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Imaging the changing role of feedback during learning in decision-making

NEUROimage 2007年第4期37卷 1474-1486页

作者： Sailer, Uta Robinson, Simon Fischmelster, Florian Ph. S. Moser, Ewald Kryspin-Exner, Ilse Bauer, Herbert Univ Vienna Fac Psychol A-1010 Vienna Austria Med Univ Vienna MR Ctr Excellence A-1090 Vienna Austria Med Univ Vienna Ctr Biomed Engn & Phys A-1090 Vienna Austria

Learning from the outcome of decisions can be expected not only to change future decisions, but also our reaction to future outcomes. Using functional magnetic resonance imaging we investigated the neural responses of healthy subjects to feedback about choice outcomes before and after learning a response strategy which led to correct choices only. The task was designed so that losses were unavoidable even when all the choices made were correct. Subjects showed a distinct pattern of learning starting with an initial exploratory phase in which hypotheses about the correct strategy were generated and tested, followed by a phase of rapid strategy acquisition before reaching a final phase of proficiency. Neural activation was more pronounced during feedback processing in the exploratory phase than in the proficiency phase in a distributed network encompassing prefrontal and parietal areas as well as the striation. These areas are involved in working memory processes, the management of uncertainty and the establishment of stimulus-outcome contingencies. Reduced activation during feedback processing following learning was not only observed within subjects across learning phases, but also between subjects with different learning speeds. Thus, controlled and automatic processing are characterised by differing amounts of activation in identical task-relevant areas. Furthermore, whereas the same brain regions coded for gains and losses, the activation following gains changed to a larger extent with learning than following losses. This suggests that positive prediction errors are more sensitive to increased reward predictability than are negative prediction errors. (C) 2007 Elsevier Inc. All rights reserved.

关键词： Adult Algorithms Analysis of Variance Brain/physiology Decision Making/physiology Feedback, Psychological/physiology Female Humans image processing, computer-assisted Learning/physiology Magnetic Resonance Imaging Male Models, Psychological Motor Cortex/physiology Motor Skills/physiology Neostriatum/physiology Nerve Net/physiology Oxygen/blood Photic Stimulation Prefrontal Cortex/physiology

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Structure of hexameric DnaB helicase and its complex with a domain of DnaG primase

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SCIENCE 2007年第5849期318卷 459-463页

作者： Bailey, Scott Eliason, William K. Steitz, Thomas A. Yale Univ Dept Mol Biophys & Biochem New Haven CT 06520 USA Yale Univ Howard Hughes Med Inst New Haven CT 06520 USA Yale Univ Dept Chem New Haven CT 06520 USA

The complex between the DnaB helicase and the DnaG primase unwinds duplex DNA at the eubacterial replication fork and synthesizes the Okazaki RNA primers. The crystal structures of hexameric DnaB and its complex with the helicase binding domain (HBD) of DnaG reveal that within the hexamer the two domains of DnaB pack with strikingly different symmetries to form a distinct two-layered ring structure. Each of three bound HBDs stabilizes the DnaB hexamer in a conformation that may increase its processivity. Three positive, conserved electrostatic patches on the N-terminal domain of DnaB may also serve as a binding site for DNA and thereby guide the DNA to a DnaG active site.

关键词： Bacillus stearothermophilus/enzymology Bacillus stearothermophilus/metabolism Binding Sites Crystallization Crystallography, X-Ray Dimerization DNA Primase/chemistry DNA Primase/metabolism DNA, Bacterial/chemistry DNA, Bacterial/metabolism DnaB Helicases/chemistry DnaB Helicases/metabolism Endodeoxyribonucleases/chemistry Endodeoxyribonucleases/metabolism Escherichia coli/chemistry Escherichia coli/enzymology Escherichia coli/metabolism Escherichia coli Proteins/chemistry Escherichia coli Proteins/metabolism Exodeoxyribonucleases/chemistry Exodeoxyribonucleases/metabolism image processing, computer-assisted Models, Molecular Protein Binding Protein Structure, Quaternary Protein Structure, Secondary Protein Structure, Tertiary

