Why Cramming Doesn't Work

Source: Ron Lach / Pexels

Cramming all the learning into one night before the exam usually doesn’t work. You memorize things a lot better if you learn them repeatedly, over multiple sessions.

What’s interesting is that this is true even if the total amount of learning stays the same: you spend the same time studying overall, but create a superior memory if the training is spaced in time.

If you think about it, it’s not obvious why that’s the case. Computers, for example, don’t care if you feed them information in one go or in multiple sittings—what they learn is what they learn, regardless of the timing. What’s different about our brains?

Our new study, published this week in Nature Communications, shows that it’s not actually about the brain, per se. This property of memory, called the spacing effect, turns out to be built into the very fabric of our body. Even kidney cells learn better and create more lasting memories from spaced repetition.

What does it even mean for a kidney cell to learn and have memory?

Consider first how memories are stored in the brain, from a perspective of a brain cell, a neuron.

To a neuron, human experience is a complex pattern of chemicals spread in time—neurotransmitters sent to it by other neurons. Neurons distinguish between fine time patterns and change parts of themselves in response. For example, a slow pulsation of incoming neurotransmitters might cause a neuron’s input endings to shrink, whereas a fast pulsation might cause them to grow.

That’s what “typical” memory is—an imprint left on our brain’s neurons by a specific time pattern of chemicals.

Other cells also receive patterns of chemicals: nutrients, hormones, signaling molecules from their neighbors. The patterns they receive are not as fast and not as complex as the neuronal ones, but they can still carry important real-life information.

In one study, for example, insulin-secreting cells from the pancreas were shown to have a short-term memory of a past meal. Insulin is a hormone that’s released in response to sugar entering the bloodstream, causing this sugar to be absorbed by the body’s cells and stored for future use. If you artificially flood those cells with sugar, as if a large pile of it entered the bloodstream all at once, the cells release all the insulin they can. Then, you give them a 20-minute break and flood them with glucose again. Now, the amount of insulin they release almost doubles.

It makes sense: if an animal found some particularly nutritious resource that maxed out its sugar-absorbing capabilities then those capabilities better adjust to make sure all of those nutrients are absorbed next time. Having them permanently elevated, however, would be counterproductive: the animal would probably feel permanently fatigued and hungry.

This example shows that non-neurons can remember past events and adjust themselves. But is that enough to call that memory without quotation marks?

Of course, it depends on your definition of the word. But I would say the key difference is how fine a time pattern of chemicals can a cell discern.

Neurons detect chemical patterns on the scale of milliseconds.

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Neurons can discern very fine patterns, on the scale of milliseconds. On the other hand, flooding an insulin-producing cell in sugar, then waiting 20 minutes, and then doing it again, is a pattern, but about as basic as it gets. Just how smart can a non-neuron be?

We engineered two separate cell lines, one from nerve tissue and one from kidney, to produce a glowing protein any time their “memory gene” was turned on—we used the same gene that neurons use when they restructure themselves during the formation of long-term memory—the usual, “brain” memory. We then exposed our non-brain cells to different sequences of chemical pulses, which we picked to activate the same parts of the cells that are usually activated in neurons during learning.

It turned out that the cells—even kidney cells!—could tell apart very specific patterns. First, they could count—at least to four. A three-minute pulse did turn on the “memory gene,” but only for an hour or two, whereas after four pulses, the gene was turned on stronger, and stayed on for days.

Most strikingly though, the cells showed the spacing effect—something so far only associated with neurons and brains.

When the cells received a single, prolonged chemical pulse equivalent in length to four spaced pulses, they turned on the “memory gene” less strongly. This “crammed” pulse also caused a weaker activation of several cellular components which we know to be involved in the formation of long-term memory in the brain.

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So learning by neurons and by other cells, including even kidney cells, shares similar mechanisms and follows similar rules.

All cells can form memories, not just neurons.

Source: Ron Lach / Pexels

Our study, then, suggests the surprising conclusion: memory exists not only in the brain, but throughout our body, and this “body memory” could play a role in health and disease.

I believe that our discovery opens new doors for understanding how memory works and could lead to better ways to enhance learning and treat memory problems.

At the same time, it suggests that in the future, we will need to treat our body more like the brain—for example, consider what our pancreas remembers about the pattern of our past meals to maintain healthy levels of blood glucose, or consider what a cancer cell remembers about the pattern of chemotherapy.