Medical Neuroscience explores the functional organization and neurophysiology of the human central nervous system, while providing a neurobiological framework for understanding human behavior. In this course, you will discover the organization of the neural systems in the brain and spinal cord that mediate sensation, motivate bodily action, and integrate sensorimotor signals with memory, emotion and related faculties of cognition. The overall goal of this course is to provide the foundation for understanding the impairments of sensation, action and cognition that accompany injury, disease or dysfunction in the central nervous system. The course will build upon knowledge acquired through prior studies of cell and molecular biology, general physiology and human anatomy, as we focus primarily on the central nervous system. This online course is designed to include all of the core concepts in neurophysiology and clinical neuroanatomy that would be presented in most first-year neuroscience courses in schools of medicine. However, there are some topics (e.g., biological psychiatry) and several learning experiences (e.g., hands-on brain dissection) that we provide in the corresponding course offered in the Duke University School of Medicine on campus that we are not attempting to reproduce in Medical Neuroscience online. Nevertheless, our aim is to faithfully present in scope and rigor a medical school caliber course experience. This course comprises six units of content organized into 12 weeks, with an additional week for a comprehensive final exam: - Unit 1 Neuroanatomy (weeks 1-2). This unit covers the surface anatomy of the human brain, its internal structure, and the overall organization of sensory and motor systems in the brainstem and spinal cord. - Unit 2 Neural signaling (weeks 3-4). This unit addresses the fundamental mechanisms of neuronal excitability, signal generation and propagation, synaptic transmission, post synaptic mechanisms of signal integration, and neural plasticity. - Unit 3 Sensory systems (weeks 5-7). Here, you will learn the overall organization and function of the sensory systems that contribute to our sense of self relative to the world around us: somatic sensory systems, proprioception, vision, audition, and balance senses. - Unit 4 Motor systems (weeks 8-9). In this unit, we will examine the organization and function of the brain and spinal mechanisms that govern bodily movement. - Unit 5 Brain Development (week 10). Next, we turn our attention to the neurobiological mechanisms for building the nervous system in embryonic development and in early postnatal life; we will also consider how the brain changes across the lifespan. - Unit 6 Cognition (weeks 11-12). The course concludes with a survey of the association systems of the cerebral hemispheres, with an emphasis on cortical networks that integrate perception, memory and emotion in organizing behavior and planning for the future; we will also consider brain systems for maintaining homeostasis and regulating brain state.
Central Visual Processing, part 3
Loading...
Aus dem Kurs von Duke University
Medical Neuroscience
1233 Bewertungen
Aus der Unterrichtseinheit
Sensory Systems: The Visual System
This module will provide lessons that are designed to help you understand the basic mechanisms by which light is transduced into electrical signals that are then used to construct visual perceptions in the brain. Your studies of the visual system will benefit you at this point in the course, but also in later studies when we use the visual system as a model for understanding general principles of developmental plasticity. Lastly, it is worth noting how much of the forebrain contains elements of the visual pathways. Thus, injuries and disease in widespread regions of the brain may have a clinically important impact on visual function. All the more reason to learn these lessons well as you progress in Medical Neuroscience.
Treffen Sie die Kursleiter
Leonard E. White, Ph.D.Associate Professor
Department of Neurology, Department of Neurobiology, Duke University School of Medicine; Department of Psychology & Neuroscience, Trinity College of Arts & Sciences; Director of Education, Duke Institute for Brain Sciences; Duke University
Visual cortical neurons can also be characterized by whether one eye or the
other drives the activity to a greater or lesser degree, this is called ocular
dominance. Now let's return to the organization of
the visual pathways for just a moment to explain where this property arises.
So, as the 2 retinas send their axons into the optic tract, representing the
same side of the visual world. It might be quite natural to assume that
that information is combined in the lateral geniculate nucleus.
but it's not. The lateral geniculate nucleus is a
layered structure. And alternating layers of the lateral
geniculate nucleus receive input from one retina or the other.
