Cortical Regions Involved in Navigation (original) (raw)
Functional magnetic resonance imaging of the human brain: Data acquisition and analysis
Experimental Brain Research, 1998
It is now feasible to create spatial maps of activity in the human brain completely non-invasively using magnetic resonance imaging. Magnetic resonance imaging (MRI) images in which the spin magnetization is refocussed by gradient switching are sensitive to local changes in magnetic susceptibility, which can occur when the oxygenation state of blood changes. Cortical neural activity causes increases in blood flow, which usually result in changes in blood oxygenation. Hence changes of image intensity can be observed, given rise to the socalled Blood Oxygenation Level Dependent (BOLD) contrast technique. Use of echo-planar imaging methods (EPI) allows the monitoring over the entire brain of such changes in real time. A temporal resolution of 1±3 s, and a spatial resolution of 2 mm in-plane, can thus be obtained. Generally in a brain mapping experiment hundred of brain image volumes are acquired at repeat times of 1±6 s, while brain tasks are performed. The data are transformed into statistical maps of image difference, using the technique known as statistical parametric mapping (SPM). This method, based on robust multilinear regression techniques, has become the method of reference for analysis of positron emission tomography (PET) image data. The special characteristics of functional MRI data require some modification of SPM algorithms and strategies, and the MRI data must be gaussianized in time and space to conform to the assumptions of the statistics of Gaussian random fields. The steps of analysis comprise: removal of head movement effects, spatial smoothing, and statistical interference, which includes temporal smoothing and removal by fitting of temporal variations slower than the experimental paradigm. By these means, activation maps can be generated with great flexibility and statistical power, giving probability estimates for activated brain regions based on intensity or spatial extent, or both combined. Recent studies have shown that patterns of activation obtained in human brain for a given stimulus are indepen-dent of the order and spatial orientation with which MRI images are acquired, and hence that inflow effects are not important for EPI data with a TR much longer than T1.
Nature neuroscience, 2000
Visuospatial navigation in animals and human subjects is generally studied using maze exploration. We used functional MRI to observe brain activation in male and female subjects as they searched for the way out of a complex, three-dimensional, virtual-reality maze. Navigation activated the medial occipital gyri, lateral and medial parietal regions, posterior cingulate and parahippocampal gyri as well as the right hippocampus proper. Gender-specific group analysis revealed distinct activation of the left hippocampus in males, whereas females consistently recruited right parietal and right prefrontal cortex. Thus we demonstrate a neural substrate of well established human gender differences in spatial-cognition performance.
Mental maze solving: directional fMRI tuning and population coding in the superior parietal lobule
Experimental Brain Research, 2005
The superior parietal lobule (SPL) of six human subjects was imaged at 4 T during mental traversing of a directed maze path. Here we demonstrate the orderly involvement of the SPL in this function, as follows. Forty-two percent of the voxels were tuned with respect to the direction of the maze path. This suggests a coherent tuning of local neuronal populations contributing to the change of the single-voxel BOLD signal. Preferred directions ranged throughout the directional continuum of 360°. Voxels with similar preferred directions tended to cluster together: on average there were seven same-direction clusters per slice, with an average cluster membership of five voxels/cluster and an average nearest-neighbor same-direction intercluster distance of 13.1 mm. On the other hand, the average nearestneighbor intercluster distance between a given direction and all other directions was 3.1 mm. This suggests a patchy arrangement such that patches of directionally tuned voxels, containing voxels with different preferred directions, alternate with patches of non-tuned voxels. Finally, the population vector predicted accurately the direction of the maze path (with an error of 12.7°), and provided good estimates (with an error of 29°) when calculated within parts of the SPL. Altogether, these findings document a new, orderly functional organization of the SPL with respect to mental tracing.
Introduction to the Issue on fMRI Analysis for Human Brain Mapping
IEEE Journal of Selected Topics in Signal Processing, 2000
Functional magnetic resonance imaging (fMRI), one of the most recently developed forms of neuroimaging technology, allows noninvasive assessment of brain activity and has been aptly called "our window into the human brain". By enabling researchers to study temporal and spatial changes in both the healthy and the diseased brain as a function of various stimuli, fMRI has contributed significantly to our understanding of the brain, and its study has been one of the most active areas of research. The study of fMRI data is highly interdisciplinary due to its unique nature and particular challenges. Between the two main groups-the developers of the technology and the ultimate end users-there is a major shift and increasing recognition of the role signal processing plays for extracting, processing, analyzing and modeling fMRI data for human brain mapping. As a result, fMRI analysis for human brain mapping has been gaining importance and momentum within the signal processing community. This special issue aims to underline this major current trend and bring together a diverse but complementary set of contributions to address the current brain mapping challenges and the solutions where signal processing plays an important role.
