What is Agnosia and How Does it Affect the Brain’s Perception?

Episode Transcript

Dr. Daniel Correa:
From the American Academy of Neurology, I'm Dr. Daniel Correa. This is the Brain & Life podcast. This week it was so great to have our guest host, Dr. Sarah Song. She interviewed Dr. Roy Hamilton. Sarah, how did that interview go and how have you been?

Dr. Sarah Song:
I have been great. Thanks for asking. It was so wonderful to talk to Roy. He is truly an expert in how the brain works and the fascinating ways that the different parts of our brain connect to bring us a new reality that we all experience.

Dr. Daniel Correa:
A new reality? Wow, okay. There's so many different things that we experience in the world, whether it's touch, sensation, smell, taste. In TV and in movies, there's all this thing of our connections and sensations even to computers, like The Matrix or Avatar. So our brain helps us process all that information. You got into that with Roy?

Dr. Sarah Song:
We totally did. And I love the connection to something like The Matrix where what you're seeing may not be what other people are seeing. So you are seeing one thing, somebody's seeing another thing. What is the truth? How do we reconcile what the truth is of what you're seeing with what I'm seeing?

Dr. Daniel Correa:
And this term that's an alteration or an injury in this perception is the topic for this episode, agnosia, right?

Dr. Sarah Song:
That's right. So agnosia, Roy really brought it back to the roots, like the Latin roots of a word, which essentially means no knowledge, which is a stark term, but it really gets to the heart of what do we know and what do we know to be true.

Dr. Daniel Correa:
We're looking forward to bringing you guys this conversation. Sarah talks with Dr. Roy Hamilton about different types of agnosia, the different causes because it's not just one thing. It's not a condition or an injury itself. It can be a symptom of many other things. Sarah, thank you so much for bringing us this episode.

Dr. Sarah Song:
It was my pleasure. Thanks for having me on.
Hi there. I'm Sarah Song. I'm a stroke neurologist at Rush University Medical Center. I'm also the associate editor of Brain & Life. And I'm delighted today to have with me Dr. Roy Hamilton. He is a professor in the departments of neurology, physical medicine and rehabilitation and psychiatry at the University of Pennsylvania where he also directs the Laboratory for Cognition and Neuro Stimulation.
He is a classically trained, clinically trained behavioral neurologist and cognitive neuroscientist and has been conducting research into how the brain works and processes information since the late 1990s. We are so delighted to have him today to talk about agnosia.
So agnosia, some of our listeners might not know what it is. Can you tell us in your own words what agnosia is?

Dr. Roy Hamilton:
So agnosia, if I could just break the word apart, A, the first part of the word, which basically means the absence or the lack of something, something's missing. And gnosia or gnosis is basically knowledge or understanding. And so when somebody has agnosia, it's that they have the absence of a knowledge or an understanding.
And so when we use that term, what we usually mean is that someone is able to perceive something with their senses. They're looking at it or they're listening to it or they're touching it, whatever it is, and on some level they can sense that something's there, but on some other level they're unable to recognize it, understand it or otherwise make sense of it. And so it's that ability to perceive something with the senses without really recognizing or knowing what you're perceiving.

Dr. Sarah Song:
I love the fact that you broke it down. And I think that it encompasses a lot of different ideas because the lack of the knowledge, do people with agnosia know that they have agnosia?

Dr. Roy Hamilton:
There are many kinds of agnosias. I would say that for many kinds and for certainly some of the kinds that we'll talk about, the ones that are very well known, individuals have a sense that they lack some type of knowledge or understanding of some category of perception. But there are in fact agnosias where part of the problem, part of the thing that you are not perceiving or understanding is your deficit, that you have a deficit.
Actually, I don't want to wade too far into the weeds, but there's a special kind of agnosia for that where the thing you are not perceiving is the fact that you have a problem. But for many individuals who have agnosia, they are acutely aware that there is something going on with their ability to transform their perceptions into an understanding of what they're looking at.

Dr. Sarah Song:
That is so interesting. You referred a little bit to timing. Is agnosia something that develops slowly over time or is it something that happens suddenly? What can affect the timing of developing agnosia?

Dr. Roy Hamilton:
Well, like so many things having to do with the brain and certainly so many things in behavioral neurology, it isn't so much about the timing so much as it is about the real estate. In other words, as I'm sure many listeners know, different areas of the brain are useful for different operations, different aspects of what we do every day.
And so like many syndromes having to do with behavior, the agnosias arise when you have injury or something affects parts of the brain that are important for this transformation of sensory perception into recognizing and knowing things in the world. And that thing, whatever that thing might be, it might be a sudden thing, it might be a stroke. It might be a much more gradual thing, it might be a neurodegenerative condition.
In some cases it may have been a thing that you've had for as long as you can remember. I mean there are individuals who seem to have a congenital problem with certain kinds of knowledge. It can run the gamut because it's really more about where in the brain there's a process going on, or a lack of processing going on more specifically, than how it happened.

