bob.g at gmx.de (Robert Gurk) wrote in message news:<Xns90A67DFCB2D39robertgurkatgmxde at 130.133.1.4>...
> While I agree that the question that forms the subject of this
> thread that got rather emotional rather soon, is quite stupid
> and therefore does not deserve an answer, I still don't think
> that there aren't any good questions about the *way* we use our
> brains.
> So, while the statement "Humans only use a fraction their
> brain." is complete nonsense, the statement "A lot of people use
> only a fraction of their brain to remember their shopping
> lists." is quite right. Suddenly you have a statement that is
> open to scientific inquiry. Use a PET scanner or FMRI to prove
> it.
> Awaiting your flames and rants,
>> Bob
Hi Bob,
No flames or rants from me about this post. Just a couple of comments,
which I will try to keep from getting too emotional.
I think you raise good points, in that it -is- possible to take this
silly question and twist it into an actual scientific hypothesis,
which is potentially testable and falsifiable.
For me, the whole matter hinges on having a rigorous definition of the
word "use", and also some way of quantitatively and reproducibly
measuring the "fraction" of the brain that is being used. I agree that
defining, clearly and simply, specific tasks to be used as test cases
has to be a first step.
However, I would disagree that PET and fMRI are the right tools to use
in answering these questions anyway (ok, this next part is going to
get me flamed). These methods have very low temporal and spatial
resolution. My understanding about fMRI (and I assume this also
applies to PET) is that the raw signal is actually quite small
compared to the noise, and an arsenal of signal processing methods
must be used to pull it out in the first place. This doesn't make it
invalid as a neurophysiological tool, but it definitely does limit its
usefulness for answering questions involving the detection of
near-threshold phenomena. This whole question has to do with
evaluating thresholds and how often they are crossed (i.e., is a piece
of brain being "used" or not). The useful part of fMRI data comes from
-subtracting- images from each other, thus removing part of the
activity that was present. Such a subtraction means that fMRI data has
already discarded a lot of activity that may be exactly relevant to
answering the question. So I think these low-res, large-volume methods
are not the right thing to use.
I would be a lot happier with single-unit or multi-unit recordings of
spikes fired by individual neurons. This raises additional problems,
mostly statistical, for defining whether a particular neuron is
participating in "brain function" during a particular task. While it
is true that many neurons, say in V1 during a visual task for example,
do not -elevate- their firing rate during perception of a stimulus,
they still have a baseline firing rate. The typical decision on the
part of the experimenter is to -subtract- the baseline from the rate
during presentation of a particular stimulus. What's left is the
neuronal response to the visual stimulus that the experimenter chose
to show. The experimental visual stimulus, however, may make only a
small contribution to the total stimulus for the neuron. For example,
an individual V1 neuron may be simultaneously particpating in several
visual processing tasks, some related to the experimental stimulus (a
drifting grating or something), and others not related to it at all,
like visualizing an imaginary picture of a banana because the monkey
is hungry. In the typical experimental paradigm, the processing
related to visualizing the banana (which is something the monkey
really cares about) is discarded as noise because it isn't temporally
linked to the experimentally provided drifting grating (which the
monkey really doesn't give a crap about). But in reality, that "noise"
may be the more behaviorally important aspect of the neural activity
pattern.
So in addition to choosing the appropriate method of measuring and
quantifying "activity" or "use", it will also be necessary to
understand which aspects of neural activity that we can measure are
actually information-carrying processes and which are truly noise.
My own bias is that damn few of the spikes fired by neurons are truly
noise.
Cheers,
Matt
