The predicted population FA means for age 55 years are plotted against corticospinal tract location for the controls (left and right hand sides) and patients (left and right hand sides). FA values theoretically range from 0 to 1, where 0 indicates completely isotropic diffusion and 1 indicates perfectly coherent (anisotropic) diffusion. Note that there is some side dependence of FA at the internal capsules. ALS demonstrates significantly lower FA at all levels. Controls LHS (solid line), RHS (short dashed line), patients LHS (long and short alternating dashed line), RHS (long dashed line).