The electrical fields that are picked up by this technique include a variety of rhythms. Delta waves—slow brain waves that occur one to four times a second—are characteristic of deep sleep. Beta waves, which occur 12 to 30 times per second, dominate when people are actively concentrating.
At a middle tempo is the theta rhythm, which repeats three to 10 times per second. (To put this in perspective, consider that when I run along the steep trails in the San Gabriel Mountains, my heart rate plateaus at 160 beats per minute, or 2.6 beats per second.)
The theta rhythm is particularly strong when people are finding their way or looking at something novel—in other words, when they are learning. Previous experiments suggest that the stronger these oscillations are and the more often they occur during learning, the better the person will remember the new material.
So it was not a surprise that the Rutishauser team picked up prominent theta activity when the patients were memorizing the images. But their findings went deeper. Using sensitive electronics and sophisticated software, the scientists could detect the faint staccato sounds that individual neurons make as they send information to one another by way of all-or-none pulses known as spikes.
The team recorded the activity of 305 neurons in the hippocampus and the amygdala. The total number of spikes that occurred while a subject viewed an image did not predict whether or not the patient would later recall it. (On average, participants recognized two out of three of the initial pictures.) Yet the scientists found something that did predict successful recall in about one fifth of cells.
Getting into a Groove
Nerve cells do not generally operate in lockstep. They typically send out pulses irregularly, whenever their excitation levels exceed a threshold. What the Caltech team found, however, is that neuronal rhythms can be highly orchestrated at times—and that this synchrony helps people form lasting memories. Think about a freestyle swimmer. She regularly turns her head to the side to breathe within the triangle formed by her upper and lower arm and the waterline. If she takes a breath during a different phase of the crawl, she most likely will swallow water and lose her rhythm. And so it seems to be for these memory-forming neurons.
During the learning phase, the team found, if a picture flashed on the screen at a moment when neuronal spikes in the hippocampus and the amygdala lined up with the local theta clock, patients were more likely to remember the image and feel confident that their recollection was accurate. When people were viewing images that they would later fail to recognize, this coordination between individual memory-encoding neurons and overall brain activity was much reduced.
This research reveals an extra factor besides attention, novelty and emotional impact in determining what makes something memorable: timing. Neurons always spike in response to new images and experiences. But when the spikes happen to coincide with the theta rhythm, this coordinated electrical activity alters the brain’s synapses, those specialized molecular machines between neurons, enabling memories to form.
These subtle findings help to decode the mechanics of memory—how three pounds of viscous tissue produces a mind possessed of innumerable impressions, recollections and knowledge accumulated over the course of decades.
This article was originally published with the title You Must Remember This.
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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
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