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Functional neuroimaging correlates of mental fatigue induced by cognition among chronic fatigue syndrome patients and controls

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NEUROimage 2007年第1期36卷 108-122页

作者： Cook, Dane B. O'Connor, Patrick J. Lange, Gudrun Steffener, Jason Univ Wisconsin Dept Kinesiol Unit Gym 2 Madison WI 53706 USA William S Middleton Mem Vet Adm Med Ctr Dept Vet Affairs Madison WI 53706 USA Univ Georgia Dept Kinesiol Athens GA 30602 USA New Jersey Hlth Care Syst Dept Vet Affairs E Orange NJ 07018 USA Univ Med & Dent New Jersey New Jersey Med Sch Dept Radiol Newark NJ 07103 USA Columbia Univ Cognit Neurosci Div Taub Inst Res Alzheimers Dis Aging Brain New York NY 10032 USA

The neural mechanisms underlying feelings of fatigue are poorly understood. The primary purpose of the study was to use functional magnetic resonance imaging (fMRI) to determine the association between feelings of mental fatigue and blood oxygen level dependent (BOLD) brain responses during a mentally fatiguing cognitive task. Healthy, non-fatigued controls and chronic fatigue syndrome (CFS) patients were included to determine the influence of chronic levels of fatigue on brain responses. We hypothesized that mental fatigue would be significantly related to brain activity during a fatiguing cognitive task but not during either a non-fatiguing motor (finger tapping) or cognitive (auditory monitoring) task. Patients (n = 9) and controls (n = 11) completed a finger tapping task, a simple auditory monitoring task and a challenging working memory task, designed to induce mental fatigue, while undergoing fMRI. Fatigue was measured prior to scanning and following each task during fMRI data collection. Results showed that mental fatigue was significantly related to brain activity during the fatiguing cognitive task but not the finger tapping or simple auditory monitoring tasks. Significant (p <= 50.005) positive relationships were found for cerebellar, temporal, cingulate and frontal regions. A significant (p=0.001) negative relationship was found for the left posterior parietal cortex. CFS participants did not differ from controls for either finger tapping or auditory monitoring tasks, but exhibited significantly greater activity, in several cortical and subcortical regions during the fatiguing cognitive task. Our results suggest an association between subjective feelings of mental fatigue and brain responses during fatiguing cognition. (C) 2007 Elsevier Inc. All rights reserved.

关键词： Adult Arousal/physiology Attention/physiology Awareness/physiology Brain/physiopathology Cerebellum/physiopathology Dominance, Cerebral/physiology Fatigue Syndrome, Chronic/physiopathology Female Frontal Lobe/physiopathology Gyrus Cinguli/physiology Hippocampus/physiopathology Humans image processing, computer-assisted Magnetic Resonance Imaging Male Memory, Short-Term Mental Fatigue/physiopathology Middle Aged Motor Activity/physiology Parietal Lobe/physiology Problem Solving/physiology Psychomotor Performance/physiology Semantics Speech Perception/physiology Temporal Lobe/physiology

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The neural correlates of sign versus word production

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NEUROimage 2007年第1期36卷 202-208页

作者： Emmorey, Karen Mehta, Sonya Grabowski, Thomas J. San Diego State Univ Lab Language & Cognit Neurosci 6495 Alvarado RdSuite 200 San Diego CA 92120 USA Univ Iowa Iowa City IA USA

