In this video I describe the two pathways leading to the emotion processing areas of the brain described in the previous video. The fast pathway (or low road) goes to the amygdalae and allows for a quick and dirty emotional response to stimuli. The slow pathway (or high road) involves areas of the cortex for a higher-resolution interpretation of the stimulus and assessment of the appropriate response. The fast pathway highlights the amygdala’s role in creating links between external stimuli and quick fear responses and also the role of unconscious processing of emotional information. This dual-pathway processing of emotional stimuli can also be seen in patients with blindsight who show emotional reactions to stimuli but do not have conscious awareness of seeing them.
Joseph LeDoux – The Emotional Brain (Amazon): http://amzn.to/2A5CNWM
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Video Transcript
Hi, I’m Michael Corayer and this is Psych Exam Review. In the previous video we looked at parts of the brain that are involved in emotional processing and in this video we’re going to take a look at how information actually gets to these different areas of the brain. And so this brings us to some work by Joseph LeDoux, and I’ll post a link in the video description to his book The Emotional Brain, if you’re interested in reading more about this.
But the basic idea is that there’s two main pathways that information travels on; a fast pathway and a slow pathway. So the fast pathway, which LeDoux also calls the “low road“, goes quickly to the amygdalae and this allows us to have a simple good or bad assessment of a stimulus. Then based on this simple assessment, we can prepare for immediate action. That’s why this is the fast pathway.
But simultaneously the information is also traveling on the slow pathway and so the slow pathway, or the “high road“, also involves areas of the cortex and so this allows us to have more detailed processing. And so we can consider the importance of this stimulus and then based on this more detailed processing, we might decide that we should modify our course of action. Because in many cases we’ve actually already responded to the stimulus because of the fast pathway. But we then might decide that we need to change our course of action if our simple assessment wasn’t quite right. And this idea that the cortex is involved in processing of emotional information and emotional regulation, led Dutch researcher Walle Nauta to propose that we should actually think of some parts of the cortex, particularly the prefrontal cortex, to be a part of the limbic system.
Ok, so let’s take a look at a brain here and see these different pathways. So let’s imagine that we see some stimulus and so we’re going to go from the retina here, you know, there’s no eyes drawn here but the information is going to hit the retina, it’s gonna travel on the optic nerves, and it’s going to go to the thalamus. And then from the thalamus, it’s going to go, in the case of the fast pathway, it’s going to go immediately out to the amygdala on either side here. So that’s the fast pathway. We go from the retina right to the thalamus out to the amygdala and that’s going to give us sort of an immediate assessment of the stimulus.
But at the same time from the thalamus, it’s going to be projected out to the occipital lobe and that’s where we have our basic visual processing so in the v1 area here. We’re going to have feature detectors that are sort of, you know, responding to the shapes that we’re seeing, the lines, and then they’re going to send their information out to association areas of the brain that are going to help us to organize and interpret and sort of perceive what those sensations are. And then we’re also going to go out to the areas of the prefrontal cortex here which are going to give us a more detailed assessment, going to do some of that decision-making and emotional regulation part, to sort of figure out how should we respond to the stimulus now that we actually know what it is. And so we can see why that slow pathway is going to be much slower. It’s going to involve a lot more processing, whereas the fast pathway or the low road is much more immediate.
Ok, now you can understand this difference between the fast pathway and the slow pathway if you think about a time you’ve been startled by something that’s actually harmless. So let’s imagine, you know, I don’t think anybody actually is fooled by these things, but let’s imagine a friend gives you one of those, you know, cans of peanuts that actually has snakes inside that pop out. So let’s say you fall for this prank.
So you’re opening what you think is a can of peanuts and then suddenly something comes jumping out at you and if you’ve ever had something like this happen, of course, you jump immediately. You have this very fast response. The fast pathway response to visual input is something around, you know, 75 milliseconds later. So this is very, very quick. And so, you know, you open the can, something is jumping at you, and you’re immediately startled and you have a very quick fear reaction. But of course, at the same time, that information is going to the other areas of the cortex and you’re figuring out “ok, these are not real snakes that are jumping out at me, this is a prank. And so what I should be doing is probably laughing”. And so a second or two later after this startle response, you realize it’s a joke, you laugh, you’ve considered the importance of this because “ok, it’s not really a threatening stimulus and so I don’t need to continue this fear response that I’ve been having”.
If, on the other hand, you open to some box and a real snake actually came out; you’d have the immediate startle response and then, of course, you continue that fear reaction rather than modifying it. Ok, so that helps us to see that we have these two different pathways for responding to a stimulus and it also helps us to clarify a little bit about what exactly the amygdala is doing. So we can see that what the amygdala does is it links some external stimulus to defense reactions. And this can involve a process of learning, so you can learn that certain stimuli are dangerous and that you should respond with a fear reaction very, very quickly.
And so the amygdala plays a crucial role in this process and one way that we can see this is that you can have animals who have their amygdalae removed and now they can actually no longer learn this sort of Pavlovian conditioned response to fear. So we can condition a fear, you know, if every time I show you a particular image of something harmless, I don’t know I show you a picture of a teddy bear, but every time I show it to you I poke you with a pin. Well, then I could very quickly condition you to have a fear response to this picture of a teddy bear, right? And your amygdala is involved in forming that association and that’s also going to involve other areas of the limbic system like the hippocampus for forming that memory.
But what we see is if you remove the amygdalae from animals, then they can no longer learn this fear reaction to a new stimulus. So you can, you know, pair some stimulus with an electric shock repeatedly and the animal will never learn to have the fear reaction to that stimulus because their amygdalae have been removed.
Ok, this also brings the idea that some of the process of appraisal is happening unconsciously and this brings us to some work by Richard Lazarus, who I will talk about in a future video, and should also remind you of some work by Robert Zajonc that I talked about in a previous video in the unit on consciousness. And this is the idea that we can have fear reactions to stimuli that are too fast to be perceived and so this shows there’s some unconscious processing going on. And what Zajonc has done is shown people things like a frightened face, and you’ll have a fear reaction if you see another person looking afraid. That is going to trigger a very quick fear reaction in you and so what Zajonc did was show people fearful stimuli, or faces that were afraid, and what he found is people would have a fear reaction to those pictures, even if they were presented too quick to be consciously perceived. So you flash the image for just a few milliseconds and people actually have a fear response because of this fast pathway, even though it’s actually too quick to involve any conscious process. Alright, so that again demonstrates that some of this emotional appraisal is occurring at an unconscious level.
And I think a really fascinating demonstration of this is patients who have what’s called “blindsight“. And so in the case of blindsight, these are people who consciously are blind; they report that they can’t see anything. They say “I’m blind, I can’t see anything” but if you present something like a face showing fear to these people they actually have an emotional response to it. And this demonstrates that they actually can see and so what’s happening in people with blindsight is that there’s damage to the conscious pathway but there’s not damage to the unconscious pathway. So they have the fast reaction to something if you, if you were to, you know, flash something or you know put something front of their face very quickly, they would jump back. They would have a startle response even though consciously they say they don’t see anything. They aren’t ever able to figure out what it was that they were seeing because this pathway that’s going to the cortex has been damaged. And so they don’t have the conscious awareness of seeing even though they can still respond in an unconscious way to visual information.
Ok, so I hope you found this helpful, if so, please like the video and subscribe to the channel for more. Thanks for watching!
