Psychologists have been trying to understand why people forget things for more than 100 years. Do memories just slip away with time? Are old memories supplanted by new ones? When these two competing theories were being batted about in the 1920s, the latter won when it was discovered that people remembered more if they memorized a list and then slept, versus memorized a list and stayed awake. The theory went that sleeping prevented the formation of competing memories. So it was decided that we forget things because new information kicks out old information.
Then arose a theory that upended that idea. In it, old memories reach their tentacles forward and prevent the formation of new ones. This was based on the observation in the late 1950s that college students who memorized lists of nonsense syllables had variable rates of retention. The students who were repeat test subjects (and so had memorized many lists) fared worse than those who were seeing the lists for the first time. Clearly, the thinking went, those old lists were throwing their weight around and preventing the brain from memorizing new lists.
By the late 60s/early 70s, psychologists had poked enough holes in all these ideas to necessitate new ones. So they speculated that memories need time to be cemented in the brain. According to this, even reading the newspaper interferes with memory formation because the brain’s processing power is distracted from the job of memory consolidation.
While psychologists have been wondering how the box that is your brain gets filled with memories, significant advances have been made in the field of neuroscience to help address this very question. The most recent discovery describes a cellular mechanism behind the act of forgetting, and goes a long way towards explaining the aforementioned observations of the human condition.
A paper published May 10th, 2012 in Neuron by Ron Davis’s lab at TSRI Florida might bring a collective sigh of relief from the more forgetful of us. It seems that we were supposed to forget…whatever it was that we forgot. Davis’s group found that forgetting is an active process, controlled by dopamine. Using fruit flies as their model system, they tested the ability of fruit flies to remember smells. They found that memory formation involves an initial surge of dopamine, which binds to a dopamine receptor called dA1 and initiates a cascade of events to form a new memory. Constant, low levels of dopamine are released following the initial surge. This low-level dopamine is sensed by a different receptor, called DAMB. Signaling through DAMB causes forgetting. Unless a memory is assigned some importance and consolidated, DAMB signaling erases it. The scientists could make fruit flies more or less forgetful by altering DAMB expression on neurons.
What’s really interesting about all of this is that the psychologists’ original observations were not wrong. Their explanations were just off the mark. Dopamine, a neurotransmitter with wide-ranging functions, may be differentially regulated by stress, mental exertion, or sleep. Interestingly, the work by the Davis lab might also explain why some people seem to remember more than others. Their brains might really be wired differently, with different dopamine receptor levels, for example.
We have a strong desire to understand the human brain. As neuroscience informs psychology, maybe future experiments on college students will account for what we learn from fruit flies. If there’s one thing that both fields can agree on, it’s that your brain was designed to forget.