Figure 2.

Variational free energy and metabolism in health and with PTSD impairment. (I) Threat or safety undetermined (high uncertainty average, high variance / exploratory sensing, i.e., environment-centric attention). (II) Threat determined (low uncertainty average, low variance / motor preparation, i.e., ego-centric attention). (III) Safety determined (low uncertainty average, high variance / dynamic attentional allocation). The dotted line at t₀–t₁ depicts initial surprisal by a high-energy auditory stimulus outside of foveal range. A healthy individual may engage in exploratory sensing (a₁) with momentary high uncertainty, and obtain fine-grained stimulus information at t₂. If no threat is detected, a safety condition with low uncertainty is designated, with fluid, flexible, reality testing, as self-evidencing environment-body-brain dynamics (see Figure 1a), continuing in a_2-4. If a threat is detected, metabolic resources are directed away from exploratory sensing toward motor preparation (b₂), with intermittent exploratory sensing to ascertain if the threat is no longer present (c₃), in which case, a₄ is reached. Most of the same line may be followed if the healthy person immediately classes the ambiguous stimulus as a threat (b₁), continuing as with the previous case to b₂, c₃, and a₄. In contrast, PTSD impairs both the a₁ and c₃ trajectories, such that the surprising stimulus is disproportionately classed as a threat (b₁), and further exploratory sensing is not permitted to escape the threat condition in b₂, continuing instead to b_3–4 (see Figure 1c).