Dr. Sarah Song:
You mentioned the sensory coming in and then the processing of that information. What are some of the different sensory modalities that could be affected that cause different types of agnosia?

Dr. Roy Hamilton:
We could probably spend much more time than we have breaking down and finding different names for different agnosias, each of which has a long name that we also have to break down the way we did with agnosia itself. But suffice it to say, you can have agnosias in your various sensory modalities.
Certainly the most classically described are visual agnosias, but you can have agnosias for sound. Within sound, you can have agnosias for language as you hear it, the inability or a problem processing specific sounds like words. You can have agnosia with respect to touch, not being able to recognize things that you're feeling even though you'd be able to recognize them visually. And so on and so forth.
It's worth noting that often these agnosias affect specific sensory modalities, in other words, something that you wouldn't be able to recognize through one sensory modality. Let's take the touch modality for example. If a person has what's referred to as stereognosis, which I'm going to break it down, a lack of knowledge for solid objects.
So stereognosis, they could look at the object and recognize it by sight, but then they can't recognize it by touch because there's something wrong with the incorporation of touch information into recognition. And you can imagine it being so for the other sensory modalities as well.

Dr. Sarah Song:
And this kind of goes along with that, but what parts of the brain might be affected by the different types of agnosia, that cause the different types of agnosia?

Dr. Roy Hamilton:
So it varies. It varies based on, amongst other things, the sensory modality and the kind of information that we're talking about. So it's hard to make one uniform statement and say, well, it's always going to be this part of the brain or that part of the brain because we have different senses and so it's going to vary with those different senses, but we can point to some common areas.
Like I said before, probably the most historically documented, classically described agnosias are the visual agnosias. And so, one thing I'll do is I'll make a basic distinction between different stages of recognition. And this distinction goes back into the antiquity of how this disorder was characterized. So one classical distinction is something called apperceptive agnosias versus associative agnosias.
And so apperceptive, and I'm going to try every time I throw out a term to dissect it a little bit. So there again, that A, that lack of. So apperceptive agnosias is the lack of accurate perception. And that's where visual information's coming in, I mean the basic sensory information is coming in, but somewhere in the middle stages of processing that information, putting together the building blocks, in this case we're going to talk about visual agnosia, so the building blocks of visual information, it can't get put together right. Something goes wrong in that stage of the process.
And so that tends to be a more posterior, back of the brain process. The visual cortex is in the occipital lobes, the back of the brain. And then areas around that occipital cortex are really important for processing different aspects of visual information. And so often having injuries to this, more posterior areas of the brain around those visual areas will result in this kind of intermediate level visual processing error where the person can't form a coherent visual percept of what they're looking at.
So then, let's put that aside. If you were to get past that stage of recognition perception, here's what's called associative agnosias, and there's not much language to decode there. It's the inability to associate things. And here in this case we're talking about associating your percept with the meaning. And so this means that you have built a cohesive perceptual representation of the thing that you're looking at, you just don't know what it means.
And those tends to be a little bit more inferior, moving from your back of the head down towards what's called your temporal lobes. Those are the two lobes on the side. If you imagine a southern road that goes from the visual parts of the brain down south to those temporal lobes, often individuals who are having injury along that more southern route.
We sometimes casually refer to it as the what pathway of visual processing where, as you go further and further down that road, the temporal lobes have a lot to do with your representation of meanings of things in the world, your network of connections around understanding what certain things are. A dog is a four-legged mammal that people sometimes domesticate and tends to like bones, all that sort of representation is in there.
So if you have an injury in between the area where you're processing the sensory information, leading to the area where you're representing these concepts, well, then you can have a well-formed sensory representation. Definitely looking at something, if you gave me a piece of paper, I could copy what you're showing me. But because it's disconnected from the parts of my brain that have to do with meaning, I can't tell you what it is. I can't draw up the meaning of the thing that I'm looking at. So there's an example of anatomy that links to a specific set of problems.
If I haven't clarified that distinction between those two different stages, let's stick with dogs for a second. Let's say I was to show a person several images of the same dog. The person with associative agnosia, they're able to build a coherent representation, but they can't connect it to the meaning. That person's going to say, "Okay, you're showing me three pictures. They're the same thing. Look, I can make a copy of that picture myself. See? And it's pretty good. I just can't tell you what that thing is."
Now I do the same thing with the person with the apperceptive agnosia. They might say, "Well, gosh, I can't really make heads or tails of this thing. I mean, I know you're handing me something and I can't tell whether necessarily they might be the same. I'm not sure. I surely can't draw you a copy of it because I just am having trouble putting it together."
That's the difference between those stages of recognition, how they relate to this anatomy and how they're perceived differently, even though they're both examples of problems with recognition.

