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PROFESSOR: Normally, I would give a quiz on Wednesdays.
But I didn't do it in time.
I forgot it about until shortly before the class.
And even though I have a quiz, didn't have
time to print it up.
So we'll have it on Friday.
Normally, quizzes are just three four-point questions,
occasionally, four three-point questions.
They're just short answer questions.
Their purpose is mainly to make sure that you are
reading, keeping up with the class.
So are there any questions about that?
Are there any questions about anything we've
talked about so far?
Well, what I want to do today is the slides that occurred
for the last class--
I may not have posted them.
I moved them all into this lecture.
We've been talking about evolution and
multicellular organisms.
And I've checked off the things we've already talked
about here, including the generalized conception of the
CNS where we defined some basic terms we use throughout
the whole term and in anatomy in general.
And then we started talking about the
body plan of the chordates.
And today, I want to talk about how that was elaborated
in evolution.
And after that, we'll start talking about more specific
connections and pathways in the vertebrate brain.
So at the left here, this is my first stage.
You see just a very simple neural tube similar to what we
see in the most primitive chordates that we can find.
It was with the evolution of forward locomotion and head
receptors--
which of course occurred very, very early--
that you begin to get specialized
receptors at the head end.
And so for example, in my little sketch here, I have
olfactory at the front.
Some kind of light detection, visual input here also coming
into the forebrain.
And then I have a couple here.
And of course, there's many more other than those two
coming into the hindbrain.
This metasensory information coming from the head end, the
head of the animal, vestibular sense, which evolved for
maintaining stability in space.
And so with these head receptors, of course, the
neurons that they projected to in the CNS had to be able to
analyze that input.
So we get the beginnings of evolution of sensory analyzing
mechanisms connected to those inputs.
And with those, of course, new motor requirements existed.
We have to direct those receptors.
So we get development of orienting movements.
When you have a head and turn the head in various directions
not only to move in different directions, but also to
increase sensory input from selected parts of the
environment.
And mechanisms for controlling alterations in posture and
locomotion under the guidance of those receptors, those
evolve too.
And we'll see multiple examples
of that as we continue.
And all the while, you have to maintain stability, the
internal milieu.
Now mechanisms for controlling the internal environment exist
at all levels of the nervous system,
including the spinal cord.
But every level of the nervous system, as it evolved,
developed mechanisms for doing this.
They're so critical for survival.
So the structures now that evolved were the enlargements
at the rostral end of the brain.
And we talk about the brain vesicles,
hindbrain, midbrain, forebrain.
Now these have different components that we
learn about very soon.
The added motor control focused initially on hindbrain
and midbrain for control of the head, and the mouth, eyes
and ears, head turning, all in addition to the basic spinal
and hindbrain mechanisms for control of the body, including
locomotion.
And then the major factors that the forebrain was
involved in.
First of all, the inputs that come into the forebrain,
olfactory and visual, and then the high end that controlled
visceral system, endocrine secretions and
visceral motor control.
That centers on the ventral part of the [UNINTELLIGIBLE]
caudal forebrain in all the vertebrates.
So now we're going to talk about the factors that cause
these different brain components to expand.
And we'll start here with the hindbrain which we see
evidence in comparative neurology of existing species,
evidence of very marked expansions of the hindbrain
with the evolution of particular kinds of sensory
analyzers, particularly taste specializations and then also
vestibular, and auditory, and electroreception, which we
don't have.
But many animals do, and they're very important.
Animals that swim around in murky waters that can't use
vision, but they can detect disturbances in the electric
field around there.
Some of them just detect electric fields being
generated by, say, a prey animal.
Others generate their own electric field by electromotor
organs, specialized muscle cells.
So powerful in the electric eel that it can actually stun
the prey animal, the torpedo fish likewise.
But they also detect disturbances in that field
that they themselves are generating.
And then along with those specialized senses, you get
the evolution of particular programs for controlling
actions triggered by those sensory inputs.
So let's look at some evidence from comparative neuroanatomy
here about how the functional demands in evolution resulted
in an expansion of central nervous system components.
Some very dramatic examples have been found
in studies of fish.
