Evidence Matters

Evidence Matters

Quite often, I suspect, readers of my memory columns wonder (complain?) about my emphasis on memory studies, what they show and do not show. Editors and publishers have told me that readers do not want to read about the evidence behind my advice. “Do this, don’t do that” is the kind of thing they want me to say. I, after all, am the authority and readers expect to take my word for it. However, I am constitutionally reluctant to pose as a know-it-all, and more so am opposed to believing that people don’t benefit from introspection about what they are doing and why they don’t change to become better at learning and memory.

A more practical reason is that improving learning and memory ability requires breaking old habits and the imposing difficulty of forging new and better approaches and mental habits. Just telling people what they should do (because I and fellow scientists know best) is not likely to be very effective. Change does not come easy to anybody and is even more difficult if clear and good reasons are not provided for making the change.

For example, in my e-book Better Grades, Less Effort (available at Amazon for Kindle and at Smashwords.com for all other readers), I tell students not to cram for exams. But that advice is largely ignored if I don’t explain why cramming is inefficient and unreliable. I have to be convincing, and that requires presenting the evidence for my position. Cramming is something students naturally do. It is not easy to get students to stop procrastinating and discipline themselves into routine study protocols.

There is also this: knowledge is often partial and temporary. What we think is the best way to go about things may even be wrong or sub-optimal at best. If we don’t know the evidence for the various options, how can we make the best choice?

How Memory Is Stored

When you look up a phone number, the digits are coded as patterns of nerve impulses flowing around in a group of neurons. As long as the encoded numbers are “on-line” like this, your memory has access to the numbers.

But what if you start thinking about something else before you dial? Those neurons now have been recruited for another purpose and no longer carry the original number encoding. So you have to look up the number again.

But if the on-line activity goes on long enough, your memory of the number encoding can become stored permanently. How does that happen? Evidence indicates that new learning, as it becomes stored permanently causes new junctions (synapses) to be formed in the neurons of the circuit that originally encoded the information. You can even see physical signs in the form of new growths, called spines, on the nerve fiber terminals.

But what creates these new spines and their functional connections? This involves new RNA and protein synthesis. This in turn requires some genes to be activated to manufacture and maintain the new spines. There are apparently memory genes that are activated by nerve impulse activity. Gene activation is typically driven by specific regulatory proteins, and one such activity-dependent regulatory protein is called CREB.

For a short UTube video on gene expression, click here.

Formation of long-term memory first requires nerve impulse activation of the compound, cyclic AMP. The early studies on CREB were done in different labs, one of which used the mollusc, Aplysia, and the other using the fruit fly. So what does activated AMP do? One of the things is that it binds to a pre-existing protein (called protein kinase), causing part of the protein’s subunits to be liberated. The liberated components move to the neuron’s nucleus, where they bind to another protein, called CREB. Activated CREB then binds to the memory genes, switching them on.

Most recently, another activity-dependent memory gene activator has been discovered called Npas4. This one is especially important because it exists in mammals (mice were the experimental animal) and because it occurs in the hippocampus, the part of the brain necessary to form explicit long-term memories. Moreover, this protein regulates many well-known activity-regulated genes, which suggests that Npas4 might be a “master” control protein. In the study, Npas4 emerged in response to a contextual learning task. A knock-out gene strain of mice that had no Npas4 were poor at learning this task, and the deficit was restored by reversing the Npas4 knockout.

Research on drugs affecting activity-dependent gene regulator proteins is exciting, and may lead to a memory pill. In the meanwhile, the best you can do for your memory is to provide learning situations where original encoding is preserved intact long enough for these gene activation processes to be accomplished.

Sources:

1. Kandel, Eric R. (2005), "The Molecular Biology of Memory Storage: A Dialog Between Genes and Synapses", Bioscience Reports 24 (4–5): 475–522, doi:10.1007/s10540-005-2742-7, PMID 16134023

2. Ramamoorthi, K. et al. (2011). Npas4 regulates a transcriptional program in CA3 required for contextual memory formation. Science. 334: 1669-1675.

To Cram or Not to Cram? -- That Is the Question

Most students, at one time or another, have crammed for an examination. Researchers refer to this as massed trials, where objects of learning are studied all at the same time in one session. Students may be forced to cram because they have procrastinated or did not have a regular, organized, and disciplined approach to study. Non-students may cram too, as in lawyers briefing a case, speakers rehearsing a speech, professors preparing a lecture, salesmen practicing a pitch, and so on.

In most situations research has made it abundantly clear that spacing the learning over many shorter sessions is much more effective than trying to do it all in one big session. Surprisingly, longer intervals between learning sessions are more effective than shorter intervals. For example, one study of students learning foreign-language words found that recall was highest at 56-day intervals as opposed to 28-day or 14-day intervals. The total amount of study time was cut in half: 13 sessions spaced 56 days apart produced comparable recall as 26 sessions with a 14-day interval.

Unfortunately, most academic courses are not designed to support longer study intervals (perhaps educators need to re-think how things are done). Not enough studies have been performed to examine which spacing protocol works best for certain kinds of learning tasks, but it is clear that massed trials are not efficient.

Why spacing makes such a big difference is not understood either, but it does have to do with basic biology. A recent study on seal snails, of all things, showed that the gene expression underlying long-term memory was affected by how five training shocks were spread out over time. Compared with a control test where snails got five shocks at 20-minute intervals, the most effective pattern (developed by computer model) was to give three shocks at 10-minute intervals, followed by a fourth at five minutes later and the fifth shock 30-minutes later.

There is no reason to think this protocol is optimal for humans learning a variety of tasks. But it does help make the point that spaced learning is more effective and perhaps irregular intervals might be better than evenly spaced ones.

Why does spacing work? Two ideas prevail. One is that in massed trials, there is not much time for each presentation to be processed in context. In spaced trials, each learning presentation occurs in a slightly different context, thus providing many more implicit cues that can be unconsciously accessed during retrieval attempts.

Finally, a host of recently reported studies show that each time you are re-exposed to a learning object, the memory is re-consolidated. Successive consolidation events reinforce each other. Multiple consolidations do not occur in massed trials because consolidation takes many minutes or even hours.

Given what I have explained elsewhere on the benefits of self-testing, I suspect that spaced learning would be optimized if the learner self-tested first during each rehearsal session and then checked the recall against the original learning material.

Sources:

Bahrick, H. P. et al. (1993). Maintenance of foreign language vocabulary and the spacing effect. Psychological Science. 4 (5): 316-321.

Zhang, Y. et al. (2011). Computational design of enhanced learning protocols. Nature Neuroscience. Published online Dec. 28, doi: 10.1038/nn.2990

Neat summary graphic on memory

One of the followers of this blog called my attention to a neat summary graphic on memory that her group at Online Colleges has posted. See http://www.onlinecolleges.net/2012/01/09/memory-works/ I think it is a good summary and consistent with what I have been published in my books (http://thankyoubrain.com) and this blog.

... nice job.