Teresa Cheung

Changes in mu rhythm during action observation and execution in adults with Down syndrome : Implications for action representation

The human mirror neuron system is thought to be the underlying basis of perception-action coupling involved in imitation and action understanding. In order to examine this issue we examined the recruitment of the mirror neuron system, as reflected in mu rhythm suppression in a population of adults with Down syndrome (DS) with known strengths in imitation but with impairments in perceptual-motor coupling. Ten healthy adults and 10 age-matched adults with (DS) participated in the study. Subjects were asked to make self-paced movements (execution), and view movements made by the experimenter (observation). The action consisted of reaching with the dominant hand to grasp and lift a cup. Cortical responses were recorded with a whole head magnetoencephalography (MEG) system. Both groups demonstrated significant attenuation of the mu rhythm in bilateral sensorimotor areas when executing the action. Typical adults also demonstrated significant mu suppression in bilateral sensorimotor areas during observation of the action. In contrast, when observing the movement, adults with DS showed a significantly reduced overall attenuation of mu activity with a distinct laterality in the pattern of mu suppression. These results suggest that there is a dysfunction in the execution/observation matching system in adults with DS and has implications for the functional role of the human mirror neuron system.

Neural activity involved in the perception of human and meaningful object motion

We characterized magnetoencephalographic responses during observation of point-light displays of human and object motion. Time courses of grand-mean source estimates were computed and time frequency maps were calculated. For both conditions, activity began in the posterior occipital and mid-parietal areas. Further, late peaks were observed in the parietal, sensory-motor and left temporal regions. Only observation of human motion resulted in activation of the right temporal area. Both viewing conditions resulted in &agr; and &bgr; event-related desynchronization over the parietal, sensory-motor and temporal areas. A significant increase in &bgr; activity was seen in the posterior temporal region in the human motion condition. The visual analyses of human and object motion appear to involve both overlapping and divergent patterns of neural activity.

Magnetoencephalography Reveals Slowing of Resting Peak Oscillatory Frequency in Children Born Very Preterm

Resting cortical activity is characterized by a distinct spectral peak in the alpha frequency range. Slowing of this oscillatory peak toward the upper theta-band has been associated with a variety of neurological and neuropsychiatric conditions and has been attributed to altered thalamocortical dynamics. Children born very preterm exhibit altered development of thalamocortical systems. To test the hypothesis that peak oscillatory frequency is slowed in children born very preterm, we recorded resting magnetoencephalography (MEG) from school age children born very preterm (≤32 wk gestation) without major intellectual or neurological impairment and age-matched full-term controls. Very preterm children exhibit a slowing of peak frequency toward the theta-band over bilateral frontal cortex, together with reduced alpha-band power over bilateral frontal and temporal cortex, suggesting that mildly dysrhythmic thalamocortical interactions may contribute to altered spontaneous cortical activity in children born very preterm.

Spatial-temporal dynamics of cortical activity underlying reaching and grasping

How humans understand the actions and intentions of others remains poorly understood. Here we report the results of a magnetoencephalography (MEG) experiment to determine the temporal dynamics and spatial distribution of brain regions activated during execution and observation of a reach to grasp motion using real world stimuli. We show that although both conditions activate similar brain areas, there are distinct differences in the timing, pattern and location of activation. Specifically, observation of motion revealed a right hemisphere dominance with activation involving a network of regions that include frontal, temporal and parietal areas. In addition, the latencies of activation showed a task specific pattern. During movement execution, the earliest activation was observed in the left premotor and somatosensory regions, followed closely by left primary motor and STG at the time of movement onset. During observation, there was a shift in the timing of activation with the earliest activity occurring in the right temporal region followed by activity in the left motor areas. Activity within these areas was also characterized by a shift to a lower frequency in comparison with action execution. These results add to the growing body of evidence indicating a complex interaction within a distributed network involving motor and nonmotor regions during observation of real actions. Hum Brain Mapp, 2010.

