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Blogging at Psychology Today


I've arranged to submit occasional posts to Psychology Today at a blog I'm calling Purple Brain.  It's one of their many Neuroscience blogs, and at least in the near term I'll keep my posts there to topics related to the brain and mind.  In other words, I'll avoid the kinds of posts I sometimes slip in here: ones about funny characters I know from the Hungarian Pastry Shop, or the drama of having a pair of bluejeans with a zipper that looks like it's unzipped all the time, or the woman looking down from her sixth floor window who saw me yelling at a dog.  I won't write about any of that type of stuff there.

I'm not going to make it formal either- life's too short (and funny) for formality.  But at least for now I'll try not to come off there as a nut. 

In the meantime, please click to see my first post there.  They keep track of web traffic, and with your help, they may think I'm a real popular guy.

The Conscious Brain


When people are not conscious, e.g. those in a vegetative state, their brains show very low levels of neuronal activity.  Their neurons may occasionally respond to stimuli, say a loud sound, but not many neurons, and not for very long.

Those in a minimally conscious state, with only occasional periods of awareness, show somewhat higher and more sustained levels of brain activity.

When we are fully conscious, the things we see, think, remember, and our other conscious experiences, are accompanied by strong activation of the neurons in the brain.

So there’s a relationship between conscious awareness and the activity of brain cells.    As I write this post, I’m picturing a brain.  To do this, I'm activating certain neurons in visual areas of my brain that give rise to the mental image.

But not all neuronal activity gives rise to consciousness. Some neurons, for instance, become active just before you grasp a cup, and determine the position for you to place your fingers as you move your hand toward it. If your grasp is wide, these brain areas will quickly send updated commands to your hand muscles so that you grasp the cup in a way that allows you to lift it, and not drop it. Next time you grab for a similar-sized cup, your brain may instruct your hand muscles to produce this 'narrower' grasp. Lots of neurons in several areas of your brain are activated in order to adjust your hand position, and usually this activity falls outside your awareness. The neurons are activated but they don’t give rise to a conscious experience of adjusting your hand position.

What is the difference between the neuronal activity that gives rise to conscious awareness and the neuronal activity that doesn't.
  • Maybe it depends on the part of the brain that's activated.  There may be some brain areas where neuronal activity is off-limits to conscious awareness. You might imagine these areas to include those that control aspects of body movement; habitual, automatized behaviors; and the kinds of thoughts and goals that Freud envisioned residing within the unconscious.
  • Maybe most of the neurons in the brain are off-limits to consciousness. It could be that conscious experiences are made up of the neuronal signals that transmit information to a privileged brain region, a kind of 'seat of consciousness'.  This area (which some neuroscientists imagine to be in the frontal cortex) would be the stage upon which the drama of our inner-lives (the hopes, plans, memories, regrets, and so on) unfold. 
  • Maybe any of my 100-billion-or-so neurons can contribute to a conscious experience -- so long as the neurons fire rapidly enough, or so long as their activity is synchronized with the activity of enough other neurons in the brain.
There are many other 'maybes' about how neural activity could relate to consciousness. But whichever explanations turn out to be true, the nagging and interesting questions would remain: "Why should neurons in those brain areas, and not others, give rise to a conscious experience?" "What's so special about brain area X that I'm only conscious of inputs to that area?" "Why do neurons have to fire at a certain rate, or in a certain rhythm with respect to other neurons, in order to produce a conscious sensation?"

A brain part mouse, part human


Researchers placed human cells into the brains of mice. The human brain cells began to replicate and take over much of the mouse brain, and the effects on mouse behavior were bizarre.  True.  Not science fiction.

Researchers at the University of Rochester in New York figured out a way to put human brain cells into mouse brains, taking steps to ensure that the mouse immune system wouldn't reject the human cells.   The mice they created are 'chimeric', their brains are part mouse, part human. (Chimera were mythical hybrid creatures with body parts from more than one animal.)

