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The Musical Brain
Music is Movement
Movement is the most fundamental feature of animals. 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. Our speech and music grow from spacetime motion 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 out 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. 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. Musicians play instruments that require skilled movements and add a variety of dance-like body movements or really dance as they play. Virtuoso musicians acquire fast motors skills and accurate motor memory to play complex passages accurately.
Humans learn by imitating what they see and hear. An astute observer knows that learning movements is a mimetic task and recognizes that observing and performing movements is closely integrated. Sensory and motor systems are not separate entities. One well studied mechanism that underlies mimetic learning has been called mirroring. Mirror neurons were originally discovered in the ventral premotor cortex of the macaque monkey. These neurons are active when a monkey performs a motor act and again when the monkey, at rest, observes another individual performing a similar motor act. The term mirroring is somewhat in error since similarity is based on a common purpose or goal of the action such as grasping more than a mirror image of the movements performed.
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. To learn, you copy the skillful movements of others and practice these movements until you match or surpass the teacher's skills. 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 expand this modeling capacity by using musical instruments. We can learn to handle sounds much like objects and do sound and 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 playing and instrument.
Three cortical regions control voluntary movement:
Primary motor cortex M1
Premotor cortex (PM)
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 the motors which are 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 discrete. If the map is displayed as pieces of a jig saw puzzle, the pieces are not placed side by side, 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. Schieber described general and specific activation. "During natural movements of discrete body parts, activity is distributed across a wide territory in M1. In monkeys trained to perform individuated movements of each finger, single M1 neurons are active during movements of multiple fingers and neurons throughout M1 hand area are active during movement of any given finger. In humans, performing movements of different fingers, activity is distributed over the primary sensorimotor hand area whether the subject is moving the whole hand or a single finger."
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."
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