Actually, there are two inner layers that are a bit different from the four outer
layers, and the two inner layers are divided into these two components where
one layer, layer one receives input from the contralateral eye, layer two from the
ipsilateral eye and then the four outer layers,are divided with layers four and
six receiving input from the contralateral eye and layers three and
five. Receiving input from the ipsilateral eye.
So the point is, is that even within the thalamus, the information from the two
eyes, while it's representing the same half of the visual world.
It's still monocular at this single cell level.
In fact, as the lateral geniculate nucleus projects to the visual cortex the
information remains monocular, which is to say that these binocular layers of the
lateral geniculate nucleus project in an interdigitated fashion to nearby regions
and the visual cortex. As if my fingers are representing the
inputs driven by either the left eye or the right eye.
And you can see that the fingers of my left and right hands are interdigitating
as this thalamic input reaches layer four of the visual cortex.
This establishes a set of columns that we can see both physiologically and
anatomically . And we call them ocular dominance
columns. So the input layer to the cortex, layer
4, remains monocular. It's only in the upper layers of cortex
as layer 4 projects to the circuitry above layer 4, layers 2 and 3 does
information from the two eyes begin to get mixed for the first time.
And that mixing of input from the two eyes is quite important because this
makes possible the phenomenon of stereopsis.
And stereopsis is that component of binocular vision that requires two eyes
seeing slightly different views of the same object.
And this is a perspective of depth that is possible for objects that are near
within about a meter or so is where it works best.
And beyond that distance or so, the lines of sight become increasingly parallel and
therefore, increasingly similar. But for objects that are within about an
arms length this dimension of depth is really quite rich as it's elaborated by
convergence by these two monocular channels in the upper layers of the
visual cortex. So, here's how this works.
Imagine that we are fixating with our two eyes on a particular location in space
And all objects that are closer to us and that fixation point are going to be seen
by what we call non-corresponding regions of the retinas.
That is, there, there are points on the retina that don't project to the same
point in the thalamus so, these slightly offset regions of the retina project
their axons centrally. And the slight disparity in inputs that
are rising on to the same cells in the upper layers of the visual cortex from
these two disparate locations of the retinas give rise to signals that allow
us to appreciate the fact that an object at location a is near in depth relative
to the fixation point. A similar phenomenon would occur for
background objects where we might have a stimulation of non corresponding points,
but now on the opposite side of the fixation point.
So locations indicated by this letter A would give rise to near disparities, and
locations at a distance, indicated by letter C, would give rise to far
disparities. Of course, there are other cues about
depth, other than stereopsis. we can convince ourselves easily of this
fact. All one has to do is cover an eye.
And the world does not all of a sudden seem to collapse from 3D to 2D.
As we move our head around, we can see the movement of foreground objects
relative to background objects. And that gives us important information
about depth. but nevertheless, stereopsis can be a, a
quite valuable tool. As we navigate the world around us.
And especially as we interact with objects within arms length.
One can demonstrate for yourself stereopsis by getting two pencils and
holding them out at arms length. And then bringing them together and you
can see how well you can get those tips to touch.
So I'm not so bad at this. But if you close one eye and make
stereopsis go away we'll see if this presents any further challenge.
So I'm going to close my left eye, and now try the same, touching of the pencil
tips. Whoa, I'm not so good anymore.
Okay that's a little better. Let's try the, the a right eye now.
So I'm closing, I'm going to close my right eye.
So let's try now closing my right eye and seeing how well I do with my left.
And, I seem to be worse when I try to use my left eye.
Okay so, the increased performance of using your two eyes together is not so
difficult to demonstrate. So next we come to the topic of parallel
pathways. So we've been talking about parallel
pathways in different context, first in the somatosensory system, now in the
visual system so it should be no surprise to you to discover that there are
parallel pathways even arising from the very same retina as visual information is
processed and then projected back into the brain.
If one were to look at the ganglion cells that are present in the retina we find
actually a rather rich assortment of ganglion cells.
They can be characterized in different ways, by size.
