Author
Ali Mazaheri
Other affiliations: Radboud University Nijmegen, University of California, Davis, University of Amsterdam ...read more
Bio: Ali Mazaheri is an academic researcher from University of Birmingham. The author has contributed to research in topics: Electroencephalography & Visual cortex. The author has an hindex of 30, co-authored 72 publications receiving 5325 citations. Previous affiliations of Ali Mazaheri include Radboud University Nijmegen & University of California, Davis.
Papers published on a yearly basis
Papers
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TL;DR: It is proposed that information is gated by inhibiting task-irrelevant regions, thus routing information to task-relevant regions and the empirical support for this framework is discussed.
Abstract: In order to understand the working brain as a network, it is essential to identify the mechanisms by which information is gated between regions. We here propose that information is gated by inhibiting task-irrelevant regions, thus routing information to task-relevant regions. The functional inhibition is reflected in oscillatory activity in the alpha band (8-13 Hz). From a physiological perspective the alpha activity provides pulsed inhibition reducing the processing capabilities of a given area. Active processing in the engaged areas is reflected by neuronal synchronization in the gamma band (30-100 Hz) accompanied by an alpha band decrease. According to this framework the brain should be studied as a network by investigating cross-frequency interactions between gamma and alpha activity. Specifically the framework predicts that optimal task performance will correlate with alpha activity in task-irrelevant areas. In this review we will discuss the empirical support for this framework. Given that alpha activity is by far the strongest signal recorded by EEG and MEG, we propose that a major part of the electrophysiological activity detected from the working brain reflects gating by inhibition.
2,448 citations
TL;DR: It is found that DBS targeted at the nucleus accumbens (NAc) normalized NAc activity, reduced excessive connectivity between the NAc and prefrontal cortex, and decreased frontal low-frequency oscillations during symptom provocation in patients with obsessive-compulsive disorder.
Abstract: Little is known about the underlying neural mechanism of deep brain stimulation (DBS). We found that DBS targeted at the nucleus accumbens (NAc) normalized NAc activity, reduced excessive connectivity between the NAc and prefrontal cortex, and decreased frontal low-frequency oscillations during symptom provocation in patients with obsessive-compulsive disorder. Our findings suggest that DBS is able to reduce maladaptive activity and connectivity of the stimulated region.
378 citations
TL;DR: By examining the state of the brain before a stimulus, it is shown that it is possible to predict lapses of attention before they actually occur and supports the case that the stateof the brain is important for how incoming stimuli are processed and for how subjects respond.
Abstract: Do certain brain states predispose humans to commit errors in monotonous tasks? We used MEG to investigate how oscillatory brain activity indexes the brain state in subjects performing a Go-noGo task. Elevated occipital alpha and sensorimotor mu activity just prior to the presentation of the stimuli predicted an upcoming error. An error resulted in increased frontal theta activity and decreased posterior alpha activity. This theta increase and alpha decrease correlated on a trial-by-trial basis reflecting post-error functional connectivity between the frontal and occipital regions. By examining the state of the brain before a stimulus, we were able to show that it is possible to predict lapses of attention before they actually occur. This supports the case that the state of the brain is important for how incoming stimuli are processed and for how subjects respond.
274 citations
TL;DR: Using MEG, it is demonstrated that asymmetric amplitude fluctuations of the oscillatory alpha rhythm explain the generation of slow event-related fields, which provide new insight into the physiological basis of cognitive modulation in event- related brain activity.
Abstract: Electrophysiological data measured by electroencephalography and magnetoencephalography (MEG) are widely used to investigate human brain activity in various cognitive tasks. This is typically done by characterizing event-related potentials/fields or modulations of oscillatory activity (e.g., event-related synchronization) in response to cognitively relevant stimuli. Here, we provide a link between the two phenomena. An essential component of our theory is that peaks and troughs of oscillatory activity fluctuate asymmetrically; e.g., peaks are more strongly modulated than troughs in response to stimuli. As a consequence, oscillatory brain activity will not "average out" when multiple trials are averaged. Using MEG, we demonstrate that such asymmetric amplitude fluctuations of the oscillatory alpha rhythm explain the generation of slow event-related fields. Furthermore, we provide a physiological explanation for the observed asymmetric amplitude fluctuations. In particular, slow event-related components are modulated by a wide range of cognitive tasks. Hence, our findings provide new insight into the physiological basis of cognitive modulation in event-related brain activity.
