Non-retinotopic feature integration decreases response-locked brain activity as revealed by electrical neuroimaging

When presented with dynamic scenes, the brain integrates visual elements across space and time. Such non-retinotopic processing has been intensively studied from a psychophysical point of view, but little is known about the underlying neural processes. Here we used high-density EEG to reveal neural correlates of non-retinotopic feature integration. In an offset-discrimination task we presented sequences of lines for which feature integration depended on a small, endogenous shift of attention. Attention effects were observed in the stimulus-locked evoked potentials but non-retinotopic feature integration was reflected in voltage topographies time-locked to the behavioral response, lasting for about 400 ms. Statistical parametric mapping of estimated current densities revealed that this integration reduced electrical activity in an extensive network of brain areas, with the effects progressing from high-level visual, via frontal, to central ones. The results suggest that endogenously timed neural processes, rather than bottom-up ones, underlie non-retinotopic feature integration.

The electrophysiological effects of the serotonin 1A receptor agonist buspirone in emotional face processing

Fosco Bernasconi

Emotional face processing is critically modulated by the serotonergic system, and serotonin (5-HT) receptor agonists impair emotional face processing. However, the specific contribution of the 5-HT1A receptor remains poorly understood. Here we investigated the spatiotemporal brain mechanisms underpinning the modulation of emotional face processing induced by buspirone, a partial 5-HT1A receptor agonist. In a psychophysical discrimination of emotional faces task, we observed that the discrimination fearful versus neutral faces were reduced, but not happy versus neutral faces. Electrical neuroimaging analyses were applied to visual evoked potentials elicited by emotional face images, after placebo and buspirone administration. Buspirone modulated response strength (i.e., global field power) in the interval 230-248 ms after stimulus onset. Distributed source estimation over this time interval revealed that buspirone decreased the neural activity in the right dorsolateral prefrontal cortex that was evoked by fearful faces. These results indicate temporal and valence-specific effects of buspirone on the neuronal correlates of emotional face processing. Furthermore, the reduced neural activity in the dorsolateral prefrontal cortex in response to fearful faces suggests a reduced attention to fearful faces. Collectively, these findings provide new insights into the role of 5-HT1A receptors in emotional face processing and have implications for affective disorders that are characterized by an increased attention to negative stimuli. (C) 2015 Elsevier B.V. and ECNP. All rights reserved.

Elsevier Science Bv2015

Three sequential brain activations encode mental transformations of upright and inverted human bodies: a high resolution evoked potential study

Olaf Blanke

Human bodies provide a particularly rich source of visual information. Whereas most previous studies have focused on the neural mechanisms during the perception and recognition of human bodies, the aim of the present study was to investigate the time course and location of brain activation during mental imagery of human bodies. When participants were asked to imagine themselves in the position of a visually presented human body as seen from many different angles and at two orientations (upright or inverted), their reaction times were faster for upright as compared to inverted bodies and correlated differently with the tested angles. These behavioral effects were also reflected in brain activation patterns, but only during the time period from 220 to 490 ms after stimulus onset. Evoked potential mapping and electrical neuroimaging revealed three distinct and sequential steps of processing related to mental body transformation: (1) an early activation in temporo-occipital and temporo-parietal cortex (220-360 ms) that does not distinguish between upright and inverted bodies, but closely reflects the effort of mental transformation, followed (2) by an activation in temporo-occipital and medial parieto-occipital cortex (350-460 ms) that encodes mental transformation for upright bodies, and (3) a later activation in temporo-occipital and prefrontal cortex (390-490 ms) that encodes mental transformation for inverted bodies. These data suggest that the mental transformation of human bodies is not a single process but a sequence of temporally distinct processing steps, where each step reflects a distinct aspect of the transformation process that consists of activations in a network of posterior brain areas including extrastriate cortex, temporo-parietal cortex, and medial parieto-occipital cortex, as well as an anterior brain region in prefrontal cortex.

Elsevier2009

Self in time: imagined self-location influences neural activity related to mental time travel

Olaf Blanke

Conscious awareness of the self as continuous through time is attributed to the human ability to remember the past and to predict the future, a cogitation that has been called "mental time travel" (MTT). MTT allows one to re-experience one's own past by subjectively "locating" the self to a previously experienced place and time, or to pre-experience an event by locating the self into the future. Here, we used a novel behavioral paradigm in combination with evoked potential mapping and electrical neuroimaging, revealing that MTT is composed of two different cognitive processes: absolute MTT, which is the location of the self to different points in time (past, present, or future), and relative MTT, which is the location of one's self with respect to the experienced event (relative past and relative future). These processes recruit a network of brain areas in distinct time periods including the occipitotemporal, temporoparietal, and anteromedial temporal cortices. Our findings suggest that in addition to autobiographical memory processes, the cognitive mechanisms of MTT also involve mental imagery and self-location, and that relative MTT, but not absolute MTT, is more strongly directed to future prediction than to past recollection.

2008

Three sequential brain activations encode mental transformations of upright and inverted human bodies: a high resolution evoked potential study

Olaf Blanke

Elsevier2009