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C J Aine

Publications and source records attributed to C J Aine.

14 recordsLinked to original sources
PubMed1999

Single vs. paired visual stimulation: superposition of early neuromagnetic responses and retinotopy in extrastriate cortex in humans.

Neuromagnetic techniques were used in conjunction with magnetic resonance imaging (MRI) techniques to: (1) localize and characterize cortical sources evoked by visual stimuli presented at different locations in the lower right visual field; (2) examine the superposition of cortical responses by comparing the summation of responses to the presentation of single stimuli with responses to paired stimuli; and (3) examine the spatial resolution of magnetoencephalographic (MEG) techniques by comparing the identified source locations evoked by the presentation of single vs. paired stimuli. Using multi-dipole, non-linear minimization analyses, three sources were localized for each stimulus condition during the initial 80-170 ms poststimulus interval for all subjects. In addition to an occipital source, two extrastriate sources were identified: occipital-parietal and occipital-temporal. Each source evidenced a systematic shift in location associated with changes in stimulus placement parallel to the vertical meridian. To our knowledge, this is the first demonstration of retinotopic organization of extrastriate areas, using non-invasive neuromagnetic techniques. The paired presentation of stimuli reflected superposition of the responses evoked by single stimuli but only for early activity up to 150 ms poststimulus. Undersummation was evident after 150 ms. All sources identified for single stimuli were also identified in the paired-stimulus responses; but at the expense of larger errors for some of the estimated parameters.

Evoked Potentials, Visual↗
PubMed1998

Multi-start downhill simplex method for spatio-temporal source localization in magnetoencephalography.

A multi-start downhill simplex method is examined as a global minimization technique for fitting multidipole, spatio-temporal magnetoencephalography (MEG) data. This procedure has been performed on both simulated and empirical human visual data, known to exhibit complex field patterns due to multiple sources. Unlike some other non-linear fitting techniques the multi-start downhill simplex method does not require users to provide initial guesses for the dipole parameters, hence the fitting procedure is less time-consuming, more objective, and user-friendly. In addition, this method offers more than one adequate solution thus providing a range of uncertainty for the estimated parameters. The Multi-start downhill simplex method is used to fit the non-linear dipole spatial parameters, while the linear temporal parameters are fit using a separate linear fitting procedure. Singular value decomposition (SVD) is also used in order to improve the procedure for determining the adequate number of modeled dipoles.

Brain Mapping↗
PubMed1995

Mapping function in the human brain with magnetoencephalography, anatomical magnetic resonance imaging, and functional magnetic resonance imaging.

Integrated analyses of human anatomical and functional measurements offer a powerful paradigm for human brain mapping. Magnetoencephalography (MEG) and EEG provide excellent temporal resolution of neural population dynamics as well as capabilities for source localization. Anatomical magnetic resonance imaging (MRI) provides excellent spatial resolution of head and brain anatomy, whereas functional MRI (fMRI) techniques provide an alternative measure of neural activation based on associated hemodynamic changes. These methodologies constrain and complement each other and can thereby improve our interpretation of functional neural organization. We have developed a number of computational tools and techniques for the visualization, comparison, and integrated analysis of multiple neuroimaging techniques. Construction of geometric anatomical models from volumetric MRI data allows improved models of the head volume conductor and can provide powerful constraints for neural electromagnetic source modeling. These approaches, coupled to enhanced algorithmic strategies for the inverse problem, can significantly enhance the accuracy of source-localization procedures. We have begun to apply these techniques for studies of the functional organization of the human visual system. Such studies have demonstrated multiple, functionally distinct visual areas that can be resolved on the basis of their locations, temporal dynamics, and differential sensitivity to stimulus parameters. Our studies have also produced evidence of internal retinotopic organization in both striate and extrastriate visual areas but have disclosed organizational departures from classical models. Comparative studies of MEG and fMRI suggest a reasonable but imperfect correlation between electrophysiological and hemodynamic responses. We have demonstrated a method for the integrated analysis of fMRI and MEG, and we outline strategies for improvement of these methods. By combining multiple measurement techniques, we can exploit the complementary strengths and transcend the limitations of the individual neuro-imaging methods.