2000
ited by the latency of the hemodynamic response (about 1 s) but can provide millimeter spatial sampling (Belli- † Department of Radiology University of Utah veau et al., 1991; Kwong et al., 1992). Conversely, methods based on direct measurement of the electric and Salt Lake City, Utah 84108 ‡ Institut National de la Sante ´et magnetic fields produced by neuronal activity can provide temporal resolution of less than 1 ms, adequate for de la Recherche Me ´dicale E9926, Marseilles detecting the orchestration of complex cognitive activity (Regan, 1989). However, the spatial configuration of neu-France § Department of Psychology Anatomy, and ronal activity cannot be derived uniquely based on electroencephalography (EEG) and/or magnetoencephalog-Neurobiology, and Radiology Washington University raphy (MEG) recordings alone (Nunez, 1981; Ha ¨ma ¨la ¨inen et al., 1993). In order to make this so-called inverse St. Louis, Missouri 63130 problem well posed, it is necessary to impose additional constraints on the solution. One common approach is to assume that the EEG/ Summary MEG signals are generated by a relatively small number of focal sources (Sherg and VonCramon, 1985; Schmidt Functional magnetic resonance imaging (fMRI) can et al., 1999). An additional constraint can be derived provide maps of brain activation with millimeter spatial from the assumption that the sources are temporally resolution but is limited in its temporal resolution to uncorrelated (Mosher et al., 1992). These assumptions the order of seconds. Here, we describe a technique are particularly appropriate when analyzing early senthat combines structural and functional MRI with magsory responses, where the activity might reasonably be netoencephalography (MEG) to obtain spatiotemporal expected to be relatively focal and constrained to a maps of human brain activity with millisecond tempofew primary sensory areas. On the other hand, such ral resolution. This new technique was used to obtain assumptions are less justified in higher-level cognitive dynamic statistical parametric maps of cortical activexperiments, which have been found by intracranial reity during semantic processing of visually presented cordings in humans to involve extensive networks of words. An initial wave of activity was found to spread more or less synchronously activated brain areas (Halrapidly from occipital visual cortex to temporal, parigren et al., 1994a, 1994b, 1995a, 1995b; Baudena et al., etal, and frontal areas within 185 ms, with a high de-1995). Similarly, the interictal spikes characteristic of gree of temporal overlap between different areas. Reppartial epilepsy typically spread very rapidly to involve etition effects were observed in many of the same a network extended across multiple cortical and limbic areas following this initial wave of activation, providing regions (Chauvel et al., 1987). evidence for the involvement of feedback mechanisms An alternative approach to analyzing EEG/MEG sigin repetition priming. nals is to impose constraints based on anatomical and physiological information derived from other imaging
Human Brain Mapping, 1994
Localized brain activation in response to moving visual stimuli was studied by functional magnetic resonance imaging (FMRJ). Stimuli were 100 small white dots randomly arranged on a visual display. During the Motion condition, the dots moved along random, noncoherent linear trajectories at different velocities. During the Blink condition, the dots remained stationary but blinked on and off every 500 ms. The Motion and Blink conditions continuously alternated with 10 cycles per run and 6-8 runs per experiment. In half of the runs, the starting stimulus condition was Motion, while in the remaining runs it was Blink.
Applications of fMRI for Brain Mapping
Brain-mapping techniques have proven to be vital in understanding the molecular, cellular, and functional mechanisms of the brain. Normal anatomical imaging can provide structural information on certain abnormalities in the brain. However there are many neurological disorders for which only structure studies are not sufficient. In such cases it is required to investigate the functional organization of the brain. Further it is necessary to study the brain functions under normal as well as diseased conditions. Brain mapping techniques can help in deriving useful and important information on these issues. Brain functions and brain area responsible for the particular activities like motor, sensory speech and memory process could be investigated. The authors provide an overview of various Brain Mapping techniques and fMRI signal processing methods.
Proceedings of The National Academy of Sciences, 1994
It is now feasible to create spatial maps of activity in the human brain completely non-invasively using magnetic resonance imaging. Magnetic resonance imaging (MRI) images in which the spin magnetization is refocussed by gradient switching are sensitive to local changes in magnetic susceptibility, which can occur when the oxygenation state of blood changes. Cortical neural activity causes increases in blood flow, which usually result in changes in blood oxygenation. Hence changes of image intensity can be observed, given rise to the socalled Blood Oxygenation Level Dependent (BOLD) contrast technique. Use of echo-planar imaging methods (EPI) allows the monitoring over the entire brain of such changes in real time. A temporal resolution of 1±3 s, and a spatial resolution of 2 mm in-plane, can thus be obtained. Generally in a brain mapping experiment hundred of brain image volumes are acquired at repeat times of 1±6 s, while brain tasks are performed. The data are transformed into statistical maps of image difference, using the technique known as statistical parametric mapping (SPM). This method, based on robust multilinear regression techniques, has become the method of reference for analysis of positron emission tomography (PET) image data. The special characteristics of functional MRI data require some modification of SPM algorithms and strategies, and the MRI data must be gaussianized in time and space to conform to the assumptions of the statistics of Gaussian random fields. The steps of analysis comprise: removal of head movement effects, spatial smoothing, and statistical interference, which includes temporal smoothing and removal by fitting of temporal variations slower than the experimental paradigm. By these means, activation maps can be generated with great flexibility and statistical power, giving probability estimates for activated brain regions based on intensity or spatial extent, or both combined. Recent studies have shown that patterns of activation obtained in human brain for a given stimulus are indepen-dent of the order and spatial orientation with which MRI images are acquired, and hence that inflow effects are not important for EPI data with a TR much longer than T1.