Monday, October 25, 2010
posted under Mellon New Directions Fellowship , neuroscience , paul gold , Samantha Frost by Unit for Criticism
[Kritik is pleased to publish the third in a series of posts by Samantha Frost, associate professor in Political Science and Gender and Women’s Studies. As the recipient of a Mellon New Directions Fellowship, Sam is enrolled in undergraduate courses in biology and neuroscience with the aim of enhancing her research on materialist accounts of perception, judgment, and subjectivity. Last spring and over the summer, she took the pre-requisite courses in organic chemistry, basic physiology, and molecular biology. This semester, she is taking a further 12 credits of courses in biochemistry, cell biology, and neuroscience.]
"WELL, WHAT DO YOU KNOW?"
Written by Samantha Frost (Political Science, GWS)
Imagine this scenario: I drop my kids off at school, I set off to the grocery store to pick up a few things before my day begins, and then I find myself pulling into the driveway of my home, sans groceries… because I did not actually go to the store.
Has this ever happened to you?
The semester is galloping along and everything I am learning is so extraordinarily fascinating that it is difficult to know what to select to talk about. So I decided to share a neuroscience insight (courtesy of Paul Gold) that stands out because it explains some of life’s peculiarities.
Neuroscientists who are interested in the processes of learning and memory study which parts of the brain are involved in different aspects of memory formation. To this end, they train rats to do tasks that are known to use specific parts of the brain, they inactivate said brain area or hyper-activate others, and then observe what the rats do when confronted with the learned task again.
In many cases, if a task-specific brain region is inactivated, the affected rat will no longer know how to do the associated task. In some cases, however, the rat will know how to do that task—or a different one—even better than before. Such results suggest that different areas of the brain have characteristic strategies for learning and that these different areas can function antagonistically, cooperatively, or weirdly in tandem. It is this kind of weird—cool, complex, but weird—interaction that I want to highlight today.
Enter the players: the hippocampus and the striatum.
The hippocampus is a part of the brain that tends to be most active when rats learn to run a maze by orienting themselves via environmental cues outside the confines of the maze. Its prototypical instruction is something like: always run in the direction of the corner near the poster, no matter which way the maze is rotated in the room. This is called place-learning.
In contrast, the striatum tends to be most active when rats learn to run a maze by remembering which ways they should turn at a particular junction. Here, the body is the reference point for coordination. The striatum says, figuratively speaking: always turn left, no matter which way the maze is rotated in the room. This is called response-learning.
It turns out that rats are predisposed to learn either one way or another: my sense (although I could be mistaken) is that it is a fairly even split among the experimental rat population. And yet, if the rats are trained at the same task over and over, eventually they all habitually adopt the response-strategy. In other words, turning left or right is what they come to know.
This is the interesting part: Once the rats have been trained to this level of habituation (i.e. always turn left), if the striatum is experimentally knocked out, it is not the case that the rats then do not know what to do. Rather, they exhibit the hippocampus’s strategy—or place-learning. In other words, the well-trained rats rely on environmental or spatial cues and do the equivalent of always heading towards the corner near the poster.
What this means is that even as one brain area and learning strategy predominates (always turn left), the other brain area is nevertheless learning (always head towards the poster). We could say that the rats know both of these things. Yet, given the pre-dominance of the striatum, what it knows is what the rats know to do, i.e., what they exhibit in their behavior when the orientation of the maze in the room is switched. When the striatum is deactivated, what the hippocampus knows becomes what the rats know to do.
So—and here we make a transition from rat brains to human brains—when we are engaged in a task, different areas or systems of our brains are learning different things about what the task demands. We think we are learning one thing but our brains are actually learning several different things. And what these several things are can become evident when we find ourselves in novel situations—will you do the equivalent of turning left? or of heading towards the poster? These things that we know can also become evident when the function of one of the brain areas in question is boosted, distracted, or somehow underpowered.
Back to my non-trip to the store. It wasn’t that I was distracted; I wasn’t forgetting something. In fact, I felt I was doing exactly what I was supposed to do. At that crucial traffic light on Prospect Avenue, at the determining intersection, it didn’t even occur to me to turn west onto Springfield to head toward the grocery store. I knew what I was doing. I simply took a right and drove home. It appears to have been something akin to a striatal move: At this intersection, always turn right!
But of course, even as this neuroscience stuff possibly answers the question of why I sometimes miss getting to the grocery store—or whatever errand is on the agenda—it raises yet another: What is my hippocampus doing when I find myself inadvertently “turning right” instead of going to the store? Clearly, turning right at that light is a habit—hence the likelihood of the striatum being dominant in that moment. But why was the striatum dominant at that moment?
Apparently, the balance between the different brain systems is regulated by brain areas known as modulators—I haven’t learned yet what enables modulators to shift the balance one way or another, but it is coming up soon. However, it is clear that modulators, as well as the different learning or memory systems themselves, are variously affected by the chemicals released into our brains in response to specific task demand, anxiety, stress, the food and alcohol that we consume, as well as the other things we (and our bodies) are doing.
There is a complex chemical flux between the outside and the inside of our bodies—and the various parts of the inside—that affects what among the many things we know we happen to know effectively. In this context, Descartes’ argument culminating in “cogito ergo sum” seems not mistaken, really, but rather a gross misrepresentation of what is at issue in our knowing what we know.
Not only are we not self-mastering, self-transparent subjects—an insight that is still sometimes difficult to grasp at the mundane level even as it makes sense theoretically. We are also not possessed of a brain that functions as a singular, internally unified entity—although one must acknowledge that coordination among the bits is such that we often do end up roughly succeeding, and sometimes spectacularly succeeding, in the tasks to which we set ourselves.
My point, however, is that we can know different and sometimes contradictory things about, say, a task. And when we know that we know one of those things, we may not be aware that we also know the other. In other words, our brains are internally plural, with systems that function in competition, cooperation, or concert without our awareness and depending upon our state of hunger, stress, inebriation, caffeination, or hormonal calibration. At any given moment, what we know, and what we know ourselves to know, is in some sense beyond our ken and control.
When I consider this, I am profoundly aware of myself as an organism.
And that’s unsettling.
These are some of the materials we read in class related to this issue:
E. McNay and P. Gold. “Food for Thought: Fluctuations in Brain Extracellular Glucose Provide Insight Into the Mechanisms of Memory Modulation”. Behavioral and Cognitive Neuroscience Reviews. 1:4 (December 2002): 264-80
P. Gold. “Coordination of multiple memory systems”. Neurobiology of Learning and Memory. 82 (2004): 230–42
P. Gold. “Memory-Enhancing Drugs”. In H. Eichenbaum (Ed.), Memory Systems. Vol.  of Learning and Memory: A Comprehensive Reference, 4 vols., ed. J.Byrne (Oxford: Elsevier, 2008), pp.555-76.