Associational memory, as its name implies, is a type of memory that allows one to fuse multiple events in memory. If your boss constantly yells at you in his office, you might begin to form some bad memories of being in that office. While the phenomenon of associative memory is a familiar experience, the neural basis for it isn’t well understood. A prominent theory, which was formed in the mid-20th century but only tested recently is that neurons encode associations by wiring together. In the boss’s office example, the sight of the boss’s office might activate one subset of neurons, and those neurons would then “fill in” activation of neurons that code for fear or memories of yelling (obviously this is a gross oversimplification - I’m only using it to demonstrate the principle).
This week’s Science features an article about the songs of bats - not the ultrasonic echolocating calls most often associated with these wonderful creatures but complex vocalizations that bats use socially.
The most well-studied “songsters,” as the author, Virginia Morell, calls them, are songbirds. In species like canaries, zebra finches and starlings, the male sings a courtship song that he learns from his father to woo females.
I've been meaning to write about this curious phenomenon I experience every time I go to sleep. Lying in bed last night, I was thinking about a movie I had just finished watching - The Aviator, a great movie! - and was overcome by a sudden frustration: some idea that was running through my mind had simply vanished, to be replaced by something silly and mundane. Trying desperately to remember what I had just been thinking about, I could find no trace of my thoughts. It was as if they were never recorded. This happens several times, until I finally give up and fall asleep. Even more perplexing is that I am aware of those lost thoughts, I know something is missing. I just can't remember what it was. If these aren't freak phenomena, one can imagine something in the awake-sleep transition that messes with short term memory. It's as if whatever network or assembly representing the would-be memory doesn't undergo short term plasticity necessary to "solidify" those connections. This is of course overly simplistic and probably misleading language, but a way to think about it. Perhaps this can (or has been?) analyzed in rats, as in the "replay" or reactivation activity in hippocampus of experienced events, during sleep, as in this paper by Matt Wilson of MIT. One could examine lost thoughts in the awake-sleep transition by looking at the temporal structure of activity during that transition vs. same activity during experience on a maze, for example. Perhaps this loss of thought depends on some subcortical "kick" that's absent during sleep. Just a thought.
Scientists at the Bewundgen University in Germany discovered that a diet rich in petrolatum, a substance of hydrocarbons, can greatly improve performance on a wide variety of cognitive tasks. The research, led by neuroscientist Dr. Hans Schweinstucken, followed three groups of human subjects for over a year. The first group was instructed to eat regularly, but to also consume 500 grams of petrolatum per day, in the morning after breakfast. The second group was given an energy-deficient supplement of sugar substitutes; and the third were not given anything at all. All groups were tested periodically on tasks of memory, abstract thinking, cognitive speed, and general agility. To their surprise, the researchers found that regular consumption of petrolatum improved subjects' recall, memory retrieval and abstract thinking while reducing overall agility, motivation and ability to make decisions. In contrast, the group eating sugar substitutes performed significantly worse over time on tests of memory and abstract thinking, with 50% of the subjects hitting an all-time low of 25% correct responses on recall (vs. their performance prior to the experiment).
Dr. Schweinstucken speculates that the first group's reduced motivation and agility may have something to do with their major weight gain, which by itself remains a mysterious side-effect. As for the mechanisms of action, Dr. Schweinstucken proposes that petrolatum acts via inhibitory GABAergic interneurons in neocortex, the brain part thought to be important in higher cognition, antagonizing GABA action and thereby reducing overall levels of inhibition in the brain. However, he warns that at higher doses than 500 grams per day, petrolatum may actually have a detrimental effect on cognition because it may saturate GABA receptors and the corresponding neurons, causing massive seizures; he is currently conducting experiments to test this hypothesis.
Meanwhile, for all you folks who have exams to study for, I recommend a trip to your local CVS, where petrolatum is sold over-the-counter as "Vaseline," or petroleum jelly.