Julia M. Stephen

Multistart Algorithms for MEG Empirical Data Analysis Reliably Characterize Locations and Time Courses of Multiple Sources

We applied our newly developed Multistart algorithm (M. Huang et al., 1998, Electroencephalogr. Clin. Neurophysiol. 108, 32-44) to high signal-to-noise ratio (SNR) somatosensory responses and low SNR visual data to demonstrate the reliability of this analysis tool for determining source locations and time courses of empirical multisource neuromagnetic data. This algorithm performs a downhill simplex search hundreds to thousands of times with multiple, randomly selected initial starting parameters from within the head volume, in order to avoid problems of local minima. Two subjects participated in two studies: (1) somatosensory (left and right median nerves were stimulated using a square wave pulse of 0.2 ms duration) and (2) visual (small black and white bulls-eye patterns were presented to central and peripheral locations in four quadrants of the visual field). One subject participated in both of the studies mentioned above and in a third study (i.e., simultaneous somatosensory/visual stimulation). The best-fitting solutions were tightly clustered in high SNR somatosensory data and all dominant regions of activity could be identified in some instances by using a single model order (e.g., six dipoles) applied to a single interval of time (e.g., 15-250 ms) that captured the entire somatosensory response. In low SNR visual data, solutions were obtained from several different model orders and time intervals in order to capture the dominant activity across the entire visual response (e.g. , 60-300 ms). Our results demonstrate that Multistart MEG analysis procedures can localize multiple regions of activity and characterize their time courses in a reliable fashion. Sources for visual data were determined by comparing results across several different models, each of which was based on hundreds to thousands of different fits to the data.

Sources on the anterior and posterior banks of the central sulcus identified from magnetic somatosensory evoked responses using Multi-Start Spatio-Temporal localization

A Multi‐Start Spatio‐Temporal (MSST) multidipole localization algorithm was used to study sources on the anterior and posterior banks of the central sulcus localized from early somatosensory magnetoencephalography (MEG) responses. Electrical stimulation was applied to the right and left median nerves of 8 normal subjects. Two sources, one on the anterior and one on the posterior bank of the central sulcus, were localized from 16 data sets (8 subjects, 2 hemispheres). Compared with the more traditional practice of single‐dipole fits to peak latencies, MSST provided more reliable source locations. The temporal dynamics of the anterior and posterior central sulcus sources, obtained using MSST, showed considerable temporal overlap. In some cases, the two sources appeared synchronous. On the other hand, in the traditional single‐dipole peak‐latency fit approach, there is no time course other than a focal dipole moment activated only at the selected peak latency. The same group of subjects also performed a motor task involving index‐finger lifting; the anterior central sulcus source obtained from electrical median nerve stimulation localized to the same or similar region in the primary motor area identified from the finger‐lift task. The physiological significance of the anterior central sulcus source is discussed. The findings suggest that one can test the integrity of cortical tissue in the region of primary motor cortex using electrical somatosensory stimulation. Hum. Brain Mapping 11:59–76, 2000.

Central versus peripheral visual field stimulation results in timing differences in dorsal stream sources as measured with MEG

Small, achromatic circular sinusoids were presented in the central and peripheral visual fields to investigate dorsal visual stream activation. It was hypothesized that peripheral stimulation would lead to faster onset latencies, as well as preferentially activate dorsal stream visual areas relative to central field stimulation. Although both central and peripheral stimulation activated similar areas, the onset latencies of neuromagnetic sources in two dorsal stream areas were found to be significantly shorter for peripheral versus central field stimulation. The results suggest that information from central versus peripheral fields arrives in the higher-order visual areas via different routes.

