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Zhang Z.,Nanjing University | Lu G.,Nanjing University | Zhong Y.,Nanjing University | Tan Q.,Nanjing University | And 5 more authors.
Brain Research | Year: 2010

Increasing evidence from behavioral and neuroimaging studies suggests that mesial temporal lobe epilepsy (mTLE) is possibly associated with the default-mode brain function. However, the alteration of coherent neural activities in such a default-mode network (DMN) in mTLE has yet to be investigated. The present study analyzed the resting-state functional MRI data from two groups of mTLE patients with left and right hippocampal sclerosis using independent component analysis. In comparison with healthy controls, decreased functional connectivity in the dorsal mesial prefrontal cortex, mesial temporal lobe and inferior temporal cortex was observed in these two patient groups. Moreover, the right but not left mTLE patients showed bilaterally decreased functional connectivity in the mesial temporal lobe and increased functional connectivity in the posterior cingulate cortex. The decreased functional connectivity of the mesial temporal lobe was related to the epilepsy duration, suggesting that the posterior cingulate cortex may play a compensatory role for the altered DMN in the right mTLE. These findings indicate that the DMN is widely affected even if a single network node is impaired. An extensive regional overlap between the DMN and the previously described epileptic network suggests that the widespread functional impairments in mTLE may attribute to an aberrant DMN. The distinct patterns of the DMN between the left and right mTLE support a view that there are different pathological mechanisms underlying these two types of epilepsies. © 2010 Elsevier B.V. All rights reserved.

Li L.,University of California at Berkeley | Li L.,Key Laboratory for NeuroInformation | Gratton C.,University of California at Berkeley | Yao D.,Key Laboratory for NeuroInformation | Knight R.T.,University of California at Berkeley
Brain Research | Year: 2010

We investigated the contribution of frontal and parietal cortices to bottom-up and top-down visual attention using electrophysiological measures in humans. Stimuli consisted of triangles, each with a different color and orientation. Subjects were presented with a sample triangle which served as the target for that trial. An array was subsequently presented with the target and three additional distractor stimuli, which were constructed to induce either automatic "pop-out" (50%) or effortful "search" (50%) behavior. For pop-out, both the color and orientation of the distractors differed from the target, which attracted attention automatically. For search, only the orientation of the distractors differed from the target, so effortful attention was required. Pop-out target detection generated a P300 event-related potential (ERP) with a peak amplitude over parietal sites whereas the search condition generated a fronto-centrally distributed P300. Reaction times and associated P300 latency in frontal areas were shorter for pop-out targets than for search targets. We used time-frequency analysis to compare pop-out and search conditions, within a 200-650 ms time-window and a 4-55 Hz frequency band. There was a double dissociation, with significantly increased power from 4 to 24 Hz in parietal areas for pop-out targets and increased power from 4 to 24 Hz in frontal regions for search targets. Taken together the ERP and time-frequency results provide evidence that the control of bottom-up and top-down attention depend on differential contributions from parietal and frontal cortices. © 2010 Elsevier B.V.

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