I should begin this post with an advisory message: the following should be read while secured to a strong anchor point as it will turn your world upside down. I can’t overstate the awesomeness of what is revealed below. There’s also a fair wad of toilet humour which might be unpleasant as your world is being turned upside down.
In the previous post I discussed Snake Detection Theory and the experiments that showed people have a perceptual bias toward detecting snakes. Fair enough, I’ve had a few snake detection experiences and I certainly detect them better than I do my car keys when I’m in a hurry to go out. But what is the neurological basis for this detection bias? What happened in my brain when I found myself jumping in the air in response to a snake I didn’t even know was there?
The psychologist Joseph LeDoux explained all this when he mapped out the neural pathways that cause us humans to express fear. There are two different pathways that have become known as DeDoux’s High and Low Roads. Here’s a picture to give you a better idea of how these pathways transform visual information into fear responses:
As you can see, before it reaches the visual cortex, visual information travels through a primitive part of the brain called the thalamus. This overgrown soybean is like the front desk of your consciousness. It filters every bit of information and decides on where it should be sent. If it’s something from the peripheral vision that has no relevance to you it is hastily sent out the door. If it’s something that the upstairs department – consciousness central – is dependent on, then it’s sent along the high road to the visual cortex for conscious processing. If it’s something dangerous, i.e. a snake, the information is immediately copied and the equivalent of a red button is pushed at the front desk.
The first copy is very hastily made and the rather rough information is sent to another primitive part of the brain that we share with all vertebrates: the amygdala. Yes, lizards have these, as do fish and it’s as crucial to your survival as your seat belt . The amygdala quickly holds the information up against a bunch of templates of things that should be feared, such as snakes, heights, my dad, and if it finds a match the amygdala initiates a fear response. This is the physiological equivalent of an evacuation of the building. Hair is raised, heart rate increased, blood supply directed to the muscles, and if the information is sufficiently fearful, bowels voided. A literal evacuation.
But remember I said the information is quick and dirty. It has to be, as speed is of the essence and in terms of things like snakes, ignoring a potential danger can be a lot more costly than an over-reaction. Meanwhile the thalamus sends a better picture upstairs via the high road to the visual cortex for conscious processing. This is the copy from the good printer that has more detail to go on. And if the conscious processing confirms the presence of a danger then another signal is sent to the amygdala to keep on voiding those bowels. But if the information proves to be non-threatening. i.e ‘Oh it’s just a damaged power-lead lying across the ground,’ then a signal is sent to the amygdala to cancel the fear-response. Heart rate decreases, hair flattens, sphincter closes, and you calmly step on the power-lead, getting an electric shock from hell.
Now here is the awesome bit: Sometimes the amygdala doesn’t trust the information from the visual cortex and says, nope, I’m going to keep on voiding those bowels. No matter how hard you try to control your fear response you only have limited conscious control over your amygdala and literally none over your thalamus down there at reception. What this means is that there is no singular mind in a singular body. Our minds are actually bunches of connected parts, usually cooperating to get us through the challenges of day-to-day survival but not entirely trusting each other to send the right information. What’s more is that there is no separation between the mind and the body in this sense because there is no mind. Our eyes are no more separated as our thalamuses and amygdalae (my spell check is going crazy). So while you might think your upstairs department is quite special and separate from the rest of the organisation, it’s actually just another level of cognitive processing that is often at the mercy of the other departments. This is mind-body pluralism.
How does this relate to your own experience? Have you ever had your amygdala take over and send you scurrying? In the next post I’ll finally get around to the subject of blindsight. This is where the lines to the upstairs department are damaged but the rest of the organisation keeps on operating.
This is such a huge topic 🙂 Just before I read this I was watching Susan Blakeslee on Body Maps where she talks about grid cells and place cells and there role in location and detection of the body in space and how human body maps extend to extensiosn of the body such tools – and animals. (https://www.youtube.com/watch?v=J0Pu-drebFU) The old mind/body dualism just doesn’t stack up very well when dealing with all this. Gives new meaning to the snake in Eden 🙂 Really looking forward to where this goes.
Hey thanks for the comment and the link! Interesting to hear the bit about horse-riders extending their body maps to include their horses