The production of sign language involves two large articulators (the hands) moving through space and contacting the body. In contrast, speech production requires small movements of the tongue and vocal tract with no observable spatial contrasts. Nonetheless, both language types exhibit a sublexical layer of structure with similar properties (e.g., segments, syllables, feature hierarchies). To investigate which neural areas are involved in modality-independent language production and which are tied specifically to the input-output mechanisms of signed and spoken language, we reanalyzed PET data collected from 29 deaf signers and 64 hearing speakers who participated in a series of separate studies. Participants were asked to overtly name concrete objects from distinct semantic categories in either American Sign Language (ASL) or in English. The baseline task required participants to judge the orientation of unknown faces (overtly responding 'yes'/,no' for upright/inverted). A random effects analysis revealed that left mesial temporal cortex and the left inferior frontal gyrus were equally involved in both speech and sign production, suggesting a modality-independent role for these regions in lexical access. Within the left parietal lobe, two regions were more active for sign than for speech: the supramarginal gyros (peak coordinates: -60, -35, +27) and the superior parietal lobule (peak coordinates: -26, -51, +54). Activation in these regions may be linked to modality -specific output parameters of sign language. Specifically, activation within left SMG may reflect aspects of phonological processing in ASL (e.g., selection of hand configuration and place of articulation features), whereas activation within SPL may reflect proprioceptive monitoring of motoric output. (C) 2007 Elsevier Inc. All rights reserved.

关键词： Brain Mapping Brain Mapping Cerebral Cortex/physiopathology Deafness/physiopathology Deafness/rehabilitation Dominance, Cerebral/physiology Frontal Lobe/physiopathology Humans image processing, computer-assisted Imaging, Three-Dimensional Occipital Lobe/physiopathology Parietal Lobe/physiopathology Pattern Recognition, Visual/physiology Positron-Emission Tomography Proprioception/physiology Semantics Sign Language Sign Language Speech/physiology Temporal Lobe/physiopathology

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Endogenous cortical rhythms determine cerebral specialization for speech perception and production

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NEURON 2007年第6期56卷 1127-1134页

作者： Giraud, Anne-Lise Kleinschmidt, Andreas Poeppel, David Lund, Torben E. Frackowiak, Richard S. J. Laufs, Helmut INSERM U742 F-75005 Paris France Univ Paris 06 F-75005 Paris France Ecole Normale Super Dept Etudes Cognit F-75005 Paris France Univ Frankfurt Dept Neurol D-60590 Frankfurt Germany CEA INSERM U562 F-91091 Gif Sur Yvette France Univ Maryland Cognit Neurosci Language Lab College Pk MD 20742 USA Copenhagen Univ Hosp Danish Res Ctr Magnet Resonance Hvidovre 2650 Denmark UCL Inst Neurol Wellcome Trust London WC1 3BG England IRCCS Santa Lucia I-00179 Rome Italy

Across multiple timescales, acoustic regularities of speech match rhythmic properties of both the auditory and motor systems. Syllabic rate corresponds to natural jaw-associated oscillatory rhythms, and phonemic length could reflect endogenous oscillatory auditory cortical properties. Hemispheric lateralization for speech could result from an asymmetry of cortical tuning, with left and right auditory areas differentially sensitive to spectro-temporal features of speech. Using simultaneous electroencephalographic (EEG) and functional magnetic resonance imaging (fMRI) recordings from humans, we show that spontaneous EEG power variations within the gamma range (phonemic rate) correlate best with left auditory cortical synaptic activity, while fluctuations within the theta range correlate best with that in the right. Power fluctuations in both ranges correlate with activity in the mouth premotor region, indicating coupling between temporal properties of speech perception and production. These data show that endogenous cortical rhythms provide temporal and spatial constraints on the neuronal mechanisms underlying speech perception and production.

