Interlimb coordination

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Human locomotion Muybridge human male walking animated.gif
Human locomotion

Interlimb coordination is the coordination of the left and right limbs. It could be classified into two types of action: bimanual coordination and hands or feet coordination. Such coordination involves various parts of the nervous system and requires a sensory feedback mechanism for the neural control of the limbs. A model can be used to visualize the basic features, the control centre of locomotor movements, and the neural control of interlimb coordination. This coordination mechanism can be altered and adapted for better performance during locomotion in adults and for the development of motor skills in infants. The adaptive feature of interlimb coordination can also be applied to the treatment for CNS damage from stroke and the Parkinson's disease in the future.

Contents

Types of interlimb coordination

Bimanual coordination

Bimanual coordination involves the coordination of two arms in bimanual action, which allows two hands to move simultaneously to do tasks. [1] Examples of bimanual coordination include clapping hands, opening the cap of a bottle with two hands or typing words on a keyboard with both hands.

Hands/ feet coordination

Hands/ feet coordination involves the coordination of the upper limbs and the lower limbs, including the ipsilateral side of the body (e.g. left hand and left foot), or the contralateral side (both sides of the limbs). Examples include walking and climbing.

Mechanisms of interlimb coordination

Nervous system involved in interlimb coordination

Different parts of the brain are included in such coordination, including the premotor cortex (PMC), the parietal cortex, the mesial motor cortices, the supplementary motor area, the cingulate motor cortex, the primary motor cortex cerebellum and the spinal cord. [2]

Sensory feedback mechanism

Sensory feedback mechanism is involved in interlimb coordination. The sensory receptors including muscle spindles, golgi tendon organs in the limbs will first be stimulated by the external stimuli (e.g. pressure of touching an object), then generate sensory feedbacks and send information to the nervous system through the afferent pathways. [3] After receiving the feedback, the central nervous system (CNS) will then generate an internal schema of the orientation and motion of the limbs, [4] which allows the nervous system to monitor the consequence of action so that efficient sensory regulation of the limbs could be made. This allows independent modification of the movements of the limb to better manipulate the tasks.

Types of sensory feedback mechanism

There are two types of sensory feedback, intrinsic and extrinsic pathways. Intrinsic feedback will be received only from the organism's own movement, [5] which means it is the internal physical feeling of the movement performed by the organism. For example, a person can feel its movement of making a fist without any external stimulus because it requires the folding of the fingers tightly into the centre of the palm and placing of the thumb over the folding fingers. In contrast, extrinsic feedback to be received must be provided from external sources from the environment. For instance, our fingers can detect heat from boiling water and pain from the poking of needle because the heat and pain receptors receive external stimuli from the surroundings.

Modelization of interlimb coordination

Basic features

The coordination of interlimb can be represented by an integrated model which contains a central pattern generator (CPG), nonlinear muscles, hexahedral geometry, and a representative proprioceptive sensory pathway. One-dimensional phase oscillators are used to stimulate the movement of agonist-antagonist muscle pairs. Different phases of the oscillators are responsible to demonstrate the movements between the limbs. A specific oscillator with respect to the specific muscle from a specific limb could show the progression and development of that limb through its movement, for instance, the progression and development of the step cycle of the left limb in walking motion. Reflex response (e.g. biceps contracts and triceps relaxes to bend the elbow) is also incorporated in the model using stereotypical spike trains to represent, such that the reflexive feedback mechanism can also be demonstrated during the movement of muscles. [6]

Control centre of locomotor movements

The spinal cord is the core of the neural control of locomotion. This organ is the integrative centre of the CNS for motor control, it is done by receiving sensory information from peripheral receptors to control and adjust movements. [7] The central pattern generator (CPG) from the model is simulated as a network of spinal neurons that controls the basic locomotor output. [8] An effective locomotion of the model must involve a flexible coordination of spinal cord neuronal networks, thus allowing various gait patterns and independent use of the limbs. This flexible coordination can be accomplished by integrating the intrinsic regulation mechanism of the spinal cord, somatosensory feedback from the limbs and various supraspinal pathways in the model. [9]

The mechanical linkages between the limbs and trunk is important for the stabilization of multi-limb coordination movements. In return, the CNS will receive information of mechanical state of the limbs and trunk as it interacts with the environment through somatosensory feedback from the periphery. [9]

Control of arm-leg coordination during human locomotion

Rhythmic movement of the arms during bipedal walking is generated by passive biomechanical linkages and neural commands generated by spinal locomotor CPGs that control rhythmic arm and leg movements. [10] Although movement of the arms is less important to maintain dynamic stability during bipedal walking, the arms remain rhythmically coordinated with the legs. The human CNS integrated new control mechanisms into circuits already present to meet the need for new functional demands.

The neural coupling between arms and legs can be presented by the association between electromyography (EMG) activity from the upper limb and leg kinematics. Muscles of the upper limb show rhythmic activity related to arm swing, even when the arm is paralyzed. [11] The EMG activity shows that coordination of arm-leg movement still provide stimulation to the limb regardless to the mobility of limbs.

