Category: Consciousness


It looks like my goal of world domination have gotten a few steps closer, if two of the popular press articles I posted in the webliography are any indication.

The two articles form a theme of sorts about control.  One of the articles talks about how scientists hacked into a monkey’s brain to control its movements.  There have been reports in the literature describing procedures by which monkeys can control objects in the real world with their brains.  This is usually achieved by an implant of some sort that can be affected by certain patterns of electrical activity in the surrounding brain tissue that then sends a signal to a device in the real world.  This research seems promising for a variety of things, particularly people with paralysis or prosthetic limbs,   Imagine being able to control the prosthetic not only with the muscles near it, but also with your brain to some extent.

Schematic of brain showing the ventral tegmental area (VTA).

Schematic of the brain showing the ventral tegmental area.

Researchers have figured out an elegant way to influence the decision making process of monkeys.  They implanted electrodes into the ventral tegmental area (VTA) of the brain, which is one of the places (as you will learn more about in the coming weeks) that produces dopamine and is involved in reward circuitry of the brain.  Then, they conducted a simple preference test by showing monkeys two pictures of random objects and had them indicate which one they liked better.  This initial preference test was their control procedure since they were interested in what choices the monkeys made without any interference from the experimenters.  Once this was done, they demonstrated that by sending brief electrical bursts through the electrodes implanted in the monkeys brains the researchers could get the monkeys to reliably switch their preferences for pictures.  Now, this doesn’t mean an evil mustache-twirling mastermind, or the government, or the NSA are going to take over your mind or anything like that, though that possibility is certainly there.  But this does build on some fascinating research from the 1950s that helped to further our understanding of the role the brain plays in motivating our specific choices.  The fact that this can be manipulated artificially is an interesting finding.

Long-term potentiation

A schematic of a regular synapse and one that has undergone stimulation to produce a long-term potentiation (LTP).

In the other interesting article, researchers were able to turn memories off and on.  This was done in genetically engineered rats using light pulses that strengthened or weakened synapses in the hippocampus.  This is another thing you’ll be learning about (in Week 5 I think).  One of the amazing things about our nervous system is that it is dynamic and is constantly changing due to our experiences.  It’s why we can learn new things.  One of the ways memories are formed is through strengthening and weakening of synapses, or long-term potentiation (LTP) and long-term depression (LTD).  This strengthening and weakening can be achieved through everyday use, such as when you memorize information for this class, or become classically or operantly conditioned to perform a response to a specific stimulus.  It can also be artificially induced, using different frequencies of light pulses that stimulate the synapse.  If you can find the right frequency of pulses (high or low) you can make the synapse stronger or weaker.  This is the mechanism by which the researchers in this particular study were able to manipulate memory in the rats. They were able to turn a conditioned fear off and on using light pulses to the hippocampus.

Both of these studies are interesting for a couple of reasons.  First, they tie together a lot of the information you’ve already learned in the course, particularly how synapses and neurotransmitters work, as well as brain structure (VTA and hippocampus) and shows how they all work together to produce complex behavior.  The added layer that makes this particularly fascinating to me is the fact that researchers can control behavior through selective brain stimulation, an idea that is exciting and a little terrifying.  I will admit it does conjure up images of a MatrixThe Matrix-like culture where people’s thoughts and behaviors are controlled by others by directly accessing their brains.  It’s easy to see how something like that could be abused at some future point, though we’re a long way from that.

I can see some tremendous potential for good, here, too.  In particular, imagine what the treatment of extreme phobias, Alzheimer’s disease, PTSD, and other types of problems related to memories would look like if we had the ability to either enhance memories or take some memories away at will.  It’s tempting to shrink from an idea like that, because our memories are what make us who we are, and common sense tells us we might be better off learning to just cope with them.  But imagine memories so awful, so debilitating and disturbing, that it becomes difficult or impossible to cope with them, and they begin to affect every aspect of your life.  I’ve never suffered from PTSD, but I imagine it can be quite horrible, and if conventional treatment doesn’t help then perhaps being able to suppress the memories, at least for a little while so that other coping mechanisms can be acquired and strengthened might offer some people a desperately needed reprieve.  And being able to counter the synapse weakening amyloid beta proteins in the brains of people with Alzheimer’s Disease seems like a promising idea worth investigating.

It’s a little harder to see the benefits of influencing choice.  One can easily envision unscrupulous advertisers using something like this to force people to choose their products, but again, I doubt that would ever happen.  I think the significance of this centers on the issue of motivation.  They were able to manipulate motivation, and got monkeys to choose things they might not otherwise choose.  Though it’s a stretch, this might be something beneficial to people suffering from depression or inactivity of one sort or another.  The idea is interesting, anyway. I wouldn’t mind being able to give my brain a little zap to get me motivated.