关键词： Acoustic Stimulation/methods Adult Auditory Cortex/blood supply Auditory Cortex/physiology Brain Mapping Brain Mapping Electroencephalography Female Functional Laterality/physiology Humans image processing, computer-assisted Male Oxygen/blood Periodicity Reaction Time/physiology Spectrum Analysis Speech Speech Perception/physiology Speech Production Measurement/methods

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Abnormalities of language networks in temporal lobe epilepsy

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NEUROimage 2007年第1期36卷 209-221页

作者： Powell, H. W. Robert Parker, Geoff J. M. Alexander, Daniel C. Symms, Mark R. Boulby, Philip A. Wheeler-Kingshott, Claudia A. M. Barker, Gareth J. Koepp, Matthias J. Duncan, John S. UCL Inst Neurol Dept Clin & Expt Epilepsy London WC1N 3BG England Univ Manchester Manchester Lancs England UCL Dept Comp Sci London England UCL Inst Neurol NMR Res Unit London England Kings Coll London Inst Psychiat Dept Clin Neurosci Ctr Neuroimaging Sci London WC2R 2LS England

Functional magnetic resonance imaging (fMRI) in patients with temporal lobe epilepsy (TLE) has demonstrated reorganisation of language functions with greater involvement of the non-dominant hemisphere. The structural brain connections supporting this atypical language dominance have not previously been identified. We performed fMRI of language functions and imaging of white matter connections using MR tractography in 14 patients with unilateral TLE and hippocampal sclerosis and 10 controls. Verb generation and reading comprehension paradigms were used to define functional regions which were used to generate starting regions for tractography. Controls and right TLE patients had a left-lateralised pattern of both language-related activations and the associated structural connections. Left TLE patients showed more symmetrical language activations, along with reduced left hemisphere and increased right hemisphere structural connections. Subjects with more lateralised functional activation had also more highly lateralised connecting pathways. We provide evidence for structural reorganisation of white matter tracts that reflects the altered functional language lateralisation in left TLE patients. The combination of fMRI and tractography offers a promising tool for studying the reorganisation of language functions in many neurological conditions and may prove useful in predicting language deficits following temporal lobe surgery. (C) 2007 Elsevier Inc. All rights reserved.

关键词： Adult Comprehension/physiology Diffusion Magnetic Resonance Imaging Dominance, Cerebral/physiology Epilepsy, Temporal Lobe/physiopathology Female Frontal Lobe/physiopathology Hippocampus/physiopathology Humans image processing, computer-assisted Imaging, Three-Dimensional Language Development Disorders/diagnosis Language Development Disorders/physiopathology Magnetic Resonance Imaging Male Middle Aged Nerve Net/physiopathology Neuronal Plasticity/physiology Prognosis Reading Verbal Behavior/physiology

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Neural pathways link social support to attenuated neuroendocrine stress responses

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NEUROimage 2007年第4期35卷 1601-1612页

作者： Eisenberger, Naomi I. Taylor, Shelley E. Gable, Shelly L. Hilmert, Clayton J. Lieberman, Matthew D. Univ Calif Los Angeles Cousins Ctr Psychoneuroimmunol Los Angeles CA 90095 USA Univ Calif Los Angeles Dept Psychol Los Angeles CA 90095 USA N Dakota State Univ Dept Psychol Fargo ND 58105 USA

It is well established that a lack of social support constitutes a major risk factor for morbidity and mortality, comparable to risk factors such as smoking, obesity, and high blood pressure. Although it has been hypothesized that social support may benefit health by reducing physiological reactivity to stressors, the mechanisms underlying this process remain unclear. Moreover, to date, no studies have investigated the neurocognitive mechanisms that translate experiences of social support into the health outcomes that follow. To investigate these processes, thirty participants completed three tasks in which daily social support, neurocognitive reactivity to a social stressor, and neuroendocrine responses to a social stressor were assessed. Individuals who interacted regularly with supportive individuals across a 10-day period showed diminished cortisol reactivity to a social stressor. Moreover, greater social support and diminished cortisol responses were associated with diminished activity in the dorsal anterior cingulate cortex (dACC) and Brodmann's area (BA) 8, regions previously associated with the distress of social separation. Lastly, individual differences in dACC and BA 8 reactivity mediated the relationship between high daily social support and low cortisol reactivity, such that supported individuals showed reduced neurocognitive reactivity to social stressors, which in turn was associated with reduced neuroendocrine stress responses. This study is the first to investigate the neural underpinnings of the social support-health relationship and provides evidence that social support may ultimately benefit health by diminishing neural and physiological reactivity to social stressors. (c) 2007 Elsevier Inc. All rights reserved.