Dr. Sarah Song:
That is utterly fascinating. And I can imagine that for the person who suffers from agnosia that they can have a lot of problems just perhaps living their daily life. What are some challenges that someone with a type of agnosia might have in their daily life?

Dr. Roy Hamilton:
Well, I think that one of the challenges is that functionally it is often the case that having an agnosia is very much like having a sensory impairment, I mean the net effect of it. Let's stick with visual agnosias for the time being. If you can't make sense of visual images, well, then in many ways it is functionally similar to having severely impaired sight even though the actual acuity of your vision is unaffected.
But one challenge that these individuals face, individuals who don't have other reasons for visual acuity loss is the lack of understanding, generally speaking, amongst the population, including amongst the clinical population as to what agnosias are and what to anticipate.
Let me give you an example. There is a degenerative disorder called posterior cortical atrophy. Now this is going to be related to but slightly different, visual type of knowledge loss, type of perceptual information loss. And so those patients will have degeneration, a lot of atrophy, loss of brain volume and function again, near the back of the brain. It's why it's called posterior cortical atrophy. And so as we just discussed, visual cortex, areas around it, really important for visual perception, that occipital lobe.
And so they're having atrophy, it tends to be more in the northern route. We talked about the southern route, going to object identity, the northern route. Sometimes people casually or colloquially will refer to more as you go north from that occipital lobe as the where pathway, where are things. So it's sort of a rough breakdown of the kinds of information that get processed.
What often these individuals will experience is a failure amongst other things, the ability to integrate visual information. And in particular, one of the common things is the inability to perceive more than one visual element at a time. They can, with effort, work out what a tiny piece of a picture might be, but they can't put it all together, something called simultagnosia.
And they have other visual processing deficits as well. I'm going to focus on this one. So you imagine, it's as if you're looking at the whole world through a straw. It's really hard for you to put a coherent worldview together, at least visually.
When I see these patients in my clinic, they routinely have been to optometrists, ophthalmologists, ophthalmological specialists, so on and so forth, because the base assumption is that there's something wrong with their eyes. They've been worked up six ways from Sunday to figure out what's wrong with their eyes when the problem isn't there.
And that's what I'm talking about getting back to your question in my point is that one of the challenges that these individuals who have different agnosias will experience is they often don't get seen by specialists who understand what their problem is and can represent to them what their problem is because they're relatively uncommon in the population and hard to distinguish from other much more common deficits of perception.

Dr. Sarah Song:
And that must be so tricky because it's difficult to diagnose if perhaps you don't even necessarily know that you have a problem or you can't put the words to exactly what's going on because you're perceiving things to be a specific way. How might agnosia affect someone's personal relationships?

Dr. Roy Hamilton:
I think that there is room for friction in interpersonal relationships. Let's step broadly back and say that a lot of what happens in relationships is both on a symbolic level and often on a more concrete level, the ability to share perspectives, to understand where the other person is coming from. And if you have a radically different way of perceiving or not perceiving the world, it can be hard for other people to really understand what you're going through.
And so I could easily imagine, and to some extent I'm extrapolating from the patients I've known with this, the category of deficits and other changes of experience where it's very hard to articulate exactly what the experience is. It's pervasive, it's happening to them all the time, but other people don't have any way of relating to it. That can be a point of friction and a challenge for individuals who interact with love and or need to take care of these individuals.

Dr. Sarah Song:
Yeah, I can really see how it might be difficult for caregivers especially to take care of people who have debilitating forms of agnosia. So in that realm, is there any effective treatment for agnosia or effective therapy for agnosia generally and more specifically, perhaps?

