After a brief, painful hiatus in the form of Ironman Texas, we’re back, exploring to tracking the pathway a karate front kick takes through the nervous system all the way from inception through completion. How do we take in all the sights, smells, and tastes around us and decide what to do with it? In our case,we are tracking the signals that drive a frontal kick through our nervous system. If we were sparring, how would we see our our partner has dropped their guard, and decide the best option is to kick her?

So far, we tracked the signal through much of our visual system, from our eyes, to the back of our brain in our occipital lobes, where much of early visual processing takes place. We do not yet have a meaningful image of our situation, opponent, or the dojo, at this point. We have yet to layer on our other senses, the sounds of our opponent taunting us, the smells of the dojo, the feel of the mat under our feet. The images have no meaning either until we can recognize what is going on, for this we need to access memories.

That raw visual information splits into two parallel streams, called the dorsal and ventral streams, and travels forward again from our occipital lobes for further processing and integration (fig 1). Parallel processing decreases processing times, so for our kick, it decreases reaction times.  The dorsal stream is the ‘where’ stream- distance, movement, spatial awareness, which is important for us as our kick is primarily visually guided. The ventral stream is the ‘what’ stream- information like color and basic image recognition (like recognizing our sparring partner) are processed via this pathway. The information in this area comes predominantly from the fovea. This pathway will travel forward and is important in memory and emotion, which will be play into our kick later.

 This integration happens in the creatively named, multimodal sensory association areas. Three pairs of these areas layer on our other senses, emotions, and memories. The posterior multimodal sensory association area, at the junction between the parietal, occipital, and temporal lobes (fig 2) receives input from the dorsal stream, and is important in visuospatial organization, attention, adding other senses- figuring out distances like how far our opponent is, are they moving away or closer, is their front guard arm dropping, where are we in relation to the boundaries of the sparring mat, lots of stuff we need to know to place an effective front kick. The limbic association area, by the temporal lobe is where memories and emotion are integrated and receives input from the ventral stream (fig 3). Now, we can identify what we are looking at and add context- we’re sparring, have done this a hundred times before, but still nervous. And lastly the anterior multimodal motor association area in the frontal cortex, is important in early motor planning and judgement. In our case, should we kick or punch, if so, how hard, or maybe just run away. It is right about here, halfway through our paper, or 100-150 msec in real time, that we have finally started planning our front kick.

So we have a fairly complete understanding of the situation at this point.  We know that we are sparring and have created an exploitable opening in partner’s midsection.  We know how far away we are, that our left leg is forward, and maybe we are maybe a little annoyed at all the jabs to the shin and the fact that she left her cereal bowl out this morning, again.  We know from memories of previous sparring sessions that she will keep backing up rather than move to the side.

Each step along this pathway added a more complex layer of processing to our sensory input, but we have finally neared the end. It is probably also worth mentioning that while the more basic sensory processing is unilateral, it becomes more bilateral (uses both sides of the brain) as becomes more complex. The reverse will hold true for the execution phase of our kick.  

So how does that sensory picture get converted into a front kick? Via a process creatively named sensorimotor transformation which we will talk about next time.