Brain Plasticity Science
This hub is primarily concerned with memory and recent discoveries and insights into the way we remember things, where memory is stored, and how accurate memory actually is.
Where Memories are Stored
To date brain science has found no specific place in the brain where memories are stored. Refer to the graphic at right. So far regions of the brain have been found for vision (Primary Visual Cortex), reading, comprehension, speaking (areas of Wernike's Region), and logical reasoning. Also, motor coordination (Primary Motor Cortex), sound processing (Primary Auditory Cortex), and touch (Primary Somatosensory Cortex). There is even a central region of the brain, the hippocampus, that acts and an "index" to these other regions of the brain.
Instead of specific physical regions set aside for memory, it is now thought that the processing regions of the brain (mentioned above) are also memory repositories. The hippocampus acts as a coordinator for these memories; an index of sorts. For that reason it is now thought that the majority of the brain is responsible for memory.
Hippocampus, the Coordinator of Memory
In order to prove the hippocampus had a hand in memory a novel experiment was designed based on the memory skills of London Cabbies.
People hoping to work as London cab drivers are required to study maps and have intimate knowledge of the city of London. To pass a test, and get a license to "hack" in London, cabbies must pass both oral and written exams filled with random questions about how to get from one place to another. Correct answers must include each street name, direction, distance, and travel times varied by time of day. This is quite a bit to remember.
The experiment measured, via FMRI scans, the hippocampus region of the subject's brains both before and after study and final examination.
It was found that the cab-driver hippocampus not only grew in size, but displayed signs of new neuron cell growth as well as enhanced connections between new and existing neurons.
Morris Water Maze
Before you decide to run out and get running shoes, shorts, and sweats the mice that showed the marked memory improvement ran up to ten hours a day. Those that ran a minimum of three hours a day had a less marked memory improvement, but still about thirty percent better than a mouse that did not run or have access to an exercise wheel.
Exercise Enhances Memory
In another experiment with mice memory was improved by exposing the mice to an "enriched environment." There were three parts to this experiment.
One part involved a large tub of opaque liquid in which there was a hidden platform. This is called the Morris Water Maze. Mice were placed in this large tub and naturally sought out a place to rest and stay elevated above the liquid. Since the platform is just below the surface it cannot be readily seen. The purpose is to train the mice to find the platform and then time them on subsequent forays into the tub. This allows the researcher to gather a set of times (minutes or seconds) before the mouse finds the platform again. This provides a means of measuring improvement (or degrading) of memory that is readily quantifiable in units of time.
The mice are then injected with a toxin known to impair memory. The mice are then exposed to the tub again and a marked decrease in memory was noted.
Finally, some of the the mice were exposed to a "rich" environment, one with a lot of toys, cubby-holes, and an exercise wheel to determine if that environment would improve, have no effect upon, or further hamper memory retention. The enriched mice performed better than the controls.
In an attempt to introduce an additional control some of the mice were allowed into the rich environment and some only to an exercise wheel. The assumption was that the "enriched environment" was the memory improver.
Much to the researcher's surprise mice exposed only to the exercise wheel had as much of a marked memory improvement as mice exposed to the "fully-enriched" environment. It is now thought that exercise, running in particular, somehow increases the number of new neurons and brain pathways and thereby improves memory.
Another experiment was designed to determine how easy it is to implant false memories and also to determine how those memories are stored in the brain.
In the experiment the subject and a researcher observe a scene staged by some actors. The subject is told to observe how many times the actors do a particular thing, but is not told that s/he will be asked to remember what the actors did. After the subject and researcher leave, the actors are then photographed doing things the subject saw and also doing things the subject did not witness. e.g. the subject may have observed the actors eating, talking, reading, wearing glasses, etc. The photographs might all of the activies above, but also be photographed doing things the subject did not see.
Back in the lab, in a relaxed setting, the subject is then shown all of the photographs including those activies that s/he did not witness.
The subject is then asked a series of questions about what the actors did or did not do. Interestingly, about 1/3 of the positive responses (the actor did this or that) involved photographed scenes that the subject did not directly observe. This demonstrates the placidity of memory and the ability of researchers to "implant" memories.
Finally, the subject is asked the same series of questions while undergoing an FMRI scan. Much to everyone's surprise the areas of the brain responsible for storing tactile memory did not activate when the subject gave a positive response to a false memory, even though the visual cortex did. The brain is therefore aware of the "truth" even if the subject is not.
Memory, Sleep, and the Hippocampus
In a final experiment subjects were given a modified sleep study designed to test memory storage and coordination.
In this experiment subjects were outfitted with sensors to monitor REM sleep. They were wakened from time to time to take a word comparison test.
In the test the subject was shown two words and asked to give a "true" score if the words were associated or a "false" score if there was no relation between the two words or even if one (or both) of the words were misspelled (nonsense words).
During the course of the experiment subjects were awakened and given the test before sleep, without a dream state, and after a dream state.
Subjects scored far better immediately after a dream state indicating that the hippo-campus has a hand in making sense of the random thoughts produced during REM sleep. These test scores were remarkably better than even a fully awake (base-line) state.
A "Functional Magnetic Resonance Imaging" scan is a scan taken while a test subject is performing some function. Functions could include reading, performing basic math and verbally supplying answers. or even having some part of the subject's body "stimulated" with skin contact of various textured items such as brushes, pins, and feathers. (no kidding). Many of these FMRIs are designed to determine what part of the human brain becomes active during these functional tests. This in turn helps neural-scientists fine tune their understanding of physical brain function.
This is the second in a series of articles discussing the new field of research called "Brain Plasticity."
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