Neuroimaging investigations of dorsal stream processing and effects of stimulus synchrony in schizophrenia.

Impairments in auditory and visual processing are common in schizophrenia (SP). In the unisensory realm visual deficits are primarily noted for the dorsal visual stream. In addition, insensitivity to timing offsets between stimuli are widely reported for SP.

MEG biomarker of Alzheimer's disease: Absence of a prefrontal generator during auditory sensory gating.

Magnetoencephalography (MEG), a direct measure of neuronal activity, is an underexplored tool in the search for biomarkers of Alzheimer's disease (AD). In this study, we used MEG source estimates of auditory gating generators, nonlinear correlations with neuropsychological results, and multivariate analyses to examine the sensitivity and specificity of gating topology modulation to detect AD. Our results demonstrated the use of MEG localization of a medial prefrontal (mPFC) gating generator as a discrete (binary) detector of AD at the individual level and resulted in recategorizing the participant categories in: (1) controls with mPFC generator localized in response to both the standard and deviant tones; (2) a possible preclinical stage of AD participants (a lower functioning group of controls) in which mPFC activation was localized to the deviant tone only; and (3) symptomatic AD in which mPFC activation was not localized to either the deviant or standard tones.

Multimodal Classification of Schizophrenia Patients with MEG and fMRI Data Using Static and Dynamic Connectivity Measures.

Mental disorders like schizophrenia are currently diagnosed by physicians/psychiatrists through clinical assessment and their evaluation of patient's self-reported experiences as the illness emerges. There is great interest in identifying biological markers of prognosis at the onset of illness, rather than relying on the evolution of symptoms across time. Functional network connectivity, which indicates a subject's overall level of "synchronicity" of activity between brain regions, demonstrates promise in providing individual subject predictive power.

Magnetoencephalographic and functional MRI connectomics in schizophrenia via intra- and inter-network connectivity.

Examination of intrinsic functional connectivity using functional MRI (fMRI) has provided important findings regarding dysconnectivity in schizophrenia. Extending these results using a complementary neuroimaging modality, magnetoencephalography (MEG), we present the first direct comparison of functional connectivity between schizophrenia patients and controls, using these two modalities combined. We developed a novel MEG approach for estimation of networks using MEG that incorporates spatial independent component analysis (ICA) and pairwise correlations between independent component timecourses, to estimate intra- and intern-network connectivity.

Multisensory stimuli elicit altered oscillatory brain responses at gamma frequencies in patients with schizophrenia.

Deficits in auditory and visual unisensory responses are well documented in patients with schizophrenia; however, potential abnormalities elicited from multisensory audio-visual stimuli are less understood. Further, schizophrenia patients have shown abnormal patterns in task-related and task-independent oscillatory brain activity, particularly in the gamma frequency band. We examined oscillatory responses to basic unisensory and multisensory stimuli in schizophrenia patients (N = 46) and healthy controls (N = 57) using magnetoencephalography (MEG).

Same task, different strategies: how brain networks can be influenced by memory strategy.

Previous functional neuroimaging studies demonstrated that different neural networks underlie different types of cognitive processing by engaging participants in particular tasks, such as verbal or spatial working memory (WM) tasks. However, we report here that even when a WM task is defined as verbal or spatial, different types of memory strategies may be used to complete it, with concomitant variations in brain activity. We developed a questionnaire to characterize the type of strategy used by individual members in a group of 28 young healthy participants (18-25 years) during a spatial WM task.

Modulatory role of the prefrontal generator within the auditory M50 network.

The amplitude variability of the M50 component of neuromagnetic responses is commonly used to explore the brain's ability to modulate its response to incoming repetitive or novel auditory stimuli, a process conceptualized as a gating mechanism. The goal of this study was to identify the spatial and temporal characteristics of the cortical sources underlying the M50 network evoked by tones in a passive oddball paradigm. Twenty elderly subjects [10 patients diagnosed with mild cognitive impairment (MCI) or probable Alzheimer disease (AD) and 10 age-matched controls] were examined using magnetoencephalographic (MEG) recordings and the multi-dipole Calibrated Start Spatio-Temporal (CSST) source localization method.

Unisensory processing and multisensory integration in schizophrenia: a high-density electrical mapping study.

In real-world settings, information from multiple sensory modalities is combined to form a complete, behaviorally salient percept - a process known as multisensory integration. While deficits in auditory and visual processing are often observed in schizophrenia, little is known about how multisensory integration is affected by the disorder. The present study examined auditory, visual, and combined audio-visual processing in schizophrenia patients using high-density electrical mapping.

Aging-related changes in auditory and visual integration measured with MEG.

As noted in the aging literature, processing delays often occur in the central nervous system with increasing age, which is often attributable in part to demyelination. In addition, differential slowing between sensory systems has been shown to be most discrepant between visual (up to 20ms) and auditory systems (<5ms). Therefore, we used MEG to measure the multisensory integration response in auditory association cortex in young and elderly participants to better understand the effects of aging on multisensory integration abilities.

Somatosensory responses in normal aging, mild cognitive impairment, and Alzheimer's disease.

As a part of a larger study of normal aging and Alzheimer's disease (AD), which included patients with mild cognitive impairment (MCI), we investigated the response to median nerve stimulation in primary and secondary somatosensory areas. We hypothesized that the somatosensory response would be relatively spared given the reported late involvement of sensory areas in the progression of AD. We applied brief pulses of electric current to left and right median nerves to test the somatosensory response in normal elderly (NE), MCI, and AD.

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.

Aging: compensation or maturation?

Neuroimaging studies of healthy aging often reveal differences in neural activation patterns between young and elderly groups for episodic memory tasks, even though there are no differences in behavioral performance. One explanation typically offered is that the elderly compensate for their memory deficiencies through the recruitment of additional prefrontal regions. The present study of healthy aging compared magnetoencephalographic (MEG) time-courses localized to specific cortical regions in two groups of subjects (20-29 years and >or=65 years) during a visual delayed-match-to-sample (DMS) task.

Differentiability of simulated MEG hippocampal, medial temporal and neocortical temporal epileptic spike activity.

Previous studies have shown that magnetoencephalography (MEG) can measure hippocampal activity, despite the cylindrical shape and deep location in the brain. The current study extended this work by examining the ability to differentiate the hippocampal subfields, parahippocampal cortex, and neocortical temporal sources using simulated interictal epileptic activity. A model of the hippocampus was generated on the MRIs of five subjects.

Aging changes and gender differences in response to median nerve stimulation measured with MEG.

Objective: The current study uses magnetoencephalography (MEG) to characterize age-related changes and gender differences in the amplitudes and timing of cortical sources evoked by median nerve stimulation.

Methods: Thirty-four healthy subjects from two age groups: 20-29 and >64 years of age were examined. After measuring the MEG responses, we modeled the data using a spatio-temporal multi-dipole modeling approach to determine the source locations and their associated timecourses.

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.

Temporal dynamics of age-related differences in auditory incidental verbal learning.

Auditory response profiles for a group of ten healthy young and ten healthy elderly subjects, evoked by implicit memory and delayed verbal recognition tasks, were evaluated to determine if effects of stimulus repetition could be identified in the superior temporal gyrus (STG) and prefrontal cortical regions. We hypothesized that effects of stimulus repetition should occur both early in time and at early levels of the nervous system (STG) followed by later effects in prefrontal regions. Magnetoencephalographic (MEG) responses were recorded using a whole-head MEG system and automated, multi-start analysis methods were applied to the data in order to characterize the temporal response profiles from distributed but focal, cortical regions engaged in memory-related tasks.

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).

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.