NeuroImage
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In the last 20 years or so, functional MRI has matured very rapidly from being an experimental imaging method in the hands of a few labs to being a very widely available and widely used workhorse of cognitive neuroscience and clinical neuroscience research internationally. FMRI studies have had a considerable impact on our understanding of brain system phenotypes of neurological and psychiatric disorders; and some impact already on development of new therapeutics. However, the direct benefit of fMRI to individual patients with brain disorders has so far been minimal. Here I provide a personal perspective on what has already been achieved, and imagine how the further development of fMRI over the medium term might lead to even greater engagement with clinical medicine.
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Review Historical Article
Intracortical recordings and fMRI: an attempt to study operational modules and networks simultaneously.
The brain can be envisaged as a complex adaptive system. It is characterized by a very high structural complexity and by massive connectivity, both of which change and evolve in response to experience. Information related to sensors and effectors is processed in both a parallel and a hierarchical fashion; the connectivity between different hierarchical levels is bidirectional, and its effectiveness is continuously controlled by specific associational and neuromodulatory centers. ⋯ In other words, multimodal methodologies that include invasive neuroscientific methods as well as global neuroimaging techniques are required, such as the various functional aspects of magnetic resonance imaging. These facts were the driving force behind the decision to begin animal-MRI in my lab. The wonderful idea of the editors of NeuroImage to publish a Special Issue commemorating 20years of functional fMRI provides me with the opportunity of sharing not only our first moments of frustration with the readers, but also our successful results.
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The opportunity to explore the human connectome using cutting-edge neuroimaging methods has elicited widespread interest. How far will the field be able to progress in deciphering long-distance connectivity patterns and in relating differences in connectivity to phenotypic characteristics in health and disease? We discuss the daunting nature of this challenge in relation to specific complexities of brain circuitry and known limitations of in vivo imaging methods. We also discuss the excellent prospects for continuing improvements in data acquisition and analysis. Accordingly, we are optimistic that major insights will emerge from human connectomics in the coming decade.
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Blood inflow from the upstream has contribution or contamination to the blood oxygen level-dependent (BOLD) functional signal both in its magnitude and time courses. During neuronal activations, regional blood flow velocity increases which results in increased fMRI signals near the macrovasculatures. The inflow effects are dependent on RF pulse history, slice geometry, flow velocity, blood relaxation times and imaging parameters. ⋯ This article reviews the basic principle of the inflow effects, its appearances in conventional GRE, fast spin-echo (FSE) and echo-planar imaging (EPI) acquisitions, methods for separating the inflow from the BOLD effect as well as the interplay between imaging parameters and other physiological factors with the inflow effects in fMRI. Based on theoretical derivation and human experiments, the inflow effects have been shown to contribute significantly in conventional GRE but negligible in FSE acquisitions. For gradient-echo EPI experiments, the blood inflow could modulate both amplitude and the temporal information of the fMRI signal, depending on the imaging parameters and settings.
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Review Historical Article
Future trends in Neuroimaging: Neural processes as expressed within real-life contexts.
Human neuroscience research has changed dramatically with the proliferation and refinement of functional magnetic resonance imaging (fMRI) technologies. The early years of the technique were largely devoted to methods development and validation, and to the coarse-grained mapping of functional topographies. This paper will cover three emerging trends that we believe will be central to fMRI research in the coming decade. ⋯ In the last section, we highlight the trend towards more ecologically valid fMRI experiments, which engage neural circuits in real life conditions. We note that many of our cognitive faculties emerge from interpersonal interactions, and that a complete understanding of the cognitive processes within a single individual's brain cannot be achieved without understanding the interactions among individuals. Looking forward to the future of human fMRI, we conclude that the major constraint on new discoveries will not be related to the spatiotemporal resolution of the BOLD signal, which is constantly improving, but rather to the precision of our hypotheses and the creativity of our methods for testing them.