References

Arsenault, J.T., Rima, S., Stemmann, H., Vanduffel, W. (2014). Role of the primate ventral tegmental area in reinforcement and motivation.  Current Biology, 24(12), 1347–1353 DOI: http://dx.doi.org/10.1016/j.cub.2014.04.044

Nabavi, S., Fox, R., Proulx, C.D., Lin, J.Y., Tsien, R.Y., and Malinow, R. (2014). Engineering a memory with LTD and LTP.  Nature, doi:10.1038/nature13294

As I’ve mentioned many times in class, one of the main jobs of the parietal lobe is to integrate sensory information coming from your body and the external world.  The reason for this is so you can navigate more effectively.  The back half of the brain is generally thought to be involved in processing all the sensory information that feeds into it, then that information is sent to the front half of the brain which is responsible for acting on that information.  One piece of information the parietal lobe sends forward to the front half of the brain is a priority map of the environment (Bisley & Goldberg, 2010).

Essentially, sensory information from your eyes and ears pours into your brain through various sense organs, and from that, after some initial processing in association areas that surround the primary sensory cortices in the bran, this information is integrated into a priority map that gives precedence to those things in the environment to which you need to pay attention.  What is particularly interesting about this map is that it isn’t  driven by features in the environment that are perceptually distinct.  It’s tempting to think that the map is constructed such that bright and noisy and smelly and tasty things stand out, and that is partially the case. This is what we would expect if the mapping were produced through bottom-up processes.

In bottom-up processing, we start with the small details, the little pieces of information that make up the whole.  We begin to put the information together until we have the whole thing.  This is in contrast to top-down processing which says just the opposite, that we start with the larger picture, the bigger concept, and work our way down to the smaller details.  As with many things in psychology there has always been a debate about whether information processing is top-down or bottom-up.  As is also often the case, it is a combination of the two, and the priority map the parietal lobe produces is a very good example of the combination of both types of processing information.

As I mentioned, sensory information from the environment is sent to the cortex, processed in association areas, and then integrated in the parietal lobe and other parts of the brain.  From all that information, which is processed in a bottom-up fashion, the parietal lobe then creates a map of things in the environment that you should be behaviorally interested in and paying attention to.  This is where the top-down processing is added to the mix.  When you are in a familiar environment, there may be several perceptually salient features.  There may be a bright light shining nearby, or intermittent ambient noise coming from the weather or other organisms.  But there may also be an area that you should remember and should consider exploring because it might have something good for you to eat contained within it.  If your attention was guided strictly by the brightest, loudest, smelliest things in the environment, you wouldn’t be able to focus your attention onto areas that might be useful to you.  So we obviously need a mechanism to tune out things that might be perceptually strong, but behaviorally irrelevant.  That’s exactly what a priority map does (Bisley & Goldberg, 2010).

How is this represented in the brain?  That is a good question, because if you recall, in an earlier lecture I mentioned that one of the ways the nervous system encodes for stimulus intensity is through frequency.  A strong stimulus is encoded either by neurons having a lot of action potentials, or by a large number of neurons firing at the same time, or a combination of both of these.  It turns out, that’s exactly how priority is encoded in the parietal lobe.  Those things in the environment that should be paid attention to because they are behaviorally relevant are encoded by greater neural activity on the map than those things that are of less interest.  So while physical intensity is directly encoded at least partially by frequency, the increase in neural activity that corresponds to behaviorally significant things in the environment is an aspect the brain adds to the information once it’s been processed.

As I was reading through material about this, it got me thinking about habituation, and the neural mechanisms that mediate that.  Habituation is a type of non-associative learning in which we stop responding to stimuli that are repetitive and contain no important information.  For example, when I first moved to New York City, I lived right next to the emergency room of Bellevue Hospital.  For the first month or so, I barely was able to sleep due to the constant sound of sirens.  New York is a large city, and emergencies are always happening, so there were a lot of ambulances.  Over time, however, I gradually began tuning the sound of the sirens out, until I no longer heard them.  This was brought home to me when my family called a few months after I had been there, and as we were talking, my father asked me what in the world was going on because he could hear all the sirens.  I actually asked “What sirens?” that’s how well I was able to tune them out at that point.  In the laboratory, habituation can be tested by repeatedly presenting a stimulus, such as a particular flavor or a particular sound, and measuring physiological and behavioral responses to it.