By morphology and as investigators over the years have done so, we've adopted a
nomenclature for different types of ganglion cells in different species and
here's a nomenclature of that is used in the primate retina, there are small cells
that we call P ganglion cells. Much larger cells that we call M ganglion
cells and then an intermediate type of cell that's called the K ganglion cell.
And the different morphologies that we see here are associated with different
physiological properties. more so, these different types of cells
give rise to axonal projections that terminate in different parts of the
lateral geniculate nucleus. There are projections from those small
p-cells that terminate Among the small celled layers of the lateral geniculate
nucleus. These are called the Parvo cellular
layers. Parvo means small.
And we've illustrated them here in green. These are layers 3 through 6.
meanwhile, the larger m type ganglion cells
terminate in the first two layers of the laterals geniculate nucleus, illustrated
here in blue layers one and two. So conveniently, the m cells project to
the magnocellular layers and the p cells project to the parvocellular layer.
Now the k cells project to a zone in between the layers, so there's a region
Between each of these layers that we call the koniocellular layers.
It's a region where there's a band of white matter or a[UNKNOWN] of white
matter between these cell dense layers that have the numbers.
So the k cells terminate in those spaces. These different neurons in the lateral
geniculate nucleus, send distinct patterns of projection on up to the
visual cortex. The Parvo-cellular layers of the lateral
geniculate nucleus A synapse into the bottom part of layer four, a zone in the
primate that we call layer 4c beta. The magnocellular layers from the
anterior part of the lateral geniculate nucleus, send their axons into layer 4c
alpha, right on top of the input derived from those parvocellular neurons.
The koniocellular cells of the lateral geniculate nucleus do something just a
bit odd. They don't project to layer four at all.
Rather, they send their axons up into layer three, where they synapse in the
zones that are rich in oxidative metabolism.
And you may have heard about them. If you're more familiar with visual
cortical anatomy or physiology. They're called blobs.
literally blobs of high enzymatic activity for oxidative metabolism.
So this is an example of parallel processing.
We have a small cell pathway that's concerned especially with form and with
color that runs through the parvocellular layers of the lateral
geniculate nucleus, and into the bottom of layer 4, 4c beta.
There is a large cell pathway that runs through the magnocellular layers of the
lateral geniculate nucleus. It's not particularly concerned with high
special detail or color, but rather it's concerned with broad patterns of notion
and this signal is terminated in layer C4 alpha just above that parvocellular
termination. And what about the koniocellular layers?
Well, these are the more mysterious of the lateral geniculate nucleus layers.
It's, they've been not as well studied but they do devise to this very peculiar
projection up until layer three. And we think these koniocellular cells
May have a particular role to play in color vision.
But that remains an issue for ongoing investigation.
Now you may be wondering what happens to these parallel pathways once we get
beyond the primary visual cortex. Well this remains a matter of active
investigation, it was very attractive to assume that the parallel organization is
highly conserved. And rather quite rigid.
I think we now know that that's probably not the case.
That there's likely to be some mixing of information from one parallel pathway to
another. Nevertheless when we look beyond the
primary visual cortex, it's possible to recognize two broad streams of processing
that emanate out from the primary visual cortex through a set of areas that we
call extrastriate visual cortex. so recall that that striavginary helps us
to recognize a cortex that we call the striate visual cortex, area v1.
And then beyond that we see these concentric zones of cortex almost like
concentric rings that surround our primary vision cortex.
And it was attractive to call them areas of ET, B3, and B4 and so on.
to emphasize our presumption that they represented progressively higher levels
in some kind of visual hierarchy. well that to remains an object of ongoing
investigation. Nevertheless, it is safe to conclude that
beyond our primary visual cortex There are rings of higher order visual areas.
Now what we're looking at here on the right is a cortical representation as if
it were possible to peel off the cerebral hemisphere, flatten out the cortex and
then map out these visual areas. Well, in order to make that hemisphere
flat, we have to make a cut along the cortex in the calcerine sulcus so that we
can relax this three-dimensional shape into a two-dimensional sheet.
