Well, one dimension of attentional processing in the parietal lobe that has garnered quite a bit of interest by clinicians, but also by cognitive neuroscientists, refers to a, an asymmetry of attention that is often revealed in patients that have damage to the parietal associational network, particularly when that damage is localized to the right hemisphere. Now, I really hesitate to do this because for a variety of reasons, I'm uncomfortable representing a patient or pretending to be a patient with impairments that I don't actually have. I think that's a complex business and I don't do it lightly. But I do want to illustrate for you a couple of simple clinical tests that are used to assess the possibility of there being an attentional problem with patients with parietal lobe injury. So here's a very simple test. And this test simply is to bisect the middle of the line. So, presumably, you and I would survey the challenge and just draw a line somewhere around there. Well, this is what a normal person would do. But an individual that has a condition that we call hemineglect syndrome might be inclined to put their line somewhere over here. so there's a significant rightward shift in the perceived assessment of the center of this line. Well, here's another challenge, a little bit more demanding. which you may find yourself doing with some patients depending upon their capacity to, to move and articulate their drawing hand. But you might ask this patient to simply copy a scene. So here's a photograph of our fabulous Duke Chapel that we have here on campus, that I took not long ago. And I may be asked to copy this scene. And if I were such a patient that had parietal lobe injury, I may look at this and I may say, okay, well my attention is certainly drawn to the chapel tower. And I may begin to do something like this. may look a little bit more detailed. There's some shadow in here. Well, there's some trees in the foreground, so I'll try to represent that somehow, and I'll, you know, maybe continue to add some detail over here. And as my visual gaze, my visual search is changed, I might eventually come over here. I might add a few of these spire details. I might return and draw some more shadows in here. And I think you, basically, get the idea that what I am inclined to do is to illustrate features that are largely present over on the right hand side of this scene. Without providing much detail, if at all, for what might be left of the midline of the actual visual scene. Okay. Here's one additional test that often is quite striking and sometimes, frankly, somewhat disturbing when this is observed. You've probably noticed that I have a clock on my wall and you've heard the ticking over our time together. There's my clock. I hope you can see the blue devil on the face of the clock. Well one can be asked by a clinician in a simple test to simply draw the clock face. So, obviously this can be done by a person with an intact nervous system. They will draw a circle, and they will being to think about, okay, well, what does a clock look like? Well, the number 12, at least in our Western cultures, is up above, six is to the bottom, three is to the right. Nine is to the left and so on. And someone might be asked to draw a time like, not a clock, and you'd say, okay, well the large hand is pointing towards 12 and the shorthand is pointing towards 9. There is 9 o'clock. Well, if one were to ask a patient to do the same challenge that has had damage to their parietal associational network, especially on the right hemisphere. Here's what one might draw. One might know perfectly well that the clock face is round. There are numbers 1 through 12. So number 12 is on top. Now, what the patient very well might do is to place all of the numbers from 1 to 12 on the right hand side of the clock face. [SOUND]. And if asked to demonstrate 9 o'clock, the knowledge of the position of the hands might direct the patient to make a drawing that is clearly incorrect in some way, but, but also clearly correct in terms of the rules about where the large hand and the small hand of the clock would be pointing. Well, these are just some simple representations of what a patient that has had damage to the right parietal lobe might present on simple clinical evaluation. Of course, there are many more sophisticated means of daring/g, doing diagnostic neuropsychological testing that's beyond the scope of my presentation here. Rather, I want to emphasize to you simply the functional localization of damage that produces this so-called contralateral hemineglect syndrome, often called left hemineglect syndrome because it's most frequently, the left side of body and world that is the object of neglect. Well, here's a simple compilation of a series of patients that have presented with Hemineglect syndrome. And as we can see, there seems to be a region of overlap that is focused here in the inferior parietal lobule of the right hemisphere. That's not to say that damage of this region is necessary to produce a hemineglect syndrome. Indeed one might have damage to the frontal cortex, perhaps damage into the temporal cortex, that can be associated with hemineglect syndrome. But the most common network that is impacted with brain injury that results in the Hemineglect syndrome seems to be focused right here in this inferior parietal lobule of the right hemisphere. And for those of you that recall the actual gyri of this region we're talking about an impact on the sup-, supramarginal gyrus. And just behind it, the angular gyrus. [BLANK_AUDIO]. Well why should this be the case. Well, we think this is the case because in all of us there is very likely an asymmetry to the attentional functions of our parietal