Now that we have finished our backstory, we can get back to the story of our karate kick.  So far, we have covered some basics of neuroanatomy and physiology. If you are just joining us, we are talking about the neural pathways involved in a karate kick. How do we look at something, or someone, decide to kick it, and then well, kick it.

For this discussion we were talking about a front kick, but it can apply to any kick. Really, where our story begins depends on why we are kicking.  Are we motivated by something external- like are we are sparring and see an opportunity, or maybe we are in class and were told to do a front kick. Maybe the motivation is internal- like the next step in a karate form (called kata). Or some combination of the above.

Lets say we are sparring and we see an opening to kick.  Maybe our partner has been a little irritating with the punches to the face (or more likely to the shin) and now has her guard way too high. There it is, an opening, perfect for a crushing front kick to her midsection.  Blam, she has been knocked clear across the dojo floor, and now it is time for a victory dance. So how did we do it? How did we see she had her guard too high, and use that to plan and execute a stepping front kick?

As far as senses go, we are visual creatures, and not just for sparring. In many neurodegenerative diseases, like Parkinson’s, loss of sense of smell commonly precedes any other signs of the disease, sometimes by years, and frequently goes unnoticed. Loss of vision does not go on unnoticed. (Anton’s Syndrome, or cortical blindness, is a disorder in which a person thinks they can see, but they obviously cannot). Blindly landing the perfectly placed front kick on a moving target, would be nearly impossible. Even standing on one foot becomes difficult when you can’t see (try it, stand on one foot, then close your eyes, or stand on one foot and keep looking around), because for most people, the majority of our input for balance comes from vision. Visual processing, converting light into a meaningful image of our surroundings is a wonderfully complex process, and like I will say many times, not completely understood (and not just by me).

To be able see where we are going to kick, or see anything at all, we need electromagnetic radiation with a wavelength somewhere in the range of 400-700 nanometers, which is the visible light spectrum. Some of that light that has reflected off our opponent and everything else in our line of sight heads our direction and enters our pupils (fig 1 &2). It lands upside down and backwards (thanks to the biconvex lens) on the retinas at the back of our eyes, which is the part of the eye that processes visual information. (We never actually see an object itself, but only the light reflected off it, which is strange to me when I really think about it).

They have called light sensitive photoreceptors (which if you recall from our post Starting Small, is a specialized type of receptor on a neuron). They are also known as rods and cones, based loosely on the shape of the cells.  Cone cells process color vision, and also contribute to visual acuity; rod cells are sensitive to black and white and better able to pick up movement.  Our retinas capture a series of still images that our brains piece together.

As an aside, because our eyes are close together, the image that each eye captures is very similar, but not completely identical. The difference between the images from each eye, called steropsis, is one of the ways we use to judge distances for nearby objects, like how far away our sparring partner is. And, just like we have a dominant hand, we have a dominant eye.

The spatial layout of the visual information is relatively maintained as it travels from the retina through the brain (called a retinotopic map). From the retina, the visual information is carried via the optic nerves, to the optic chiasm where they briefly join up, reorganize, pick up a different name, and head off to the occipital lobes (fig 3). There is a shift in the way the visual information travels from here. Half of the right optic nerve crosses over to the left, and vice versa. What ends up happening, is that everything in our vision from midline out to the farthest reach of our L peripheral vision (called L visual field) is processed in the right occipital lobe, and vice versa (fig 3). So if we are focused on our sparring partner’s nose, everything to the right of her midline is processed on the left side of our brain. Not just images from the right eye, but the R half of both eyes.

From the optic chiasm, the optic tract as it is now called, heads to the lateral geniculate nucleus in the thalamus, changes names again to optic radiations, and heads for the primary visual cortex in the occipital lobe (fig 3).

In the primary visual cortex, visual processing really starts. The visual information can be mapped onto the surface of the primary visual cortex in pretty much the same way it landed on the retina. The macula recieves a relatively large portion of the visual cortex because of the amount of visual processing required, but the retinotopic map remains relatively preserved. There are columns of neurons in the visual cortex, each responsible for a small piece of the visual field, akin to a pixel. Each column has layers of neurons, each responsible for a different aspect of the image. One layer, for example, might only process the teal color of her sparring gear.

All those columns have to be flattened (our pixels) and integrated with all the other pixels, then the still images are stitched together so we can understand what it is we are looking at and how it is changing.   We have raw information that needs to be put into context, and from here, visual processing becomes a little more theoretical. From the primary visual cortex, visual information makes the short jump to visual association areas also in the occipital lobes, where higher level processing starts. From there, it seems to split into two parallel pathways (fig 4) called the dorsal and ventral streams and head for the parietal, and temporal lobes. Why? One reason is speed. According to researchers from MIT, we can process some visual information in 13 milliseconds. Parallel pathways allow for faster processing, and therefore faster reaction times.

The dorsal stream (fig 4) is the ‘where’ stream- it is responsible for spatial awareness, which is important to visually guide the placement of the kick. The ventral stream is the ‘what’ stream- information like color and basic image recognition are processed via this pathway. The information in this area comes predominantly from the macula.  This pathway will travel forward and is important in memory and emotion, which will be play into our kick later.

The process of putting visual streams back together into a meaningful complete visual image (our sparring partner, wearing teal and black, is moving towards us, ready to punch) is called binding. If I seem to have glossed over details, I did, how it happens is debated.

So, for our front kick, visual streams might work something like this- Hey, I am standing in a dojo, that is my sparring partner, and those fist shaped things on her hands are teal sparing gloves (ventral). Huh, wow, that teal glove (ventral) seems to be headed towards my face (dorsal, though shin is probably more realistic) . Wow, she is faster than she looks (ventral). Well, she doesn’t seem to be slowing down (ventral), and she looks much more threatening close up (dorsal), probably should do something. Yep, need to do something. I was going to kick her, but I think I should just run (haha- this is a teaser for next week’s post).

So far, the visual stimuli that will drive our front kick, the visual representation of our sparring partner, has bounced from the front our brain to the back via a series of action potentials and is moving forwards again.

Next week we will look at how we layer memories and other sensory information onto that visual image, and how we convert that into action. As always, please direct questions or comments to frontal.lobe@duramatters.com.