关键词： Adolescent Adult Cerebral Cortex/physiology Emotions/physiology Female Humans Hydrocortisone/metabolism Hypothalamus/physiopathology image processing, computer-assisted Magnetic Resonance Imaging Male Neural Pathways/physiopathology Neurosecretory Systems/physiopathology Prefrontal Cortex/physiology Saliva/chemistry Saliva/metabolism Social Isolation Social Support Stress, Psychological/physiopathology

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Evidence for cervical cord tissue disorganisation with aging by diffusion tensor MRI

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NEUROimage 2007年第3期36卷 728-735页

作者： Agosta, Federica Lagana, Marcella Valsasina, Paola Sala, Stefania Dall'Occhio, Luca Sormani, Maria P. Judica, Elda Filippi, Massimo Inst Sci MRI Res Grp Fdn Don Gnocchi I-20148 Milan Italy Inst Sci Dept Neurol Neuroimaging Res Unit Milan Italy Univ Milan Osped San Raffaele I-20127 Milan Italy Univ Genoa DISSAL Biostat Unit I-16126 Genoa Italy

This study investigated the influence of normal aging on cervical cord volumetry and diffusivity changes and assessed whether magnetic resonance imaging (MRI) abnormalities of the aging cervical cord and brain are associated. Conventional and diffusion tensor (DT) MRI of the brain and cervical cord were acquired from 96 healthy subjects (age range=13-70 years). Cross-sectional area, mean diffusivity (MD) and fractional anisotropy (FA) of the cervical cord were measured. Volumetry and diffusivity metrics were also obtained for the brain white matter (WM) and grey matter (GM) (overall and cortical). No cervical cord lesions were seen on conventional MR images from all subjects. Degenerative vertebral column changes (not associated to cord compression) were found in 41 subjects (43%). Average FA of the cervical cord, but not average MD and cross-sectional area, was correlated with age (r=-0.70, p < 0.001). Additionally, T2 brain lesion volume, normalised brain volume (NBV), normalised global and cortical brain GM volumes and average MD of the brain GM and WM also correlated with age (r values ranging from -0.83 to 0.62). Only brain WM average FA was weakly correlated with cervical cord average FA (r=0.25, p=0.02). The final multivariate model retained cord average FA (r=-0.37, p < 0.001), normalised cortical GM volume (r=-0.56, p < 0.001) and NBV (r=-0.22, p=0.04) as independent correlates of age (r(2)=0.76). Cervical cord is vulnerable to aging. The decrease of FA, in the absence of atrophy and MD changes, suggests gliosis as the most likely pathological feature of the aging cord. (c) 2007 Elsevier Inc. All rights reserved.

关键词： Adolescent Adult Aged Aging/pathology Anisotropy Atrophy Brain/pathology Cervical Vertebrae/pathology Cohort Studies Diffusion Magnetic Resonance Imaging Female Humans image processing, computer-assisted Magnetic Resonance Imaging Male Middle Aged Nerve Degeneration/pathology Spinal Cord/pathology

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Morphometry of corneal endothelium in patients with corneal guttata

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OPHTHALMOLOGY 2007年第8期114卷 1469-1475页

作者： Giasson, Claude J. Solomon, Leon D. Polse, Kenneth A. Univ Montreal Sch Optometry Montreal PQ H3C 3J7 Canada Univ Montreal Res Unit Vis Hlth Montreal PQ Canada St Sacrement Hosp Lab Organogenese Expt Quebec City PQ Canada Sir Mortimer B Davis Jewish Hosp Montreal PQ H3T 1E2 Canada McGill Univ Montreal PQ Canada Univ Calif Berkeley Sch Optometry Berkeley CA 94720 USA

