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9 results

  • Chapter 17 - Neuroimaging of attention and alteration of processing capacity in sleep-deprived persons
  • from Section 3 - Neuroimaging, sleep loss, and circadian misalignment
  • Edited by Eric Nofzinger, University of Pittsburgh, Pierre Maquet, Université de Liège, Belgium, Michael J. Thorpy
  • Book: Neuroimaging of Sleep and Sleep Disorders
  • Published online: 05 March 2013
  • Print publication: 07 March 2013, pp 137-144
  • View abstract

    Summary

    Low-resolution brain electromagnetic tomography (LORETA) was one of the first attempts to solve both the inverse problem and the reference electrode problem. It is able to localize deep sources as well by minimizing the squared three-dimensional (3D) spatial Laplacian operator to determine the unique solution. In 2001, the authors published the first study that applied LORETA to sleep electroencephalogram (EEG) data. They selected artifact-free epochs with sleep spindles and determined LORETA power in the frequency domain via the EEG cross-spectral matrix. LORETA revealed cortical spindle sources predominantly medially in the frontal and parietal lobe. The cortical generators localized for delta waves in slow-wave sleep (SWS) showed considerable overlap with the spindle generators. LORETA was applied to reveal changes in brain activity due to chronic hypoxia in patients with obstructive sleep apnea syndrome (OSAS).
  • Chapter 16 - Functional neuroimaging of sleep deprivation
  • from Section 3 - Neuroimaging, sleep loss, and circadian misalignment
  • Edited by Eric Nofzinger, University of Pittsburgh, Pierre Maquet, Université de Liège, Belgium, Michael J. Thorpy
  • Book: Neuroimaging of Sleep and Sleep Disorders
  • Published online: 05 March 2013
  • Print publication: 07 March 2013, pp 129-136
  • View abstract

    Summary

    This chapter outlines basic aspects of magnetoencephalography (MEG) technology, and provides an example of how the method is used clinically. In the clinical arena, MEG is most commonly used for presurgical planning purposes with the goal of localizing epileptogenic regions in patients with medically refractory seizures. In many of these cases, MEG provides unique clinical information that alters clinical care in a positive manner. Resective surgery was performed in the epileptogenic zone as originally identified by MEG and the patient has been seizure free for more than 2.5 years. The chapter describes how MEG is being used in sleep research. MEG is starting to play an increased role in the understanding of how brain circuits are modulated during sleep, with the most significant insights coming in relationship to the origins of sleep spindles and the complex modulation of neural interactions during rapid eye movement (REM) sleep.
  • Chapter 19 - Functional imaging of inter-individual differences in response to sleep deprivation
  • from Section 3 - Neuroimaging, sleep loss, and circadian misalignment
  • Edited by Eric Nofzinger, University of Pittsburgh, Pierre Maquet, Université de Liège, Belgium, Michael J. Thorpy
  • Book: Neuroimaging of Sleep and Sleep Disorders
  • Published online: 05 March 2013
  • Print publication: 07 March 2013, pp 154-162
  • View abstract

    Summary

    This chapter reports results on spontaneous brain activity during wakeful rest. It focuses on findings obtained with electroencephalography (EEG) and functional magnetic resonance imaging (fMRI), either acquired separately or simultaneously. The chapter discusses two approaches to analyze resting state activity with fMRI, namely reverse subtraction (activity correlated with task deactivation) and independent component analysis (ICA)-based region analysis. A third way to explore resting state blood oxygen level-dependent (BOLD) activity is to add information obtained with independent recording modalities, in particular EEG. When EEG and fMRI are recorded simultaneously, fMRI activity patterns associated with EEG-defined brain states can be analyzed. Relaxed wakefulness in the EEG is characterized by alpha and beta band oscillations. A thorough analysis of EEG and fMRI patterns during wakeful rest yields a complex relationship where certain EEG patterns can be associated with different BOLD maps and vice versa.
  • Chapter 18 - Economic decision-making and the sleep-deprived brain
  • from Section 3 - Neuroimaging, sleep loss, and circadian misalignment
  • Edited by Eric Nofzinger, University of Pittsburgh, Pierre Maquet, Université de Liège, Belgium, Michael J. Thorpy
  • Book: Neuroimaging of Sleep and Sleep Disorders
  • Published online: 05 March 2013
  • Print publication: 07 March 2013, pp 145-153
  • View abstract

