Welcome back to Medical Neuroscience in Unit Six, Complex Brain Functions. In this tutorial, I'd like to explore together with you the associational cortex of the temporal lobe. This topic pertains to two of our core concepts in the field of neuroscience. We are exploring the associational cortex and its from these vast networks of cortical regions in the human brain that intelligence arises. These are the parts of the brain that are in significant ways responsible for our capacity to reason to plan for the future, and to solve problems. This is also the networks of brain regions that gives us the capacity for curiosity. And this is what has driven us all together as a learning community, and for that I'm very grateful. Well, my learning objectives for us in this tutorial are to discuss the major functions, that are localized to the associational cortex of the temporal lobe. I want us to be able to focus on a few of those functions in particular, one of them will be human memory. So I want us to differentiate categories of human memory and discuss the relevant neuroanatomical systems that support these different forms of memory. I want us to focus a bit in this tutorial on language. And how language function is represented in the brain. And there are two very famous parts of the brain that we'll discuss today Broca's area and a region that we call Wernicke's area. And I want you to be able to differentiate the functions of these two different regions and how they contribute to language function. And also differentiate the problems that people who experience injury to these brain systems experience. So I want you to be able to differentiate the aphasias, that's the medicalise term that we use to describe language problems. Associated with one of these regions or the other. So objective three is to differentiate Broca's and Wernicke's aphasia. And then finally, our fourth learning objective in this session is to focus on the concept of dementia. dementia is a syndrome that characterizes a disordered cognition. So I'd like for us to think together a little bit about, Dementia. And just very briefly discuss the most common cause of Dementia. That would be Alzheimer's disease. So I want you to be able to relate the various signs, of dementia to specific regions of the associational cortex that we're now learning about. Well, let's begin again, as we did in the last session by just considering the distribution of cortical areas in the cerebral mantle. And the basic point to bear in mind is that as we describe associational cortices. What we're really concerned with is the vast stretches of the cerebral cortex, that are between the primary sensory and primary motor regions. So this really accounts for, again, about 75% of the entire cerebral mantle that is present. And the two cerebral hemispheres. While much of unit three of the course was focused on sensation and sensory processing. We really hadn't yet gotten into, a full description of how for example the sematic sensory cortex feeds signals into the perirtal association cortex and likewise. we've only briefly touched on how the visual cortex feeds signals into the parietal associational cortex as well as the Temporal association of cortex. Well, today, we're going to be talking about the temporal lobe. So we could easily spend entire sessions, just on several of the important functions that are associated with this temporal cortex. so, unfortunately time and space does not allow But I hope to give you at least a bit of a feel for some of the important aspects of cognition. That are dependent upon the operation of networks that we find in this temporal association cortex. And I, I hope to wet your appetite. And I hope that that appetite will be satiated in other learning experiences might pursue should your interests lead you in that direction. Okay well I think we're ready to, begin our discussions of the temporal associational cortex focusing on one particular domain of function at a time. And so what I'd like to turn our attention to now really is the associational cortex that we find on the inferior surface of the brain. And it's here that we have networks that are receiving input, largely from the visual system. But also from the auditory system, that are responsible for building up our ability to recognize a sensory stimulus. Be it a simple sensory stimulus, such as the shapes that define an object in the visual field, or something more complicated, like a human face. So, let's turn our attention, then, to the inferior portion of the cerebral cortex that we find here, on the temporal lobe. And it's there in the human brain that we find these regions that have been well studied in nonhuman primate models. And what I'm referring to here is this Ventral object recognition pathway. You may recall that we spent just a little bit of time talking about this when we considered the central processing of visual signals in unit three. And what I described for you is the elaboration of a series of higher order visual processing centers. As one progresses from early visual cortex, that would be our first primary visual cortex. Brodmann's area 17, Brodmann's area 18, our secondary visual cortex. And then from here signals are sent down through a network of regions that are in the inferior part of the temporal lobe. Now, just so that we get the anatomy straight, in the nonhuman primate, these regions are associated with the inferior temporal gyrus. In the human brain, these regions tend to be more on the ventral aspect or the inferior aspect of the temporal