In order to be more concrete, let's make a little theory of how a frame might actually work. Consider, for example, a Trans-frame that is filled in to represent this sentence:
Jack drove from Boston to New York on the turnpike with Mary.
Whenever this particular frame is active, if you wonder about the Destination of that trip, you'll almost instantly think of New York. This suggests that the polyneme for New York must be aroused by the coincidence of two mental events, namely, the arousal of this particular travel-frame and the arousal of the pronome for Destination. Now how could a brain-agent recognize such a coincidence? Simple: we need only assume that the polyneme for New York is attached to an AND-agent with two inputs; one of them represents the arousal of the travel-frame itself, and the other represents the arousal of the Destination pronome. Accordingly, each terminal of our frame could simply be an AND-agent with two inputs.
According to this simple scheme, a frame could consist of little more than a collection of AND-agents, one for each of the frame's pronome terminals! Then the entire frame for the New York trip would look like this:
When a frame-agent is activated — either by seeing, hearing, or imagining something — this supplies each of those AND-agents with one of these two inputs. The second input is provided by some pronome which can thereby activate whichever agent or frame is presently assigned to that terminal. If several pronomes are active at the same time, all the corresponding agents will be activated, too. When the frame above is active, the pronome for Origin will activate the K-line for Boston, and the pronome for Vehicle will activate the K-line for car.
How could such a frame be made to learn which polynemes should fill its terminals? We could begin with each terminal initially connected to a virgin K-line; then each terminal will represent whatever the corresponding K-line learns. Notice that to build frames this way, we need only connect AND-agents to K-lines that can in turn be constructed from little more than simple AND-type agents. One of the great surprises of modern computer science was the discovery that so much can be done with so few kinds of ingredients.