Objective: To study the morphology of the corneal endothelium in patients diagnosed with corneal guttata using an image processing algorithm based on a contour detection method. Design: Retrospective observational case series. Participants: Twenty-four subjects with known corneal guttata. Methods: Two hundred eight images of corneal endothelium, captured with a noncontact specular microscope were analyzed using the Contour method, which demonstrates endothelial cell density (ECD), coefficient of variation of cell area, percentage of 4- to 8-sided cells as well as the number, area, and coefficient of variation of corneal guttata. Main Outcome Measures: The number, surface area, and coefficient of variation of corneal guttata. Results: Corneal position had no significant effect on ECD or on the percentage of endothelial cells with 4, 5, 7, or 8 sides. However, the coefficient of variation of images taken from the central cornea was significantly larger than those taken at the 2- and 6-o'clock positions. In addition, the percentage of hexagonal cells was significantly lower in pictures of the central position compared to those located in the upper paracentral position. The numbers and surface areas of guttata were significantly larger in pictures of the central compared to some paracentral positions. Subjects who had previously undergone cataract surgery with intraocular lens (IOL) implantation did not show different areas of corneal guttata, but exhibited a significantly lower cell density (1825 +/- 582) compared with unoperated patients (2400 +/- 457/mm(2)). Analogously, the only significant change observed in paired comparisons between the operated eye of patients with unilateral cataract extraction with IOL implantation and their unoperated fellow eye was a lower cell density obtained in operated eyes. Compared with normal subjects, subjects with corneal guttata were shown to have a significantly lower ECD, a lower proportion of hexagonal cells, and a higher coeffi

关键词： Aged Aged, 80 and over Algorithms Cell Count Cell Count Corneal Diseases/pathology Endothelium, Corneal/pathology Female Humans image processing, computer-assisted Lens Implantation, Intraocular Male Microscopy/methods Middle Aged Phacoemulsification Phacoemulsification Pseudophakia/complications Retrospective Studies Retrospective Studies

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Dynamics of hemispheric activity during metaphor comprehension: Electrophysiological measures

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NEUROimage 2007年第1期36卷 222-231页

作者： Arzouan, Yossi Goldstein, Abraham Faust, Miriam Bar Ilan Univ Gonda Brain Res Ctr IL-52900 Ramat Gan Israel Bar Ilan Univ Dept Psychol Ramat Gan Israel

Brain imaging studies have lead to conflicting findings regarding the involvement of the right hemisphere (RH) in metaphor comprehension. Some report more relative RH activation when processing figurative expressions but others have shown just the opposite. The inconsistencies might be a result of the low temporal resolution related to current brain imaging techniques which is insufficient to uncover patterns of hemispheric interaction that change over time. Event-related potentials and a source estimation technique (LORETA) were used to investigate such temporal interactions when processing two-word expressions denoting literal, conventional metaphoric, and novel metaphoric meaning, as well as unrelated word pairs. Participants performed a semantic judgment task in which they decided whether each word pair conveyed a meaningful expression. Our findings indicate that during comprehension of novel metaphors there are some stages of considerable RH involvement, mainly of the temporal and superior frontal areas. Although the processing mechanisms used for all types of expressions were similar and require both hemispheres, the relative contribution of each hemisphere at specific processing stages depended on stimulus type. Those stages correspond roughly to the N400 and LPC components which reflect semantic and contextual integration, respectively. The present study demonstrates that RH mechanisms are necessary, but not sufficient, for understanding metaphoric expressions. Both hemispheres work in concert in a complex dynamical pattern during literal and figurative language comprehension. Electrophysiological recordings together with source localization algorithms such as LORETA are a viable tool for measuring this ty. pe of activity patterns. (C) 2007 Elsevier Inc. All rights reserved.

关键词： Brain Mapping Brain Mapping Cerebral Cortex/physiology Comprehension Dominance, Cerebral/physiology Electroencephalography Evoked Potentials/physiology Humans image processing, computer-assisted Imaging, Three-Dimensional Judgment Metaphor Problem Solving/physiology Reading Semantics

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