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.
Temporal Associational Cortex: Language, part 1
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From the course by Duke University
Medical Neuroscience
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From the lesson
Complex Brain Functions: Associational Cortex
It may surprise you to know that in all of our studies of the neural systems for sensation and action, we have yet to properly account for the organization and function of roughly 75% of the entire cerebral mantle. Thus, only 25% of the cerebral cortex is accounted for by the modal sensory and motor cortical areas. The majority of the human cerebral cortex is multi-modal cortex that associates signals derived from one or more modal systems. We now turn our attention to this “associational cortex” as we consider more complex aspects of brain function.
Meet the Instructors
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
Well, we need to move on and consider one other domain of function associated with
the temperal lobe and that would be language.
again, another facinating topic. We could have a whole course just
devolted to the brain and language. Well, in fact, we do.
We have courses here at Duke University on this very topic.
So my aim with you rather is to simply give you some of the basics that you need
to understand functional localization in the human brain.
Well, humor me for a moment, will you? And let's test your facility for the
recognition of words, at least in presentation in English language form.
So, let's read together the following text.
According to research at Cambridge University it doesn't matter in what
order the letters in a word are the only important thing is that the first and
last letter be at the right place. The rest can be a total mess and you can
still read it without a problem. This is because the human mind does not
read every letter by itself but the word as a whole.
Well for those of you who may not be native English speakers, perhaps you've
struggled a little bit with this challenge.
But you can create your own such text in your native language and demonstrate for
yourself and your friends and your family really this amazing facility of the human
brain. To take these arbitrary visual symbols
and interpret them with meaning and semantic content.
And to run them through our language circuit in a way that allows us to
produce the articulated vocal sounds that are associated with these relatively
arbitrary visual symbols. Well, this is evidence of the amazing
facility of the human brain for manipulating symbolic representation
derived from sensory stimuli and using it to communicate complex ideas and complex
thought in the form of speech. So how does this work in the brain.
Well, there are regions of our associational cortex primarily in the
left hemishpere that are responsible for such amazing linguistic feats.
Two regions in particular we need to discuss for just a few moments.
One, we find associated with the lateral part of our temporal associational
cortex. And this is named after a German
physician, Carl Wernicke and most of us in the west will pronounce that as
Wernicke, Wernicke's area. And it is often found in the superior
temporal gyrus. Roughly the posterior 1 3rd of the
superior temporal gyrus. But I think the reality is, is that there
is not a single module in this lateral temporal cortex that we can identify as
Wernicke's area. Rather I think we need to understand that
there is probably vast network. Of nodal points that are critical for the
recognition of these sensory stimuli and their interpretation their encoding in
terms of semantic contact. So the actual critical nodes in this
network. Maybe found in any one of a number of
places. And indeed for those of you that are
bilingual or multi-lingual, you may have distinct nodal points that represent
meaning the language that is native to your personal life history.
Some of you I'm sure can communicate using the symbols and gestures that we
call American Sign Language. And for the representation of those
sensory stimuli there may yet another set of key nodal points that establish an
associational network here in this lateral temporal cortex.
So in, in my view and I think this is the view of the neurosurgeons that actually
map out these regions in the human brain. There's unlikely to be a single region
that is consistently localized in every human brain that we can label as
Wernicke's area. Rather at least the job of the
neurosurgeon will be to figure out what are those key nodal points in the
networks that represent the semantic knowledge that you operate with.
that are essentially, untouchable from a neuro-surgical perspective that is.
The key nodes that the surgeon is trying to identify so that she or he can
preserve those nodal points during the course of an operation.
So from this point I think this figure from our book is just a little bit
misleading. I would suggest that there's not a single
modual that we can vocalize and call Wenicke's area.
Rather I believe that there is a more extended network in the associational
cortex of the lateral temporal lobe that is processing these sensory symbols that
are derived primarily through vision and auditory senses.
And then interpreting them and applying semantic meaning to those sets of
symbols. And this network then does the job of
encoding the meaning of these symbols. And in terms of language function, this
is where the understanding or the comprehension of language is built up in
the human brain. So I think you can understand what might
happen then if there would be some damage to key nodes in this lateral temporal
associational network. One might still have the capacity to make
speech but one would expect severe impairments in the ability to comprehend
speech. Now our focus in this session is indeed
on the temporal associational cortex. But I can't help but to jump across the
lateral fissure and get into a inferior lateral region that we call Broca's Area.
