When you see a bargain, your brain releases the “feel good” hormone dopamine.

At one time or another, most of us have bought a product we didn’t really want or need, simply because it was on sale.

But why is it that we get so excited by the prospect of a discount?

The answer lies in the human brain: the sudden possibility of receiving a discount activates a flow of dopamine, a chemical which is considered part of the brain’s reward system. The moment dopamine is released, we feel elated and excited.

However, as we learn to expect a discount, that excitement begins to wane. This was demonstrated in the following experiment. A rat was dropped into a maze in which a small treat was hidden in the center, and its dopamine levels were monitored.

The first time the rat located the treat, its brain released a massive surge of dopamine. However, after it had found a treat a few times, the amount of dopamine released was practically zero.

Why? Because the rat expected to find the treat in the maze’s center. In short, the element of surprise had diminished.

Our response to discounts works in a similar way: in order for discounts to prompt a dopamine-fueled rush of excitement, they have to surprise us and exceed our expectations. Say you’re visiting your favorite electronics store with the intention of purchasing a new TV, and expecting to pay full price. If you see a “50 percent OFF!” sign as you enter the store, a dopamine surge – and the excitement this produces – is all but guaranteed.

Why, then, do we sometimes find it harder to resist purchasing discounted products than at other times?

If there’s too much dopamine coursing through the brain, we’re less able to control our behavior. An overabundance of dopamine limits the functioning of the brain region responsible for weighing the pros and cons of any action – the dorsolateral prefrontal cortex (DLPFC).

This dopamine flood can be caused by stress; thus, when we’re anxious, we’re prone to respond unreasonably to discounts and special offers (e.g., “buy one, get one free”) and to make impulsive purchases – even of products we really don’t need or want.