204 citations
TL;DR: The analysis of the literature suggests that the NAc is currently the most promising DBS target area for patients with treatment-refractory addiction, and the mPFC is another promising target, but needs further exploration to establish its suitability for clinical purposes.
Abstract: Deep brain stimulation (DBS) is an adjustable, reversible, non-destructive neurosurgical intervention using implanted electrodes to deliver electrical pulses to areas in the brain. DBS is currently investigated in psychiatry for the treatment of refractory obsessive-compulsive disorder, Tourette syndrome and depressive disorder. Although recent research in both animals and humans has indicated that DBS may be an effective intervention for patients with treatment-refractory addiction, it is not yet entirely clear which brain areas should be targeted. The objective of this review is to provide a systematic overview of the published literature on DBS and addiction and outline the most promising target areas using efficacy and adverse event data from both preclinical and clinical studies. We found 7 animal studies targeting six different brain areas: nucleus accumbens (NAc), subthalamic nucleus (STN), dorsal striatum, lateral habenula, medial prefrontal cortex (mPFC) and hypothalamus, and 11 human studies targeting two different target areas: NAc and STN. Our analysis of the literature suggests that the NAc is currently the most promising DBS target area for patients with treatment-refractory addiction. The mPFC is another promising target, but needs further exploration to establish its suitability for clinical purposes. We conclude the review with a discussion on translational issues in DBS research, medical ethical considerations and recommendations for clinical trials with DBS in patients with addiction.
202 citations
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01 Jan 2010
TL;DR: In this paper, the authors describe a scenario where a group of people are attempting to find a solution to the problem of "finding the needle in a haystack" in the environment.
Abstract: 中枢神経系疾患の治療は正常細胞（ニューロン）の機能維持を目的とするが，脳血管障害のように機能障害の原因が細胞の死滅に基づくことは多い．一方，脳腫瘍の治療においては薬物療法や放射線療法といった腫瘍細胞の死滅を目標とするものが大きな位置を占める．いずれの場合にも，細胞死の機序を理解することは各種病態や治療法の理解のうえで重要である．現在のところ最も研究の進んでいる細胞死の型はアポトーシスである．そのなかで重要な位置を占めるミトコンドリアにおける反応および抗アポトーシス因子について概要を紹介する．
2,716 citations
TL;DR: It is proposed that information is gated by inhibiting task-irrelevant regions, thus routing information to task-relevant regions and the empirical support for this framework is discussed.
Abstract: In order to understand the working brain as a network, it is essential to identify the mechanisms by which information is gated between regions. We here propose that information is gated by inhibiting task-irrelevant regions, thus routing information to task-relevant regions. The functional inhibition is reflected in oscillatory activity in the alpha band (8-13 Hz). From a physiological perspective the alpha activity provides pulsed inhibition reducing the processing capabilities of a given area. Active processing in the engaged areas is reflected by neuronal synchronization in the gamma band (30-100 Hz) accompanied by an alpha band decrease. According to this framework the brain should be studied as a network by investigating cross-frequency interactions between gamma and alpha activity. Specifically the framework predicts that optimal task performance will correlate with alpha activity in task-irrelevant areas. In this review we will discuss the empirical support for this framework. Given that alpha activity is by far the strongest signal recorded by EEG and MEG, we propose that a major part of the electrophysiological activity detected from the working brain reflects gating by inhibition.
2,448 citations
TL;DR: It is suggested that alpha-band oscillations have two roles that are closely linked to two fundamental functions of attention (suppression and selection), which enable controlled knowledge access and semantic orientation (the ability to be consciously oriented in time, space, and context).
2,196 citations
TL;DR: Several rhythms and their interplay render neuronal communication effective, precise, and selective in neuronal groups.
1,899 citations
Journal Article•
TL;DR: It is hypothesized that beta oscillations and/or coupling in the beta-band are expressed more strongly if the maintenance of the status quo is intended or predicted, than if a change is expected.
Abstract: In this review, we consider the potential functional role of beta-band oscillations, which at present is not yet well understood. We discuss evidence from recent studies on top-down mechanisms involved in cognitive processing, on the motor system and on the pathophysiology of movement disorders that suggest a unifying hypothesis: beta-band activity seems related to the maintenance of the current sensorimotor or cognitive state. We hypothesize that beta oscillations and/or coupling in the beta-band are expressed more strongly if the maintenance of the status quo is intended or predicted, than if a change is expected. Moreover, we suggest that pathological enhancement of beta-band activity is likely to result in an abnormal persistence of the status quo and a deterioration of flexible behavioural and cognitive control.
1,837 citations