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Visual stimulation is frequently employed in electroencephalographic (EEG) research. However, despite its widespread use, no studies have thoroughly evaluated how the morphology of the visual event-related potentials (ERPs) varies according to the spatial location of stimuli. Hence, the purpose of this study was to perform a detailed retinotopic mapping of visual ERPs. We recorded EEG activity while participants were visually stimulated with 60 pattern-reversing checkerboards placed at different polar angles and eccentricities. Our results show five pattern-reversal ERP components. C1 and C2 components inverted polarity between the upper and lower hemifields. P1 and N1 showed higher amplitudes and shorter latencies to stimuli located in the contralateral lower quadrant. In contrast, P2 amplitude was enhanced and its latency was reduced by stimuli presented in the periphery of the upper hemifield. The retinotopic maps presented here could serve as a guide for selecting optimal visuo-spatial locations in future ERP studies., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Mechanisms underlying exogenous attention to central and peripheral distracters were temporally and spatially explored while 30 participants performed a digit categorization task. Neural (event-related potentials-ERPs-, analyzed both at the scalp and at the voxel level) and behavioral indices of exogenous attention were analyzed. Distracters were either biologically salient or neutral, in order to test whether the exogenous attention bias to the former observed in previous studies is independent of, or interacts with, distracter eccentricity. Two subcomponents of the N2 component of the ERPs, N2olp and N2ft, reflected processes related to peripheral distracters processing. N2olp effects, located in the dorsal attention network (supplementary motor area), were probably related to covert reorientation to peripheral distracters. N2ft effects, located in the default mode network (posterior cingulate cortex), appeared to reflect less effort in the ongoing task when peripheral distracters were presented. N2ft also showed a biological saliency effect which was independent of eccentricity and was located in the polar/ventral prefrontal cortex. P3 showed greater amplitudes to centrally presented distracters. These latter effects were located in TEO (visual cortex), and would be functionally associated with spatial interference between the target and central distracters. Behavior showed the relevance of both central and peripheral distracters in exogenous attention. These results indicate that exogenous attention to peripheral distracters differed in temporal and spatial terms from exogenous attention to central distracters and that it is biased towards biologically salient events irrespective of their eccentricity., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Functional magnetic resonance imaging studies have repeatedly provided evidence for temporal voice areas (TVAs) with particular sensitivity to human voices along bilateral mid/anterior superior temporal sulci and superior temporal gyri (STS/STG). In contrast, electrophysiological studies of the spatio-temporal correlates of cerebral voice processing have yielded contradictory results, finding the earliest correlates either at ∼300-400 ms, or earlier at ∼200 ms ("fronto-temporal positivity to voice", FTPV). These contradictory results are likely the consequence of different stimulus sets and attentional demands. Here, we recorded magnetoencephalography activity while participants listened to diverse types of vocal and non-vocal sounds and performed different tasks varying in attentional demands. Our results confirm the existence of an early voice-preferential magnetic response (FTPVm, the magnetic counterpart of the FTPV) peaking at about 220 ms and distinguishing between vocal and non-vocal sounds as early as 150 ms after stimulus onset. The sources underlying the FTPVm were localized along bilateral mid-STS/STG, largely overlapping with the TVAs. The FTPVm was consistently observed across different stimulus subcategories, including speech and non-speech vocal sounds, and across different tasks. These results demonstrate the early, largely automatic recruitment of focal, voice-selective cerebral mechanisms with a time-course comparable to that of face processing.

The tip-of-the-tongue state (TOT) in face naming is a transient state of difficulty in access to a person's name along with the conviction that the name is known. The aim of the present study was to characterize the spatio-temporal course of brain activation in the successful naming and TOT states, by means of magnetoencephalography, during a face-naming task. Following famous face presentations, subjects indicated whether they knew the name, did not know the name, or experienced a TOT state. Next they produced the name aloud, if they could, although they did not indicate whether they retrieved any other information about the person. The TOT state was characterized by lower activation than for successful retrieval, in the 310-520 ms poststimulus interval, localized to left temporal and frontal areas, bilateral parahippocampal gyrus, and right fusiform gyrus, which may underlie the genesis of TOT. Greater activation was also found in the 740-820 ms interval, localized to bilateral occipital, left temporal, and right frontal and parietal areas, corresponding with the unfruitful search for the name after the TOT state was produced. These results showed the differential brain dynamics underlying searching for the name of a known individual according to whether the search was successful or subjectively rated as just short of success., (2010 Elsevier Ltd. All rights reserved.)