Dr. Roy Hamilton:
A lot depends on what is the cause of the agnosia. Unlike what I told you a few minutes ago where I said that the fact that one has an agnosia may be more related to real estate than cause, I would argue that what one does about the agnosia has probably more to do with cause than it has to do with real estate.
So if it's because of some type of focal lesion, that can be intervened on. Let's say that you discover that someone has developed a mass of some type, a tumor, then that needs to be intervened on. If there's a infectious process, whatever it is, you treat the process if the process can be treated.
Now in cases where the process can't necessarily be treated, let's say for example if a person has had a stroke and a certain amount of damage to the brain has occurred and you're not anticipating remediating that damage per se, or in the case of neurodegenerative diseases, at least in 2023, then we're talking a lot more about compensatory strategies where one understands that one has a specific problem in a particular sensory modality.
And here again, I'll remind you what we talked about before that often it's the case that we're talking about a particular modality, whereas other modalities may be relatively spared. And so often that is a point of leverage that individuals can use to try and compensate for some of their deficits.
So I'll give you a very specific example. So there is a particular kind of recognition deficit that maybe some of your listeners have heard of, prosopagnosia. It is the inability to recognize faces, usually not that something is a face, but rather recognize the faces of specific individuals when they see them, including people they know very well.
And so you can imagine that that would be a significant challenge, humans being social creatures that we rely a lot on being able to distinguish one another by the face. Many people who have prosopagnosia have either by instruction or by their own process and insight developed a strategy of looking for other markers that individuals have that tell them that that's so-and-so. So recognize the sound of a person's voice or if an individual recognize, what, their hair or other distinguishing facial features that aren't necessarily the typical features of a face like those other features are.
I happen to know a couple of colleagues, colleagues in the field of medicine, at least one in neurology who have a prosopagnosia that impacts their perception. You would never know it as a person who knows them because of their deftness at using ancillary cues about a person's appearance, dress, voice, these other markers to compensate for the fact that there's a challenge in one specific sub-domain of visual perception. But that's just one example of how people use compensatory information to try and overcome the specific perceptual issue that they have.

Dr. Sarah Song:
So essentially looking at treating the root cause if you can, and hopefully it improves from that perspective. And then if there's something that you cannot fix, then working perhaps with therapists, be it visual, occupational, physical therapists to find new strategies to make up for the sensory input that you're lacking. That's so interesting because it seems very multidisciplinary and a lot of different people working together to try to help the people who have agnosia.
I have a question, has treating people with agnosia and even knowing people with agnosia given you a different perspective on how you see things or how you process information?

Dr. Roy Hamilton:
I'm not sure if it has given me a perspective on how I process information, but you know what I do think it does is it throws into sharp relief, the idea that our world is in some senses perceptual intersubjective reality, like the way we perceive things is our reality.
The reason why we can have a common understanding of how certain things exist in the world is because we have certain shared perceptions around those things, but even between individuals who don't have deficits, there are bound to be subtle differences that inform our way of understanding the world.
And I do think that having these really profound examples of individuals who otherwise have perceptions that we relate to, but then in specific domains clearly have these big differences, is a good reminder of the importance of how the information we take in and how the perceptions we have are integral to our lived experience, the opinions we form, how we put everything together and what we assume about ourselves and other people.
I do think that if one's thinking about it when one sees these patients, it's an opportunity to reflect on and grow from perspective-taking around these patients and all patients and all people.

Dr. Sarah Song:
I could not agree more. I think that is so interesting to think about how we do have a shared perspective, but we all have our own inner life and what we see and feel and hear and all those things that we're taking in ourselves, and then somehow we all share it with each other.
I am really interested to hear about any research you're working on. I know that you are a very prolific researcher. Is there anything you're really excited about that you're working on right now that you can share with us?

Dr. Roy Hamilton:
Well, a lot of our focus is not specifically in this particular space, let me say that. I will say a word about what I do research on. I do hope someday that it has some application to things like agnosia.
So my laboratory does non-invasive brain stimulation, so that's magnetic and electrical stimulation of the brain using tools like transcranial magnetic stimulation, transcranial direct current stimulation. Those are the names of the tools. Those are basically long terms for we stick magnets on your head or we stick electrodes on your head and we try to make your brain more active or we change its patterns of activity.
And the reason that we do that is that we are trying to do two things. We're trying to understand the relationship between different brain structures and networks and behavior because after hundreds of years of looking into this, we still don't understand all those relationships, what different brain areas do for us in this complex and vibrant thing we call behavior.
And then if we understand elements of that, we try to use these same magnets and electrodes to try and spur the brain to function more fully in areas where individuals have lost certain cognitive functions on the basis of neurologic disease.
And so a lot of our work thus far has actually gone into aphasia, which is again, to break things down, there's that A again, aphasia is the acquired loss of language. And so we spend a lot of time thinking about people who've lost words.
But I think in general, we're hoping that we can use these kinds of tools to help brain networks to become reengaged. And if we can do that well, well, then we can apply it to all sorts of As in the brain, so to speak, including agnosias. That I think would be the eventual goal.

Dr. Sarah Song:
That has been so fascinating to hear about. And I just want to thank you for talking with us today and sharing your insights and your research. And I think it's going to probably change the field of neurology, so I can't wait to see what you do with it. Thank you so much.

Dr. Roy Hamilton:
Thank you so much. It has been such a pleasure.

Dr. Daniel Correa:
Thank you again for joining us today on the Brain & Life podcast. Follow and subscribe to this podcast so you don't miss our weekly episodes. You can also sign up to receive the Brain & Life magazine for free at brainandlife.org and even get the Espanol version. For each episode, you can find out how to connect with our team and our guests along with great resources in our show notes.
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What is Agnosia and How Does it Affect the Brain’s Perception?

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