And I took some pictures from Clarence
Herrick, C.L. Herrick.
The Herrick brothers--
C. Judson Herrick was the other one--
they helped establish the field
of comparative neurology.
And their books even now are very interesting.
And I looked at one of these in order
to get these pictures.
We're going to go through these particular fish, the
brain of a freshwater mooneye, the brain of a freshwater
buffalo fish, then a catfish, and talk a little bit more
about the catfish seventh cranial nerve.
So here's the mooneye, and I'm picking this for comparison.
Here is the spinal cord down at the bottom.
It's been cut off.
Everything between the two arrowheads that I've put in
there is hindbrain.
And you see cranial nerves coming in.
They're cut off, but that's a nerve coming into the rastral
end of the hindbrain.
In higher vertebrates, that's exactly where the fifth
cranial nerve comes in, carrying some of the sensory
input, which may be what that is.
You also have the beginnings of evolution of a cerebellum
there, another major component of the hindbrain.
Then you see the beginning of an expansion of the midbrain,
which we'll talk about in a minute.
And then what there is of the forebrain or rastral to it.
They're calling it the endbrain there, but below it,
you would have the tween-brain or diencephalon too and then
olfactory bulbs up in front.
That olfactory stalk is not a nerve.
It's part of the central nervous system, carrying the
processed olfactory input to the rest of the brain,
particularly the endbrain.
So with that shape of the brain in mind, look at this
one, the buffalo fish.
What is this enormous enlargement
of part of the hindbrain?
It's called the vagal lobe because the input coming into
it is coming from the vagus nerve.
Now the vagus nerve is a nerve that innervates a lot of the
gut cavity.
It innervates the thorax and right down into the abdomen.
But one of the things the vagus nerve
innervates is the palate.
And even in us, it carries input from taste receptors.
Now in humans, most of the taste input comes in through
the seventh cranial nerve, but it also comes in the ninth and
tenth particularly when you're a little child.
You lose some of those receptors in your throat as
you grow older.
But this animal has a specialized palatal organ
that's exquisitely sensitive to tastes in water that it's
filtering through.
It comes through the mouth and out through the gills.
In fact, that palatal organ has a motor component too, so
it can trap particles that the animal is feeding on.
So that's just an example of how a specialization for
sensory processing and sensory motor control can evolve and
lead to enlargements of the brain.
And that's been happening throughout evolution.
Yes?
AUDIENCE: Are there any other animals that are as
specialized for taste as the buffalo fish?
PROFESSOR: Well, perhaps not quite as specialized.
But yes, let's look at this one.
There's several.
I brought along pictures of two catfish.
And the catfish also has a vagal lobe here.
It's not as large as in this animal, but it's still there.
It's still an enlargement.
It's still enlarged because of the secondary sensory neurons
of the taste system that is also carried by the vagus
nerve, the tenth cranial nerve.
But it also has this enlarged facial lobe.
Now the facial lobe also is concerned with taste analysis.
Remember, I said, most of our taste input
comes through the seventh.
But the interesting thing about the catfish is the
seventh cranial nerve is distributed throughout almost
the entire body surface.
Here's another species of catfish where
I found this picture.
Here's this enormous seventh cranial nerve.
I implied that cranial nerves were just
innervating the head end.
But in fact, some of these nerves expanded to innervate
other parts of the body too.
In fact, the vagus nerve, I said, it comes in to the
hindbrain, but it actually innervates everything from the
gut cavity to the thorax, and throat, and palate.
So it's carrying taste input from various
parts of the body.
There are other animals too that can taste with their feet
or with other parts of the body other than the tongue.
In the natural world, we see all kinds of sensory
specializations that are different from what the
mammals we're familiar with have.
So that was from Herrick back in 1903.
So I've just pictured that enlargement in this picture--
oops, this one--
in a general way, showing an enlargement of the hindbrain.
But it happened in various due to particular enlargements of
particular parts of the hindbrain.
So the third stage that I'm defining here was an expansion
of the forebrain, an early expansion of the forebrain.
I will outline at least three major
expansions of the forebrain.
