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. 2010 Jan;81(1):30-40.
doi: 10.3357/asem.2532.2009.

Cerebral cortex plasticity after 90 days of bed rest: data from TMS and fMRI

Donna R Roberts  1 , David Ramsey, Kevin Johnson, Jejo Kola, Raffaella Ricci, Christian Hicks, Jeffrey J Borckardt, Jacob J Bloomberg, Charles Epstein, Mark S George
Affiliations

Cerebral cortex plasticity after 90 days of bed rest: data from TMS and fMRI

Donna R Roberts et al. Aviat Space Environ Med. 2010 Jan.

Abstract

Introduction: Microgravity animal models have demonstrated corticospinal plasticity; however, little is understood of its functional significance. In this pilot study, we explored corticospinal plasticity in a bed rest model. We hypothesized that the lack of weight bearing would induce cortical reorganization correlating with performance.

Methods: Four subjects underwent functional MRI (fMRI), transcranial magnetic stimulation (TMS), and functional mobility testing (FMT) before and after 90 d of bed rest. Recruitment curves (RC) were created by measuring motor evoked potentials over a range of TMS intensities with changes in the slope of the RC reflecting changes in corticospinal excitability.

Results: Significant leg RC slope decreases were observed on post-bed rest day 1 (P1) (t(2805) = -4.14, P < 0.0001), P2 (t(2805) = -6.59, P < 0.0001), P3 (t(2805) = -6.15, P < 0.0001), P5 (t(2805) = -7.93, P <0.0001), P8 (t(2805) = -3.30, P = 0.001), and P12 (t(2805)= -3.33, P = 0.0009), suggesting a group decrease in corticospinal excitability in the immediate post-bed rest period with recovery approaching baseline over the following 2 wk. Significant effects were observed for hand RC slopes only for P2 (t(2916) = 1.97, P = 0.049), P3 (t(2916) = -2.12, P = 0.034), and P12 (t(2916) = -2.19, P = 0.029); no significant effects were observed for days P0 (t(2916) = -1.32, ns), P1 (t(2916) = 1.00, ns), P5 (t(2916) = -0.21, ns), or P8 (t(2916) = -0.27, ns). fMRI showed no change in activation for the hand but an increase in activation post-bed rest for the leg. On an individual basis, a more heterogeneous response was found which showed a potential association with performance on FMT.

Discussion: Results of this research include a better understanding of the cortical plasticity associated with leg disuse and may lead to applications in patient and astronaut rehabilitation.

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Figures

Fig. 1
Fig. 1
Timeline of study showing the data collection points for transcranial magnetic stimulation (TMS), functional MRI (fMRI), and functional mobility testing (FMT).
Fig. 2
Fig. 2
Examples of the leg recruitment curves. These curves were acquired during the pre-bed rest period on day BR −2.
Fig. 3
Fig. 3
Diagram of the functional mobility testing (FMT) obstacle course.
Fig. 4
Fig. 4
Means (and SE) of the log recruitment curve slope values across all study measurement periods for the leg.
Fig. 5
Fig. 5
Means (and SE) of the log recruitment curve slope values across all study measurement periods for the hand.
Fig. 6
Fig. 6
Means (and SE) of individual log recruitment curve slope values across all study measurement periods for the leg.
Fig. 7
Fig. 7
Fig. 7A. fMRI activation map in a subject for the leg movement task obtained before bed rest. The plot shows the time course of activation. The y-axis is percent signal change. Fig. 7B. fMRI activation map in a subject for the leg movement task obtained after bed rest. The plot shows the time course of activation. The y-axis is percent signal change.
Fig. 8
Fig. 8
fMRI percent signal change (PSC) calculated from rest intensity to task intensity, using values extracted at the voxel of maximum Z statistic. The y-axis is fMRI PSC. The x-axis represents three discrete time points: baseline pre-bed rest scan (performed on day BR −4), immediate post-bed rest performed on day P0, and scan performed on day P12. Error bars are SE. Note that the hand percent signal change progressively decreases with scans, while the leg PSC increases dramatically with bed rest and then begins to decline during the recovery period.
Fig. 9
Fig. 9
fMRI percent signal change (PSC) for individual subjects.
Fig. 10
Fig. 10
Functional mobility testing (FMT) course completion times for each subject.
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