Gain-field encoding

Gain field encoding is a hypothesis about the internal storage and processing of limb motion in the brain. In the motor areas of the brain, there are neurons which collectively have the ability to store information regarding both limb positioning and velocity in relation to both the body (intrinsic) and the individual's external environment (extrinsic). The input from these neurons is taken multiplicatively, forming what is referred to as a gain field. The gain field works as a collection of internal models off of which the body can base its movements. The process of encoding and recalling these models is the basis of muscle memory.

Neurons involved in gain field encoding work multiplicatively, taking the input from several together to form the gain field. It is this process that allows the complexity of motor control. Instead of simply encoding the motion of the limb in which a specific motion is desired, the multiplicative nature of the gain field ensures that the positioning of the rest of the body is taken in to consideration. This process allows for motor coordination of flexible bimanual actions as opposed to restricting the individual to unimanual motion. For example, when considering the movement of both arms, the body calls upon gain field models for each arm in order to compensate for the mechanical interactions created by both.

Most gain field activity is based in the premotor cortex found in the frontal lobe anterior to the primary motor cortex, however it receives input from a variety of locations in the brain. These incoming signals provide frame of reference information through the individual's senses. Further evidence suggests that the cerebellum and posterior parietal cortex (PPC) also play major functional roles in gain field encoding. The intrinsic and extrinsic properties of the gain field can be shown as products of the PPC. In Brodmann area 7 of the PPC, the positioning of objects with respect to the eyes is represented completely extrinsically with no input from the positioning of the body involved. This opposes the case of other parts of the PPC such as Brodmann area 5 which represents objects in relation to body defined coordinates. Due to the extrinsic and intrinsic properties of motor functioning, it is speculated that these types of signals are both taken multiplicatively to form the gain field. With input from each area, a three-dimensional representation of the objects in space can be arranged for use by the rest of the motor system.

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