Intermittent "real-time" fMRI feedback is superior to continuous presentation for a motor imagery task: a pilot study

Abstract

Background: Real-time functional MRI feedback (RTfMRIf) is a developing technique, with unanswered methodological questions. Given a delay of seconds between neural activity and the measurable hemodynamic response, one issue is the optimal method for presentation of neurofeedback to subjects. The primary objective of this preliminary study was to compare the methods of continuous and intermittent presentation of neural feedback on targeted brain activity.

Methods: Thirteen participants performed a motor imagery task and were instructed to increase activation in an individually defined region of left premotor cortex using RTfMRIf. The fMRI signal change was compared between real and false feedback for scans with either continuous or intermittent feedback presentation.

Results: More individuals were able to increase their fMRI signal with intermittent feedback, while some individuals had decreased signal with continuous feedback. The evaluation of feedback itself activated an extensive amount of brain regions, and false feedback resulted in brain activation outside of the individually defined region of interest.

Conclusions: As implemented in this study, intermittent presentation of feedback is more effective than continuous presentation in promoting self-modulation of brain activity. Furthermore, it appears that the process of evaluating feedback involves many brain regions that can be isolated using intermittent presentation.

Fig 1

Unfiltered percent signal change from all voxels in the individually selected region of interests. A region of interest was selected for each individual from a no feedback baseline scan. The mean percent signal change, with no temporal filtering, from all voxels in the individual region of interest is plotted for the continuous feedback paradigm (A) and for the intermittent feedback paradigm (B). The hemodynamic rest (and intermittent feedback) periods are shaded and the “Imagine Movement” periods are unshaded in the plots, comparing the no feedback baseline scans (dotted thin line), false feedback scans (thin solid line), and real feedback scans (thick solid line).

Fig 2

No feedback baseline scans of imagine movement task for ROI localization. Pattern of activation for “Imagine Movement—Rest” contrast (11 individuals with one or two scans, for a total of 18 scans). Scans were analyzed using a multisession (fixed effects) and multisubject (mixed effects) three level analysis, and thresholded using clusters determined by Z > 2.3 and a corrected cluster significance of P = .05. The yellow square demonstrates the manually circumscribed region, from which the ROI was dynamically defined.

Fig 3

Continuous feedback. Pattern of activation for “Imagine Movement—Rest” contrast (10 paired scan sets). Scans were analyzed using a tripled two-group difference analysis (mixed effects), and thresholded using clusters determined by Z > 2.3 and a corrected cluster significance of P = .05.

Fig 4

Intermittent feedback. Pattern of activation for “Imagine Movement—Rest” contrast (eight paired scan sets). Scans were analyzed using a tripled two-group difference analysis (mixed effects), and thresholded using clusters determined by Z > 2.3 and a corrected cluster significance of P = .05.

Fig 5

Intermittent feedback component. Pattern of activation for “Feedback—Rest” contrast (eight paired scan sets). Scans were analyzed using a multisession (fixed effects) and multisubject (mixed effects) three level analysis for all intermittent scans (top); and a two-sample paired t -test (mixed effects) for “real feedback > false feedback” and “false feedback > real feedback” contrasts. All contrasts were thresholded using clusters determined by Z > 2.3 and a corrected cluster significance of P = .05.