MEG response to median nerve stimulation correlates with recovery of sensory and motor function after stroke

OBJECTIVE Hemiparesis due to damage by stroke in primary motor cortex (MI) or its underlying projections presents a problem for functional neuroimaging technologies that attempt to evaluate the neurophysiological basis for restoration of motor function. Traditional assessments of MI function require patients to move their fingers, hands, or limbs, which can be either impossible or markedly compromised after stroke. We recently demonstrated in normal subjects that magnetoencephalography (MEG), a non-invasive neuromagnetic functional imaging technique, detects neuronal response elicited by electrical median nerve stimulation in MI, as well as primary somatosensory cortex (SI). In the present study, we used the MEG response from median nerve stimulation to investigate the recovery of primary motor and somatosensory in acute ischemic stroke patients. METHODS Twelve patients with unilateral ischemic strokes that affected sensorimotor functions of their hand were studied in the acute stage (4.4+/-1.2 days, mean+/-SD) and during a 1-month follow-up (38.6+/-5.6 days, except for one patients follow-up done 6 month after stroke). RESULTS Among the multiple cortical sources localized after median nerve stimulation, one source localized to SI and another localized to the vicinity of MI. Changes in the source strengths of the first component post-stimulus of MI and SI correlated with the extent of recovery of sensorimotor functions as determined by neurological exams. CONCLUSIONS This study provides a novel way of indirectly assessing MI function using MEG during the acute stroke phase, when many patients often cannot perform motor tasks due to paralysis.

An Event-related fMRI Study of Exogenous Facilitation and Inhibition of Return in the Auditory Modality

The orienting of attention to different locations in space is fundamental to most organisms and occurs in all sensory modalities. Orienting has been extensively studied in vision, but to date, few studies have investigated neuronal networks underlying automatic orienting of attention and inhibition of return to auditory signals. In the current experiment, functional magnetic resonance imaging and behavioral data were collected while healthy volunteers performed an auditory orienting task in which a monaurally presented tone pip (cue) correctly or incorrectly cued the location of a target tone pip. The stimulus onset asynchrony (SOA) between the cue and target was 100 or 800 msec. Behavioral results were consistent with previous studies showing that valid auditory cues produced facilitation at the short SOA and inhibition of return at the long SOA. Functional results indicated that the reorienting of attention (100 msec SOA) and inhibition of return (800 msec SOA) were mediated by both common and distinct neuronal structures. Both attention mechanisms commonly activated a network consisting of fronto-oculomotor areas, the left postcentral gyrus, right premotor area, and bilateral tonsil of the cerebellum. Several distinct areas of frontal and parietal activation were identified for the reorienting condition, whereas the right inferior parietal lobule was the only structure uniquely associated with inhibition of return.

Age-related effects on superior temporal gyrus activity during an auditory oddball task.

We used magnetoencephalography in combination with magnetic resonance imaging to investigate the effects of aging on the temporal dynamics of activity localized to several brain regions during an auditory oddball task. The most interesting effects were noted in the superior temporal gyrus as follows: (1) responses were generally stronger to rare than to frequent tones throughout the entire 600-ms time interval, and (2) increases in the amplitude of the 40-ms peak and the latency of the maximum late response were evident in the elderly. Although superior temporal gyrus activity has traditionally been associated with early sensory processing, these results suggest that superior temporal gyrus activity is also important for later decision-related processing.

Investigation of the normal proximal somatomotor system using magnetoencephalography

OBJECTIVE The role of the ipsilateral cortex in proximal muscle control in normal human subjects is still under debate. One clinical finding, rapid recovery of proximal muscle relative to distal muscle use following stroke, has led to the suggestion that the ipsilateral as well as the contralateral motor cortex may be involved in normal proximal muscle control. The primary goal of this project was to identify contralateral and ipsilateral motor cortex activation associated with proximal muscle movement in normal subjects using magnetoencephalography (MEG). METHODS We developed protocols for a self-paced bicep motor task and a deltoid, electrical-stimulation somatosensory task. The MEG data were analyzed using automated multi-dipole spatiotemporal modeling techniques to localize the sources and characterize the associated timing of these sources. RESULTS Reliable contralateral primary motor and somatosensory sources localized to areas consistent with the homunculus. Ipsilateral M1 activation was only found in 2/12 hemispheres. CONCLUSIONS Robust contralateral motor cortex activation and sparse ipsilateral motor cortex activation suggest that the ipsilateral motor cortex is not involved in normal proximal muscle control. SIGNIFICANCE The results suggest that proximal and distal muscle control is similar in normal subjects in the sense that proximal muscle control is primarily governed by the contralateral motor cortex.

