Habituation

Or: When the Difference Engine Gets Bored

In the last post we arrived at a rather elegant conclusion.

The brain is not a camera.
It is not measuring absolutes.
It is a Difference Engine.

Sensors idle. Neurons fire continuously. Information is encoded not in the size of the spike — because there is no such thing as a “big” spike — but in the frequency of firing.

Warmer means more spikes per second.
Colder means fewer.

Light brighter? Increase frequency.
Light dimmer? Decrease frequency.

The brain detects deviation from baseline.

Which raises a rather practical question.

What happens when the deviation stops?

The World That Won’t Go Away

Imagine the hum of a refrigerator.

At first, your auditory system registers it clearly. Hair cells in the cochlea convert vibration into electrical impulses. Auditory neurons alter their firing rate. The signal ascends to cortex.

Difference detected.

But after a few minutes?

You stop hearing it.

The refrigerator did not stop humming.
Your ears did not switch off.
The neurons did not “get tired.”

Something more interesting happened.

The baseline moved.

Baseline Migration

If the nervous system is a difference detector, then sustained input presents a problem.

A stimulus that does not change is, from the brain’s perspective, no longer informative.

And remember — every spike costs energy. Sodium must be pumped out. Potassium must be restored. ATP must be spent.

Why waste glucose on the predictable?

So the system recalibrates.

Synaptic transmission subtly decreases.
Firing frequency drifts toward a new equilibrium.
Cortical response amplitude diminishes.

The signal is still there.
But the difference has shrunk.

Habituation is not suppression.

It is baseline migration.

Peripheral vs Central Habituation

Some adaptation happens at the sensory receptor level.

Thermoreceptors adjust their firing rate over time.
Olfactory receptors desensitise quickly — which is why you cannot smell your own house after a few minutes inside it.

But much of habituation is central.

The thalamus gates.
Cortical circuits dampen.
Prediction circuits suppress redundancy.

The brain, once again, is not asking:“Is it there?”

It is asking: “Is it changing?”

When the Difference Engine Misbehaves

Habituation is efficient. Elegant. Necessary.

Without it, every shirt sleeve brushing your arm would demand attention. Every background sound would be a crisis.

But there are circumstances where habituation fails.

In hypervigilant states — trauma, chronic anxiety, certain sensory processing disorders — the baseline does not migrate easily. The system continues to treat the predictable as novel.

Difference is perceived where none exists.

Conversely, there are times when we habituate too well.

We stop noticing the persistent stressor.
The slow environmental degradation.
The cultural hum that should concern us.

When baseline shifts too far, warning signals fade.

Habituation shapes not only perception — but awareness.

Silence Speaks

Because the brain measures change, the absence of change can become invisible.

But if the refrigerator hum suddenly stops?

Instant attention.

Difference reappears.

Silence, in that moment, is louder than sound.

The Editor Behind the Curtain

A neuron obeys physics.

It fires or it does not.
It encodes intensity in frequency.
It costs energy to spike.

Layer billions of these together, and you get a system that edits reality in real time.

Not maliciously.
Not philosophically.
Just economically.

Habituation is what happens when the Difference Engine decides:

“No new information here.”

And quietly turns the volume down.

Next time you stop noticing something, pause for a moment.

The stimulus may still be present.

It is the baseline that has moved.

And that was Signal Over Noise for today.