Perhaps one of the most intriguing aspects of the human mind is the formation and retention of memories. The brain’s habit of not only reacting to and perceiving events but also pocketing them for later viewing can be simultaneously its most cherished and its most debilitating function. For every happy memory, there is a memory of pain or loss. For those suffering from PTSD or recovering from addiction, memory can often seem like a curse.
A lot of physical and chemical changes are required in order for the brain to create a new memory. Sensory perception is first analyzed by an area of the brain known as the hippocampus. This structure determines whether or not the experience is worth remembering, depending on a wide range of factors such as attentiveness and past experience. The hippocampus integrates information from all five sense into a single, coherent memory and sends it off as bits of information to be stored in different areas of the brain. Memories are stored via the reinforcement of nerve pathways. The connections between nerves cells, called synapses, become stronger each time a signal is sent over them. Thus, as sensory experiences, translated into electrical and chemical signals, pass between cells, the brain is slightly rewired.
As things are experienced, the brain begins to form distinct neural pathways associated with certain perceptions. When an experience is repeated, the connections become stronger, reinforcing the pathway. It is in this way that memories are formed. Keep in mind that this is a very general overview. The gaps in the explanation reflect just how little is understood about the inner workings of the human mind. Indeed, even less understood than memory formation is memory retrieval. How the brain retrieves the myriad of information bits associated with a memory and reforms them into a thought is still the subject of research. There likely won’t be a complete explanation for many years.
This does not mean that our current knowledge hasn’t been put to use. New research out of The Scripps Research Institute (TSRI) offers hope, and raises questions, for the eventual control and elimination of negative memories. Researchers have succeeded in erasing drug-associated memories in mice while leaving other memories intact. Prior to the experiment, the mice were trained to associate a number of sensory stimuli, such as sights and scents, with the uplifting effects of methamphetamine. After the experiment, the same mice had lost all interest in the stimuli. Essentially, they had forgotten that the drug and its effects were ever associated with them. This was accomplished through the manipulation of actin, a protein that forms the infrastructure of every cell.
In normal memory formation, actin plays an integral role in adjusting the structure of nerve cells in order to reinforce synapses. This is in turn what ingrains most memories. Using an inhibitor molecule, the scientists were able to halt this action completely. The result was a complete loss of the neural pathways attributed to the various sensory cues. More importantly, the study was able to prove that all other memories, such as those associated with food, were completely unaffected.
It should be noted that past experiments have shown that memories associated with drug use are often more fragile and thus easily manipulated. As such, this experiment does not open the doors to complete control over every memory the mind creates. However, it is certainly a step towards a more comprehensive control over human recollection, calling to mind a number of disturbing possibilities as to what such technology could be used for. However, the scientists involved point to the positive benefits which could result from the research. It may be possible to one day eliminate the harmful memories that lead to recurring addiction, or to help those recovering from traumatic events or wars. Overall, it is one more step towards the holy grail of neurobiology: the reverse-engineering of the human mind.
This research was originally published in the journal Biological Psychiatry.