1,721,393 research outputs found
Electrophysiological correlates of stimulus-driven reorienting deficits after interference with right parietal cortex during a spatial attention task: a TMS-EEG study
No full textTMS interference over right intraparietal sulcus (IPS) causally disrupts behaviorally and EEG rhythmic correlates of endogenous spatial orienting before visual target presentation [Capotosto, P., Babiloni, C., Romani, G. L., & Corbetta, M. Differential contribution of right and left parietal cortex to the control of spatial attention: A simultaneous EEG-rTMS study. Cerebral Cortex, 22, 446-454, 2012; Capotosto, P., Babiloni, C., Romani, G. L., & Corbetta, M. Fronto-parietal cortex controls spatial attention through modulation of anticipatory alpha rhythms. Journal of Neuroscience, 29, 5863-5872, 2009]. Here we combine data from our previous studies to examine whether right parietal TMS during spatial orienting also impairs stimulus-driven reorienting or the ability to efficiently process unattended stimuli, that is, stimuli outside the current focus of attention. Healthy volunteers (n = 24) performed a Posner spatial cueing task while their EEG activity was being monitored. Repetitive TMS (rTMS) was applied for 150 msec simultaneously to the presentation of a central arrow directing spatial attention to the location of an upcoming visual target. Right IPS-rTMS impaired target detection, especially for stimuli presented at unattended locations; it also caused a modulation of the amplitude of parieto-occipital positive ERPs peaking at about 480 msec (P3) post-target. The P3 significantly decreased for unattended targets and significantly increased for attended targets after right IPS-rTMS as compared with sham stimulation. Similar effects were obtained for left IPS stimulation albeit in a smaller group of volunteers. We conclude that disruption of anticipatory processes in right IPS has prolonged effects that persist during target processing. The P3 decrement may reflect interference with postdecision processes that are part of stimulus-driven reorienting. Right IPS is a node of functional interaction between endogenous spatial orienting and stimulusdriven reorienting processes in human vision
Anticipation of somatosensory and motor events increases centro-parietal functional coupling: an EEG coherence study
No full textObjective: Does functional coupling of centro-parietal EEG rhythms selectively increase during the anticipation of sensorimotor events composed by somatosensory stimulation and visuomotor task? Methods: EEG data were recorded in (1) 'simultaneous' condition in which the subjects waited for somatosensory stimulation at left hand concomitant with a Go (or NoGo) visual stimulus triggering (50%) right hand movements and in (2) 'sequential' condition where the somatosensory stimulation was followed (+ 1.5 s) by a visuomotor Go/NoGo task. Centro-parietal functional coupling was modeled by spectral coherence. Spectral coherence was computed from Laplacian-transformed EEG data at delta-theta (2-7 Hz), alpha (8-14 Hz), beta 1 (15-21 Hz), beta 2 (22-33 Hz), and gamma (34-45 Hz) rhythms. Results: Before 'simultaneous' sensorimotor events, centro-parietal coherence regions increased in both hemispheres and at all rhythms. In the 'sequential' condition, right centro-parietal coherence increased before somatosensory event (left hand), whereas left centro-parietal coherence increased before subsequent Go/NoGo event (right hand). Conclusions: Anticipation of somatosensory and visuomotor events enhances contralateral centro-parietal coupling of slow and fast EEG rhythms. Significance: Predictable somatosensory and visuomotor events are anticipated not only by synchronization of cortical pyramidal neurons generating EEG power in parietal and primary sensorimotor cortical areas (Babiloni C, Brancucci A, Capotosto P, Arendt-Nielsen L, Chen ACN, Rossini PM. Expectancy of pain is influenced by motor preparation: a high-resolution EEG study of cortical alpha rhythms. Behav. Neurosci. 2005a; 119(2):503-511; Babiloni C, Brancucci A, Pizzella V, Romani G.L, Tecchio F, Torquati K, Zappasodi F, Arendt-Nielsen L, Chen ACN, Rossini PM. Contingent negative variation in the parasylvian cortex increases during expectancy of painful sensorimotor events: a magneto-encephalographic study. Behav. Neurosci. 2005b; 119(2):491-502) but also by functional coordination of these areas. (c) 2006 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved
