sensory homunculus

Rather than representing the sizes of the body parts, the sizes of the cortical representations of the various body parts are proportional to the quantities of neurons ascending to them or descending from them. The head and hands have more cortical neurons relative to their body size, and the torso and limbs have fewer cortical neurons relative to their body size. It means more sensory sensitivity on the sensory side and more action articulation on the action side

The disproportionate sizes make perfect sense once we think about the multitude of articulated actions that the face, tongue, and hands must perform and the sensory feedback needed to modulate their actions. Our tongues are involved in the intricate coordinated actions necessary for eating, sucking, and swallowing, for speaking, groaning, and singing; mouths smile and frown and scowl, they blow bubbles and whistle and kiss. Hands type and play the piano, throw balls and catch them, weave and knit, tickle babies and pat puppies. Our toes, on the other hand, are underused, incompetent.

Like our knowledge of space, we know about our bodies from a multitude of senses. We can see our own bodies as well as those of others. We can hear our footsteps and our hands clapping and our joints clicking and our mouths speaking. We sense temperature and texture and pressure and pleasure and pain and the positions of our limbs both from the surface of our skin and from proprioception, those sensations of our bodies from the inside. We know where our arms and legs are without looking, we can feel when we are off balance or about to be … so much delicate and precise coordination of so many sensory systems is needed just to stand and walk, not to mention shoot a basket or do a cartwheel. We weren’t born doing those things.

Brains not only create millions of synapses, connections between neurons, per second but also prune synapses. Otherwise, our brains would become tangled messes, everything connected to everything else, a multitude of possibilities but no focused action, no way to strengthen important connections and weaken irrelevant ones, to choose among all those possibilities and organize resources to act. Pruning allows us to quickly recognize objects in the world and to quickly catch falling teacups but not burning matches.

First Law of Cognition: There are no benefits without costs. Searching through many possibilities to find the best can be time consuming and exhausting, we simply don’t have enough time or energy to consider everything. Life, is a series of trade-offs between considering possibilities and acting effectively and efficiently.

homunculi, mind in motion

linked mentions for "sensory homunculus":

1. homunculi, mind in motion
   We map our bodies onto our brains, onto the homunculus, the “little man,” sprawled ear-to-ear across the cortex, of our brains, a thick, crenellated