This is the first one due to the adaptive value of the
olfactory sense, which led to an enlargement of the
apparatus receiving the input from the olfactory receptors
here and the nasal cavities.
That input comes in from primary sensory neurons in the
epithelium, the nasal epithelium, and coming into
the olfactory bulbs.
And those olfactory bulbs project to cortical structures
of the forebrain.
We call that the endbrain mostly, although in primitive
chordates and primitive vertebrates, you have that
input also even going into the tween-brain.
So it goes into most of the forebrain.
A very little of it, if any, reaches further back.
So that was a valuable sense for controlling
approach-avoidance functions involved in feeding, something
a little different from taste, different kinds of molecules.
Also controlled mating because of the sensitivity to what we
call pheromones, odorous molecules produced.
It can also affect a kind of taste sense.
But it's all done through the olfactory
system, controlling mating.
Also involved in predator avoidance and in predation.
Now a note here.
I show the right olfactory bulb with
projections into the forebrain.
And then I show a neuron contacted by some of those
neurons that projects caudally.
And I show it on the other side.
Now when I do that in this class, you've got to keep in
mind that almost everything--
unless I specify differently-- everything I show on one side
is also present on the other side.
If I draw it on both sides of the diagrams, so quickly get
so complicated that you throw up your hands and say, let me
out of here.
And it will happen all too often in the class.
I'll do my best to keep it simple, and outline with my
colors and things, and post pictures online, keep the
pathways as straightforward as I can.
As I present them, don't memorize them.
Simply understand what I'm saying.
And when we go through things several times, you'll begin to
understand and learn them.
So the outputs here were links to locomotion.
They went through a structure in the forebrain that is part
of what we call the corpus striatum, striated body.
Now people who study mammals don't usually think of the
corpus striatum as an olfactory structure at all.
But we are concerned with early evolution.
At the time this evolved, inputs from the visual system
and auditory system, they didn't even
come in to the endbrain.
Not yet.
What they're projecting to, through that link in the
forebrain, was into a part of the midbrain and also
hypothalamus--
there's parts of the hypothalamus and the midbrain
caudal to it that control locomotion.
Even the hypothalamic input that controls hypothalamic
structure--
often called the hypothalamic locomotor area-- it projects
to that midbrain area.
So I'm just showing it go right into the midbrain there.
I want to point out one very important aspect that I can
discern of that connection there in what we now call the
ventral striatum that got the olfactory inputs.
It was very important in evolution.
It was important because those connections were plastic.
The animal could learn.
He could alter those connections.
So if he learned that a particular odor he was
detecting--
that it was good for him to approach because it was good
to eat, he could learn to approach.
If it led to a disaster, he could learn to avoid it.
So the mechanisms started to develop very, very early in my
belief of that learning in the endbrain.
And it happened through these olfactory links
in the corpus striatum.
And you'll see in a minute why I think that was so important
in evolution.
So we've talked a little bit now about the role of the
sensory analyzing mechanisms in early evolution, the
corresponding motor control.
There were other structures that developed that linked the
two-- sensory input and motor output-- that I want to say a
little more about particularly in the midbrain.
Structures that did that were for maintaining
stability in space.
They involve vestibular, visual, and tactile
information coming into the tectum.
The vestibular information did not primarily use the tectum.
It came into the hindbrain, the rastral hindbrain, and
developed direct connections to spinal cord, as well as
hindbrain for controlling balance.
And then these structures also-- we've already
mentioned-- the avoidance in approach movements guided by
olfactory as well as other senses.
Now the structures concerned with head and body orientation
primarily in the roof of the midbrain, the midbrain tectum,
also pretectal cell groups, which connected to the medial
hindbrain, and medial cerebellar structures are also
known to be particularly important for those functions.
They get direct input, for example, from
the vestibular system.
In fact, the only cerebellar input that comes directly from
a sensory input is vestibular, that is, right, directly from
the primary sensory neurons.
So here we are in that mooneye just pointing out the midbrain
and the cerebellum.
I pointed them out briefly when I showed
this picture before.
But these are the structures I was just mentioning.
