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What your fourth-grade teacher knew that you didn't...



How do you imagine our memories work? Are there a thousand file cabinets in our heads, each dedicated to a different topic? Are there little minions running around organizing and re-organizing our stores of knowledge to incorporate all the things we learn every day? How come I can remember the atomic mass of Oxygen but I can’t remember the capital of Connecticut?

The truth is we still don’t really know. There are several theories about how we store knowledge but for the most part, it’s still up in the air. However, leaps and bounds have been made in the past 20 years to elucidate some of the mechanisms behind acquiring new knowledge. That is, scientists now think they know at least one way that we humans learn new things. 

The process is called Long-Term Potentiation and it is facilitated by events that occur at the synapse—the tiny space between two neurons where molecular signals govern cellular change. There is a molecule called the NMDA-receptor at some of your synapses that plays a role in modulating neurons’ responses to stimuli. The NMDA-receptor is like a little gate on the surface of a neuron that is receiving a signal. Depending on its state (open or closed) the signal from the first neuron will elicit a strong or weak response from the second neuron. If the receptor is “open,” special signaling molecules can go through it into the second neuron which starts responding. So far this sounds pretty normal, an open gate means more signal can get through and there will be more response. But how does that help me learn my vocabulary words?

Whether the NMDA-receptor is open or closed depends on two things: the amount of signal from the first neuron AND the amount of response from the second neuron. Not only will more signal from the first neuron open more NMDA-receptor channels but more response from the second neuron will also open more NMDA-receptor channels.  Furthermore, the more intense the signal-response event and the more often it occurs, the stronger the same signal-response event will be next time. The physiological change occurring at the molecular level strengthens the connection between the two neurons, which in turn strengthens the bit of knowledge associated with those neurons. This is precisely why the more times I copy a word and its definition, the more likely I am to remember it next week. I know you thought your fourth-grade teacher was just giving you busy-work, but that busy-work may have actually been helping you commit new facts to memory. 

So next time you’re tempted to skip a few homework problems think about your neurons. You may not feel it but every problem you do may make that connection between one neuron and the next a little bit stronger and your NMDA-receptors will thank you. In fact, I’m going to think about the capital of Connecticut for the rest of the day. Hartford…Hartford…Hartford……

Sources and further reading
Bliss, T. V. P.,  Collingridge, G. L. (1993). A synaptic model of memory: long-term potentiation in the hippocampus. Nature 361, 31-39.

Kikusui, Takefumi, Aoyagi, Atsushi, Kaneko, Tsugio (2000). Spatial Working Memory is Independent of Hippocampal CA1 Long-Term Potentiation in Rats. Behavioral Neuroscience 114, 700-706.

Tsien, Joe Z., Huerta, Patricio T., Tonegawa, Susumu (1996). The Essential Role of Hipposcampal CA1 NMDA Receptor-Dependent Synaptic Plasticity in Spatial Memory. Cell 87, 1327-1338.
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