Brain↗
PubMed1995

Temporal dynamics of visual-evoked neuromagnetic sources: effects of stimulus parameters and selective attention.

Results are reviewed from several neuromagnetic studies which characterize the temporal dynamics of neural sources contributing to the visual evoked response and effects of attention on these sources. Different types of pattern-onset stimuli (< or = 2 degrees) were presented sequentially to a number of field locations in the right visual field. Multiple dipole models were applied to a sequence of instantaneous field distributions constructed at 10 ms intervals. Best-fitting source parameters were superimposed on Magnetic Resonance images (MRI) of each subject to identify the anatomical structure(s) giving rise to the surface patterns. At least three sources, presumably corresponding to different visual areas, were routinely identified from 80-150 ms following the onset of visual stimulation. This observation was consistent across subjects and studies. The temporal sequence and strength of activation of these sources, however, were dependent upon the specific stimulus parameters used to evoke the response (e.g., eccentricity) and on the relevance of the stimulus to the subject. In addition, our results provide evidence for the recurrence of activity in striate and extrastriate regions, following the initial cycle of responses.

Adult↗
PubMed1995

A conceptual overview and critique of functional neuroimaging techniques in humans: I. MRI/FMRI and PET.

A critical evaluation of current, noninvasive brain-mapping techniques indicates that no one technique in isolation can adequately address the varied questions of interest to basic researchers and clinicians. Consequently, an integrated analysis of anatomical and functional measurements has become the ultimate goal to better characterize the nature of neuronal and hemodynamic responses to sensory and cognitive stimulation. Such an analysis will optimize both spatial and temporal resolution, thereby enabling patterns of activation to be followed throughout the central nervous system, a prerequisite for examining stages of information processing. This review, written in two parts, provides a conceptual overview of three techniques (MRI/fMRI, PET, and MEG/EEG) and examines current efforts at integrating these measures. Each technique is initially evaluated in isolation by considering a set of primary issues (e.g., spatial resolution, temporal resolution, the nature of the signal, individual variability, repeatability, etc.). The first part compares and contrasts MRI/fMRI techniques with PET. Part II, which examines MEG/EEG techniques and current attempts at integrating techniques, will appear in a subsequent volume. This two-part review focuses on issues, not results per se, and it is assumed that the reader is not proficient in any of the techniques described.

Brain↗
PubMed1993

Simulation studies of multiple dipole neuromagnetic source localization: model order and limits of source resolution.

Numerical simulation studies were performed using a multiple dipole source model and a spherical approximation of the head to examine how the resolution of simultaneously active neuromagnetic sources depends upon: 1) source modeling assumptions (i.e., number of assumed dipoles); 2) actual source parameters (e.g., location, orientation, and moment); and 3) measurement errors. Forward calculations were conducted for a series of source configurations in which the number of dipoles, specific dipole parameters, and noise levels were systematically varied. Simulated noisy field distributions were fit by multiple dipole models of increasing model order (1, 2, ..., 6 and alternative statistical approaches (i.e., percent of variance, reduced chi-square, and F-ratio) were compared for their effectiveness in determining adequate model order. Limits of spatial resolution were established for a variety of multi-source configurations and noise conditions. Implications for the analysis of empirical data are discussed.

Data Interpretation, Statistical↗
PubMed1987

Behavioral measures of multiple personality: the case of Margaret.

This report concerns the systematic study of a 28-year-old subject diagnosed as multiple personality. The purpose of this study was to examine similarities and differences in three of her distinct personalities, utilizing behavioral measures. Three tasks were presented to the personalities: a memory task; a perceptual-motor task; and an attention task utilizing event-related potentials. The memory task and perceptual-motor task indicated that the three personalities shared information and that learning extended from one personality to the next. The attention task indicated that the three personalities were differentially processing the stimuli that were presented to them, as measured by the ERPs. The results are discussed in the context of the individual case and of the phenomena of multiple personality.

Adult↗
PubMed1986

Visual event-related potentials to colored patterns and color names: attention to features and dimension.