So the importance for linking sensory inputs to these
orienting functions and also for approach-avoidance
functions--
the importance of that input coming into the membrane from
receptors other than the olfactory led to an expansion
in many animals of the midbrain.
And that's what I'm showing here.
The midbrain doesn't have any cranial nerves carrying input
directly into it.
But it was an important correlation center in the way
I'm using the term here.
For example, here is input coming in from an
image-forming eye, coming to the opposite side of the
brain, to the midbrain.
Linking to two kinds of output systems, one descending
ipsilaterally controlling escape movements, one we could
say recrossing--
because it already crossed once getting to the tectum--
controlling orienting or turning of the head and eyes.
And those are the two major output systems of the tectum.
And I also can point out that on the motor side, these kinds
of more control mechanisms could be modulated by
motivational states.
So that is the way olfaction is influencing that system.
Because that influences the motivational sense, the
motivational states.
Now I showed the decussation here.
This is the decussation.
Here's the optic tract.
It's crossing over.
Why does it cross over?
Isn't that sort of silly?
Here, to control orienting movements, it has to cross
over and go to the opposite tectum.
And then to make an orienting movement, it crosses again by
a pathway like that.
Why would it do that?
There have been a lot of speculations
in comparative neurology.
Ramon y Cahal had an interesting speculation about
that in the tectum.
None of them have really been supported.
And I'll bring this up several times, so you don't have to
learn all about it now.
But I will develop it into a hypothesis later on that I
think is more convincing than others
that have been presented.
I can summarize it for you here.
You're going to read this later.
It's a little bit to where you can read it right now if you
can see it.
Very early in the evolution of the midbrain and forebrain,
before the hemispheres appeared, visual inputs from
the lateral eyes projected bilaterally.
But then in evolution, they became crossed.
Why would I think they
projected bilaterally initially?
Because the earliest connection, the connection to
the hypothalamus coming from the optic
nerve, even in mammals--
like the hamster, the animal I study--
is bilateral.
It goes to both sides almost equally.
But then the longer connections that most have
evolved later became crossed.
Why would that be?
And that, I believe, led in later evolution to the
decussation of non-visual pathways as well, not the more
caudal ones, but the projections to the midbrain
and forebrain.
Those are the ones that became crossed.
So why did that happen?
Well, it had to be more adaptive.
It supported the better survival of the organisms.
And I believe that was because the cross pathways were able
to reach crucial output mechanisms more quickly.
Now what did they need speed for?
They needed speed probably more than anything in order to
get rapid escape or avoidance movements.
So I'll outline the actual connections involved in that
evolution later on when we study visual and
somatosensory systems.
Now I said, the forebrain has expanded more than once.
What was the second reason?
We initially said, because olfaction was important.
It was adaptive, it led to an expansion.
Because of the endbrain structures that were
processing the olfactory information and routing it to
output systems of various sorts, including for
controlling sexual functions, for controlling approach to
prey or other kinds of food, or for avoidance.
What happened was other sensory inputs other than
olfaction invaded the same endbrain structures that were
getting olfactory input.
Remember I said the connection in the striatum
was a plastic one.
Well, that was very useful.
Other systems begin to do the same,
connect to the same structure.
Here, I show a neuron in the tectum that was projecting
into the tween-brain.
And often these connections, especially as structures got
large-- like the tectum did here-- they develop widespread
connections.
Some of them reached into the tween-brain.
In here, it's connecting with neurons that had projections
into the endbrain.
And some of those connections went into
that striatum structure.
And when we study the striatum, I'll show you some
of those connections.
People don't think of them very often because we think of
what's the big pathways that are so important
now in human function.
But to me, they're important because of what they say about
the way this evolved.
So non-olfactory systems invaded the tween-brain and
endbrain in pre-mammalian vertebrates.
They went to both the subcortical and what was
evolving into cortex, an expanded cortex, the
neocortex, which is a specialty of the mammals.
The new inputs led to a second expansion.
And of course, along with that, we developed more
complex programs for goal-directed activities.
We also developed systems for modulating other systems.
Let's talk about the goal-directed activities, the
programmed activities.
For that, I mean what the ethologists call
fixed action patterns.
