Since our last appearance, and thanks in no small part to invited guest appearances on talk shows and other discussion groups, the LabRats and I have received a few emails with questions folks might like answered about science, writing, and the brain. Without further ado – a few samples from our mailbag.
"Dear Lab Monkey: Why don't you let the Rats talk more? -A. Nony Mouse"
My reply: "Dear Nony: I think you have me mistaken for Dr. Freer. Still, just for you, I will sometimes let the LabRats have their say. Do read on, and I'll translate... - Tedd"
... another ...
"Hey Ratley, Do you LabRats really talk? Signed Thomas."
Ratley squeaks. [Translation: "Doubting Thomas: You wrote to me. Are you really expecting an answer? –Ratley]"
... Okay, back to the Mail ...
"Hey Tedd: If humans were to develop telepathic or psychokinetic abilities, what parts of the brain would be responsible? - J.R."
Whoo-boy. Okay, that's a long one, let's table that and look at another. It'll take another whole blog post to answer that one.
"Dear LabRats: How is it possible that we can hear our own name spoken in the midst of a crowded, noisy room? - S.H."
Ah, another. Do be patient. Ratley and I will make a list and get back to these one by one.
... ah, here's a good one!
"Dear Dr. Roberts: We sometimes hear that humans use only 10% of their brain. Is this true? - Dave F."
Hey, Ratfink, don't startle me like that, I didn't know you were there. Okay, it's just the right size for this blog. You go ahead and answer it.
[translated from rat-squeak]
"We hear that little bit of trivia all the time. It is, as you may have guessed, a misconception. Now, we LabRats always use 100% of our brains – well, except for maybe Ratface. Oh, and Ratso, he uses 100% of his stomach to do his thinking.
"Anyway, not to get off target, it is true that one could say that at any given time, only 10% of a humans brain is active – 5% if they are watching daytime talk shows. What it really refers to is the incredible redundancy of the human brain, plus the fact that there are specialized brain areas that are only used for particular tasks.
"Let's start with vision. There are millions of cells responsible for detecting light and sending the information to the brain. If you think of the light-sensitive retina cells (photoreceptors) like pixels in a camera or TV, you can understand why you need so many – to get the maximum fine detail in anything you look at. In fact, though, there are multiple types of photoreceptors for each "patch" of our visual field. There are 'rods' which detect black vs. white, and there are 'cones' which detect color. Further, unlike us LabRats, you humans have different color sensitivities of cones: red vs. green and blue vs. yellow. Thus for each 'pixel' of image we see, there are at least three types of retinal cells.
"Redundancy – and different functions.
"Now, take that same visual information into the brain. Before it gets there, there are 'ganglion cells' in retina that combine inputs from photoreceptors. Each ganglion cell has a donut-shaped field that represents the part of a visual scene covered by the ganglion cell. For some cells, light shining in the 'donut hole' more electrical and chemical activity in the cell, while light shining on the 'donut ring' causes less activity. Again there is redundancy and different functions. There are millions of ganglion cells covering all possible combinations of photoreceptors covering our entire visual field, and there are ganglion cells with 'on-center, off-surround' fields as described above, as well as cells with 'off-center, on-surround' functions.
"But what is it all for, and why the redundancy? Well, moving to the 'visual cortex' of the brain, combinations of inputs from retinal cells result in cells that are activated by short lines of light, and by edges. Multiple redundant copies means that there are cells for every conceivable angle of line or edge, every possible location in the visual field that our eyes can detect, as well as combining two eyes, and all those colors. Working forward into the parts of the brain called 'visual association' areas, we start to find brain cells that respond to circles, shapes, even faces!
"Then we move into combining other senses, and other parts of the brain: sound, smell, touch, movement, memory, and decision making. We LabRats get to continually hear the Neuroscience student's favorite story about Grandmother Cells. That's the brain cell that is active only when it sees "Grandma's face, hears her voice, and smells her fresh-baked apple pie (with a slice of Cheddar for well-behaving LabRats). Believe it. While there may not be specific 'Grandmother Cells' in any given human's brain, there *are* brain cells tuned to respond to such high specific combinations of inputs!
"So, if the Grandmother Cell is active, does that mean that we have used only one *trillionth* of our possible brain capacity?
"In the first place, the signals that activate Grandma have traveled through five widely separated brain areas for vision alone, and an equivalent number of sections for sound, smell, touch, movement (don't forget, Grandma wants a hug and a kiss before you go!). Then we had to search through memory. Is that Grandma H. or Grandma D.?
"That's another contributor to the 10% myth. The human brain has an incredible capacity for memory. With the possible exception of Ratface, the typical LabRat has billions of brain cells available for storing memory, and that's sufficient to remember where to find the cheese, the peanut butter, fruity cereal, water, electrical cords that are fun to chew… In fact, Dr. Rob has experiments that show that no matter *how* complex an environment, the rat brain can map it and remember it.
"Now in comparison, the human brain has *trillions* of brain cells in each brain area. How much more information than a mere LabRat (except for me, of course) can it store and process? As far as we can detect, no human has ever run out of storage space in the brain. Hence, humans must use only a small portion of brain resources. However, the rest of the brain is there, active, and ready to contribute at a moment's notice.
"To finish up, some of the most fascinating examples come from the field of brain imaging. MRI scanners can be set to track the flow of water or oxygen in the brain, resulting in a map of the most active brain regions. If your everyday average human lies in a scanner and listens to music, the primary and associative auditory regions light up. Sounds with an emotional or memory content may activate brain regions involved in memory. Sort of like Ratface and Heavy Metal.
"Ask them to read written music, and the visual and reading centers light up, but very little activation occurs in auditory areas. However, if you ask a professional symphony conductor to read a musical score, the brain scan lights up with brain areas involved in reading, listening, singing, memory, even the areas responsible for moving the hands and arms in conducting motions!
"Now *that* is using your brain!
"So, final answer. At any given time, sure humans only use a portion of what the brain is capable of. The rest of it gets used at other times and for other purposes. We *still* don't know the total information capacity of the LabRat brain, let alone the human one, but it is certain that it does *not* go unused!"
Thanks, 'Fink. Not a bad explanation. Now I'll add one more piece of information before we let these good folks go back to their regularly scheduled blog reading…
How can we use all of our brain and *still* have room for more information? The most astounding thing is that information is both spread out among a lot of different brain cells (that redundancy again) yet still specific enough that activating only a few brain cells will get the whole bit of information back. SF writers like to call this "holographic." That's not a bad term, but not really accurate. The scientific terms are "sparse, distributed" and "associative." That last one is the key: "associative;" that means that the reason that the brain can keep holding more information is that it keeps making *associations* between new and old memory. Apart from diseases and injury, the reason why we forget is not a loss of the actual information, but a failure to come up with the appropriate associations.
So folks, keep those questions coming. Nestor is currently making a mess out of the discarded envelopes and YDR is now covered in paper link and ink. We'll try to answer some more of your questions in future guest blogs.