FUNCTIONAL COUPLING OF PARIETAL ALPHA RHYTHMS IS ENHANCED IN ATHLETES BEFORE VISUOMOTOR PERFORMANCE: A COHERENCE ELECTROENCEPHALOGRAPHIC STUDY
No full textIt has been shown that elite pistol shooters are characterized by a power increase of wide cortical electroencephalographic (EEG) alpha (about 8-12 Hz) and beta (about 14-35 Hz) rhythms during the preparation of air pistol shots, possibly related to selective attentional and "neural efficiency" processes [Del Percio C, Babiloni C, Bertollo M, Marzano N, lacoboni M, Infarinato F, Lizio R, Stocchi M, Robazza C, Cibelli G, Comani S, Eusebi F (2009a) Hum Brain Mapp 30(11):3527-3540; Del Percio C, Babiloni C, Marzano N, lacoboni M, Infarinato F, Vecchio F, Lizio R, Aschieri P, Fiore A, Toran G, Gallamini M, Baratto M, Eusebi F (2009b) Brain Res Bull 79(3-4):193-200]. Here, we tested the hypothesis that such processes are associated with an enhanced functional coupling of posterior cortical regions involved in task-relevant attentional processes and visuo-motor transformations. To this aim, between-electrodes spectral coherence was computed from spatially enhanced EEG data collected during a previous study (i.e. right handed 18 elite air pistol shooters and 10 matched non-athletes; augmented 10-20 system; surface Laplacian estimation). Theta (about 4-6 Hz), low-frequency alpha (about 8-10 Hz), high-frequency alpha (about 10-12 Hz), low-frequency beta (14-22 Hz), high-frequency beta (23-35 Hz), and gamma (36-44 Hz) bands were considered. Statistical results showed that intra-hemispheric low-frequency alpha (parietal-temporal and parietal-occipital regions), high-frequency alpha (parietal-temporal and parietal-occipital regions), high-frequency beta, and gamma (parietal-temporal regions) coherence values were stable in amplitude in the elite athletes but not in the non-athletes during the preparation of pistol shots. The same applies to interhemispheric low-frequency alpha (parietal regions), high-frequency alpha (parietal regions), high-frequency beta and gamma coherence values. These findings suggest that under the present experimental conditions, elite athletes are characterized by the stabilization of functional coupling of preparatory EEG rhythms between "visuo-spatial" parietal area and other posterior cortical areas. (C) 2011 IBRO. Published by Elsevier Ltd. All rights reserved
Resting state cortical electroencephalographic rhythms in covert hepatic encephalopathy and Alzheimer's disease
Full text linkPatients suffering from prodromal (i.e., amnestic mild cognitive impairment, aMCI) and overt Alzheimer's disease (AD) show abnormal cortical sources of resting state electroencephalographic (EEG) rhythms. Here we tested the hypothesis that these sources show extensive abnormalities in liver cirrhosis (LC) patients with a cognitive impairment due to covert and diffuse hepatic encephalopathy (CHE). EEG activity was recorded in 64 LC (including 21 CHE), 21 aMCI, 21 AD, and 21 cognitively intact (Nold) subjects. EEG rhythms of interest were delta (2-4 Hz), theta (4-8 Hz), alpha 1 (8-10.5 Hz), alpha 2 (10.5-13 Hz), beta 1 (13-20 Hz), and beta 2 (20-30 Hz). EEG cortical sources were estimated by LORETA. Widespread sources of theta (all but frontal), alpha 1 (all but occipital), and alpha 2 (parietal, temporal) rhythms were higher in amplitude in all LC patients than in the Nold subjects. In these LC patients, the activity of central, parietal, and temporal theta sources correlated negatively, and parietal and temporal alpha 2 sources correlated positively with an index of global cognitive status. Finally, widespread theta (all but frontal) and alpha 1 (all but occipital) sources showed higher activity in the sub-group of LC patients with CHE than in the patients with aMCI or AD. These results unveiled the larger spatial-frequency abnormalities of the resting state EEG sources in the CHE compared to the AD condition