It seems logical that habituation, which is a mechanism by which sensory thresholds are gradually increased and which biases an organism toward novelty, must factor into the priority maps of the environment that the parietal lobe constructs for us.  The same bottom-up and top-down processing is possibly at work with habituation as well, with the actual stimulus from the environment to be habituated to being part of the small details of bottom-up processing.  But then, once we have a better picture of the whole environment, and we know that that stimulus we’ve been hearing or seeing that captures our attention isn’t particularly important, we can tune it out in favor of things to which we should be paying attention.

References

Bisley, J.W. & Goldberg, M.E. (2010). Attention, intention, and priority in the parietal lobe. Annual Review of Neuroscince, 33, 1-21 doi: 10.1146/annurev-neuro-060909-15283

I joined the faculty at Cedar Crest College in August 2009, so the class of 2013 is, in some ways, also my class as they are the students who were new to Cedar Crest, and spent four years learning all about it alongside me.  I don’t teach classes that freshmen take, so I didn’t actually see many of them until they were sophomores or beyond.  One student who came in that year, Lauren Della, is someone I ended up working on research projects two years in a row with, during her junior and senior years.  One of the great privileges of teaching is to watch students grow as they learn.  Grow in knowledge, grow in confidence, grow in leadership.  And all of those were definitely true of Laurian.

brain

A lovely gift from a wonderful student.

When she graduated this past spring, Laurien gave me a wonderful gift, a ceramic brain with a figure of a man with a cane walking along the parietal lobe.  I love it.  It’s sitting on my desk, though a piece of it fell off (from the inferior temporal lobe) and people coming into my office all had to comment on my broken brain.  It was part of her Art Therapy show, and I love that she integrated brain and behavior so beautifully and creatively.  One of the many things the parietal lobe is responsible for is helping to understand and navigate the space around us, so the figure walking across the surface is especially fitting.

Gray726_parietal_lobe

The parietal lobe.

It seems appropriate, then, to make the parietal lobe the theme of this series of blogs.  The parietal lobe is located on top of the brain, slightly toward the back and center.  We began the course by looking at the role the parietal lobe plays in consciousness.  People who suffer from unilateral neglect fail to be aware of information coming in from the opposite side.  So if someone has suffered a stroke that damages their right parietal lobe they will ignore things on their left side.  They will write on half a piece of paper, draw half a house, or eat half a pancake.  It’s not that they are numb or blind on the left side;  their sensory capabilities are not diminished.  They simply are not conscious of things on the left, and act as if any objects to their left simply do not exist.

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An individual with unilateral neglect drew the flower on the right.

As I mentioned earlier, the parietal lobe helps us to organize and navigate space, not only in terms of what’s out there, but also how we orient relative to objects in the spatial environment.  Also, the parietal lobe also provides feedback for how our body is oriented in space.  So it’s easy to see why damage to this part of the brain manifests itself in an inability to attend to spatial information to the left side of the body.

Most of the sensory information that comes into the brain goes through the back half first to be processed, then is sent forward to the front half to be acted upon.  In addition to kinesthetic feedback from the muscles and joints, the back portion of the brain, including the parietal lobe, also processes information from some of the other senses, particularly touch and vision.  For many of our senses, information from the sensory organs is topographically mapped onto the brain.  The best example of this is the somatosensory cortex, which is an area in the parietal lobe, just before the central fissure and running down from the center to the side of the brain along the surface.  This is the part of the brain that receives touch information from various places around your body.  The entire surface of your body is mapped onto this area of the brain.  It is a distorted map, because some parts of your body, such as your fingertips, are more sensitive and thus require more space in the brain to process the information coming from them, than other areas, such as your back or your thighs.

somatosensory cortex

The parts of our body are topographically mapped in our brains on the primary motor cortex (in red) and the somatosensory cortex (in green). The somatosensory cortex is located in the parietal lobe, just before the central fissure.

Recently, researchers have discovered that the parietal lobe also plays an important role in numerosity or “number sense” seen in many species. Numerosity doesn’t refer to counting because that involves associating specific quantities with a symbolic representation in the form of a number, which is a pretty advanced cognitive capability.  Instead, what our number sense allows us to do is to estimate quantity in a general way, such as when we’re offered a choice between two slices of pie and know that even though we might want the bigger piece, for the sake of our diets we need to take the smaller piece.  It’s the sense that allows us to make “greater than” or “less than” distinctions.

