Self-modulation of primary motor cortex activity with motor and motor imagery tasks using real-time fMRI-based neurofeedback

Abstract

Advances in fMRI data acquisition and processing have made it possible to analyze brain activity as rapidly as the images are acquired allowing this information to be fed back to subjects in the scanner. The ability of subjects to learn to volitionally control localized brain activity within motor cortex using such real-time fMRI-based neurofeedback (NF) is actively being investigated as it may have clinical implications for motor rehabilitation after central nervous system injury and brain-computer interfaces. We investigated the ability of fifteen healthy volunteers to use NF to modulate brain activity within the primary motor cortex (M1) during a finger tapping and tapping imagery task. The M1 hand area ROI (ROI(m)) was functionally localized during finger tapping and a visual representation of BOLD signal changes within the ROI(m) fed back to the subject in the scanner. Surface EMG was used to assess motor output during tapping and ensure no motor activity was present during motor imagery task. Subjects quickly learned to modulate brain activity within their ROI(m) during the finger-tapping task, which could be dissociated from the magnitude of the tapping, but did not show a significant increase within the ROI(m) during the hand motor imagery task at the group level despite strongly activating a network consistent with the performance of motor imagery. The inability of subjects to modulate M1 proper with motor imagery may reflect an inherent difficulty in activating synapses in this area, with or without NF, since such activation may lead to M1 neuronal output and obligatory muscle activity. Future real-time fMRI-based NF investigations involving motor cortex may benefit from focusing attention on cortical regions other than M1 for feedback training or alternative feedback strategies such as measures of functional connectivity within the motor system.

Figure 1

Real-time fMRI scanning protocol with (a) continuously updated BOLD time series used for functional localization of primary motor cortex, (b) placement of square primary motor cortex ROI and whole brain axial slice for a reference ROI, (c) continuously updated neurofeedback display reflecting scan-to-scan level of BOLD signal within motor cortex ROI, and (d) monitoring of muscle movement during finger tapping and motor imagery neurofeedback tasks.

Figure 2

RtfMRI-neurofeedback task paradigms showing the alternating 20 sec rest and active conditions during the GO and FB task runs.

Figure 3

Mean percent BOLD signal change from baseline within ROI_m during GO and FB runs with (a) finger tapping and (b) tapping imagery tasks. Subjects saw the neurofeedback display only during FB runs. Six subjects performed only one imagery FB run while nine subjects performed three imagery FB runs. All subjects (N=15) performed a tapping imagery XSFR run after NF training. Standard error of the mean is shown.

Figure 4

Superimposed statistical parametric maps on axial brain slices of one participant’s brain showing significant activation changes from baseline during the finger tapping (a) GO and (b) FB tasks, as well as the tapping imagery (c) GO and (d) FB tasks. For display purpose, the parametric maps were thresholded at p=0.001 (uncorrected) using a voxel cluster size threshold of 50 voxels. Dark red square shows approximate location of ROI_m.

Figure 5

Superimposed statistical parametric maps on axial brain slices of one participant’s brain showing significant activation from contrasts of FB versus GO (a) during finger tapping and (b) tapping imagery. For display purpose, the parametric maps were thresholded at p=0.001 (uncorrected) using a voxel cluster size threshold of 50 voxels.