Memory and emotion are intimately linked biochemically, with hormones like adrenaline actively involved in forming the neurological patterns we call memories. Any kind of emotional experience will create a stronger memory than otherwise would be created. We remember our embarrassments, our failures, our fender benders.
On the face of it, that doesn't seem especially surprising: We feel strong emotion at important events, which are obviously more memorable than ordinary moments. But the connection is much deeper than that and dates back to our deepest evolutionary past. The major purpose of memory, is to predict the future. An animal that can remember the significance of that large, nasty-looking thing with the big teeth and sharp claws will survive longer and produce more offspring.
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What happens biochemically is that when faced with an emotion-charged situation, such as a threat, our bodies release the stress hormones adrenaline and cortisol. Among other things, these signal the amygdala, a tiny, neuron-rich structure nestled inside the brain's medial temporal lobes, which responds by releasing another hormone, called norepinephrine. Norepinephrine does two important things. First, it kicks the body's autonomic nervous system into overdrive: the heart beats faster, respiration quickens, and the muscles tense in anticipation of a burst of physical exertion.
Second, even as it's kick-starting the body, the amygdala sends out a crackle of signals to the rest of the brain. Some of them put the senses on high alert, ready to deal with a threat. But these signals also tell the neurons that any memories recorded in the next few minutes need to be especially robust.
Memory can indeed be enhanced artificially. It's not necessarily a good idea, though. If someone is given a shot of adrenaline, the memory temporarily improves. But it also drives up the heart rate, so it could be dangerous for the elderly. Other memory enhancers, like Ritalin or amphetamines, used by college students to cram for exams, are highly addictive. Unfortunately, for people with truly serious memory problems, existing drugs are not yet powerful enough or nice enough.
For people haunted consciously or unconsciously by painful memories, there may be hope. The Post Traumatic Stress Disorder syndrome is the result of brain chemicals reinforcing themselves in a cerebral vicious circle. In the aftermath of a traumatic event, we tend to think more about it, and the more we think about it, the more likely we are to release further stress hormones, and the more likely they are to act to make the memory of that event even stronger.
Even without anything approaching a complete understanding of the complexities of the human brain, neurologists and psychopharmacologists have come up with dozens of medications to treat schizophrenia, depression and other disorders. The next batch of psychoactive drugs could provide ammunition against the even more mysterious disorders of memory.
