Friday, September 26, 2008

Paleolithic Brain: the Hippocampus

Hippocampus” is a name inspired by the idea that these twin brain structures look like little seahorses, at least in human beings. In rodents the structure looks like little bananas, so I’m grateful they didn’t name them “bananacampus.” “Campos” means water monster. So... “banana water monster?” Well... I once found a lemon nudibranch on the rocks along the Oregon coast. That’s pretty close. The question is, does a nudibranch (sea cucumber) have a hippocampus? No. It’s kind of a mammal thing. Though it fascinates me that there’s a sort of pre-hippocampus in “teleost” fishes (I think that means bony: “ost”/osteo like osteoarthritis) and birds have a seemingly “everted” or inside-out version of that doodad.

The hippocampus, like the amygdala which is just ahead of it in the brain’s temporal lobe, is well-enough known that people use it as the name of their organizations or publications. Studies seem to show that memory, emotion, and one’s inner space map are managed here. A goldfish uses its fishy version of a hippocampus a lot, which means sense since they live by rooting around in ponds and need to remember where things are. They can also become sort of “pets” which implies a sort of emotion: attachment. But salmon seem to remember the location of their natal brook with its stony cradle by using some other sense, maybe a chemical-interpreting gizmo that lets them “taste” water.

It appears that remembering is a two-step accumulation: one “bag” is filled all day with sense impressions linked to emotions, then at night the bag is filtered and only some of it is saved to a different bag in another brain structure that is “sorted” and more permanent. What actors and therapists know is that when one remembers something, it seems to be “re-lived” complete with muscle memory, smells, music and so on. A famous patient, H.M., had both his hippocampi destroyed as a desperate effort to stop terrible epileptic seizures. The seizures stopped but his memory was destroyed. He continued to be intelligent and to be able to learn new skills but he couldn’t remember anything in the ordinary sense. (Someone ought to write a book about famous patients!)

People working with these concepts use these terms:

“Episodic or autobiographical memory:” new memories of experienced events
“Anterograde amnesia:” Inability to form new memories
“Retrograde amnesia:” Inability to remember things once remembered -- this can be partial or total. Usually earlier memories persist.
“Declarative memory:” Being able to tell what one remembers.
“Procedural memory:” Learning new skills, like a musical instrument
Place cells:” These cells tell where you are topographically.
Context-dependent cells:” Same as above except that they give different results depending on the animal’s past (retrospective) or expected future (prospective).

Fascinatingly and ingeniously, these functions have been studied in two ways. One is in the brains of people using a computer to create and navigate a “virtual” or invented place (like Sim City) and the other is in London cabbies who study “The Knowledge,” which is where everything is in that city. (You might remember the rambunctious and appealing character in the movie series “7-Up” who memorized “The Knowledge” so he could be a cabbie.) Doing this made their right hippocampus get bigger and bigger!

While working on these ideas, I went to Wikipedia because it’s usually the most basic, even though that means it might be the least reliable. Then I went to this PubMed url, which was very interesting and used wonderful logos based on NW Indian image vocabularies, the kind used on totem poles!
But the best illustrations and the most interesting and easy-to-read trail was at this url.

The hippocampus is the first place in the brain that is affected by Alzheimers. The two cases of this that I know best were in the Bozeman UU Fellowship, both in very gifted and well-loved women who had made major contributions to the lives of others. One, an artist, didn’t seem to have a family history of Alzheimers, and the other did. She had always known she was as risk. My sister-in-law had this condition and so her daughter knows she is at risk. (The condition sometimes travels with depression and alcoholism, which at first seemed like causes, but on second thought seem to simply share an underlying cause.) It’s very unclear what a person should do about all this. The research goes on in rather shrouded fashion because people get so desperate for help that they try to use treatments that are not yet checked out for efficacy and safety. As you can imagine, this is a set-up for con artists promising snake-oil cures, while at the other end of the scale is the real and practical need for expensive care and protection.

The hippocampus also seems to have something to do with epilepsy and bipolar disorder. In general it appears that this little seahorse is the carrier of much of our individual identity and personality style. Drugs can affect it positively or negatively. This is the bit of the brain that “date rape drugs” appear to affect, muffling memory.

The good news is that hippocampus seems to be able to regenerate new cells more than other parts of the brain. Also, estrogen encourages new growth in synapse density, which may be why both the sufferers I knew were older women past menopause. (The response of the other women in the fellowship was warm and generous. They came regularly to read, to bring beautiful found objects, to tell about their lives, and to watch for responses. This was about 1984, when the whole picture was just beginning to form.)

Also the hippocampus seems to have something to do with traumatic memory. I’ll come back to this some other time, but briefly the chemicals of trauma appear to make the hippocampus shrink. Here’s at least one url: and a quote: “The cognitive implications of damage to the hippocampus in PTSD are an impairment of episodic memory and novelty detection that gives rise to disruption of executive functions and results in uncertainty, distraction, and anxiety.” I can testify that when I was living in a risky neighborhood in Portland in the '90's and my cortisol tested high, I wasn’t getting much writing done. It was only when I came here, to a relatively safe place where it is far calmer and quieter (in terms of noise), that I could really concentrate and produce. In a sense then, I was right to ride the seahorse home. The banana sea monster was left behind for the rats.

1 comment:

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