Schematic representation of the neural control of interlimb coordination

Each limb has its own spinal locomotor CPG, a schematic representation can illustrate the interactions between parts of the CPG controlling flexor and extensor activity. [12]

A schematic representation of the locomotor central pattern generator in the mammalian nervous system Locomotor CPG schematic.jpg
A schematic representation of the locomotor central pattern generator in the mammalian nervous system

Adaptations of interlimb coordination

The control of interlimb coordination is precise and flexible, therefore humans can maintain dynamic stability in a continuously changing environment, such as changing speed, or transitioning from one gait pattern to another. [9]

Change in adult gait patterns

Recent studies found out that adaptive changes only occur in interlimb coordination but do not occur in intralimb coordination (coordination on the same limb but different joints). [13] A split-belt treadmill (a treadmill that contains two belts that can drive each leg at different speeds) was used in the experiment, this intervention alters the walking or running speed of the users. Participants were stimulated to walk at different speeds alternatively, and locomotor parameters were used to calculate the movement of limbs during the gait cycle. The subjects appeared to have new motor patterns after walking on the treadmill, which indicated that a new interlimb coordination pattern was adapted and stored in participants. [13]

Development of motor skills in infants

Age was found to be related to changes in interlimb coordination such as the correlation between limb positions or between limb velocities. Changes and improvements in interlimb coordination by age are recognized to be a major phenomenon in the development of gross motor skills in infants. It was also found that a combination of movement of the arms and legs might be a precursor to some goal-directed behaviors such as reaching and grasping with the arms while walking with legs by infants. [14]

CNS damage from stroke

Cerebral structures that are involved with stroke do not impair the adaptive ability of interlimb coordination and the storage of new interlimb relationships, and therefore patients of cerebral stroke are found to be able to adapt new mechanism of interlimb coordination. [15] Given that the coordination of the limbs can be adaptively change, it is expected there is a possibility that the asymmetric walking patterns as a result of CNS damage from stroke could be improved by long-term adaptive rehabilitation strategies using a split-belt treadmill. [13] [15]

Parkinson's disease

Freezing of Gait (FOG) is a disabling symptom commonly found in Parkinson's Disease. FOG is a major contributor to fall risk in Parkinson's Disease patients and can only be partially relieved by medication. Parkinson's patients with FOG are known to have more difficulty with gait adaptation in their daily movements. [16] Further, asymmetry of gait has been implicated in FOG as patients with FOG often fail to complete asymmetric tasks such as turning. Split-belt treadmill training (SBT), but not regular tied-belt treadmill training (TBT) can be used as a rehabilitation method for people with FOG by practicing their ability to adapt their gait pattern to asymmetrical circumstances. SBT improved gait adaptation immediately after the training and more importantly, improvements were retained up till 24 hours. The advantage of SBT is that it modulates gait more implicitly without attention being consciously drawn to the adaptation task. [17] [16] Furthermore, repeated adaptations of the gait pattern may improve the flexible adaptation of the movement to new tasks and may train motor switching, which could potentially improve motor performance in a more sustained manner. In addition, the cerebellar circuits became more involved in the processing of gait adaptation with repeated exposure to SBT, [18] which may possibly lead to improvement in balancing and hence reduce the risk of falling. [16]

Related Research Articles

<span class="mw-page-title-main">Gait (human)</span> A pattern of limb movements made during locomotion

A gait is a manner of limb movements made during locomotion. Human gaits are the various ways in which humans can move, either naturally or as a result of specialized training. Human gait is defined as bipedal forward propulsion of the center of gravity of the human body, in which there are sinuous movements of different segments of the body with little energy spent. Varied gaits are characterized by differences such as limb movement patterns, overall velocity, forces, kinetic and potential energy cycles, and changes in contact with the ground.

Central pattern generators (CPGs) are self-organizing biological neural circuits that produce rhythmic outputs in the absence of rhythmic input. They are the source of the tightly-coupled patterns of neural activity that drive rhythmic and stereotyped motor behaviors like walking, swimming, breathing, or chewing. The ability to function without input from higher brain areas still requires modulatory inputs, and their outputs are not fixed. Flexibility in response to sensory input is a fundamental quality of CPG-driven behavior. To be classified as a rhythmic generator, a CPG requires:

  1. "two or more processes that interact such that each process sequentially increases and decreases, and
  2. that, as a result of this interaction, the system repeatedly returns to its starting condition."

Motor control is the regulation of movements in organisms that possess a nervous system. Motor control includes conscious voluntary movements, subconscious muscle memory and involuntary reflexes, as well as instinctual taxis.

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, such as proprioception and vision.

<span class="mw-page-title-main">Scratch reflex</span> Response to activation of sensory neurons

The scratch reflex is a response to activation of sensory neurons whose peripheral terminals are located on the surface of the body. Some sensory neurons can be activated by stimulation with an external object such as a parasite on the body surface. Alternatively, some sensory neurons can respond to a chemical stimulus that produces an itch sensation. During a scratch reflex, a nearby limb reaches toward and rubs against the site on the body surface that has been stimulated. The scratch reflex has been extensively studied to understand the functioning of neural networks in vertebrates. Despite decades of research, key aspects of the scratch reflex are still unknown, such as the neural mechanisms by which the reflex is terminated.

