A recent Science News (12/12/15) has an article about new research into the hippocampus of rats. Now the hippocampus has long been a favorite of mine and I have written about it several times here (see posts on 2/21/15, 11/4/15, 10/17/14, 9/8/14, or 2/14/14). To review just a bit, the hippocampus is so named because of its seahorse shape and is a very old structure of the neocortex.
The perceptual areas of the cortex pass on their processed information, e.g., visual recognition of objects, faces, or auditory recognition of sounds, multi-modal maps of location, etc., to an area just before the hippocampus, the entorhinal cortex where the information is further processed, maybe collated and integrated, and then this is passed into the hippocampus for its distinctive processing of old and new in the service of memory which it then passes on to other areas such as frontal lobes for planning and acting, etc. A lot more could be said here about this important piece of the brain, but I want to focus on experience, or rather, how we animals experience.
A patient some years back known as H. M. had both hippocampi removed as a way to stop virtually constant seizure activity. Over the years Brenda Milner and others studied his neurological functioning in depth (See my post on ). Briefly, he could form no new memories. He could remember some things from before his surgery and he could talk and perform some cognitive tasks in a seemingly normal manner, but he would not remember meeting you if you left the room and came back in a minute. I do not believe he ever really recognized Dr. Milner who worked with him for many years. While he retained his ability to experience in a human manner, i.e., symbolically, he could not remember much, certainly not his autobiographical experience.
The hippocampus is not the only structure critical to consciously remembered experience; other structures also support our awareness and memory and they also communicate between the posterior perceptual areas and the anterior executive areas. One of the more prominent of these is the claustrum (see post on 8/17/14), that seems to play a role in organizing the blooming welter of experiential elements like, as Crick and Koch explained, a conductor leading a symphonic orchestra to produce a coherent piece of music (and a one, and a two, and . . .). When the claustrum has been rendered temporarily non-functional during surgical procedures, the patient loses consciousness and remembers nothing even as they stay awake. (Remember now that waking and consciousness are two different states).
All this brings us to the newly reported research showing that what are termed grid cells in the entorhinal cortex feeding into the hippocampus do not just keep track of the animal’s location (to be remembered then by the hippocampus) but also the animal’s distance and time traveled. The grid cells were discovered by studying how the rat brain functions as a GPS system (and Science News reminds me that this discovery was awarded the Nobel last year). This current study looked at grid cell functions as the rats ran on a treadmill; in other words their location did not change but the cells still kept up with the time and effort to travel. Now speaking like one of the rats that escaped cinematically a few years back, processing effort and time might be termed awareness of experience, or as we like to say, experience. Maybe not consciousness because of the hypothetical importance of symbolization to such as humans know, but to experience nonetheless both current and remembered, maybe even planned e.g., the rat returns to the nest or a source of food. Once again, I am amazed at the diligent ingenuity of scientists as they explore the intricacies here.
Finally one of the treatments I learned to use with children experiencing PTSD was a mindfulness technique in which the attention was focused on current percepts. Basically the kids learn to ground themselves in the moment by talking through a list of percepts. They start by saying “I see ___” for 5 different things, then “I hear ___” for 5 different things, and “I feel ____” for 5 different things, then repeating each for 4 different things, then 3, and so on. Try this; it is amazingly calming. And while it certainly involves verbal symbolizing, it does keep one’s focus on a sort of hippocampal immediacy (dare I say it, to a rat’s experiential awareness). The idea here is to disrupt the intrusive memories and reverberating echoes of trauma and emotional arousal bordering on fight/flight and anchor awareness into the boring and safe present place.
So happy holidays and for those of you with candles and evergreen scents and shiny lights and tasty food and the associated memories and memes of a special solstice time, keep the hippocampus and claustrum functioning full power. It is how experiences are made to remember.