They're not the same as reflexes.
They are controlled by motivational states unlike
reflexes, which are not very much influenced by
motivational states.
They are fixed not because they're totally rigid or they
can't be changed or modified.
They're fixed in the genes.
That's what we mean by a fixed action pattern, something that
you inherit.
And there are many examples of the instinctive movement
patterns in studies of animal behavior,
including human behavior.
And these can become modified.
Or especially, different fixed action patterns can become
linked in various ways with learning.
And we'll mention a few times the importance of that.
And here, I just mention some of the
structures involved in that.
Elaborations that were particularly prominent in the
mammals were mechanisms for reward-driven learning and
habit formation.
They used the corpus striatum and the neocortex, and these
were linked to the motivational systems that
centered on the hypothalamus.
And that's the role of that system which is for modulating
other brain systems in response to the social needs,
visceral needs.
And I just summarize here the kinds of
control that involves.
It's present even in the most primitive animals, but it was
the forebrain that became the prominent structure
particularly the hypothalamus with built-in
hierarchies of goals.
But they also learned goals.
And especially with mammals, there was an evolution of the
communication of these motivational states through
gestures, facial expressions, things we call the emotions
and the feelings.
And we look at two structures, or groups of structures, that
achieve that.
The hypothalamus is the main one, but also the epithalamus
and the structures they are connected with.
And then in the endbrain, the limbic structures of the
endbrain, which we will define as the structures most closely
connected with the hypothalamus.
And we will spend something like five classes talking
about the connections of that system.
Some people don't like to call it a single system because of
the diversity of functions.
But if we define it structurally, the way
[? Nauda ?]
did, we can see that there are good reasons to lump these
things together.
Because of the central role that hypothalamic mechanisms
play in the way they function.
The last big expansion of the endbrain resulted in the
ability to anticipate events and plan actions.
And this is the way I summarize
the cognitive systems.
Here's what I mean.
On the sensory side, the ability to form images.
What are images in the brain?
Basically, a simulation of what's out there.
If I see an object and see it as a unitary object, then what
that object does and the way it moves, I can predict the
kinds of inputs that are going to result.
On the motor side, planning and preparing for actions.
And I don't just mean the long-term planning, like, that
would lead you to buy life insurance or
something like that.
And that's certainly important too.
Mammals without the development of prefrontal
neocortex would do that.
But I mean immediate preparation of things I'm
going to do in the next few seconds, or the next second,
or the next part of a second.
We are constantly anticipating, and that is what
the neocortex does.
So these cognitive functions led to a third major expansion
of the forebrain.
And the structures that expanded the most were in the
neocortex, especially in the cortex we often call
association cortex.
But also expanding with them was parts of the corpus
striatum and cerebellum that are closely
linked with that cortex.
So they expanded too.
The striatum expanded more.
Remember, it was involved in that second
expansion of the endbrain.
But it continues to expand here, and the cerebellum does
so even more.
So if I take that brain that showed the second expansion,
the forebrain with the invasion of the non-olfactory
inputs into the forebrain, here's what happened.
This ballooning out of the cerebellar hemispheres that
grew out of the primitive diencephalon.
They grew bigger and bigger.
And here, I'm showing the way they ballooned out in, say, a
small rodent that hasn't yet developed the enormous
neocortex with the many gyri and sulci that we have in the
higher primates.
And along with that, you've got this expansion of the
cerebellum.
And I'm not showing the corpus striatum, the subcortical
structure of the hemispheres there,
that was also expanding.
So that was the third forebrain expansion.
I emphasize the sensory side in this whole discussion.
But I don't want to leave out the importance of the fine
movement control that evolved with this particularly in this
third forebrain expansion, the control of fine movements.
And we will spend some time on the study of descending
pathways and the motor system in the class and the kinds of
connections that evolved with that to
enable that to function.
So how much expansion has occurred?
There have been some pretty interesting data collected on
the total size of the brains of many
different species of animals.
Some Germans--
Heinz Stephan and his collaborator
Andy, and several others--
have, beginning in the 1960s, but then continuing for some
time, collected a lot of these kinds of data.
