Affect

States that last

New: two states that outlast what set them off: alarm after poison bites, contentment after a good meal. They build up over several bites.

Result: after a run of poison bites the animals flee the bad ground; after a good meal they stay on good ground. Both states are used in every seed.

Everything this brain does so far, it does about the present. A bush is in front of it, so it bites; the skin is cold, so it walks. When the cause is gone, the behaviour is gone in the same moment.

But some events say something about the minutes that follow. An animal that has just eaten well is probably on good ground; one that has just been hurt is probably on bad ground. To use that, the brain has to keep something of the event after it is over. So that the states have something to work with, the bushes in this world grow in patches that are mostly of one kind.

The circuit

Two modulators (substances that a few cells release and that reach many cells at once, drawn in pink) and three new cells:

  • Alarm. Pain releases the modulator alarm, which drives flee: the animal keeps going forward for a while, out of the poisoned ground.
  • Contentment. fed fires when the animal tastes food and releases serotonin, which drives settle, which switches on rest (the cell of the previous stage that holds the forward step back). After a good meal the animal stays where it ate.

hungry still shuts rest. So a fed animal stays on good ground until it is hungry again, and then forages with good bushes close by.

The states build up. A modulator is released in small amounts and cleared slowly, so its level is a running sum of what happened lately. The cells that read it fire only above a threshold: one poison bite passes without alarm, the animal flees only after more than one; it settles only after more good bites than one bush can give. One bite says little about the ground, several bites close together say much more.

The wiring and thresholds are designed. Evolution tunes the strengths, the thresholds, and how fast each modulator is cleared, which sets how long each state lasts.

Watching it work

One animal from the last generation at a poison bush. It bites three times in a row, and each bite adds to alarm (the row is full at the level where flee begins to fire). One bite is not enough. After the third, flee switches on and the animal walks away, every tick. The alarm is cleared slowly, so the flight outlasts the pain by more than ten ticks.

Biology

A drive, as in the previous stage, follows the body: the hunger cell fires as long as the stomach is empty. An affective state is different in one respect: something sets it off, and then it stays for a while by itself.

In small animals such states are carried by neuromodulators, released quickly and cleared slowly; that slowness is the memory. The worm C. elegans slows down and stays put for minutes after it has found food, under the influence of serotonin. After a harmful touch it speeds away and keeps going well after the touch has ended.

Such a state has two sides: it is good or bad, and it makes the animal more active or less. Alarm is bad and active; contentment is good and quiet.

The world

The bushes now grow in patches, mostly of one kind: after good meals the neighbouring bushes are probably good, after poison bites probably poison. Not every bush in a patch is of the patch’s kind, so knowing a bush by its look, the lesson of the association stage, still has a job.

The world is also four times larger for the same number of animals, with more food, so that animals take less food from each other and what a better forager gains is not hidden. This is the world the next chapter starts in. The rest is as before: cold, hot springs, and four kinds of berry bush, new in every life, half of them poison.

Did it work?

Both states are used in every seed. flee costs the most when silenced: in these mixed patches a run of poison bites is the clearest sign of bad ground.

Against the old brain the gain is clear when the two share a world, in every seed. Living apart, two seeds are ahead and one is behind, so that measure alone would be inconclusive.

Full results

rest, through which both staying after a meal and staying in the warmth act, costs more than fed or settle.

Two older circuits are not used in this world:

  • cold and warm_seek. A fed animal that walks off in search of warmth leaves the good ground; staying where the food is turns out to be worth more.
  • Learning. In these patches the look of a bush and the ground it stands on say much the same thing, and the animals lean on the ground: two poison bites and the alarm carries them off. The learning rate is still there in every seed. What keeps learning from paying is that a lesson about one berry spreads to the berries that look like it, the problem the next chapter starts with.

Neither was removed: the next stages need the learning.

After poison bites the animals take a few more steps than the old brain, after a good meal a few fewer. The differences are small in this measure because one bite alone no longer sets a state off.

Both populations stand still for most of their life, much of it biting at nothing: an animal held in place by rest still has its grasp programme, and a bite costs little.

Runs