Four right-handed males and 4 right-handed females were instructed to match pairs of stimuli (colored flashes with either colored patterns or color names) presented sequentially to the central retina. Subjects were to respond to the second stimulus of a pair when it matched the first stimulus in terms of sensory color or word meaning. ERPs recorded from the second stimulus of a pair over occipital and frontal cortical regions indicate the following: Interdimension effects reflect an early and more global discrimination process between colored patterns and word patterns per se. The source of this effect appears to be localized in occipital cortical regions. Intradimension effects were evident later in time and reflect a more refined discrimination process between particular features within a dimension rather than between dimensions. The intradimension color effect began earlier in time than the word effect (229 msec versus 318 msec in the occipital data) and appears to be localized in posterior temporal regions. The onset of the word effect appears to have two neural generators: an early effect localized in frontal regions (274 msec) and a later effect localized in occipital regions (318 msec). The hierarchical model of language processing seems to hold true predominantly in posterior cortical regions. Effects associated with linguistic processing were evident in frontal regions before effects were noted in the occipital regions. This result suggests that either: word information is processed simultaneously and independently in the different regions, or anterior regions feedback onto posterior regions and, therefore, influence the processing in this region.

Adult↗
PubMed1986

Discussion of neural-specificity model of selective attention: a response to Hillyard and Mangun and to Näätänen.

Hillyard and Mangun (this issue) and Näätänen (this issue) have made a number of reflective, important observations in regard to the model we described in our earlier paper (Harter & Aine, 1984). The attention they have given to our paper and model is greatly appreciated and has helped us more clearly conceptualize some of the assertions and observations set forth in our original paper. The scholarly contributions of Hillyard, Näätänen, and their colleagues during the last 20 years, along with those by others related to the neurophysiology and neuroanatomy of the visual system, have led us to propose the somewhat different perspective represented by the neural specificity model of selective attention. Hillyard's and Mangun's and then Näätänen comments will be abstracted and discussed in order.

Attention↗
PubMedDate not supplied

Nonlinear analysis of biological systems using short M-sequences and sparse-stimulation techniques.

The m-sequence pseudorandom signal has been shown to be a more effective probing signal than traditional Gaussian white noise for studying nonlinear biological systems using cross-correlation techniques. The effectiveness is evidenced by the high signal-to-noise (S/N) ratio and speed of data acquisition. However, the "anomalies" that occur in the estimations of the cross-correlations represent an obstacle that prevents m-sequences from being more widely used for studying nonlinear systems. The sparse-stimulation method for measuring system kernels can help alleviate estimation errors caused by anomalies. In this paper, a "padded sparse-stimulation" method is evaluated, a modification of the "inserted sparse-stimulation" technique introduced by Sutter, along with a short m-sequence as a probing signal. Computer simulations show that both the "padded" and "inserted" methods can effectively eliminate the anomalies in the calculation of the second-order kernel, even when short m-sequences were used (length of 1023 for a binary m-sequence, and 728 for a ternary m-sequence). Preliminary experimental data from neuromagnetic studies of the human visual system are also presented, demonstrating that the system kernels can be measured with high signal-to-noise (S/N) ratios using short m-sequences.

Computer Simulation↗
PubMedDate not supplied

Retinotopic organization of human visual cortex: departures from the classical model.

Retinotopic mapping strategies similar to those used for invasive electrophysiological studies to identify multiple visual areas in monkeys have been adapted for noninvasive studies in humans, using magnetic recordings of brain activity in conjunction with anatomical magnetic resonance imaging. The retinotopic organization of the primary visual area (V1) in the left hemisphere of human subjects was examined by presenting a small patterned stimuli near the vertical and horizontal meridians in the lower right visual field. In contrast with the classical model of V1 retinotopy, our results suggest that the representation of the horizontal meridian does not necessarily correspond in a one-to-one manner with the base of the calcarine fissure and that some lower field stimuli can activate regions in the lower bank of the fissure. The results also indicate significant individual variability in the details of how V1 maps around the calcarine fissure.

Brain Mapping↗