Most of human cognitive activity involves, to a greater or lesser extent, the integration of information from different modalities, a process also referred to as 'binding'. Although the neural basis of several forms of binding has been extensively investigated, the neurobiological mechanisms of the encoding phase of integration of words and their spatial location have not been previously investigated. This process is at the core of what Baddeley proposed in his revised model as episodic buffer. In the current experiment, the authors used magnetoencephalography to investigate the spatiotemporal patterns of brain activity related to encoding words, locations, and the integration of both types of information using a working memory paradigm. The spatiotemporal analysis showed a preferential activation of superior parietal lobe (SPL) during the integration of information, which was modulated by performance in the task. These findings are in agreement with proposals suggesting that SPL participates in binding processes by encoding and maintaining a detailed, complex integrated representation in working memory (WM). Considering Baddeley's episodic buffer, it appears that the same mechanisms involved in integrating information within one subsystem (i.e., visuospatial buffer) also support the integration of information between previously considered independent subsystems (i.e., verbal and visuospatial buffers).

The neural processes underlying tactile decisions in the human brain remain elusive. We addressed this question in a functional magnetic resonance imaging study using a somatosensory discrimination task, requiring participants to compare the frequency of two successive tactile stimuli. Tactile stimuli per se engaged somatosensory, parietal, and frontal cortical regions. Using a statistical model that accounted for the relative difference in frequencies (i.e., Weber fraction) and discrimination accuracy (i.e., correct or incorrect), we show that trial-by-trial relative frequency difference is represented linearly by activity changes in the left dorsolateral prefrontal cortex (DLPFC), the dorsal anterior cingulate cortex, and bilateral anterior insular cortices. However, a circumscribed region within the left DLPFC showed a different response pattern expressed as activity changes that were monotonically related to relative stimulation difference only for correct but not for incorrect trials. Our findings suggest that activity in the left DLPFC encodes stimulus representations that underlie veridical tactile decisions in humans.

Brain oscillations are considered to play a pivotal role in neural communication. However, detailed information regarding the typical oscillatory patterns of individual brain regions is surprisingly scarce. In this study we applied a multivariate data-driven approach to create an atlas of the natural frequencies of the resting human brain on a voxel-by-voxel basis. We analysed resting-state magnetoencephalography (MEG) data from 128 healthy adult volunteers obtained from the Open MEG Archive (OMEGA). Spectral power was computed in source space in 500 ms steps for 82 frequency bins logarithmically spaced from 1.7 to 99.5 Hz. We then applied k-means clustering to detect characteristic spectral profiles and to eventually identify the natural frequency of each voxel. Our results provided empirical confirmation of the canonical frequency bands and revealed a region-specific organisation of intrinsic oscillatory activity, following both a medial-to-lateral and a posterior-to-anterior gradient of increasing frequency. In particular, medial fronto-temporal regions were characterised by slow rhythms (delta/theta). Posterior regions presented natural frequencies in the alpha band, although with differentiated generators in the precuneus and in sensory-specific cortices (i.e., visual and auditory). Somatomotor regions were distinguished by the mu rhythm, while the lateral prefrontal cortex was characterised by oscillations in the high beta range (>20 Hz). Importantly, the brain map of natural frequencies was highly replicable in two independent subsamples of individuals. To the best of our knowledge, this is the most comprehensive atlas of ongoing oscillatory activity performed to date. Critically, the identification of natural frequencies is a fundamental step towards a better understanding of the functional architecture of the human brain. [ABSTRACT FROM AUTHOR]