Spatiotemporal mapping of cortical activity accompanying voluntary movements using an event‐related beamforming approach

Abstract

We describe a novel spatial filtering approach to the localization of cortical activity accompanying voluntary movements. The synthetic aperture magnetometry (SAM) minimum-variance beamformer algorithm was used to compute spatial filters three-dimensionally over the entire brain from single trial neuromagnetic recordings of subjects performing self-paced index finger movements. Images of instantaneous source power ("event-related SAM") computed at selected latencies revealed activation of multiple cortical motor areas prior to and following left and right index finger movements in individual subjects, even in the presence of low-frequency noise (e.g., eye movements). A slow premovement motor field (MF) reaching maximal amplitude approximately 50 ms prior to movement onset was localized to the hand area of contralateral precentral gyrus, followed by activity in the contralateral postcentral gyrus at 40 ms, corresponding to the first movement-evoked field (MEFI). A novel finding was a second activation of the precentral gyrus at a latency of approximately 150 ms, corresponding to the second movement-evoked field (MEFII). Group averaging of spatially normalized images indicated additional premovement activity in the ipsilateral precentral gyrus and the left inferior parietal cortex for both left and right finger movements. Weaker activations were also observed in bilateral premotor areas and the supplementary motor area. These results show that event-related beamforming provides a robust method for studying complex patterns of time-locked cortical activity accompanying voluntary movements, and offers a new approach for the localization of multiple cortical sources derived from neuromagnetic recordings in single subject and group data.

Visual dominance and multisensory integration changes with age

“…To obtain spatial precision without integrating power over long temporal windows, we used an event-related version of the SAM analysis technique introduced by Cheyne, Bakhtazad, and Gaetz (2006) to identify evoked brain responses from un-averaged, single trial data. Similar to previous beamforming approaches, the event-related SAM analysis uses the individual trials of each condition and the forward solution for modeling optimal current direction to calculate a spatial filter for each voxel using the minimum-variance beamforming algorithm (Cheyne, Bakhtazad, & Gaetz, 2006).…”

“…Similar to previous beamforming approaches, the event-related SAM analysis uses the individual trials of each condition and the forward solution for modeling optimal current direction to calculate a spatial filter for each voxel using the minimum-variance beamforming algorithm (Cheyne, Bakhtazad, & Gaetz, 2006).…”

Cortical activity during speech and non-speech oromotor tasks: A magnetoencephalography (MEG) study

“…An event-related beamformer (ERB, [6]) algorithm was used to compute time-locked neural activity over the whole head with 5mm spatial resolution. ERB images were created at 5ms increments, co-registered to individual MRIs, and normalized to the MNI template using SPM2.…”

“…Specifically, event-related beamforming (ERB) allows a different approach to the analysis of whole-head MEG data by identifying multiple sources, without a priori specification [6]. As well, the ERB approach has demonstrated success at artefact suppression [7].…”

Learning related activation of somatosensory cortex by an auditory stimulus recorded with magnetoencephalography

“…This process is repeated across the whole brain on a user-defined grid size to generate a volumetric map of source power change. Alternatively, temporal (Cheyne et al, 2006) and/or spectral ( [Bardouille et al, 2006] and [Bardouille and Ross, 2008]) analysis of the estimated source activity can be completed at one location, or in a region of interest, as -SAM virtual channels‖. The extension of such concepts into five dimensional data analysis, i.e.…”