March 02, 2004
Hippocampus Sorts Information Into Memory Categories

Monkey brains remember things in part by placing them into pre-existing categories.

“When you need to remember people you’ve just met at a meeting, the brain probably doesn’t memorize each person’s facial features to help you identify them later,” says Sam Deadwyler, Ph.D., a Wake Forest neuroscientist and study investigator. “Instead, it records vital information, such as their hairstyle, height, or age, all classifications that we are familiar with from meeting people in general. Our research suggests how the brain might do this, which could lead to ways to improve memory in humans.”

The researchers found that when monkeys were taught to remember computer clip art pictures, their brains reduced the level of detail by sorting the pictures into categories for recall, such as images that contained “people,” “buildings,” “flowers,” and “animals.”

The categorizing cells were found in the hippocampus, an area of the brain that processes sensory information into memory. It is essential for remembering all things including facts, places, or people, and is severely affected in Alzheimer’s disease.

“One of the intriguing questions is how information is processed by the hippocampus to retain and retrieve memories,” said Robert Hampson, Ph.D., co-investigator. “The identification of these cells in monkeys provides evidence that information can be remembered more effectively by separating it into categories. It is likely that humans use a similar process.”

The researchers measured individual cell activity in the hippocampus while the monkeys performed a video-game-like memory task. Each monkey was shown one clip art picture, and after a delay of one to 30 seconds, picked the original out of two to six different images to get a juice reward.

By recording cell activity during hundreds of these trials in which the pictures were all different, the researchers noticed that certain cells were more active when the pictures contained similar features, such as images of people – but not other objects. They found that different cells coded images that fit different categories.

One really interesting aspect of this report is that different monkeys developed different ways for categorizing the same sensory inputs:

“Unlike other cells in the brain that are devoted to recording simply an object’s shape, color or brightness, the category cells grouped images based on common features – a strategy to improve memory,” said Terry Stanford, Ph.D., study investigator. “For example, the same cell responded to both tulips and daisies because they are both flowers.”

The researchers found, however, that different monkeys classified the same pictures differently. For example, with a picture of a man in a blue coat, some monkeys placed the image in the “people” category, while others appeared to encode the image based on features that were not related to people such as “blue objects” or “types of coats."

While such categorization is a highly efficient memory process, it may also have a downside, said the researchers.

“The over generalization of a category could result in errors,” said Deadwyler. “For example, when the trials included more than one picture with people in it, instead of different images, the monkeys often confused the image with a picture of other people.”

This really matches with what one would expect intuitively. A doctor is going to look at people and remember them by disease characteristics. A fashion magazine editor is going to remember them by types of clothing and jewelry worn. Others with different previous training and life experiences are going to split people and things up in different ways. There obviously must be ways that networks of neurons have formed to favor different approaches for filtering and categorizing sensory input.

The process of choosing categories in your mind to sort what you learn and experience is an important part of becoming an effective learner and analyzer of information.

Share |      Randall Parker, 2004 March 02 01:28 AM  Brain Memory

laura kitchen said at June 13, 2004 9:14 AM:

I am a (former) temporal lobectomy patient from 1992. I had my right hippocampus removed because of a siezure disorder. I had the surgery done at Baylor College of Medicine in the Scurlock tower in 1992. The surgery went perfectly, and I suffer no long-term problems, but I am also a former psychology student, & I remember the 1953 case of H.M. well from my studies. Also, everything I have read indicates that the hippocampus is critical for new memory formation. I did not have bilateral removal, just the right one removed. Is that why I am able to form new memories??? This is not a complaint, I was very apprehensive before the surgery especially with my prior knowledge of the H.M. case of 1953. I am simply very perplexed. Why can I retain new information and H.M. could not? Is the left hippocampus performing all of the right hippocampus' former duties??? I am a right-handed person, and very logical & language-oriented, but I do have a creative eye, and lots of creative abilities, I redecorate my home all the time. My siezures are gone, and I now drive in central Houston and have 2 daughters 7 & 3 who are in perfect health. I have just always wondered, how is it possible that my memory is not greatly affected because of the right hippocampus removal? I also took Graduate Level classes in education shortly after my surgery and performed better as a graduate student (A'S & B's with GPA of 3.5)than I did as an undergraduate, in 1988 before my surgery. Why? I can remember things people have told me, how to get from one place to another, and tasks to perform during the day and all of the other essentials. I also learned more about how to use a computer since my surgery. Before surgery using a computer would trigger me to have seizures, but now, I use the computer every other hour during the day. I am currently a stay-at-home-mom. I also have enrolled in the local community college to take Anatomy and Physiology in the next year, and will take my first on-line psychology course next month. I am going to get my R.N. at the local community college.
I know this sounds like I am nagging or complaining, but I am just very curious as to why my memory has been spared? All the medical literature states that the hippocampus is the most vital part to making new memories in the brain. Is the left hippocampus enough to make new memories?