And that's what we're looking at here. Now I want to draw your attention to a
particular location. Which is found out here in the inferior
border region between the lateral temporal cortex and lateral occipital
cortex. It's where we find a couple of visual
areas that we call area MT or sometimes we call it the MT plus region.
And this is a area that was named for the corresponding location in the macaque
brain, where a middle temporal visual area was discovered that is enriched in
motion sensitive cells. So this region, area mt, which is roughly
in this position in the human brain, likewise.
Seems to be especially enriched in motion, in motion sensitive cells.
And in fact, it's from the circuitry here in this area mt plus that we derive our
notion of motion. As our chairman of neurobiology here at
Duke University likes to say So this is a higher order visual area that represents
the kind of specialization that we encounter as we get further away from our
primary visual cortex. From this area, mt, these motion signals
seem to inform a spatial analysis of the visual world.
That is happening in the parietal cortex. So we can think about this parietal area
as addressing the question: where am I looking, or where are the objects that
I'm looking at that happen to be in motion?
So this, this dorsal parietal stream, as we sometimes call it, is about Mapping
the world. Achieving a spatial analysis of motion
patterns. It's not particularly concerned with
detail, with form, with color. With the recognition of faces.
Or the identity of objects that we happen to be observing.
Those kinds of functions happen along a ventral processing stream.
That emanates from the primary visual cortex through its near higher order
areas and then out into the inferior temporal lobe.
So this process extreme addresses the question, what am I looking at?
So, we have our where and our what pathways.
Where going dorsally through the[UNKNOWN] lobe and then what.
Running ventrally through the temporal lobe.
Now you can imagine with this functional dichotomy that people can have brain
injuries in the parietal pathway or the temporal pathway.
And have deficits in one domain of visual function or another.
And that is exactly what is seen People can have injury that result from let's
say, stroke or tumor or trauma that affects this where pathway.
And consequently, there may be deficits in understanding spacial awareness in the
world around us or perhaps very particular deficits in building a notion
of motion. On the other hand, there may be strokes
or other kinds of brain lesions affecting the what pathway in the inferior part of
the temporal lobe. Those kinds of deficits can be quite
particular affecting our ability to answer this question: what am I looking
at? Or in human relations, who am I looking
at? There's a particular region of this
posterior occipitotemporal gyrus in an area that's sometimes called the
fusiform gyrus where, when damaged leads to a deficit in the Ability of people to
recognize faces. It's called prosopagnosia which means
face blindness or not knowing the identity of human faces.
People with such injuries will have problems of recognizing the faces of even
loved ones, even their spouse or their near family members.
So it's really quite a, quite a tragic situation for those individuals and you
can imagine how devastating that must be to their social relations.
Now thankfully we acquire other cues besides the visual that assist in
recognition and these individuals get along reasonably well using these
alternative cues Never the less, they remain impaired in their ability to
understand and recognize the visual features that we associate with the human
face. Now, it's important to emphasize that
these people, that they're actually they're not blind.
What they fail to do is take the structure of the visual image.
That is reflected off of the human face and interpret that in terms of the
identity. Nearby regions of this ventral or
inferior visual pathway likewise seemed to represent other kinds of, of objects
that we encounter in our world, perhaps inanimate objects.
So one might be able to see but not be able to recognize.
Well, this concludes this tutorial and this tour of visual processing.
I wish we could spend more time on this topic, I think as you've picked up today,
this is an issue that has been of concern in my own academic life and I'd love to
share with you more of my research, perhaps I'll have a chance to do so when
we move on a little deeper into the course.
So, I'll leave you here for now and look forward to speaking with you next time.
Durchsuchen Sie unseren Katalog
Melden Sie sich kostenlos an und erhalten Sie individuelle Empfehlungen, Aktualisierungen und Angebote.
Coursera arbeitet mit erstklassigen Universitäten und Organisationen zusammen, um Online-Kurse anzubieten und dadurch universellen Zugriff auf die weltweit beste Ausbildung zu ermöglichen.
© 2019 Coursera Inc. Alle Rechte vorbehalten.