    Summary

    Electroencephalogram (EEG) in combination with a fast whole-brain imaging method such as functional magnetic resonance imaging (fMRI) is an ideal tool to study sleep. This chapter covers practical aspects when planning and conducting a simultaneous EEG-fMRI experiment. It describes the choice of hardware to provide patient safety and comfort, while delivering high quality EEG and fMRI data. The chapter examines the choice of post processing methods applied to the electrophysiological data for scanner and subject-induced artifact reduction. Two empirical approaches have been mainly used to integrate fMRI and EEG data; first, using fMRI for the better determination of the source of the measured electrical EEG signal and second, trying to find the common neural origin of both the EEG and fMRI signals in a broader sense. EMG recordings are feasible but await further improved artifact reduction methods dealing with motion in the magnetic field.
  • Chapter 2 - Using fMRI to study cognitive function and its modulation in sleep-deprived persons: a selective overview
  • from Section 1 - Basic Mechanisms: Cognitive Performance and Sleep
  • Edited by Nancy J. Wesensten
  • Book: Sleep Deprivation, Stimulant Medications, and Cognition
  • Published online: 05 September 2012
  • Print publication: 23 August 2012, pp 7-22
  • View extract

    Summary

    This chapter discusses how the effects of sleep deprivation on the brain can be studied using functional magnetic resonance imaging (fMRI). Most contemporary functional brain imaging experiments are conducted using fMRI. This technique measures changes in blood oxygenation level dependent (BOLD) signal in capillaries and venules adjacent to neuronal clusters whose firing rate is modulated by task performance. Inference is most straightforward when the activated brain region participates in a circumscribed set of cognitive functions. For example, state related modulation of amygdala activity in response to affective pictures can be reasonably related to changes in emotional processing. Results of many fMRI experiments conducted on sleep-deprived subjects have consistently shown reduced superior parietal and lateral occipital activation during task performance. Results of more recent studies involve making decisions under uncertainty have shown that sleep-deprived persons tend toward riskier options, mirroring the behavior of patients with medial frontal damage.
  • 26 - Language processing in bilinguals as revealed by functional imaging: a contemporary synthesis
    • By Michael W. L. Chee, Clinician Scientist at SingHealth and an Adjunct Associate Professor in the Department of Biological Science, National University of Singapore
  • Edited by Ping Li, University of Richmond, Virginia, Li Hai Tan, The University of Hong Kong, Elizabeth Bates, University of California, San Diego, Ovid J. L. Tzeng, Academia Sinica, Taipei, Taiwan
  • Book: The Handbook of East Asian Psycholinguistics
  • Published online: 05 June 2012
  • Print publication: 27 April 2006, pp 287-295
  • View extract

    Summary

    Introduction

    Theoretical models of language processing abound, but, unlike memory where animal models are informative, only experiments involving human volunteers seem adequate to probe the complexities of human language. In order to determine which of these models is most appropriate, cognitive scientists are increasingly turning to brain imaging to provide answers to old questions as well as to provide a platform to ask new ones.

    The advent of functional magnetic resonance imaging (fMRI) has provided the opportunity for scientists from a wide variety of disciplines to investigate multiple facets of human cognition in healthy volunteers and clinical populations. Imaging with fMRI is attractive compared to previous methods like PET (positron emission tomography) and X-Ray scintigraphy because investigations can be repeated without exposing the study subject to ionizing radiation (Raichle, 1998). fMRI reveals parts of the brain where blood flow increases or decreases in response to performance of a cognitive task (Jezzard, Matthews & Smith, 2001). This review covers what has been learned regarding the topography of brain activation when bilinguals process different languages. The effects of cognitive demands of different languages, levels of processing, proficiency, and language background are considered.

    Studies on bilinguals in clinical populations

    Despite their heterogeneity and varied rigor, studies based on clinical populations are important because they provide information about brain regions that are critical to particular cognitive functions (as opposed to being merely participatory).