The N170 occipito-temporal component is delayed and enhanced to inverted faces but not to inverted objects: an electrophysiological account of face-specific processes in the human brain
Electrophysiology Evoked Potentials/*physiology
Form Perception/*physiology Humans
Male Occipital Lobe/*physiology
Psychomotor Performance/physiology Temporal Lobe/*physiology
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AbstractBehavioral studies have shown that picture-plane inversion impacts face and object recognition differently, thereby suggesting face-specific processing mechanisms in the human brain. Here we used event-related potentials to investigate the time course of this behavioral inversion effect in both faces and novel objects. ERPs were recorded for 14 subjects presented with upright and inverted visual categories, including human faces and novel objects (Greebles). A N170 was obtained for all categories of stimuli, including Greebles. However, only inverted faces delayed and enhanced N170 (bilaterally). These observations indicate that the N170 is not specific to faces, as has been previously claimed. In addition, the amplitude difference between faces and objects does not reflect face-specific mechanisms since it can be smaller than between non-face object categories. There do exist some early differences in the time-course of categorization for faces and non-faces across inversion. This may be attributed either to stimulus category per se (e.g. face-specific mechanisms) or to differences in the level of expertise between these categories.
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Central adaptation following heterotopic hand replantation probed by fMRI and effective connectivity analysisinfo:eu-repo/classification/ddc/610; Eickhoff, S. B.; Dafotakis, M.; Grefkes, C.; Shah, J. N.; Zilles, K.; Piza-Katzer, H. (Elsevier, 2008)In this functional magnetic resonance imaging (fMRI) study, we examined changes--relative to healthy controls--in the cortical activation and connectivity patterns of two patients who had undergone unilateral heterotopic hand replantation. The study involved the patients and a group of control subjects performing visually paced hand movements with their left, right, or both hands. Changes of effective connectivity among a bilateral network of core motor regions comprising M1, lateral premotor cortex (PMC), and the supplementary motor area (SMA) were assessed using dynamic causal modelling. Both patients showed inhibition of ipsilateral PMC and SMA when moving the healthy hand, potentially indicating a suppression of inference with physiological motor execution by the hemisphere controlling the replanted hand. Moving the replanted hand, both patients showed increased activation of contralateral PMC, most likely reflecting the increased effort involved, and a pathological inhibition of the ipsilateral on the active contralateral M1 indicative of an unsuccessful modulation of the inhibitory M1-M1 balance. In one patient, M1 contralateral to the replanted hand experienced increased tonic (intrinsic connectivity) and phasic (replanted hand movement) facilitating input, whereas in the other, pathological suppression was present. These differences in effective connectivity correlated with decreased behavioural performance of the latter as assessed by kinematic analysis, and seemed to be related to earlier and more intense rehabilitative exercise commenced by the former. This study hence demonstrates the potential of functional neuroimaging to monitor plastic changes of cortical connectivity due to peripheral damage and recovery in individual patients, which may prove to be a valuable tool in understanding, evaluating and enhancing motor rehabilitation.
The effect of repetition lag on electrophysiological and haemodynamic correlates of visual object priming.Henson R, Rylands AJ, Ross E, Vuilleumeir P, Rugg M. (2004-04)The modulation of repetition effects by the lag between first and second presentations of a visual object during a speeded semantic judgment task was examined using both scalp event-related potentials (ERPs) and event-related functional magnetic resonance imaging (efMRI). Four levels of lag were used within a single session, from zero to one, to tens of intervening stimuli, and which allowed partial separation of the effects of interference from the effects of time. Reaction times (RTs) showed that the magnitude of repetition priming decreased as lag increased. The ERP data showed two distinct effects of repetition, one between 150 and 300 ms post stimulus and another between 400 and 600 ms. The magnitude of both effects, particularly the earlier one, decreased as lag increased. The fMRI data showed a decrease in the haemodynamic response associated with repetition in several inferior occipitotemporal regions, the magnitude of which also typically decreased as lag increased. In general, and contrary to expectations, lag appeared to have mainly quantitative effects on the three types of dependent variable: there was little evidence for qualitative differences in the neural correlates of repetition effects at different lags.
Visuospatial attention: how to measure effects of infrequent, unattended events in a blocked stimulus designinfo:eu-repo/classification/ddc/610; Giessing, C.; Thiel, C. M.; Stephan, K. E.; Rösler, F.; Fink, G. R. (Academic Press, 2004)This fMRI study investigates the differences between a blocked and event-related analysis in a cued target detection task, the so-called Posner paradigm, using a hybrid design. Validly and invalidly cued trials were presented intermingled in different blocks containing 50%, 75%, or 100% valid trials. Four analyses were conducted: (i) an event-related analysis comparing invalid and valid trials, (ii) a blocked analysis comparing blocks with 50% valid and invalid trials to blocks with 100% valid trials, (iii) a blocked analysis detecting differences between block models when modeled as epochs or chains of events, and (iv) a blocked analysis that modeled blocks as chains of events to scale regressors equally to the event-related analysis. Irrespective of the type of analysis (blocked or event related), significant activation of the right intraparietal sulcus was observed. A larger cluster size was evident in the blocked analysis, which can be attributed to higher efficiency. In addition to this common right parietal activation, the event-related analysis revealed activations in right superior parietal cortex and left intraparietal sulcus. In contrast, the blocked analysis yielded additional activity in the right occipitoparietal junction. No influences of the block model (epoch versus chain of events) were found in regions activated in the blocked or event-related analysis, respectively. In summary, using a hybrid design and both event-related and blocked analysis techniques, we show both sustained and transient neural processes underlying reorienting of visuospatial attention.