Volumetric Variation In Subregions Of The Cerebellum Correlates With Working Memory Performance

Objective:We aimed to investigate the relationship between structural variations in the cerebellum and individual differences in working memory performance as assessed by average reaction time (RT) and correction rate (CR) on a n-back task.Subjects and Methods:311healthy right-handed subjects (152males and159females; mean age=22.6years, SD=2.5years, range=18-31years) were included in this study. Individual working memory capacity was evaluated with the n-back task. Handedness was evaluated using a Chinese questionnaire modified according to the Edinburgh Handedness Inventory. A high-resolution T1-weighted brain volume (BRAVO)3D MRI sequence with176contiguous sagittal slices was performed (repetition time=8.1ms; echo time=3.1ms; inversion time=450ms; slice thickness=1.0mm; no gap; flip angle=13°; field of view=256*256mm2; matrix=256×256).The structural images were processed with the software of SPM8in the order of the following steps:(1) tissue segmentation:to segment brain tissues into the gray matter, white matter and cerebrospinal fluid;(2) spatial normalization:to corregister the brain structural images of each subject to the normalized space;(3) smoothing: to smooth images with a Gaussian kernel of8×8×8mm3full-width at half maximum;(4) correlation analysis:Voxel-based partial correlation analyses were carried out to test relationships between GMV and both RT and CR on the working memory task. Age, gender, years of education and handedness score were entered as covariates of no interest. Correction for multiple comparisons was performed using Monte Carlo simulation.We employed a corrected threshold of P<0.01(two sided) for each voxel and a cluster size>333voxels, which was determined by the AlphaSim program in AFNI software (parameters:single voxel P=0.01,5000simulations, FWHM=8mm, cluster connection radius=2.5mm, with cerebellar gray matter mask);(5) Statistical parameter mapping was overlapped onto MNI standard template. The coordinate and size of each significant cluster were recorded.Results:Behavioral results showed that the average RT on the2-back task was715.4±133.7ms (range,324-1034ms) and that the average CR was88.7%±5.6%(range,65.6%到100%), while on the3-back task was738.1±138.2ms (range,280-1120 ms) and that the average CR was81.7%±6.5%(range,54.4%-95.6%).3-back:the RT was positively correlated with the GMV bilaterally in the bilateral cerebellar lobules Ⅳ/Ⅴ, Ⅵ, Ⅷ, vermis Ⅶ/Ⅷ and left Crus I, while the CR was positively correlated with the GMV in the left cerebellar lobule VI and Crus I.2-back: the RT was positively correlated with the GMV in the left cerebellar lobules IV/V, VI, Crus Ⅰ, vermis Ⅶ/Ⅷ and bilateral lobules Ⅷ, while the CR was positively correlated with the GMV in the left lobules VI and Crus I. The results of the2-back analyses were similar to the results of the3-back task with slight differences in the cluster size.Conclusion:1、Our findings provide further evidence that the cerebellum contributes to working memory function.2、These findings suggest that RT on a working memory task is related to structural variation in both motor and cognitive subregions of the cerebellum, while CR is mainly associated with the cognitive subregions.