Lim, S.-I. | Search bioRxiv

bioRxiv2024

Rebalance the inhibitory system in the elderly brain: Influence of balance learning on GABAergic inhibition and functional connectivity

Aging involves complex processes that impact the structure, function, and metabolism of the human brain. Declines in both structural and functional integrity along with reduced local inhibitory tone in the motor areas, as indicated by reduced {gamma}-Aminobutyric acid (GABA) levels, are often associated with compromised motor performance in elderly adults. Using multi-modal neuroimaging techniques including magnetic resonance spectroscopy (MRS), diffusion magnetic resonance imaging (MRI), functional MRI as well as transcranial magnetic stimulation to assess short interval intracortical inhibition (SICI), this study explores whether these age-related changes can be mitigated by motor learning. The investigation focused on the effects of long-term balance learning (3 months) on intracortical inhibition, metabolism, structural and functional connectivity in the cortical sensorimotor network among an elderly cohort. We found that after three months of balance learning, subjects significantly improved balance performance, upregulated sensorimotor cortical GABA levels and ventral sensorimotor network functional connectivity (VSN-FC) compared to a passive control group. Furthermore, correlation analysis suggested a positive association between baseline VSN-FC and balance performance, between baseline VSN-FC and SICI, and between improvements in balance performance and upregulation in SICI in the training group, though these correlations did not survive the false discovery rate correction. These findings demonstrate that balance learning has the potential to counteract aging-related decline in functional connectivity and cortical inhibition on the tonic (MRS) and functional (SICI) level and shed new light on the close interplay between the GABAergic system, functional connectivity, and behavior.

neuroscience↗

bioRxiv2022

Time-efficient relaxation measurements by 31P MR fingerprinting in human brain at 7T

PurposeThe goal of the study is to develop 31P spectroscopic MRF at 7T to measure T1 and T2 relaxation times simultaneously and to compare time efficiency and test-retest reproducibility of MRF with conventional inversion recovery and multi-TE methods. MethodsA 31P MRF scheme was designed based on a balanced steady-state free precession type sequence. Dictionary was generated using the Bloch equations. B0 map was acquired experimentally and incorporated into the dictionary. 7 phantoms with different T1 and T2 relaxation times were prepared for MRF validation. Simulations were performed to evaluate estimation bias. 7 volunteers were scanned twice using both MRF and the conventional methods to evaluate the reproducibility. ResultsIn phantom measurements, T1 and T2 values between MRF and conventional methods demonstrated a good agreement with Pearsons correlation coefficients of 0.99 and 0.97, respectively. In in vivo experiments, estimated T1 by MRF were in good agreement with those measured by the inversion recovery and in the literature. On the other hand, estimated T2 values by MRF were shorter than those measured by the multi-TE method. 31P MRF method can reduce the acquisition time by 15 min providing less than 10% of mean CV for T1 estimations and less than 20% of mean CV for T2 estimations of metabolites. ConclusionOur results shows the feasibility of simultaneous T1 and T2 measurement of 31P metabolites in human brain using MRF at 7T. High reproducibility can be achieved especially for T1 measurement with 40% time reduction over conventional methods.

bioengineering↗