Training Efficiency and Transfer Success in an Extended Real-Time Functional MRI Neurofeedback Training of the Somatomotor Cortex of Healthy Subjects

Abstract

This study investigated the level of self-regulation of the somatomotor cortices (SMCs) attained by an extended functional magnetic resonance imaging (fMRI) neurofeedback training. Sixteen healthy subjects performed 12 real-time functional magnetic resonance imaging neurofeedback training sessions within 4 weeks, involving motor imagery of the dominant right as well as the non-dominant left hand. Target regions of interests in the SMC were individually localized prior to the training by overt finger movements. The feedback signal (FS) was defined as the difference between fMRI activation in the contra- and ipsilateral SMC and visually presented to the subjects. Training efficiency was determined by an off-line general linear model analysis determining the fMRI percent signal changes in the SMC target areas accomplished during the neurofeedback training. Transfer success was assessed by comparing the pre- and post-training transfer task, i.e., the neurofeedback paradigm without the presentation of the FS. Group results show a distinct increase in feedback performance (FP) in the transfer task for the trained group compared to a matched untrained control group, as well as an increase in the time course of the training, indicating an efficient training and a successful transfer. Individual analysis revealed that the training efficiency was not only highly correlated to the transfer success but also predictive. Trainings with at least 12 efficient training runs were associated with a successful transfer outcome. A group analysis of the hemispheric contributions to the FP showed that it is mainly driven by increased fMRI activation in the contralateral SMC, although some individuals relied on ipsilateral deactivation. Training and transfer results showed no difference between left- and right-hand imagery, with a slight indication of more ipsilateral deactivation in the early right-hand trainings.

Keywords: human; motor cortex; neurofeedback; real-time fMRI; somatosensory cortex.

Figure 1

Functional localization of the target ROIs: (Top) overlap of individual target regions of the 16 trained subjects (MNI template) with colors indicating the number of subjects (1 to the maximum of 12) with suprathreshold activation during the pre-training overt finger movement task at a particular voxel (amount of overlap). (Middle and bottom) The two-way mixed ANOVA of the whole-brain volume for the right-hand (middle) and left-hand (bottom) transfer task without neurofeedback. Color indicates significantly higher pre- to post-training increase in activation for the training group compared to the control group (interaction TIME × GROUP).

Figure 2

Transfer success: Feedback performance, i.e., difference in percent signal change in contra- vs. ipsilateral SMC, for fMRI of motor imagery without neurofeedback for the trained and control group for the right and left hand before and after 4 weeks of neurofeedback training. **Highly significant (p < 0.01) for both hands.

Figure 3

Training efficiency: Feedback performance (group mean ± SEM) of the trained subjects across neurofeedback runs for the right (black) and left hand (gray).

Figure 4

Training efficiency: Differences of percent signal change within sessions (two runs) and between session (2 days) for the right and left hand. **Highly significant (p < 0.01).

Figure 5

Transfer success and training efficiency: (Top) individual transfer success: values above horizontal lines indicate significance relative to controls for the right and left hand. (Bottom) number of subjects per summed number of training runs with significantly increased signal. Successfully trained subjects are marked with filled bars and circles.

Figure 6

Contralateral (dashed lines) and ispsilateral SMC (dotted lines) percent signal changes of the trained subjects across neurofeedback runs for the right (black) and left (gray) hand.

Figure 7

Number of neurofeedback training runs with increased contralateral and decreased ipsilateral SMC percent signal changes for the right and left hand.

Figure 8

Mean percent signal change in the contra- and ipsilateral SMC for overt finger movements during the pre- and post-training session in the trained and control group. *Significant (p < 0.05).

Figure 9

The two-way mixed ANOVA of the whole volume for overt finger movements. Color indicates significantly higher pre- to post-training increase in activation for the training group than for the control group (interaction TIME × GROUP).