygenated haemoglobin in the lateral PFC for remembering relevant faces and in the right lateral PFC for ignoring irrelevant faces. Oxygenation for relevant and irrelevant faces did not differ significantly, indicating that memory pro- cesses and interference resolution were interdependent functions, which were subserved by comparable prefrontal regions. Conclusion: This supports the notion that the prefrontal activity during working memory tasks reflects not only maintenance processes but also attentional monitoring and selection processes.