Nociceptive and non-nociceptive sub-regions in the human secondary somatosensory cortex: a MEG study using fMRI constraints
No full textPrevious evidence from functional magnetic resonance imaging (fMRI)
has shown that a painful galvanic stimulation mainly activates a
posterior sub-region in the secondary somatosensory cortex (SII),
whereas a non-painful sensory stimulation mainly activates an anterior
sub-region of SII [Ferretti, A., Babiloni, C., Del Gratta, C., Caulo, M.,
Tartaro, A., Bonomo, L., Rossini, P.M., Romani, G.L., 2003. Functional
topography of the secondary somatosensory cortex for non-painful and
painful stimuli: an fMRI study. Neuroimage 20 (3), 1625–1638.]. The
present study, combining fMRI with magnetoencephalographic (MEG)
findings, assessed the working hypothesis that the activity of such a
posterior SII sub-region is characterized by an amplitude and temporal
evolution in line with the bilateral functional organization of nociceptive
systems. Somatosensory evoked magnetic fields (SEFs) recordings
after alvanic median nerve stimulation were obtained from the same
sample of subjects previously examined with fMRI [Ferretti, A.,
Babiloni, C., Del Gratta, C., Caulo, M., Tartaro, A., Bonomo, L.,
Rossini, P.M., Romani, G.L., 2003. Functional topography of the
secondary somatosensory cortex for non-painful and painful stimuli:
an fMRI study. Neuroimage 20 (3), 1625–1638.]. Constraints for dipole
source localizations obtained from MEG recordings were applied
according to fMRI activations, namely, at the posterior and the
anterior SII sub-regions. It was shown that, after painful stimulation,
the two posterior SII sub-regions of the contralateral and ipsilateral
hemispheres were characterized by dipole sources with similar
amplitudes and latencies. In contrast, the activity of anterior SII subregions
showed statistically significant differences in amplitude and
latency during both non-painful and painful stimulation conditions. In
the contralateral hemisphere, the source activity was greater in
amplitude and shorter in latency with respect to the ipsilateral. Finally, painful stimuli evoked a response from the posterior sub-regions
peaking significantly earlier than from the anterior sub-regions. These
results suggested that both ipsi and contra posterior SII sub-regions
process painful stimuli in parallel, while the anterior SII sub-regions
might play an integrative role in the processing of somatosensory
stimuli
Frontoparietal cortex controls spatial attention through modulation of anticipatory alpha rhythms
No full textA dorsal frontoparietal network, including regions in intraparietal sulcus (IPS) and frontal eye field (FEF), has been hypothesized to control the allocation of spatial attention to environmental stimuli. One putative mechanism of control is the desynchronization of electroencephalography (EEG) alpha rhythms (∼8 -12 Hz) in visual cortex in anticipation of a visual target. We show that brief interference by repetitive transcranial magnetic stimulation (rTMS) with preparatory activity in right IPS or right FEF while subjects attend to a spatial location impairs identification of target visual stimuli ∼2 s later. This behavioral effect is associated with the disruption of anticipatory (prestimulus) alpha desynchronization and its spatially selective topography in parieto-occipital cortex. Finally, the disruption of anticipatory alpha rhythms in occipital cortex after right IPS- or right FEF-rTMS correlates with deficits of visual identification. These results support the causal role of the dorsal frontoparietal network in the control of visuospatial attention, and suggest that this is partly exerted through the synchronization of occipital visual neurons. Copyright © 2009 Society for Neuroscience
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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