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Neuroimaging has consistently shown engagement of the prefrontal cortex during episodic memory tasks, but the functional relevance of this metabolic/hemodynamic activation in memory processing is still to be determined. We used repetitive transcranial magnetic stimulation (rTMS) to transiently interfere with either left or right prefrontal brain activity during the encoding or retrieval of pictures showing complex scenes. We found that the right dorsolateral prefrontal cortex (DLPFC) was crucial for the retrieval of the encoded pictorial information, whereas the left DLPFC was involved in encoding operations. This 'interference' approach allowed us to establish whether a cortical area activated by a memory task actually contributes to behavioral performance.

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The stronger anatomo-functional connections of the supplementary motor area (SMA), as compared with premotor area (PM), with regions of the limbic system, suggest that SMA could play a role in the control of movements triggered by visual stimuli with emotional content. We addressed this issue by analysing the modifications of the excitability of the primary motor area (M1) in a group of seven healthy subjects, studied with transcranial magnetic stimulation (TMS), after conditioning TMS of SMA, during emotional and non-emotional visually cued movements. Conditioning TMS of the PM or of contralateral primary motor cortex (cM1) were tested as control conditions. Single-pulse TMS over the left M1 was randomly intermingled with paired TMS, in which a conditioning stimulation of the left SMA, left PM or right M1 preceded test stimulation over the left M1. The subjects carried out movements in response to computerised visual cues (neutral pictures and pictures with negative emotional content). The amplitudes of motor-evoked potentials (MEPs) recorded from the right first dorsal interosseous muscle after paired TMS were measured and compared with those obtained after single-pulse TMS of the left M1 under the various experimental conditions. Conditioning TMS of the SMA in the paired-pulse paradigm selectively enhanced MEP amplitudes in the visual-emotional triggered movement condition, compared with single-pulse TMS of M1 alone or with paired TMS during presentation of neutral visual cues. On the other hand, conditioning TMS of the PM or cM1 did not differentially influence MEP amplitudes under visual-emotional triggered movement conditions. This pattern of effects was related to the intensity of the conditioning TMS over the SMA, being most evident with intensities ranging from 110% to 80% of motor threshold. These results suggest that the SMA in humans could interface the limbic and the motor systems in the transformation of emotional experiences into motor actions.

Over the last decade, passive brain-computer interface (BCI) algorithms and biosignal acquisition technologies have experienced a significant growth that has allowed the real-time analysis of biosignals, with the aim to quantify relevant insights, such as mental and emotional states, of the users. Several passive BCI-based applications have been tested in laboratory settings, and just a few of them in real or, at least, simulated but highly realistic settings. Nevertheless, works performed in laboratory settings are not able to take into account all those factors (artefacts, non-brain influences, other mental states) that could impair the usability of passive BCIs during real applications, naturally characterized by higher complexity. The present review takes into account the most recent trends in using advanced passive BCI technologies in real settings, especially for real-time mental state evaluations in operational environments, evaluation of team resources, training and expertise assessment, gaming and neuromarketing applications. The objective of the work is to draw a mark on where we are to date and the future challenges, in order to make passive BCIs closer to being integrated into daily life applications.

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