lobe. The inferior temporal gyrus contributes to this network, yes, but in the human brain, there are additional regions that I'd like to highlight for you. Namely associated with the lateral, occipital, temporal Gyrus. And if we look at my model of the human brain, what I'm really talking about is the region of the temporal lobe that we find on the ventral surface of the brain. We see just a little bit of the relevant region just peeking in the anterior side of the cerebellum. But to really talk about what we have in view here I need to actually do a little dissection here of this model. So, I can remove the cerebellar hemispheres and show you what I'm referring to. Actually, I'll just remove the one on this side and highlight the gyral formations that we find here on the Inferior side of the temporal lobe. And specifically there's a long gyrus that runs the extent of the inferior aspect of the temporal lobe down into the occipital lobe called the occipital temporal gyrus. Or sometimes lateral occipital temporal gyrus. And this is where we find this ventral visual processing stream in the human brain. In fact, there's a region of the posterior part of the lateral occipital temporal gyrus that's sometimes called the fusiform gyrus. Because of its, shape that's often seen in many human brains, a spindle type shape or a fusiform shape. So, that's where we find these regions in our brains. And when we look at an image of a non human primate sometimes. we get perhaps the erroneous impression that the relevant areas are somehow out here on the lateral aspect of the temporal lobe in our brain. That's where we would find networks that have more to do with understanding language than visual recognition. So I just want us to be clear about that anatomy. In fact, if you'd like to have a look at the human brain again, I might encourage you to view our tutorial session from unit one. Looking at the ventral side of the human brain. In fact, it would be awfully nice to have a quick look at that right about now. So, hm, I wonder what the human brain actually looks like. >> So, this bit of brain is the temporal lobe. And on its inferior surface we have a long gyrus that extends throughout the length of the inferior temporal lobe back towards the occipital lobe. That's called Occcipitotemporal Gyrus. Sometimes there's a small surface that divides it into a lateral and medial components. And then along the medial edge of the temporal lobe, there's a structure that we call the Parahippocampal Gyrus. And deep in the anterior part of the temporal lobe in this position this parahippocampal gyrus folds in upon itself. Into a structure that we call the hippocampus. And we'll see the hippocampus when we look at sections through the brain. Now, the occipital temporal gyrus and the parahippocampal gyrus extend down into the occipital lobe. And at some point In the occipital lobe, we define a region that is a boundary between the Lingual Gyrus, near the midline. And what remains here of the occipital temporal gyrus. Sometimes, this region of the Inferior occipital lobe is called the fusiform gyrus because of the superficial shape. That is sometimes appreciated as these cell sites come together. Well, that was a nice refresher. It's always to, pleasant to be confronted again with the actual form of real human brain specimens. As we continue to improve in our mind this mental image of the structure of parts of the human brain that otherwise we might not explore in great detail in this course. Such as this inferior aspect of the temporal lobe. Well, so let's talk a little bit about the actual recognition pathway, itself, that we find here. Well in non human primates, this has been very well studied using stimuli that we think would be meaningful to a non human primate. but, of course, what we'd really love to do is be able to characterize the function of these regions in our brains. And we've been able to do that with our brain imaging techniques, such as functional Magnetic Resonance Imaging. And when these experiments have been done, what is quite clear is that there are regions in this Inferior temporal lobe. Again, associated with this so called fusiform gyrus region that seem to become especially active when we are confronted with a human face. So a human face is a wonderful stimulus. for us, as social creatures, and indeed, for many nonhuman primates as well. The human face provides a complex visual structure that conveys great meaning, and that meaning is often best understood in a social context. However typically, an important step towards interpreting that social context requires the recognition of the identity of that face. we want to know is this face a friend? Is it family? Is it foe? And these recognition events are what lead us towards an understanding of the intentions of this person who's confronting us. So recognition is a key function of this inferior temporal network. Especially when it comes to visual information, and especially for us, when it comes to the human face. So these are examples of the kinds of specialized networks that we find in this inferior temporal lobe. There is a network that seems to be especially responsive to faces. There are others that might actually be specialized for the recognition of inanimate objects of various types. And there may be multiple categories of object recognition networks that we may find in this aspect of the human brain. this remains an active area investigation, and, it's really a fascinating field to follow. So, if you're interested in recognition and in