In order to appreciate what the researchers did, and what they found, it helps to know about the kind of human brain cells they introduced into the mouse brain.  Like mice, we have two basic types of brain cells: neurons and glia.  The cells they implanted into the mouse brain were human glial cells.

Most people have heard a lot about neurons, but not much about glia.  Glia are sometimes described as the brain's 'support staff'. Some glial cells clean up the debris from neurons that have been injured (the microglia), others provide nutrients to nearby neurons (they're called astrocytes, the type that were implanted into the mice), other glial cells play other roles that help neurons survive and function.

So it was surprising that mice implanted with human glial cells became smarter, or at least faster learners, than other mice. Glia aren't normally thought of as playing a key role in learning.  If you've seen the movie Good Will Hunting, you may remember Matt Damon's character working as a janitor in the halls of Harvard University.  His mathematical mind far surpassed that of the Harvard faculty.   The genius in the Harvard math building was the guy sweeping the floors.  The fact that human glial cells, our brain's support staff, would power-up the learning abilities of the mouse brain was surprising, very much in that way.

Here are some of the details:

The experimenters aimed to implant the mouse brain with a particular kind of human glial cell called astrocytes ('astro' because it's shaped like a star).
An astrocyte is a star-shaped glial cell. The image above shows an
astrocyte with its many thin processes radiating out from a round center.

Instead of implanting fully formed human astrocytes, they implanted an immature form of the astrocyte that exists in the brain during late stages of embryonic development. They're called glial progenitor cells or GPCs. The GPCs turn into astrocytes at some point during brain development. Experimenters placed human GPCs into the brains of newborn mice (Goldman, Nedergaard, & Windrem, 2015), taking steps to ensure that the mouse immune system wouldn’t reject the human cells.  This allowed the human astrocytes to develop and take their places within the mouse brain as it developed.

The brains of newborn mice were
implanted with human GPCs, immature
cells that eventually turn into astrocytes.
The immature human cells traveled throughout the mouse brain and increased in number. They soon developed into human astrocytes, which competed with and replaced most of the mouse astrocytes. Within about 10 months, most of the astrocytes in the mouse brain were human in origin! In the  figure below, the human astrocytes are stained red. As you can see, they spread to virtually all parts of the mouse brain. Researchers sometimes refer to this procedure as “glial humanization,” or more specifically, “astrocytic humanization” of the mouse brain.

The front of the mouse brain is to the left, the
back is to the right. The red dots are human  astrocytes.
They multiplied throughout the mouse brain.
The neuroscientists presented the mice with tones a few seconds before a mild shock was delivered to the floor of the cage. Once mice learned the tone-shock association, they would ‘freeze’, immobilized in their place, as soon as they heard the tone.  The more experience they had with tones followed by shock, the more time they spent freezing when the tone came on.  The black line below shows the behavior of a group of mice that was not transplanted (not grafted) with foreign cells. Over the course of 4 days of training, they increased the time they spent freezing when the tone came on. The purple line shows the behavior of another group of mice that received a graft containing astrocytes from other mice (allografted control mice). These mice gradually learned the tone-shock association as well. However, the mice with human astrocytes (the red line) were by far the fastest learners. After one day of training, they showed better learning than the other groups of mice showed after four days’ training.

The long, thin processes that radiate out from the center of the astrocytes often wrap around synapses between neurons. Evidence suggests that astrocytes enhance synaptic plasticity, the ability of neuronal connections to strengthen, and thereby enhance learning (Han et al., 2013). What is the precise role that these astrocytes, the supposed 'support staff' for the neurons, play in learning?  Do some people with learning disorders have a lack of, or dysfunction in, astrocytes? If so, can we do something to enhance their astrocyte activity? And what is going through the minds of these unusually smart mice with human astrocytes as an experimenter walks into the room?  I imagine an experimenter noticing a look of intelligence in the eyes of the chimeric mouse. Then I imagine the experimenter quickly looking away.