Forecasting (internal-state prediction)

The third arc of the sensory-control-loop, named by Petzschner et al. (2021): the CNS predicts how internal states change not only as a consequence of actions, but also as a function of their own internal dynamics.

The second clause is what distinguishes this from anything else the wiki holds. Bodies do things on their own — glucose falls, temperature drifts, inflammation runs a course — and any anticipatory regulation has to model that trajectory, not just the effect of its own interventions.

The empirical hook

The paper’s example is Zimmerman et al.’s thirst neurons: drinking terminates minutes before any appreciable change in blood osmolarity. The satiation signal cannot be a reading of the regulated variable, because the regulated variable has not moved yet. Something is running the body forward in time and reporting the predicted outcome of the action already taken. That is forecasting in the strict sense, in a genetically tractable circuit — and the cleanest existence proof the wiki has that internal-state prediction is a real computation rather than a theoretical convenience.

Two directions to run it

• Forward (action → outcome): simulate the future sensory consequences of an action, plus the intrinsic dynamics of the body. A model of what will happen.
• Backward (outcome → action): assume a desired future state and simulate which actions would reach it, selecting the most promising. This makes forecasting part of action selection rather than a separate faculty — and blurs the boundary with the second arc of the loop.

Why this page is mostly a gap

Both major frameworks of body regulation assume forecasting without formalizing it. homeostatic-reinforcement-learning needs it (to predict which action reduces drive); active-inference needs it (its descending predictions are about future states). But the paper’s verdict is that “there are few frameworks that have formalized forecasting, especially in the internal domain” — the citations it can offer are Sutton & Barto’s RL, Botvinick & Toussaint’s planning-as-inference, and one dynamic Bayesian model of homeostatic control (Penny & Stephan, 2014).

The wiki’s own shelf is emptier still. Every source here that touches anticipation touches it at the level of what anticipatory regulation accomplishes — allostasis in Sterling’s and Barrett’s senses, Paulus’s “failure to anticipate interoceptive states” as the seat of anxiety and depression, Craig’s gesture at the AIC representing “predictions of future feelings.” None of them models the trajectory being predicted.

That matters for a claim the wiki leans on hard. interoceptive-psychopathology and computational-psychiatry locate psychopathology in mis-set predictions about the body — but a mis-set prediction about a future bodily state presupposes a model of how bodily states unfold, and no one has written that model down for the internal domain. The clinical account is currently resting on the least-formalized arc of the loop.

Relation to predictive homeostasis and allostasis

Keep three things apart:

• Predictive homeostasis — acting to move away from the set-point in anticipation of a perturbation (raising temperature before expected cold).
• allostasis — changing the set-point itself.
• Forecasting — the model of future internal states that both of the above require in order to be anticipatory at all.

The first two name regulatory strategies; this page names the predictive machinery they depend on. The wiki has substantial material on the strategies and effectively none on the machinery, which is the point of recording the distinction.