[From Bruce Abbott (951009.1645 EST)]
Bill Powers (951008.1250 MDT) --
Bruce Abbott (951008.1230 EST)
Our mapping study shows that the MSH receptors concentrate heavily
in just those areas where our "wiring" studies show some of the
important neural components of the system to lie.
Of course -- how else would the MSH have an effect? What other receptors
are in that same area? What other systems are in that same area? What
other substances could have the same effect?
Well, you recently argued that MSH might work its effect on DVs by acting on
the perceptual inputs, so that the chicks simply don't recognize the
reflections in the mirror as chicks. If the neuroanatomical locus of MSH
activity does not involve this part of the system, that would seem to
provide indirect evidence against this hypothesis (more direct tests are
possible). You seem to suggest that dumping just about any biochemical into
this area would affect DVs in the way that MSH does, but this is simply not
true, as evidenced by a fair amount of drug screening that has been
conducted to evaluate just this possibility.
Ok, so what are these control systems? They would include the systems
for recognizing other chicks and the mother, for perceiving the distance
(or visual size) of the others, for determining the direction to them
relative to the perceiver's orientation, for converting errors in
distance to reference directions for motion, for converting errors in
direction into adjustments of reference signals for walking, and so on
and so on. There might be some higher-level systems involved as well.
All these control systems would be active no matter what they are being
used for -- expressing anxiety and trying to get back to mama, seeking
cover when some danger appears, foraging for bits of food, and whatever
else chicks do that requires moving toward or away from objects and
otherwise behaving relative to them.
I've been simplifying, of course, in precisely the same way we do when
discussing tracking. We talk as if the systems that locate the computer
screen, the cursor within the screen, the target position, compute the
distance between target and cursor, extract the rate of movement, identify
the relationship between mouse-movement and cursor movement, and so on are
just given. In our models the error between cursor and target somehow
produces the appropriate movements without specifying the specific muscle
control systems involved. The control systems involved in arm positioning
are used all the time for other purposes besides getting a cursor back to
target. Are you suggesting that it would not be possible to determine
whether a drug that is observed to affect tracking accuracy acts on the
lower-level arm-positioning system, the perceptual input function, the
reference level, etc.? I think you're being far too pessimistic.
So this is not the "control system whose actions typically produce DVs
(and other outputs)." You are looking at multiple control systems at
several levels that are involved in many forms of behavior.
Of course.
The only
reason they seem to be involved specifically in the distress reactions
is that you are studying distress reactions;
Yeah, and the only reason I think that alcohol affects coordination is that
I am studying coordination.
the only reason they seem
to be affected by MSH is that you are studying the effects of MSH.
It would be difficult to know that they are affected by MSH if we _weren't_
studying the effects of MSH now, wouldn't it?
You
could probably find hundreds of other substances that would interfere
with some aspect of this behavior;
Maybe, but how many of them would produce these specific effects without
producing a bunch of other changes not observed with MSH?
you could probably find many other
behaviors in which the same regions of the brain showed activity. In
fact, I'll bet that you can measure activity in this region of the brain
ALL THE TIME, and you're just picking up variations from the background
activity, subtracting out the uncorrelated activities.
I said brain _stimulation_, not monitoring. Of course those areas show
activity all the time. Stimulation of appropriate brain regions can
activate specific, organized behavioral patterns, or components of those
patterns, depending on the locus of stimulation. If I inject the
appropriate signal into a servo, I can change its reference (and the servo
will follow). It would appear that injecting current into the appropriate
circuits of the chick's brain can have similar effects. These effects have
typically been interpreted in S-R terms (the current "turns on" or "drives"
some behavior); however such results are doubtless better viewed as
artificial disturbances to the affected control systems.
