Written early in the week of July 29…
In the
July
24 issue of the Journal of Neuroscience I saw several articles that piqued
my interest.
The first article, in fact,
was
a manifesto
urging neuroscientists to be more active in communicating with the general
public about work in this field.
While the
primary goal in doing these posts has been to motivate myself to read the
Journal every week, one byproduct of this is a public dissemination of
information.
Hopefully it is acceptable
to define “public” as the 5 or 6 of you who read this blog!
There were a number of articles that were focused on the
generation of new neurons in the brain.
Many
studies have demonstrated that learning is associated with an increase in the
production of new neurons in the dentate gyrus of the hippocampus, one of two
places in the adult brain where new neurons are made (see below for the
other!).
This week’s
study by Haditsch
and colleagues showed that the increased production of new neurons caused
by learning a new task was due to more precursor cells being generated, as
opposed to the greater survival of already-formed new cells, which has been the
predominant view of how this works.
Furthermore, they showed that the signal to increase the production of
precursor cells was dependent on signals from the forebrain.
Another article about new cells was by
Tailor and
colleagues, who obtained hindbrain neuroepithelial stem cells from 5-7 week
human embryos (a controversial source, for certain) and showed that the cells
could be stimulated to multiply into functional neurons that would work as part
of a circuit in the cerebellum. With so many neural diseases in which specific
types of cells degenerate, cell replacement would be a valuable therapeutic
tool.
It’s still science fiction now,
but this type of research is making some progress.
Speaking of degenerative diseases, the third
new-neuron article was about an animal model of Alzheimer’s Disease in which
the authors,
led
by Cheng, examined the function of olfactory sensory neurons that had been
temporarily infected with humanized mutated amyloid precursor protein, which is
thought to be the main culprit in the formation of neural plaques.
Olfactory sensory neurons are the second type
of neuron that gets regenerated throughout adulthood.
Every three weeks your olfactory sensory
neurons are getting replaced by new ones, and so they have to constantly reestablish
connections in the olfactory bulb and from there, to areas in the cortex.
It’s like a new circuit gets built
continuously.
One of the earliest signs
of Alzheimer’s is an altered sense of smell, so it might be possible to use
this system as a diagnostic tool, but also as a model in animals for testing
the effects of treatments that are meant to delay or prevent the disease.
Cheng and colleagues were able to show that
if they decreased the expression of the mutant amyloid protein, the cells could
reestablish their connections and the mouse could smell normally again.
Researchers usually use aged rodents in order
to examine disease progression, but this olfactory system provides a faster
alternative.
I have unwittingly challenged myself a bit too much with the
article I chose for this week’s post. I
decided to read this particular article because the abstract seemed to be
written in a new language, which looked to me like a combination of classic
behavioral terms and computational neuroscience. I felt fairly confident that with enough
concentration and contemplation I would understand the research enough to
relate it to knitting and describe it to you.
Well, we’ll see if I can make sense of it.
Liljeholm and colleagues, from the Computational and Neural
Systems Program at California Institute of Technology, examined choice
behaviors in humans while they were being scanned for activity in specific brain
regions. There’s been a lot of research
looking at choice behavior in humans, some of which has been described here in
previous posts, but this study was unique in that they tested the degree to
which people perceived differences in how likely it was that their choice would
yield an appealing outcome. Of course,
they used food as the goal. A person
would have to choose between a banana and Milano cookies, but would need to
depend on previous experience to know how likely would their choice actually
yield the desired outcome. If all was
equal, you and I would choose the Milanos, but if the
chance of actually getting the Milanos was very small, we might instead decide
to have the banana, if it was more likely that our choice would be rewarded. They had a long list of tasty treats in the
experiment, including Godiva dark chocolate bars and peanut M&Ms.
The authors were interested in determining what brain area
was necessary to make the comparison of possible outcomes, with the idea that
every decision we make is a complex computation of the expected immediate and
long-term impacts of the decision, as well as how the situation affects the
outcome of our actions. They called this
a “cognitive map” of goal-directed behavior.
In the choice above, it’s not just about how much tastier Milanos are
compared to the banana, but when, where and under what conditions the decision
is being made. If it’s 7 a.m. and I’m
well-rested and staring at a picture on the refrigerator of me at the age of
24, I will probably choose the banana.
However, I am more likely to choose the Milanos under any other
circumstance.
Honestly, I understood very little about how the authors manipulated
the cognitive maps of their participants, but I can tell you that they
demonstrated that the anterior portion of the supramarginal gyrus of the
inferior lobule of the parietal cortex is the hot spot for comparison of
potential outcomes of a behavior. I can
also say that they confirmed the role of the medial prefrontal cortex in computing the
expected value of the items (Milanos are far superior to bananas, everyone
knows). Their article deserves a much
better description than that, but it’s going to take more time and additional
background reading to make that possible.
Here’s how I believe this relates to knitting:
|
Developing a pattern for mitts |
|
The fair isle sweater is resting in the Pretend Yarn Store |
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The Albers Pullover (from Interweave Knits summer 2013) 10 rows from being done. |
How do I decide which project to work on, the mitts, the fair isle sweater, or the Albers Pullover? Based only on the appeal of the project, I would choose the fair isle sweater. However, the cognitive map of my goal directed behavior is more complex than that. It includes considerations such as: "there are only 10 rows left on the Albers Pullover" and "I need to write the pattern for the mitts in time to test it before the Camel Knitters need to use it" and "the weather is too warm to wear the Albers Pullover, even though it is meant to be a summer sweater" and "I have done enough of the fair isle sweater to know that the pattern is working". This kept the inferior lobule of my parietal cortex busy and I'll let you know what that activity yielded in the next post.