Movement and Space
Movement is the most fundamental feature of animals. Plants can
be stationary and enjoy a long and healthy life rooted to the earth.
Animals move. If you had to limit your study of humans to two
essential features of existence, they would be eating and movement.
The brain is the organ of the mind and the organ of movement. The
brain is a matrix of meaningful connections between the body inside
and the environment outside.
Humans have an innate sense of spacetime. We live inside a
virtual spacetime frame, created by neuronal networks in the brain.
At several levels of interaction the brain creates spacetime and
body maps that intersect. Sensory information flows into these
spacetime maps and motor output flows out of these spacetime maps.
Each human has a sense of personal extension defined by the boundary
of skin and the extension of arms and legs.
We are creatures of gravity and work hard to lift our bodies and
burdens upward. We are alert and agile enough to maneuver down rocky
slopes and avoid falls that would injure or kill. Our speech grows
out of body spacetime and communication with sounds. There is rhythm
in our motion, in the sounds we hear and the sounds we make. Our
languages emerge from spacetime maps and rhythmic sounds. We speak
in terms of movement through spacetime, and of journeys both literal
and metaphoric. We project our minds into the world and merge with
the world of continuous changes and constant motion.
Humans act on the world through praxis or skilled movements. A
complete set of movement patterns such as walking and running are
innate but must be practiced to develop skills. The root
adaptive task is to learn what movements are required for survival
today. Ten thousand years age, if you were male, you learned to
throw a spear, catch a fish or carry a deer carcass on your back.
Today, you learn to learn to throw a football, move a pen across a
paper surface, push keys on a keyboard and control movement with a
mouse or joystick.
Humans learn by imitating what they see and hear. Learning
movement skills is so implicit in life experiences that most of the
lessons are not recognized as such and most of 
the practice is built
into the daily experiences of life. The central feature of
intelligence is the ability to understand what is really going on
out there and to respond to events with successful and adaptive
behavior. Praxis is skillful movement and is central to intelligent
behavior. If you add mimesis to praxis, you can start building a
meaningful model of intelligence. To learn, you copy the skillful
movements of others and practice these movements until you match or
surpass the teacher’s skills. The movements that are copied and
learned extend into speech.
The construction of language, both in form and content is based on movement
in space. While you can admire the complexity of the best examples written
language, most human communication is a mixture of sounds and gestures in the
tradition of our primate relatives and ancestors. Mimesis is the ability to
imitate and copy the movements of others. Humans learn by imitating what they
see and hear.
Humans create neuronal models of their own behavior and the
behavior of others, remember and communicate these models. We can
simulate experience and anticipate what we are going to do in the
future. We can practice skills in advance so that can improve our
performance. We can expand this modeling capacity into verbal and
body communication, invent language and substitute words for objects
and action. We can learn to handle words much like objects and do
symbolic transactions with each other.
Movement originates in several areas of the brain. The final
signals to muscles to contract emerge from the thalamus and motor
cortex and travel along the spinal cord to the motor neurons in the
anterior horn of the spinal cord grey matter. The spinal motor
neuron sends a signal along a peripheral nerve to the muscle cells.
The cerebellum does the fine-tuning of coordinated movements by
adding to the signals emerging from the motor cortex. The parietal
cortex stores maps that connect body movements with spacetime and
recall learned patterns of movement. If the motor cortex is damaged,
you are paralyzed. If the cerebellum is damaged, movement
coordination is peculiar or lost. If the parietal cortex is damaged,
you retain movements but learned motor skills may be missing and you
may ignore part of your body as if it did not exist. A typical
parietal deficit is that you cannot perform learned movements such
as dancing or using a screwdriver.
Three cortical regions control voluntary movement
1. the primary motor cortex M1
2. premotor cortex (PM)
3 supplementary motor area (SMA)
The simplest idea of the brain begins with a sensory input
entering a processor that then decides what to move and sends motor
outputs to motors (muscle cells). The first complication in this
model is that the motor cortex has sensory input and the sensory
cortex has motor output. The second complication is that some
movement is generated in response to real-time sensory input and
other movement is generated from memory that operates like internal
sensory input.
The body is mapped onto the sensory and motor cortex. Smaller
body parts such as the fingers, lips and tongue that are used for
fine manipulative movement occupy larger areas of the motor cortex
than larger body parts such as arms and legs that are involved in
more vigorous movements such as throwing and walking. A smaller
cortical area (SMA) in front of the motor cortex contains a separate
body map and at least 4 other regions of the brain contain body
maps.
While cortical maps exist, the regions in the map are not as
discrete as once thought. If the map is displayed as pieces of a jig
saw puzzle, the pieces are not placed side by side to form the map,
but overlap. The arrangement would be easier to understand if motor
neurons were assigned to one body part and made point-to-point
connections that were stable over time. However, the real cortex
appears to have a dynamic map and a scheme of connections based on
fields of activity that converge and diverge in complex patterns.
Over time, the pieces of the map change with learning and practice,
so that the construction of cortical connections is in flux.
Neuroscientists now make distinctions among many components of movement. For
example, the preparation to make a movement is regarded separately from the
volley of signals sent to implement the movement. Scheiber stated: "Neurons in
M1, SMA and PM discharge at the highest rate while a subjects waits to move in
particular direction… during the delay between instruction and movement
triggering, PM and SMA appear to store information on the direction of the
impending movement… this represents (the retrieval of) stored information...To
pick up a pencil, for example, you may glance at the pencil and then move your
hand to the same place. Insight into how cue direction is transformed into
movement direction has come from tasks in which these two features were
experimentally dissociated, similar to glancing at your pencil in a mirror and
then reaching to pick up the real pencil instead of a mirror image…The cue
direction is transformed into movement direction in the area principalis (of the
frontal lobe) during the delay period… information is sent to M1 at the time of
execution."
The cerebellum lies below the cerebral hemispheres and is connected to the
rest of the brain and spinal cord. Like the cerebrum, the cerebellum has two
hemispheres and a cortex with gyri and sulci. The cerebellum is involved in
producing smooth, coordinated movements by regulating muscle tone and the rate,
range, and force of muscle contraction. Dysfunction is expressed as disorders of
movement and equilibrium.