Harvey, Klein, Petridou, and Dumoulin (2013) recently studied the number sense in humans specifically to determine whether or not there was a similar topographic organization in the brain for numerosity despite the fact that there were no specific sense organs associated with a number sense.  They presented stimuli containing different numbers of dots and measured brain activity with a high-field fMRI.  Different areas of the parietal lobe responded to different numbers of dots in the stimuli.  When the number of dots in the stimulus was small, they found the greatest level of activity in the most forward part of the parietal lobe.  As the number of dots increased, not only did the focus of neural activity move further and further back along the parietal lobe, but the total number of neurons activated by the stimuli decreased.  These findings help to explain  why we tend to be good at estimating small numbers of objects, but become less and less accurate as the total number of objects in the stimuli increases.  The authors suggest that our parietal lobe acts as a sort of internal abacus, which is an ancient calculator that represents numbers spatially (Lewis, 2013).

Though it may not seem so, this is an important sense.  For most species, their day is spent searching for and acquiring resources such as food.  The ability to estimate quantity, or even to judge one potential source of food as better in terms of the amount it can provide over another site helps to make the foraging process more efficient.  The less energy an organism has to expend in order to acquire resources to survive, the better, and even something as simple as being able to quickly judge the richness of a resource compared to another one can make all the difference.

References

Harvey, B.M., Klein, B.P., Petridou, N., & Dumoulin, S.O. (2013).  Topographic representation of numerosity in the human perietal cortex. Science, 341(6150), 1123-1126 doi: 10.1126/science.1239052

Lewis, T. (2013). Is “Numerosity” Humans’ Sixth Sense? 

NOTE:  It looks like this site inserts links to ads sometimes.  I will make all my links boldface, and I suggest you do the same.  Any links that are in plain text are not mine and you shouldn’t click on them.  Sorry about this, but I guess it’s the price you pay for using a free site.

The first time I taught a course like this, I convinced myself that the best approach would be bottom-up, to start small and work my way up to the larger brain systems.  Dutifully, I started the course with a detailed lecture on the structure of the neuron, before moving on to action potentials and the activity of neurotransmitters.  This isn’t a bad way to begin the course, and makes a kind of intuitive sense.  But from a student perspective, it probably comes across as very abstract and disconnected from behavior.  It really isn’t, since without action potentials there probably wouldn’t be much behavior, but for students new to the material, or with only a bit of it under their belt from Introduction to Psychology, I can see how jumping into biological psychology this way can be disorienting.

To try to “cushion the blow” so to speak, I decided to open the course with much broader themes, and begin with a discussion of consciousness*.  In the lecture I talk about animism , a belief that animate and inanimate objects have some kind of animating spirit that accounts for movement.  Tides, rocks, and even living creatures had some animating force inside them that compelled them to move.  And, while a belief that rocks and trees and fish are inhabited by some intangible spirit is not quite as popular as it once was, certain aspects of this belief system persist.  While our consciousness is a definitive part of ourselves, I think many people also have the sense that our consciousness is a separate entity as well.  Certainly, the religious concept of the soul stems from this idea.  Like the animating spirits some of our ancestors believed in, many people believe there is a part of us that will continue on once our physical self has died, and that this non-corporeal, intangible animating spirit makes up the bulk of our identity.

From that discussion, I then go on to talk about consciousness as a property of our nervous system.  This perspective comes from another philosophical school of thought, called materialism, which holds that the universe is composed of matter, and that all things in the universe, including consciousness, result from interactions between matter.  I was immediately drawn in by how two such seemingly disparate perspectives on the universe could meld together.  And disparate they are, I think.  Inherent in the philosophy of materialism as it relates to consciousness is the understanding that when our corporeal form ceases to exist, so does our consciousness.  There is no animating spirit that will live on past our physical life, because the mechanism that produced the spark of life in us has gone.  Not everyone who studies consciousness believes this is the case, but I think the idea is certainly a rational conclusion.

And yet, the notion that our consciousness is somehow separate from our physical being is unshakable for many.

So the course opens with a discussion about consciousness as a property of the brain and nervous system, and I think that works very well to create interest, if not necessarily agreement.  We all know that our nervous system drives the bus, so to speak, but I think few of us really consider what that means.  Complex, abstract behavior, such as creativity, curiosity, and imagination are all properties of our nervous systems, as is consciousness.  In fact, consciousness is the umbrella sitting over not only these complex, abstract behaviors, but our everyday mundane behaviors like walking, eating, and so forth, though to a lesser extent most of the time.  (When was the last time you really had to think about walking as you did it?  Still, a part of us is conscious that we are, indeed, walking as we do it.)

After consciousness and a few other broader topics, we then delve into the electrochemistry of the nervous system, because that stuff is important.  More importantly, it’s fascinating–we see our ancient ancestry from the sea in the salt water that not only bathes our nervous system, but provides the electrochemical basis for action potentials, neurotransmitter release, and ultimately behavior.

*This is a recent article in Time about consciousness and some of the research being conducted to understand it.  Well worth taking a few moments to read.