More about memory

Memories can be strengthened and erased by all sorts of conditions.

I would bet that there are upwards of 1000 studies published each year on that topic Are we making any progress in understanding the neurobiology of memory. Certainly on a molecular level of analysis we are know loads more than we did 2 or 3 decades ago. Here is a sampling of a few recent studies.

Exercise and memory: Exercise may be good for you and your brain but not always. Surprisingly exercise can erase memories It seems that running causes rodents to forget their fears (one form of memory) in part because of increased hippocampal neurogenesis. The research was published in the May 8, 2014 issue of Science (K. G. Akers et al., “Hippocampal neurogenesis regulates forgetting during adulthood and infancy,” Science, 344:598-602, 2014). Reported finding suggest that the production of new neurons—neurogenesis—prompted by exercise wiped out the mice’s memories. This might also explain why human infants, whose brains exhibit abundant neurogenesis, do not have long-term memories.

Drug abuse and memory: Many scientists view drug abuse as involving a super strong form of memory (see earlier postings on this site). In a recently published review article in Scientific American (by Janali Gustafson) we can read about a chemical that prevents rats from recalling their drug-associated memories. This can be an important finding that has drug abuse treatment implications. Rats were first ‘trained to be addicted to methamphetamine. After establishing the addiction the rats were tested for the presence (memory) of their addiction under two conditions. One of them after receiving placebo and the other after being administered Latrunculin A (LatA). This chemical interferes with actin, a protein known to be involved in memory formation. Animals administered LatA showed no preference for running to a place they remember getting their fix, even up to a day later: their choices seemed not to be driven by a memory of meth.

Brain synapses and memory: Some synapses in our brain (memory neural hardware necessary for establishing and maintaining memories) can be so ‘sticky’ that they can impair the formation of new memories. Maybe the silly old ideas that you have to get rid of some old knowledge to establish new learning and memories.

It has been known for decades that memories are formed by strong synaptic connections between nerve cells. Recently scientists at the University of British Columbia have found that “synapses that are too strong or “sticky” can actually hinder our capacity to learn new things by affecting cognitive flexibility, the ability to modify our behaviors to adjust to circumstances that are similar, but not identical, to previous experiences.”

The findings from this important study are reported by  Fergil Mills and colleagues in the Proceedings of the National Academy of Sciences. The authors were quoted as saying, “But our study shows that cognitive flexibility involves actively weakening old memory traces. In certain situations, you have to be able to ‘forget’ to learn.”

The study design focused on manipulations of beta-catenin, which is known to be important in disorders such as Alzheimer’s disease and Huntington’s disease.

Sleep: There is no shortage of studies of the impact of sleep on brain function. Here is another one that links sleep and the consolidation of memories (based on research in mice led by Wenbiao Gan of the Skirball Institute of Bimolecular Medicine at New York University Medical School and his colleagues.  Sleep has a role in the consolidation of memories.

Erasing and then restoring memories in a rat’s brain:Roberto Malinow and colleagues used light to stimulate key nerve connections in the brains of rats. By doing that they were able to erase certain memories, and then restore them with a second type of light (see the June 1, 2014 issue of Nature). The researchers first genetically altered some nerve bundles to make them light sensitive. They taught the rats via simple conditioning methods and established that the stimulated nerve areas showed chemical changes that indicated the synapses between the memory-linked brain cells had gotten stronger after the stimulation (learning).

Next they were also able to weaken those memory-cell connections by delivering a low-frequency set of light pulses at the same nerves (unlearning, erasing the memory).

Finally, coming full circle, the research team re-stimulated the nerve bundle with another high-frequency pulse of light reestablishing the learning (memory) that they had just erased.

Not bad, eh?