Altered Long-Range Phase Synchronization and Cortical Activation in Children Born Very Preterm

Children born very preterm, even with broadly normal IQ, commonly show selective difficulties in visuospatial processing and executive functioning. Very little, however, is known what alterations in cortical processing underlie these deficits. We recorded MEG while eight children born very preterm (≤32 weeks gestational age) and eight full-term controls performed a visual short-term memory task at mean age 7.5 years (range 6.4 - 8.4). Previously, we demonstrated increased long-range alpha and beta band phase synchronization between MEG sensors during STM retention in a group of 17 full-term children age 6-10 years. Here we present preliminary evidence that long-range phase synchronization in very preterm children, relative to controls, is reduced in the alpha-band but increased in the theta-band. In addition, we investigated cortical activation during STM retention employing synthetic aperture magnetometry (SAM) beamformer to localize changes in gamma-band power. Preliminary results indicate sequential activation of occipital, parietal and frontal cortex in control children, as well as reduced activation in very preterm children relative to controls. These preliminary results suggest that children born very preterm exhibit altered inter-regional functional connectivity and cortical activation during cognitive processing.

Neural Mechanisms Underlying Action Observation in Adults With Down Syndrome

Results of a magnetoencephalography (MEG) brain imaging study conducted to examine the cortical responses during action execution and action observation in 10 healthy adults and 8 age-matched adults with Down syndrome are reported. During execution, the motor responses were strongly lateralized on the ipsilateral rather than the contralateral side in the Down syndrome group. Observation of movement activated a network of cortical regions that was similar to the control group; however, there was no significant peak activity in the motor areas. In addition, the overall pattern of neural activation was more scattered and less organized in the Down syndrome group. These results further support the hypothesis of a dysfunction in the execution/observation matching system in adults with Down syndrome.

External landmark and head-shape-based functional data normalization.

Functional data, as obtained from magnetoencephalography (MEG) techniques, is frequently transformed to a template brain space for pooling data across the population. This transformation is often performed via an intermediate magnetic resonance image (MRI) of the subjects brain that is first registered to the template brain MRI. However, in many instances, it is difficult, expensive or undesirable to acquire MRIs, and since reconstructed functional data is lower resolution, the full information in MRIs is not required for registration. We present here two alternative options for computing the transformation of functional data to a common template space. These alternatives compute the registration based on external landmarks placed on the head, and the external shape of the head, features that are considerably simpler and inexpensive to acquire than MRIs. We present quantification of the accuracy of using these alternative features for registration, and show that they give accuracy for functional data registration that is sufficient given the functional data resolution, and is comparable to existing methods that are commonly used.

A New Technique for Magnetic Nanoparticle Imaging Using Magnetoencephalography Frequency Data

Nanoparticles are objects of nanometer dimensions. Magnetic nanoparticles consist of an inorganic core of iron oxide. An outer coating of bioactive molecules such as peptides or antibodies surrounds this core, which can be chemically functionalized to conjugate with specific molecules in cells. There is potential to utilize the magnetic properties of these particles for internal imaging of living organisms using magnetoencephalography (MEG). While it is clear that bulk movement of a collection of particles should be detectable by MEG either as a flow or via rigid mechanical motion, it would be far more useful to detect the particles in situ. We have taken the first step towards this goal by demonstrating that MEG can detect these particles at fixed locations by focusing on the magnetic noise generated from random rotations of the particles’ magnetic moments. Using a 151-channel MEG device, a glass vial of Fe3O4 in a colloidal suspension was measured at stationary locations within the MEG helmet region. The data was collected at 300, 1200 and 12000 Hz with up to 4000 Hz bandwidth. Between 10 and 50 ten-second trials were collected. Fast Fourier transforms for each MEG channel was generated. The net effect of these fluctuations was not detectable in the time domain. However, these fluctuations appeared as an increase in noise in the frequency domain. The character of the noise had a 1/f^n slope where 0<n<1 with n approaching 0 (= white noise) as the concentration of the sample was reduced. Spatial contour maps of the frequency data showed a distinct peak near the location of the sample. These results suggest that MEG is sensitive enough to detect and potentially localize a stationary vial of magnetic nanoparticles in a colloidal suspension.