associational networks. And that asymmetry is illustrated with these ray lines that are shown in this illustration from our textbook. Notice that, for the left parietal cortex, attention is focused across the midline to the right side of the visual world. However, for the right parietal cortex, attention is distributed throughout the entire visual field. There may be a bias towards the contralateral side. That is, attention may be focused more particularly on the left side of the visual world than the right, but there does seem to be an asymmetry. this can be revealed in functional brain imaging studies where subjects are directed to attend to one side of the midline or the other. And what we discover is that, when subjects are directed to attend to the left side of the visual field, the right parietal cortex increases its functional activity. However, when subjects are directed to attend to the right side of the visual field, what we find is much more bilateral activation of the parietal associational network. Well, there are consequences of this asymmetry for patients that have damage. For example, imagine a patient that has had damage throughout the right hemisphere, including, of course, that inferior parietal lobule of the right side. One might expect a severe neglect of the left side of the visual world because we've now taken out the capacity of that parietal network to direct attention across the midline. One might still have a capacity to attend to the right side of the visual world, because of preservation of the left parietal network and its ability to direct attention to the right side of the visual scene. Now i'ts much more common to find left hemineglect than it is right hemineglect. And, again, this is reflecting the fact that with damage to the left parietal associational network, there is still the capacity to direct attention to the right side of the visual world. And that, again, is related to the fact that this right parietal cortex also can direct our attention to the ipsilateral field, that would be the right field, in addition to its capacity to direct our attention to the contralateral or to the left visual field. Now, I've been emphasizing vision and visual field, but I want to make the point that hemineglect is not just about vision. It's not just about seeing the world on the outside. Patients with contralateral hemineglect may also fail to appreciate The significance of their own body parts that are on the left side of the midline. imagine the challenge of rehabilitating a patient that perhaps has had a stroke involving the right middle cerebral artery, that may have affected sensory motor control of the left arm and hand. So this patient is in need of nerve rehabilitation. But, should there be a hemineglect syndrome due to damage of the nearby right parietal associational cortex. This patient might actually deny impairment of that left arm. Furthermore, the patient may not even recognize that left arm as part of themselves. [BLANK_AUDIO] You might even find the disturbing situation of a patient who gets up in the morning and only dresses the right side of their body. It's hard to imagine what might be going on in the networks of a person with such an injury. It's not that they have a visual deficit, it's that they fail to appreciate that what is here actually belongs to them. There are certainly stories in the medical literature of patients who have assumed that this body part belongs to someone who must be behind me and sticking their left hand in my visual field. Well, I think what this does is it goes to illustrate that the concept of self, the brain's construct of the body's image is, in fact, the product of associational networks that are largely localized to the parietal cortex, but, of course, also extend throughout each of the lobes of the human brain. Including the networks that are localized to the insular cortex, which are mainly concerned with our internal visceral state. Pardon me for baring a little bit of my skin. I hope that wasn't offensive, although I suspect it may have been to some. But maybe that will help emphasize the importance of appreciating the associational functions of the parietal cortex with respect to attention. Well the last point that I'd like to emphasize with you before we conclude is that indeed the parietal cortex is critical for building this body image, this body schema, this neural concept of self. You know, perhaps one fact of our existence that we most often take for granted is that our brain is embodied. We are embodied cognate creatures. That is to say that our sense of self is intimately related to this body that we use to interact with the world around us. And that sense is subject to injury and disorder, with damage to the posterior parietal networks. And this can lead to some rather bizarre and intriguing phenomenon, as we've already discussed some, with respect to phantom sensations, when there is nerve injury or limb loss. And now, we see the hemineglect syndrome, which reflects also a disordered body schema. And this can present in very extreme forms that some of you may want to go read about, including people that seek surgical amputation of body parts. Evidently, because in their evaluation, they would be more complete as a person, as self, without that body part attached. Very likely, these are people that have dysfunction and disorder, perhaps disease, afflicting the associational networks that produce this sense of self embodied in the the networks of our poros-, posterior parietal cortex. So I'll conclude this tutorial now and when we resume, we'll be looking into the associational networks of the temporal lobe. So, thanks for listening and I will see you next time.