Broca's area as many of you know, is an area that is involved in the production
of speech. Broca's area was named after Pierre Paul
Broca who described a patient with damaged this part of the brain and in
life following this injury, the patient was severely impared in his capacity to
make speech. Now, we now understand Broca's area
really as part of a premotor cortical network.
You recall, we described a mosaic of frontal cortical areas that are
associated with the planning of movement. Especially movement that's directed away
from personal space. So this aspect of, of planning for
movement also applies to the governance of our vocal articulatory apparatus in
our throat. Our larynx, our pharynxy the coordination
of our breathing muscles. So, this is, in a sense, a premotor
cortex that interacts closely with the nearby regions of the precentral gyrus
that have upper motor neuronal control over our vocal motor apparatus.
So from that standpoint we can understand Broca's area as a premotor cortex for
vocal articulation. But it's not just for vocal articulation,
Broca's area also seems to be involved with the production of written language.
Which would have it affiliating with not just the lateral segment of the
precentral gyrus but also the middle segment of the precentral gyrus that
governs the movements of the distal upper extremities.
The part of our body that we use to write with.
So damage to this part of the inferior frontal lobe, specifically what we're
referring to is the posterior one-third of the inferior frontal gyrus.
And, there are various subdivisions of this part of the inferior frontal gyrus
that we could identify. I think from neural surgical procedures,
it seems clear that there may be, a set of nodal points within the networks of
this posterior inferior frontal gyrus. That are critical for the expression of
language. So again like Wernicke's area is not a
single module that we can point to and identify.
I think the same is likely to be said of Broca's area although the localization
seems to be much more consistent from one person to the next.
In our brains than would be Wernicke's area in the lateral temporal cortex.
So here's roughly the location of Broca's area in the human brain and this is a
region that if damaged can produce a severe impairment in the fluency of
speech. With an understanding then that Broca's
area can be conceived of as an essential premotor network for the production of
speech. One can imagine that damage to Broca's
area would lead to a severe inability to produce speech.
Not just speech in oral form but also the written language will also be affected
with damage to Broca's area. So it's critical for anyone headed
towards a career in health professions. Or indeed practising in health
professions to be able to differenciate between two forms of impairment that are
associated with these critical language areas in the human brain.
So an impairment of language function is called aphasgia and if the impairment is
afflicting the lateral temporal cortex then we call this Wernicke's aphasia.
If the injury is to the inferior frontal gyrus then the aphasia that we would
expect is called Broca's aphasia. So let's differentiate these two
conditions. So the key differentiation between these
two forms of aphasia is that with injury to the inferior frontal gyrus in Broca's
aphasia, comprehension is intact. But there is a severe impairment in the
fluency of speech. Whereas with Wernicke's aphasia, the
situation is somewhat reversed. There is fluency of speech.
But the capacity for comprehension is severely impaired.
Now these two parts of the brain. The lateral temporal associational cortex
in the inferior frontal gyrus are interconnected by white matter structures
that span this space within the brain. Between this temporal lobe around the
lateral fissure of the brain and into the posterior part of the inferior frontal
lobe. One can have damage of those white matter
pathways. And see some combination of these
deficits that reflect the failure of communication between this
lateral/temporal associational cortex, and the inferior frontal gyrus.
One might also have. Let's say a stroke involving the higher
distribution of the middle cerebral artery and have a global aphasia that
affects both the lateral temporal associational cortex and the inferior
frontal gyrus. So while it's possible to have one type
of aphasia or the other. One can see elements of both or one can
see a global aphasia impacting all aspects of language function.
Now since we're talking about aphasia and Broca's aphasia in particular, I just
can't help. But to point you to a fantastic video
that, was, juried and awarded, the grand prize in our inaugural, brain awareness
week video contest sponsored by the society for neuroscience.
And, this is a beautifully produced and just wonderfully rich.
story told by our graduate student in the field of neuroscience from Australia.
Her name is Shiree Heath and she's telling the story of her grandfather's
stroke who suffered from a Broca's aphasia.
So I would encourage you to just take a few minutes.
Navigate to this page at brainfacts.org. And you can search aphasia or The
Treasure Hunt, which is actually the title of this short video.
And, I think you'll agree with the judges of this contest that, Sheree was.
very much deserving of the grand price, given her insight.
Given the accuracy of the neuroscience in her presentation.
And of course her marvelous creativity with which she pulls all this together.
And in the end you'll get a change to explore and reinforce some of what we've
been talking about here recently about the language centers of the human brain.
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