Thanks for your input,

Laura Kitchen,

evelyn davis said at December 26, 2004 5:42 PM:


BRENDAN said at October 7, 2005 12:34 PM:



JEANNINE LITTY said at March 17, 2007 1:22 PM:


Al said at June 29, 2007 7:40 AM:

Jeannine, Two years ago, my wife had her right hippocampus removed due to seizures. Candidacy for this procedure requires that you have not had past head trauma, you are right handed, and your meds are becoming unmanageable. The meds caused violent outbursts, poor short-term memory, and did not end seizures. Since then, my wife is med-free since November. The heavy meds take perhaps six months to get rid of. She hasn't had a seizure in two years, her short-term memory is back, and she is less prone to violent outbursts. She still (inappropriately) flys off the handle when things don't go her way, but it is ten times better than before surgery. She's getting better with every passing day. She has been driving for a year and a half now and I don't need to treat her like a two year old anymore. I wouldn't let her go for a walk or a swim without me. I would yell at her like a two year old if she disobeyed. We had to drive her to the store daily. She likes to shop. We hate to shop. I would highly recommend this procedure.

Karl Brewer said at July 30, 2007 7:42 AM:

In November 1998 I underwent a left temporal lobectomy for complex partial seizures related to my right hemispheric cerebral palsy.I have been told that I was born right handed and, since the anoxia causing the damage occured during the birth process when I was without air for two minutes,I had to learn to use my left side. Prolonged video-monitored and in-depth electrode EEG monitoring revealed left temporal lobe damage. An Arteriogram Wada performed pre-surgically revealed I had bilateral speech and memory with the strongest side being on the right side, not the left. With this information and the results of the EEG monitoring, the decision was made to remove the focal point of the seizures in the left temporal lobe. During the opreation, I had 10 cm of the left temporal lobe, the left hippocampus (due to sclerosis) and part of the left amygdala. I underwent a significant personality change and became a more mellow and laid-back individual. The seizures, constant and unresponsive to meds before surgery, have all but disappeared with a minimal dose of anticonvulsive meds. Most of my short-term memory is intact although I have difficulty remembering some things. My wife can relate some long term memories that I have no memory of and cannot retrieve. Some memories my wife relates, I have no memory of initially but the memory comes back ewventually. I have been curious as to why some memories are retrievable but others are not. I also remember some of the most trivial items but cannopt remember important information about my children's growing up. What accounts for this?

Karl Brewer said at July 30, 2007 7:52 AM:

My email address is if anyone has any information about this subject I wrote about above. Thanks in advance.


Jenny said at November 8, 2007 3:44 PM:

I have been epileptic for about thirteen years now, I am now 27 and thinking about having surgery. I have partial seizures, where I just stare off into space. I have been on many meds and always build up a tolerance to them. I have scar tissue on my left hippocampus so that is the area that they will have to remove. Right now I am weighing my options to see which way I should go. I am just looking for some input. If anyone has any advice let me know.

Sami said at January 1, 2008 10:10 PM:

I underwent a right-amigdhalohippocampectomy (the other word for right temporal lobectomy) in 2001. I, too, was curious as why so much of my memory and cognitive functions were spared. Some of the research that is available is not necessarily applicable to everyone. The terms amigdalohippocampectomy and temporal lobectomy are, also, misleading. Initially, others will claim that it is a removal of the hippocampus--as true as it may be--what most will fail to say is that it is only a partial removal(also known as a resective procedure). How much is removed depends on the patient's case. I had a scar on the tip of the hippocampus, therefore, only 2 to 2.5 cm was removed. In any case, those of you who underwent a unilateral removal still have part of the hippocampus that may or may not be functioning to create new memories and do other cognitive task.

As for those of you, who are contemplating surgery, keep in mind that we, who have lesions or have some part of the brain removed or exhibit memory deficits of any kind, are a rare commodity to the medical community. Many those specialists that you consult with will definitely have their biases, since many of these nuero-surgeons, nuero-psychologists, nuerologists/epileptologists, and others are writing papers to further their careers. It is rare that a patient will be able to go medication-free after surgery (I personally do not know one case of it). In their jargon, "success" can mean anything from a reduction in seizures and convulsions to those, who are seizure-free assisted by medications. Therefore, the published success-rate for the procedure is not necessarily a cure-rate.

I have read some of these research papers, since I volunteered to be a ph.d. thesis for a graduate student and had donated part of my hippocampus to my school for research. The statistics these guys use are very subjective since its based on their choice of an alpha-significance level to measure differences in data.

A year and a half after my surgery I tried to go medication-free based on the prescribed procedure for it, but that made me revisit the hospital for status-epilepticus--a state, in which, the patient is having mutiple seizures and for some reason the brain does not know how to stop. I was lucky there, because the statistics on status-epilepticus are extremely morbid. I was able to go seizure-free for about five years after status-epilepticus and unfortunately, they have returned again.

All in all, be very thorough in your research, before commiting to such a procedure.

