how is the activation value converted to loading/percentage?

[LiLabFSU]

My group and others have been wondering how the activation of a network in a given state was converted into % (Fig. 1). Specifically, we gather that you used the Z scores to compute the activation, but it is unclear to us if you then convert the Z scores into % based on Gaussian probability or some other scale?
Many thanks in advance for your clarification!