And their data have been used in various studies, especially
here in the USA.
And what we find is if you just look at brain weights,
humans aren't even at the top.
You'll have animals that we consider--
the way we test intelligence--
to not be nearly as smart as humans
will have bigger brains.
So how do we handle that?
Well, we find that the same is true if you
just look within humans.
Some humans have much bigger brains than others.
So what we're mostly concerned with is the relative size of
the brain with respect to body size.
Especially Jerison, back in the '70s, began doing these
kinds of plots.
He's plotting here on the abscissa the body weight in
grams and here the brain weight in
grams on the ordinate.
So where is human?
Human's right there.
And then we have the elephant and the blue whale.
So the largest brain is in the blue whale.
But if we're looking in this dimension, if we go along that
arrow, perpendicular to the diagonal line where brain and
body weight are matching, we get relative brain weight with
respect to the body.
And there we see that humans are the farthest out.
This is just another of these plots where I've put in the
position of human.
And as is done in this one also, you look at various
groups of animals, you can see that they
have different envelopes.
Here are the birds, which can include some birds with
relatively large brains with respect to body weight.
That's true for the cartilaginous fishes too, the
sharks and the rays that contain a few that have
relatively large brains.
Reptiles are considerably lower.
The most primitive vertebrates, the hagfishes,
the lampreys, and cyclostomes, they're all relatively
small-brained animals with respect to body weight.
In this plot, it's taken individual data for individual
species and plotted them just for the mammals.
These are all whales.
There's another whale, there's another whale.
You have other large animals here that have relatively
smaller brains than the cetaceans, the hippopotamus
and rhinoceros for example, down here.
Although they have pretty large brains, it's because
they have pretty large bodies.
Here, I just took the mammals in a simpler diagram, body
weight in kilograms.
And notice that these are both on log scales, so we can get
the straight lines.
The diagonal line is straight there.
And we can again look at this dimension to get relative
brain size with this kind of plot.
What affects, besides body weight, the
amount of brain tissue?
AUDIENCE: I have a question about that graph.
On the porpoises, porpoises look closer in the maximum
amount of brain weight to body size to modern humans there
than the chimpanzee or the gorilla.
But are they intelligent?
PROFESSOR: Sure, they're intelligent.
But remember, each animal is intelligent for its species
and its environment.
If we try to test these animals on things that humans
are good at, humans are always going to come up a lot better.
If I say, I'm going to test a hamster and find an area that
he's better than a human, what would I pick?
AUDIENCE: Escaping from an owl or something?
PROFESSOR: I could pick the hamster's ability to get a
little kernel of a sunflower seed out of a shell.
And you say, well, that's easy, I can do that.
Well, I've tried it.
I've raced hamsters many times.
They always win.
They can get that little seed out with their
tiny, little hands.
They rotate it around rapidly.
They quickly get it out, and they stick it in their pouch.
And I can't even do that.
So what factors other than just body weight?
Well, special functions.
Remember, the vagal lobe of the buffalo fish.
He's incredibly intelligent at sifting little particles from
the muddy bottom of a river and selecting it for his food
because he's specialized for that.
So you see, one of the things we're biased about is wanting
to come up with a general measure of intelligence.
And there are some people that argue that there's no real
general measures at all.
We are collections of specialized functions.
That, of course, can be a moot point.
But I think in general when you approach things from an
evolutionary point of view, you have to take that view.
Yes.
AUDIENCE: Has anybody ever tried to plot, say, something
like prefrontal cortex relative to body weight rather
than the brain as a whole?
PROFESSOR: I've not seen a plot like that.
Of course, it could be done.
And there you would find even more dramatic differences for
humans because of the enlarged prefrontal cortex.
One of the problems is drawing careful lines around these
structures and defining them structurally.
It's not always easy.
With imaging techniques, it's becoming a little easier to
discriminate different areas functionally.
But these are all interesting questions.
And we won't have final answers on any of this.
But we can set the stage for it, and then you'll understand
what you'd have to do to get to such answers.
Any other questions?
So keep in mind this general point.
Go through the slides, make sure you get the major points.