homunculi, mind in motion

Homunculi

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 layer splayed over the parts of the brain that are evolutionarily older. The walnut-shaped brain is divided front to back into two not quite symmetric halves (right and left hemispheres). For the most part, the right hemisphere controls and has inputs from the left side of the body and the reverse, each divided into plateaus called lobes that are separated by valleys, or sulci (singular, sulcus).

The inputs from the various sensory systems are partly channeled to separate lobes of the cortex, for example, vision to the occipital lobe at back of the head and sound to the temporal lobes above the ears, each lobe is wondrously complex, with many regions, layers, connections, kinds of cells, and many functions. Remarkably, even single neurons can be specialized, for a specific view of a face or for tracking an object that moves behind a screen. A recent estimate is eighty-six billion neurons.

There are two pairs of homunculi splayed along the central sulcus (and face each other); one pair maps the sensations from the body, the other pair maps motor output to the body. The pair on the left side of the brain maps the right side of the body and the pair on the right side of the brain maps the left side of the body.

The motor homunculus, positioned more forward (anterior or frontal) toward the eyes and nose, controls the output, how to move muscles. The sensory homunculus, positioned toward the back of the head (posterior or dorsal), brings the input from the many kinds of sensations our bodies respond to, position, pain, pressure, temperature, and more.

sensory homunculus

linked mentions for "homunculi, mind in motion":

1. 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