human faces in particular, I would encourage you to get into this, aspect of neuroscience. At least, through study of the literature. And, it's a rapidly evolving field. And as you might imagine, there's a lot of interest in understanding how it is that we come to recognize and interpret meaning in these complex stimuli. Especially those associated with the face and facial expressions. Well, as we've been discussing throughout our sensory and motor systems. one can experience particular neurological signs and symptoms with damage to these cortical networks. And in this case, damage to these recognition pathways can lead to a phenomenon that we call Agnosia. Agnosia is a Greek term that means, not knowing. And it can be modified by a variety of prefixes that describe the specific modality of information that is missing from the cognitive awareness of the subject. And in the case of this region that seems to be specialized for the recognition of human faces. Damage to this inferior temporal cortex can lead to an inability to recognize a human face. This is called Prosopagnotia, which, to expand upon, the Greek there and those of you that, are, native speakers. Perhaps you can chime in with additional nuance of the fantastic, detail and beauty of the Greek language. But for our purposes, we can define prosopagnosia as not being able to recognize the personhood that is represented by this stimulus, this sight of a human face. But let's get back to the non human primate model. Because I'd like to show you some data that helps us understand why prosopagnosia would occur with damage to this part of the brain. some years ago now, dating back to the early 90s, neuroscientists began to record from neurons and this inferior part of the temporal lobe. And again in the nonhuman primate, the relative regions would be in the inferior temporal cortex associated with this inferior temporal gyrus. And it was discovered that neurons could be found there that were responsive to visual stimuli. But not simple stimuli like moving lines and, and patterns and textures. But more complex stimuli that often conveyed, some understanding of the world in which we interact with. And certainly for nonhuman primates an important stimulus for these higher order associational areas is the sight of a face. And what was perhaps surprising is that neurons responded vigorously well to not only the presentation of a conspecific face. But also to the presentation of even a human face. So here are post-stimulus time histograms that show us the responses of a neuron to the presentation of facial stimuli. Which is indicated by the presence of this green bar in the background here. So, it's quite interesting to note that variations in the details of these faces such as the face presented in trial 1, trial 4, and trial 5. still a list of vigorous responses even though some of the details have been changed. But when the elements of the image are changed such that we don't recognize the stimulus as presenting a cogent human or nonhuman primate face. Then the response is severely diminished. That would be what we see here, for example, in trial number 2, where the elements of the face have been scrambled. Now, quite interestingly, in trial number 3, there's still a vigerous response in this neuron. Perhaps not as much with a full view of the face, but it's consistent with our capacity to fill in the missing details. And still achieve the job of recognition. So, trial 3 actually makes a pretty good case for this neuron being interpreted as involved in recognition of the stimulus. Rather than in the details of the textures, and the orientations, and the movements of the elements that comprise that phase. Those would be more lower order visual cortical functions. here in the Inferior temporal gyrus and for us, in that lateral occipital temporal gyrus, these neurons are recognizing the identity of this face. Now, of course, it's a bit more challenging to understand, what this might mean for a nonhuman primate. But one can do additional variations of these experiments to try to understand more about coding of faces in this part of the brain. One experiment that has shed significant light on the way information is coded here has been to vary the view of the face from a full frontal view to a full profile view. And what was discovered is that, there are indeed neurons that seem to be selective for particular views of the face. So, for example, in this figure from your book. We find recordings from a neuron that seems to prefer these profiles of use here in trials 4 and 5 compared to the full frontal view in trial number 1. So why would that be important? Why should you want to be able to recognize the face in profile versus the face in frontal view. Well, there may be quite different kinds of social cues conveyed, via a frontal view of the face compared to a lateral or profile view. One can interpret intention through the frontal view in a way that is perhaps less clear with a profile view. On the other hand, understanding a profile view of a face, can convey it's own meaning. one might be interested to know, what is this individual looking at? Perhaps there is something that I might want to look at. So, we continue to build up this model of intentionality, based on the social cues that are associated with the face be it a frontal view or a profile view. So, I think it makes a certain amount of sense that we ought to have some selectivity in the ability to recognize not just the presence of the face. But the meaning that is presented in, in that face.
