In physiology, motor coordination is the orchestrated movement of multiple body parts as required to accomplish intended actions, like walking. This coordination is achieved by adjusting kinematic and kinetic parameters associated with each body part involved in the intended movement. The modifications of these parameters typically relies on sensory feedback from one or more sensory modalities (see multisensory integration), such as proprioception and vision.
Properties
Large Degrees of Freedom
Goal-directed and coordinated movement of body parts is inherently variable because there are many ways of coordinating body parts to achieve the intended movement goal. This is because the degrees of freedom (DOF) is large for most movements due to the many associated neuro-musculoskeletal elements. Some examples of non-repeatable movements are when pointing or standing up from sitting. Actions and movements can be executed in multiple ways because synergies (as described below) can vary without changing the outcome. Early work from Nikolai Bernstein worked to understand how coordination was developed in executing a skilled movement. In this work, he remarked that there was no one-to-one relationship between the desired movement and coordination patterns to execute that movement. This equivalence suggests that any desired action does not have a particular coordination of neurons, muscles, and kinematics.
Complexity
The complexity of motor coordination goes unnoticed in everyday tasks, such as in the task of picking up and pouring a bottle of water into a glass. This seemingly simple task is actually composed of multiple complex tasks. For instance, this task requires the following:
(1) properly reaching for the water bottle and then configuring the hand in a way that enables grasping the bottle.
(2) applying the correct amount of grip force to grasp the bottle without crushing it.
(3) coordinating the muscles required for lifting and articulating the bottle so that the water can be poured into the glass.
(4) terminating the action by placing the empty bottle back on the table.
Hand-eye coordination is also required in the above task. There is simultaneous coordination between hand and eye movement as dictated by the multi-sensory integration of proprioceptive and visual information. Additional levels of coordination are required depending on if the person intends to drink from the glass, give it to someone else, or simply put it on a table.
Types of Motor Coordination
Inter-limb
Inter-limb coordination is concerned about how movements are coordinated across limbs. In walking for instance, inter-limb coordination refers to the spatiotemporal patterns and kinematics associated with the movement of the legs. Prior work in vertebrates showed that distinct inter-limb coordination patterns, called gaits, occur at different walking speed ranges as to minimize the cost of transport. Like vertebrates, drosophila change their interleg coordination pattern in a speed-dependent manner. However, these coordination patterns follow a continuum rather than distinct gaits.
In bimanual tasks (tasks involving two hands), it was found that the functional segments of the two hands are tightly synchronized. One of the postulated theories for this functionality is the existence of a higher, "coordinating schema" that calculates the time it needs to perform each individual task and coordinates it using a feedback mechanism. There are several areas of the brain that are found to contribute to temporal coordination of the limbs needed for bimanual tasks, and these areas include the premotor cortex (PMC), the parietal cortex, the mesial motor cortices, more specifically the supplementary motor area (SMA), the cingulate motor cortex (CMC), the primary motor cortex (M1), and the cerebellum.
Several studies have proposed that inter-limb coordination can be modeled by coupled phase oscillators, a key component of a central pattern generator (CPG) control architecture. In this framework, the coordination between limbs is dictated by the relative phase of the oscillators representing the limbs. Specifically, an oscillator associated with a particular limb determines the progression of that limb through its movement cycle (e.g. step cycle in walking). In addition to driving the relative limb movement in a forward manner, sensory feedback can be incorporated into the CPG architecture. This feedback also dictates the coordination between the limbs by independently modifying the movement of the limb that the feedback is acting on.