This is one that I've been wanting to do on a tangential topic and for whatever reason, in the middle of the night, while preparing to teach a workshop, in a hotel room, in an insomniatic mood, my brain picks this time for this post. So, what the hey.. here we go.. (there is nothing pressing first thing in the morning - I can sleep in, so I don't have to stay in bed and try to force myself to sleep when I'm wide awake with all this stuff rolling around wanting to be written down).
Remember how Melzack said, "You don't need a body to feel a body"? (I don't remember which blogpost that was in, or paper it was from, but I made a picture. Here it is. )
Lately, and serendipitously, I've seen some things in my internet travels and stumbles-upon that might pertain to this.
Deep cortical layers are activated directly by thalamus
The first thing was a paper by Constantinople & Bruno, Deep Cortical Layers Are Activated Directly by Thalamus, about how information going to the somatosensory cortex is processed in two batches in two places within the layers, unlike what people previously thought, that it was processed in one batch by all the layers working together. I wrote about processing here, Part 11c, and included the picture from the paper, also below:
|From Constantinople & Bruno 2013|
Emx2, Pax6, Joan Stiles, Brain Development
The second thing was a video that Ginger Campbell shared, Joan Stiles talking about brain development. Great video. About minute 30:35, she describes the genetic battle for territory-building between the two main genes that help the cortex develop, Emx2, and Pax6. It's been worked out what happens if one of them is slightly more influential than the other. Here is a screenshot of a cartoon shown in the video that depicts this:
|SOURCE, Joan Stiles, Brain Development, minute 30:35|
The third thing, was this, from just the other day, from La Jolla, news that provided the tipping point for planning this post. By manipulating Pax6, researchers were able to manipulate development of the main somatosensory representational map in the brain.
"In order to study cortical layout, O'Leary's team altered a regulatory gene, Pax6, in the cortex in mice. In response, S1 became much smaller, demonstrating that Pax6 regulates its development. They found that the shrinkage in S1 subsequently affected other regions of the brain that feed sensory information into the cortex, but more interestingly, it also altered the body maps in these subcortical brain regions, overturning the idea that once established, these brain regions could only be changed by external experience. They dubbed this previously unknown phenomenon "top down plasticity."
"Top-down plasticity complements in a reverse fashion the well-known bottom-up plasticity induced by sensory deprivation," says O'Leary.
"Normally, the body map in S1 cortex mirrors similar body maps in the thalamus, the main switching station for sensory information, which transmits somatosensation from the body periphery to the S1 cortex through outgoing neural "wires" known as axons. In the newly discovered top-down plasticity, when S1 was made smaller, the sensory thalamus that feeds into it is also subsequently reduced in size.
"But the story has a more intriguing twist. "According to our present knowledge about the development of sensory circuits, we anticipated that all body representations in S1 would be equally affected when S1 was made smaller," says O'Leary. "It was a surprise to us that not only was the body map smaller, but some parts of it were completely missing. The specific deletion of parts of the body map is controlled by exaggerated competition for cortical resources dictated by S1 size and played out between the connections from thalamic neurons that form these maps in the cortex."
Carl Zimmer wrote a wonderful blogpost two days ago, about how this was done, Mouseunculus: How the brain draws a little you. Note Pax6, the gene mentioned by Stiles in the video. Implications for autism apparently.
Not quite sure how all this fits together, but I think it does fit somehow with Melzack's point, that you don't need a body to feel a body, and has implications for other phenomena besides autism, like xenomelia, mirror therapy, all kinds of things to do with pain and perception and manipulation thereof.
There is the internal regulation system/critter brain being phylogenetically a lot older and fairly independent of cortex (other than perhaps as an annoying stressor to it, much of the time..), so already we know the brain isn't monolithic, but this is a new way of seeing how function slices up into different levels of processing and awareness, and maybe some day, clever treatment. False memories are now being implanted into mice, at least the latest buzz says so.. It would be cool if some day a false memory of "no back pain ever" could be implanted into people with back pain, for instance...
OK, end of insomnia post. Back to where we left off in Melzack & Katz's paper, later.