Sami said at January 1, 2008 10:12 PM:

Sami (

Connie said at October 13, 2008 3:14 PM:

We have a 12 year old son who has been diagnosed with complex partial seizures. An MRI showed a lesion on the right temporal lobe. After multiple tests: ambulatory EEG, video EEG, PET scan, MRI and neuropsyc testing, the doctors are recommending surgery to remove the lesion and possibly the right hippocampus. He scores in the 90+% range on all tests except the visual memory where he scored in the 1% range. He is currently on Trileptal, which is controlling the seizures. He has been on Trileptal 5 weeks without a seizure--pre-medication he was having seizures every other day and the frequency and severity of the seizures was increasing rapidly. They are going to perform a WADA test to determine if the right hippocampus needs to be removed along with the lesion. Can anyone give me input on the pros/cons of this procedure? Also, will the visual memory return or is that now gone? Also, exactly where would we research this procedure and the potential outcome?

Monica Elliott said at November 16, 2008 3:54 PM:

I am looking for some feedback. I just recently had a right amigdalohippocampectomy, just last week in fact and am in the healing process. I feel Ok, but am noticing everything that appeared as familiar before my hospital stay, seems new - my home, my neighborhood, it's odd and I don't know why it's happening - should it? Is my left hippocampus compensating now? Would love some feedback. Thank you.

Sami said at December 14, 2008 4:27 PM:

Give it some time, Monica Elliot. When I went through the right-amigdalohippocampectomy many things had seemed different. It's the natural psychological side effect of the procedure. I'm pressuming that they also gave you a couple drugs to take to cope with the swelling that you must be experiencing. Those drugs also have side effects that have not been fully explored. I think it took me a full three months to recover, while most of the recovery happened after they had removed the staples from my head.

Your brain "may" have utilized the left hippocampus, more (especially if your procedure was a full unilateral removal). Provided you undergo something like the Pet scan or the Functional Magnetic Resonance Imaging (FMRI), then they can confirm wether you are activating your left hippocampus for certain memory functions or not. Otherwise, we can only speculate what's going on in your brain.

There are many things that happen to us right after the surgery and most of them go unreported. Like in your case, these experiences are hard to gauge the severity of the symptom and since many are not life threatening, most of us neglect to mention these to the surgeon and other M.D.s. This experience will most definitely be an asset to you if you ever decide to study neuro-psychology or cognitive science (two of the medical disciplines that explore patients like us). Hope I answered your question. :)


Kathleen Keane said at August 10, 2009 9:38 PM:

Interesting. My daughter just underwent hippocampus amygdala and left temporal lobe tissue removal for seizures that we could not control. She had seizures from age 18 to 4 1/2 years and then again from 12 to 17. She tolerated the surgery beautifully and is ecstatic about not having seizures. She says that she cannot even "force" herself to feel like she is going to have a seizure. She had none of the side effects that they talked about her having, slurred speech, etc. She is the happiest I have ever seen her. She has not had her staples removed yet. She even looks the best I have ever seen her. The decision for her to have the surgery was excruciatingly hard to make. However, I really feared that one day she would not wake up from one of her night-time seizures. We are looking forward to a beautiful senior year and one without aids following her every where. I honestly felt like I was stepping out onto the ocean with the faith that God would not let me sink. I am very glad she had the surgery, but would tell people considering it to be sure to have a good support system in place -- a wig -- and plenty of time off from work available.

Raz said at February 12, 2010 9:51 AM:

I had complex partial seizures from the age of 7-16 thats when i considered i have nothing to lose and had the lobectomy and had my right hippocampus removed at the age of 16,today im 27years,married with 2 kids and never had any side effects or seizures.Its been 11years since the opperation and im perfectly happy and healthy,thank god because its god that gives and takes.I would encourage anyone to go for it and leave the rest to god

Anonymous said at October 16, 2010 6:28 PM:

in 2005 I had the lesion (about the size of a nickle) taken out of the right side. Now 2010, I am being told that it will help if I take the entire right side of the hippocampus out.

After my surgery in 2005, I had a lot of memory & anger issues. That hasn't gotten any better. So the biggest fear of mine, is will my memory & anger be even worse if I do decide to remove my right hippocampus???

toddles said at November 16, 2011 9:22 PM:

My son has a lesion on his left temporal lobe tht causes seizures that cannot be controlled with meds. We met witht he surgeon today and he says he needs to have part of the left temporal lobe and the left hippocampus removed. I am so confused as what to do, everything I read about the hippocampus says that with out it you cannot create any new memories or learn new things. If it is the right side this is not supposed to be the case but the left side seems to be crucial. Has any one had their left hippocampus removed and what is life like now?

alicia puente said at May 31, 2012 1:45 PM:

Hi I am alicia puente:

I am a mother of one, I was 16 when I had found out I have seizures,
And had to under go surgery to have my left temporal lobe
To be removed, and now going on 23, an I am still having seizures,
An all medications I've been on still, have know control
Of my seizures.

Now I'm scheduled to have surgery again, to have my left hippocampuse
Removed for that is were my seizures are coming from,
An now I ask for anyone's opinion, on weather or not this surgery
Will come out be a excellent surgery for me but also for my son.

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