[From Frank Lenk (2010.08.14.13.55)]
Another article that may be of interest –
Saw this on the Science Daily web site - not just individual
neurons but the dendrites of individual neurons are capable of perceiving
sequences.
The living perceptual machinery that sits inside the “Perceptual
Function” boxes of our control loops is truly amazing!
Frank
Single
Neurons Can Detect Sequences
ScienceDaily
(Aug. 13, 2010) — Single neurons in the brain are surprisingly good at
distinguishing different sequences of incoming information according to new
research by UCL neuroscientists.
···
The study,
published August 12 in Science
and carried out by researchers based at the Wolfson Institute for Biomedical
Research at UCL, shows that single neurons, and indeed even single dendrites,
the tiny receiving elements of neurons, can very effectively distinguish
between different temporal sequences of incoming information.
This challenges
the widely held view that this kind of processing in the brain requires large
numbers of neurons working together, as well as demonstrating how the basic
components of the brain are exceptionally powerful computing devices in their
own right.
First author
Tiago Branco said: "In everyday life, we constantly need to use
information about sequences of events in order to understand the world around
us. For example, language, a collection of different sequences of similar
letters or sounds assembled into sentences, is only given meaning by the order
in which these sounds or letters are assembled.
“The brain
is remarkably good at processing sequences of information from the outside
world. For example, modern computers will still struggle to decode a rapidly
spoken sequence of words that a 5 year-old child will have no trouble
understanding. How the brain does so well at distinguishing one sequence of
events from another is not well understood but, until now, the general belief
has been that this job is done by large numbers of neurons working in concert
with each other.”
Using a mouse
model, the researchers studied neurons in areas of the brain which are
responsible for processing sensory input from the eyes and the face. To probe
how these neurons respond to variation in the order of a number of inputs, they
used a laser to activate inputs on the dendrites in precisely defined patterns
and recorded the resulting electrical responses of the neurons.
Surprisingly,
they found that each sequence produced a different response, even when it was
delivered to a single dendrite. Furthermore, using theoretical modelling, they
were able to show that the likelihood that two sequences can be distinguished
from each other is remarkably high.
Senior author
Professor Michael Hausser commented: "This research indicates that single
neurons are reliable decoders of temporal sequences of inputs, and that they
can play a significant role in sorting and interpreting the enormous barrage of
inputs received by the brain.
“This new
property of neurons and dendrites adds an important new element to the
“toolkit” for computation in the brain. This feature is likely to be
widespread across many brain areas and indeed many different animal species,
including humans.”
Funding for this
study was provided by the Gatsby Charitable Foundation and the Wellcome Trust.
Email or share this story:
Story
Source:
The above story is reprinted (with editorial adaptations by
ScienceDaily
staff) from materials provided by University
College London.
Journal
Reference:
Tiago Branco, Beverley A. Clark, and Michael Hausser. Dendritic discrimination of temporal
input sequences in cortical neurons. Science, August 12 2010
DOI: 10.1126/science.1189664
A neuron in the visual cortex of the mouse was filled with a
fluorescent dye so that the dendrites could be visualised. A laser was targeted
to small spots on single dendrites to activate groups of inputs in different
orders. The electrical response of the neuron was recorded and was found to be
be different for each of the input sequences. (Credit: Tiago Branco/Hausser
Lab: UCL)
-----Original Message-----
From: Control Systems Group Network (CSGnet)
[mailto:CSGNET@LISTSERV.ILLINOIS.EDU] On Behalf Of Martin Taylor
Sent: Wednesday, August 11, 2010 1:33 PM
To: CSGNET@LISTSERV.ILLINOIS.EDU
Subject: [CSGNET] Changing the foundations of PCT (was Testing for Control In Experiments)
[Martin Taylor 2010.08.11.14.06]
A few days ago, Bill sent a series of very strange
messages to which my
reaction has varied from day to day as I contemplated
them. Apart from
one obviously correct technical point that I will deal
with in my
experimental model on another thread, I was initially
flabbergasted, and
since then I have been by turns annoyed, puzzled, worried
and generally
at a loss as to how to respond. I will not respond to the
main themes
here. This message is only about Bill’s radical
redefinition of PCT,
which once meant “PERCEPTUAL Control Theory”,
and now seems to mean
something quite different, at least to Bill.
[From Bill Powers (2010.08.07.0210 MDT)]RM: I also
don’t agree with
calling p[p[S]-A] a controlled variable.
MMT: Of course it is a controlled variable. Just
as with any control
system, the output signal influences the
perceptual signal, and
changes its value to approach its reference
value. What’s not a
controlled variable about that?
RM: Bill addressed this in his comments
earlier. A controlled
variable (in PCT) has an environmental
correlate, the controlled
quantity, which can be detected by an
experimenter.
MMT: The controlled quantity is ALWAYS a
perception, never an
environmental variable. That’s PCT 101, first
lesson.
BP: Here we go again. Rick is defining a controlled
variable as
something the external observer can see. If you
would read his words
that would be obvious.
Yes, it was blindingly obvious.
It was equally obvious that the idea violates the
foundations of PCT,
which is why I wrote my correction: "The controlled
quantity is ALWAYS a
perception, never an environmental variable. That’s PCT
101, first lesson."
If for some reason you no longer think that perceptions
are the only
variables that can be controlled, and that environmental
variables
(“something the external observer can see”)
also can be controlled, I’m
afraid I cannot agree. Your PCT has fallen into the
supernatural void.
Failing some clairvoyant abilities in the subject that
would allow the
true state of an externally observable variable to serve
as the input to
the comparator of a control system, the perceptual signal
is the only
way that the control unit can get information about the
state of
ANYTHING the external observer can see. I know you have
considerable
disdain for “conventional” science and
scientists, but I think this
change to the foundation of PCT goes too far beyond the
bounds of normal
(or quantum) physics, even for you.
If, as has seemed the case recently, you are controlling
strongly for
perceiving me to be wrong in just about everything I
write, nevertheless
it seems a bit extreme to use your authority as
originator to alter the
very foundations of Perceptual Control Theory as a means
of controlling
that perception. I don’t accept it, and if this leads to
a conflict
(something I usually try to avoid), so be it.
For my part, I will continue to write about PCT as though
only
perceptions can be controlled.
Martin