The choice of an action likely to lead to a reward must to be based on a predictive process. Prediction in turn requires some representation of the environment. Say that environmental state A is followed by state B1 if action a1 is performed and by B2 if a2 is performed. If sometimes B1 is more desirable and sometimes B2, then the appropriate action must be selected given A, based on internal desire state D1 or D2. This is done so that percept A together with D1 can be considered a predictive representation of B1 and the activation of a1 a prediction of B1.
Prediction is clearly the key to autonomy.
Consider a continuously working predictor. If it is nontrivial it will look like an autonomous system in that it produces a sequence of states which are not directly caused by its inputs. On the other hand, prediction is clearly caused by the input, but by a representation of the causality of the environment, such that, since this representation is internal to the predictor, the predictor is indeed in a certain sense autonomous. It is beyond the scope of this review to give more than an idea of how prediction is the key to autonomy. The distinction between inside and outside a brain is arbitrary and depends on what the distinction is aimed at.