White matter in the older brain is more plastic than in the younger brain

Abstract

Visual perceptual learning (VPL) with younger subjects is associated with changes in functional activation of the early visual cortex. Although overall brain properties decline with age, it is unclear whether these declines are associated with visual perceptual learning. Here we use diffusion tensor imaging to test whether changes in white matter are involved in VPL for older adults. After training on a texture discrimination task for three daily sessions, both older and younger subjects show performance improvements. While the older subjects show significant changes in fractional anisotropy (FA) in the white matter beneath the early visual cortex after training, no significant change in FA is observed for younger subjects. These results suggest that the mechanism for VPL in older individuals is considerably different from that in younger individuals and that VPL of older individuals involves reorganization of white matter.

Figure 1. Experimental procedure

(A) The complete experimental procedure. (B) The procedure of each trial. The time interval between the onsets of a target display and a mask (SOA) was varied. The red dotted ellipse indicates the target location. It is for an illustrative purpose and did not appear in the experiment.

Figure 2. Behavioral improvement in the older people

(A) The mean threshold SOA (± s.e.) as a function of training session (day) for the older group. (B) TDT performance during the two MRI sessions that showed the specificity in the training location (mean ± s.e). n=17 for a and b.

Figure 3. FA changes in the older subjects

(A) An inflated format of the left brain of a subject and an ROI. First, using an inflated format of the brain^{, ,} and a standard retinotopic mapping technique, the visual borders of V1, V2, and V3 were determined to make cortical surface ROIs. The red line indicates one of the ROIs, the ventral cortical area, which retinotopically corresponds to a trained quadrant of visual field in V1. (B) Sagittal image of an anatomical MRI and the white matter VOI. The cortical ROI shown in (A) was converted into a folded format of the brain, and the white matter beneath the cortical ROI was selected as the white matter VOI (illustrated in red). (C) Raw FA map and white matter VOI. The rendered white matter VOI was applied to the raw FA map where FA value in each voxel is available. (D) Resultant FA volume within the white matter VOI. The FA value in voxels within the white matter VOI were averaged. Note the ROI and VOI oversimplified here for an illustrative purpose. (E) The mean subtraction (± s.e., n=17) of FA obtained by DTI in the pre-training scan from that in the post-training scan for the trained region (red) and untrained region (blue) in V1, V2 and V3 for the older subjects.

Figure 4. Behavioral improvement in the younger people

(A) The mean threshold SOA (± s.e.) as a function of training session (day) for the younger group. (B) TDT performance during the two MRI sessions that showed the specificity in the training location (mean ± s.e). n=21 for a and b.

Figure 5. FA changes in the younger subjects

The mean subtraction (± s.e.) of FA obtained by DTI in the pre-training scan from that in the post-training scan for the trained region (red) and untrained region (blue) in V1, V2 and V3 for the younger subjects (n=21).