Manipulating memories at the cellular level

Last month I wrote about the stories that good scientists tell at conferences — stories that illuminate whole areas of creation. I was reminded this past month that one reason such stories are significant and valuable is that they can be linked together to form larger bodies of knowledge, like jigsaw pieces snapped together to reveal more of the final picture. Here’s one example of two science stories, or “puzzle pieces,” being snapped together.

At May’s conference in Montreal, one story I heard featured a new technique that makes neurons light-sensitive. The new technique, called optogenetics, uses genetic manipulations to produce light-sensitive molecules in brain neurons. These molecules turn light into electrical signals (just like what happens in our retina) so a laser light can then “turn on” these neurons.

Then in early June I read that this optogenetics technique is being used to explore an important aspect of our brain’s functioning: memory. Each morning we wake up from some form of unconsciousness but know who we are. This remarkable ability to quickly go from complete unawareness to full functioning is possible because of the information stored and accessed in our brain, a capability we call memory. Having studied memory extensively, psychologists and neuroscientists can tell us a lot about the psychology of memory and where in the brain different types of memories are stored, but they have not understood how it worked at a neuron-by-neuron level.

Researchers have long studied two phenomena that could form the basis for memory, not in live animals, but in live neurons dissected from the brains of animals and maintained in a glass dish. Long-term potentiation (LTP) is a relatively permanent increase in a neuron’s effectiveness that can be induced with the appropriate electrical stimulation. Long-term depression (LTD) is the opposite, whereby a decrease in a neuron’s effectiveness can be induced by a different set of electrical stimulations. Neuroscientists have long believed that these two types of changes may form the neural basis of generating and losing memory, but they have never been able to link these changes to memories in a live creature.

The memory switch

Now in the June 1st issue of Nature, Sadegh Nabavi and his associates have shown that “fear memory” in rats is based on LTP and LTD. Using optogenetic molecules that turn light energy into electrical signals in a rat’s brain, Nabavi’s team could activate neurons by shining a laser light on them through an optical fibre inserted into the brain. They then trained these rats in a standard fear learning experiment, pairing stimulation of the light-sensitive neurons with an electric shock. The next day the rats exhibited fear when the same neurons were again stimulated with light. By using different parameters of light stimulation, the researchers then induced LTD in the neurons and found that the fear was gone. They then induced LTP and found the fear returned. Another round of LTD caused the fear to disappear, and a second round of LTP made it return. Thus they could turn the memory on or off in rats by techniques that induced LTD and LTP, effectively demonstrating that in a real creature’s memory, the same processes worked as had been seen in neural tissue studies. Nabavi’s study directly links these two areas and confirms experimentally that at least some memories are based on the specific changes in how neurons function (LTP and LTD), a functioning reasonably well understood within the research community.

It is still a long step from fear learning in rats to the memories I have of my parents, but we now have a link to understanding the mysteries of memory at a cellular level. With such knowledge and of course further discoveries, perhaps someday we can help people keep memories they need (such as those lost in the dementias) or lose memories that are harmful (such as in Post-Traumatic Stress Disorder).

This article in Nature following so quickly on the talk I heard in Montreal demonstrates something in science that we also see in Scripture: stories are linked. One aspect of creation has links to other aspects, and an insight into one part of the creation tells us something about other parts. Scripture is the same: one story about God’s faithfulness links and explains what happens in other contexts. The stories in science and Scripture form fabrics that show us in science how God created the world and in Scripture how God’s love enfolds us. Learning to listen to God’s stories and how they are linked to our lives and actions today is an important part of our walk in God’s world.


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