Frequency-Following and Connectivity of Different Visual Areas in Response to Contrast-Reversal Stimulation

The sensitivity of visual areas to different temporal frequencies, as well as the functional connections between these areas, was examined using magnetoencephalography (MEG). Alternating circular sinusoids (0, 3.1, 8.7 and 14 Hz) were presented to foveal and peripheral locations in the visual field to target ventral and dorsal stream structures, respectively. It was hypothesized that higher temporal frequencies would preferentially activate dorsal stream structures. To determine the effect of frequency on the cortical response we analyzed the late time interval (220–770 ms) using a multi-dipole spatio-temporal analysis approach to provide source locations and timecourses for each condition. As an exploratory aspect, we performed cross-correlation analysis on the source timecourses to determine which sources responded similarly within conditions. Contrary to predictions, dorsal stream areas were not activated more frequently during high temporal frequency stimulation. However, across cortical sources the frequency-following response showed a difference, with significantly higher power at the second harmonic for the 3.1 and 8.7 Hz stimulation and at the first and second harmonics for the 14 Hz stimulation with this pattern seen robustly in area V1. Cross-correlations of the source timecourses showed that both low- and high-order visual areas, including dorsal and ventral stream areas, were significantly correlated in the late time interval. The results imply that frequency information is transferred to higher-order visual areas without translation. Despite the less complex waveforms seen in the late interval of time, the cross-correlation results show that visual, temporal and parietal cortical areas are intricately involved in late-interval visual processing.

The lifespan trajectory of neural oscillatory activity in the motor system

Highlights • The lifespan trajectory of resting and motor-related beta oscillations is unknown.• These beta dynamics were examined in participants aged 9–75 years using MEG imaging.• Resting beta levels and motor-related beta oscillations follow unique trajectories.• The dynamic relationship between these two measures predicts motor performance.

Dietary Intake Among Opioid- and Alcohol-Using Pregnant Women

ABSTRACT Background: Substance abuse in nonpregnant adults has been associated with increased intake in calories and decreased intake of nutrient-dense foods; however, studies examining dietary intake in opioid-using and alcohol-using pregnant women are lacking. Objective: The objective of this study was to evaluate dietary intake in opioid-using pregnant women with or without concurrent light-to-moderate alcohol use as compared to abstaining controls. Methods: This prospective birth cohort included 102 pregnant women classified into four study groups: controls (n = 27), medication-assisted treatment (MAT; n = 26), alcohol (ALC; n = 22), and concurrent use of both substances (MAT + ALC; n = 27). Percentage differences in macro- and micronutrient intake were estimated from the food frequency questionnaire and compared among the study groups. Proportions of participants with intakes below the estimated average requirements (EAR) based on diet and diet with supplements were estimated. Results: Three exposed groups had lower prevalence of multivitamin use in periconceptional period (11.5–31.8%) than controls (44.4%). Unadjusted mean energy intake was significantly higher in the MAT + ALC group compared to controls, while micronutrient intake per 1000 kcal was the highest in the control group for almost all of the micronutrients analyzed. After adjustment for energy intake and sociodemographic characteristics, MAT group had lower estimated dietary intake of iron (−15.0%, p = 0.04) and folate (−16.8%, p = 0.04) compared to controls. A high proportion of participants in all study groups had dietary intake below the EAR for vitamin E, iron, and folate. Conclusion: Results highlight the need for targeted dietary interventions for opioid-using pregnant women.