One of the signature discoveries of cognitive neuroscience is that a structure called the hippocampus, deep within the brain, is intimately involved in creating memories. This fact was dramatically illustrated by a singular patient, Henry Molaison, who experienced severe epileptic seizures. In 1953, when Molaison was 27, doctors removed his hippocampus and nearby areas on both sides of his brain. The operation controlled his epilepsy, but at a price—from that time on, he was unable to remember the things that happened to him. He could learn skills, such as mirror writing, but would be puzzled by his expertise, because he could not recall having acquired it.
H.M., as he was known during his lifetime to protect his privacy, taught scientists three lessons. First, certain brain structures—the hippocampus and the amygdala, the brain’s emotion center—specialize in remembering. Second, there are different kinds of memory—the ability to recall facts, or personal experiences, or physical skills like riding a bike—each with its own properties. Third, memory is distinct from the brain’s intellectual and perceptual abilities.
Fifty years later these conclusions have been strengthened by laboratory studies on mice, rats and monkeys and by further clinical observation. A case in point is transient global amnesia, a rare but enigmatic loss of memory that is sometimes triggered by a stressful event. The patient suddenly cannot recall facts or experiences—anything that is not deeply encoded, such as his name. He also becomes unable to form new memories. There is no impairment in motor or sensory function, judgment, intellectual faculties or consciousness. As the name suggests, transient global amnesia is temporary, disappearing within 24 hours with little long-term effect. But within a day or two of the attack, high-resolution imaging reveals small areas of damage in a specific part of the hippocampus.
Having established the critical role of the hippocampus, the next question is: What makes something memorable? Of the countless things a person encounters in a given day, why do some become indelibly imprinted, whereas others vanish like soap bubbles? Scientists know that many factors play a role in determining what people remember, among them how much attention the person is paying, how novel and interesting the experience is, and the kinds of emotions that are evoked. But recently a team led by neuroscientist Ueli Rutishauser of the Howard Hughes Medical Institute at the California Institute of Technology delved into the cellular workings of the hippocampus, chronicling the activity of individual brain cells as people absorbed and recalled new information. Their findings, though delivered in the technical language of action potentials and electrical frequencies, provide intriguing insights into the Proustian mystery of memory.
Electrodes Thinner Than a Hair
Epilepsy treatments, though less invasive than in H.M.’s day, continue to offer unique opportunities for neuroscientific insight. To pinpoint where seizures originate, doctors sometimes implant electrodes thinner than a hair in the affected brain areas. Then for a few days they eavesdrop on the electrical activity that takes place while the patient talks, watches television, moves around and sleeps in the hospital ward.
Rutishauser and his colleagues piggybacked their memory experiment on this medical protocol. They asked nine epileptics who were undergoing electrode monitoring to view 100 slides, each of which showed an image of a person, an animal, or an everyday object such as a car or a tool. The patients had one second to commit each picture to memory as best they could before the next one appeared. The team later tested the patients’ recall by showing them a second set of 100 photographs, half of which were novel and half of which were repeats from the initial slide show, and asking them to identify which ones they had already seen. During the two slide shows, the team used the implanted microelectrodes to track electrical activity in the hippocampus and the amygdala.
See what we're tweeting about
8 Comments
Add CommentHave people with photographic memory developed or been born with a natural rhythm between their theta waves and neuron spikes? Surely they have other mechanisms for memory that others don't/can't access, but I was wondering if other "normal" processes were more refined as well.
Reply | Report Abuse | Link to thisSo much of modern science is becoming frightening in terms of its potential abuse. The reliable mapping of the subconscious represents an unprecedented capability for manipulation and control which, in conjunction with biochemical and genetic insights could facilitate passive yet potentially criminal, or even deadly results. The notion of political, or professional abuse of such information on an individual, serial or cultural basis will prove too tempting to resist.
Reply | Report Abuse | Link to thisBlamelessness is already the sole property of the DOE, am I crazy for seeing a burgeoning pattern here? Intellectual gravity is, after all, the most definitive indicator of character.
Would a method for increasing theta rhythms in the aging brain help to solve loss of memory?
Reply | Report Abuse | Link to thisIt would seem that the beta waves would be more conductive to memory recall since they occur during active concentration. Does the concentration increase the number of brain waves? Do these brain waves show up in the hippocampus or the amgdala or both? Does age have a bearing on the brain waves?
Reply | Report Abuse | Link to thisThank you for this amazing data! Simply remarkable and promissing to yield more future discoveries study... Bravo! (love the music terms used, by the way...)
Reply | Report Abuse | Link to thisWRQ9- The potential danger you speak of is feasible, due to the ability for any one individual to become corrupt. Neurosurgeons in the start can begin to use it to treat or possibly cure diseases such as Alzheimer or other psychological diseases. This will prove to be beneficial at the current moment since many of these diseases are currently viewed as very problematic and have no authentic long-term cure. This process has a double-edged sword because at the same time neurosurgeons can perform surgery that could induce memory loss. This would be catastrophic by they can make world leaders forget their position on a topic and make laws that would normally be denied pass through legislation. In turn the world would end up under the control of whoever controlled the top neurosurgeons. All conflicts are surrounded based on political views and a nation's self-interest. To be able to edit either one of these could become the deciding factor in whether or not a nation goes to war. The potential risk of this scientific breakthrough needs to have restrictions set in law to protect the minds of our planet's most prominent leader.
Reply | Report Abuse | Link to thisThe body-brain combination stores every observation of the body. To recall the observation it is stored in a associative way. Connected to a smell and or music. Conected with the touch of the left foot is an event of sexual experience. The touch of that foot makes remember the sexual event. Etcetera.
Reply | Report Abuse | Link to thisEven the experience of the body after the conception and before birth is stored. To recall that memory can be done using the words and the voice of the now grow up parts of the person.
When we talk about memory we mean the memories that can be made conscious. The ready to recall memories is just a very small part of the stored memories in total.
I hope that science will be clear about what we communicate.
Cees de Vrieze, Bloemendaal, The Netherlands
'Executive skills' such as memory are the first to go when you're tired as Delta waves are not conducive to learning. Rutishauser's memory test experiment is very similar to this excellent 'face memory test' I found on this BBC sleep page: www.bbc.co.uk/science/humanbody/sleep
Reply | Report Abuse | Link to this