The problem lies not in your techniques for measuring brain activity,
but in your classification of the behavior. In my not-so-humble opinion,
the first step in any investigation of the brain has to be to determine
the variables that the organism can control. The words we use to
describe behavior are, despite the scientific trappings of the
situations in which we use them, informal and intuitive, and oriented
around the observer's background and interests instead of the test
subject's structure of perceptions and goals. Instead of just
classifying the peeping and the movements as "distress vocalizations,"
you could look at what the chick is actually doing, and find out what is
being controlled by those actions. Obviously the peeping is only part of
what is going on, the part you chose as a measure of the whole. The
vocalizations are what a human being hears; there may be lots of fine
structure in it that the human observer doesn't notice, particularly at
frequencies beyond human hearing. The "mute" chick might not have been
mute at all. And along with the vocalizations are, I have no doubt, lots
of other motor activities.
In fact a great deal of observation and experimentation preceded any attempt
to identify the neural substrates of attachment behaviors. You seem to be
suggesting that one day someone observed that chicks peep loudly when placed
in an isolation box, and drew from this observation the idea that the
peeping must indicate separation distress. In fact a great deal is known
about the phenomena labeled "attachment" or (in fowl) "imprinting,"
including their functional significance in the life of the chick, ontogeny,
necessary conditions, some of the controlled perceptions involved, and the
aftermath of failure to form an attachment. The parallels in animals
ranging from chicks to human children are obvious and compelling.
It is difficult to know the extent to which these perceptual systems and
associated reference levels are built into the chick. The chick has few
degrees of freedom in its vocalizations (that anyone has recognized),
and few alternative behaviors it can produce to control anything. It is
possible that the main control system that matters here is in the mother
hen, who seems compelled, at least some of the time, to seek the
position of anything that is peeping like a chick. The chick, as a
consequence, has the opportunity to learn very early that peeping loudly
enough will summon the mother hen into close proximity. So the main
thing we would have to speculate about in that case is the origin of the
respective reference signals.
No doubt the chick learns through its experience that its loud peeps are
soon followed by the reappearance of its mother, as does the human infant
with respect to its crying. However, both the peeping and the crying occur
spontaneously as soon as conditions permit, before any opportunity for
learning. Human infants initially emit crying when there is error in just
about any system (thirst, hunger, pain, etc.); crying induced by separation
emerges later, after the infant is able to discriminate parents from
strangers and after attachments have begun to form. It can be discriminated
from other reasons for crying in that the crying can be quickly eliminated
by bringing the child into close physical contact with its parent.
As you (and I) have noted, control by vocalization depends on the action of
a complementary control system in the parent. If crying did not bring the
parent into contact with the child, it would fail to correct the error it is
designed to correct. Evolution has favored the selection of such
complementary systems as the offspring served by them are better protected
from dire consequences and are thus more likely to survive and reproduce.
I just don't think there's any shortcut. We have to do the basic studies
of what animals are controlling before we can even characterize behavior
in a relevant way, a way that's not conditioned by the observer's
private interpretations, categories, and labels.
I'm not claiming that all the basic studies have been done, but certainly a
good start has been made. I don't think this is a case of taking shortcuts.
My grandson is standing at my elbow demanding that I send this and turn
the computer over to him. I have no defenses -- he wins. Bye for now.
How old is he? If he becomes "lost" at the mall (suddenly becomes aware
that nobody he knows is in view, and that he is surrounded by strangers),
what does he do? If he is two or three or possibly even four, I'll bet I
can guess. At those ages, I can remember going absolutely ballistic. Not
all children that age would react the way I did, but certainly most would.
Samuel Saunders [951009:0051 EDT] --
Sam, thanks for the info regarding the chick's auditory capacities. I
believe Jaak Panksepp may have collected some data (I know he did for the
rat). Chick peeps are fairly pure tones centered, as I recall, around 2-3
kilohertz., well within the range of human hearing. To screen out
irrelevant noise, our "peep detectors" were equipped with band-pass filters
to reject all frequencies except those close to the 2-3 kilohertz center
frequency.
Regards,
Bruce