<span class="mw-page-title-main">Undulatory locomotion</span>

Undulatory locomotion is the type of motion characterized by wave-like movement patterns that act to propel an animal forward. Examples of this type of gait include crawling in snakes, or swimming in the lamprey. Although this is typically the type of gait utilized by limbless animals, some creatures with limbs, such as the salamander, forgo use of their legs in certain environments and exhibit undulatory locomotion. In robotics this movement strategy is studied in order to create novel robotic devices capable of traversing a variety of environments.

<span class="mw-page-title-main">Spinal locomotion</span>

Spinal locomotion results from intricate dynamic interactions between a central program in lower thoracolumbar spine and proprioceptive feedback from body in the absence of central control by brain as in complete spinal cord injury (SCI). Following SCI, the spinal circuitry below the lesion site does not become silent; rather, it continues to maintain active and functional neuronal properties, although in a modified manner.

In neuroscience and motor control, the degrees of freedom problem or motor equivalence problem states that there are multiple ways for humans or animals to perform a movement in order to achieve the same goal. In other words, under normal circumstances, no simple one-to-one correspondence exists between a motor problem and a motor solution to the problem. The motor equivalence problem was first formulated by the Russian neurophysiologist Nikolai Bernstein: "It is clear that the basic difficulties for co-ordination consist precisely in the extreme abundance of degrees of freedom, with which the [nervous] centre is not at first in a position to deal."

<span class="mw-page-title-main">Neural substrate of locomotor central pattern generators in mammals</span>

Central pattern generators are biological neural networks organized to produce any rhythmic output without requiring a rhythmic input. In mammals, locomotor CPGs are organized in the lumbar and cervical segments of the spinal cord, and are used to control rhythmic muscle output in the arms and legs. Certain areas of the brain initiate the descending neural pathways that ultimately control and modulate the CPG signals. In addition to this direct control, there exist different feedback loops that coordinate the limbs for efficient locomotion and allow for the switching of gaits under appropriate circumstances.

<span class="mw-page-title-main">Arm swing in human locomotion</span>

Arm swing in human bipedal walking is a natural motion wherein each arm swings with the motion of the opposing leg. Swinging arms in an opposing direction with respect to the lower limb reduces the angular momentum of the body, balancing the rotational motion produced during walking. Although such pendulum-like motion of arms is not essential for walking, recent studies point that arm swing improves the stability and energy efficiency in human locomotion. Those positive effects of arm swing have been utilized in sports, especially in racewalking and sprinting.

When treating a person with a spinal cord injury, repairing the damage created by injury is the ultimate goal. By using a variety of treatments, greater improvements are achieved, and, therefore, treatment should not be limited to one method. Furthermore, increasing activity will increase his/her chances of recovery.

Neuromechanics of orthoses refers to how the human body interacts with orthoses. Millions of people in the U.S. suffer from stroke, multiple sclerosis, postpolio, spinal cord injuries, or various other ailments that benefit from the use of orthoses. Insofar as active orthoses and powered exoskeletons are concerned, the technology to build these devices is improving rapidly, but little research has been done on the human side of these human-machine interfaces.

Motor adaptation, a form of motor learning, is the process of acquiring and restoring locomotor patterns through an error-driven learning process.

<span class="mw-page-title-main">Spinal interneuron</span> Interneuron relaying signals between sensory and motor neurons in the spinal cord

A spinal interneuron, found in the spinal cord, relays signals between (afferent) sensory neurons, and (efferent) motor neurons. Different classes of spinal interneurons are involved in the process of sensory-motor integration. Most interneurons are found in the grey column, a region of grey matter in the spinal cord.

<span class="mw-page-title-main">Proportional myoelectric control</span>

Proportional myoelectric control can be used to activate robotic lower limb exoskeletons. A proportional myoelectric control system utilizes a microcontroller or computer that inputs electromyography (EMG) signals from sensors on the leg muscle(s) and then activates the corresponding joint actuator(s) proportionally to the EMG signal.

<span class="mw-page-title-main">Cutaneous reflex in human locomotion</span>

Cutaneous, superficial, or skin reflexes, are activated by skin receptors and play a valuable role in locomotion, providing quick responses to unexpected environmental challenges. They have been shown to be important in responses to obstacles or stumbling, in preparing for visually challenging terrain, and for assistance in making adjustments when instability is introduced. In addition to the role in normal locomotion, cutaneous reflexes are being studied for their potential in enhancing rehabilitation therapy (physiotherapy) for people with gait abnormalities.

<span class="mw-page-title-main">Mesencephalic locomotor region</span>

The mesencephalic locomotor region (MLR) is a functionally defined area of the midbrain that is associated with the initiation and control of locomotor movements in vertebrate species.

Postural control refers to the maintenance of body posture in space. The central nervous system interprets sensory input to produce motor output that maintains upright posture. Sensory information used for postural control largely comes from visual, proprioceptive, and vestibular systems. While the ability to regulate posture in vertebrates was previously thought to be a mostly automatic task, controlled by circuits in the spinal cord and brainstem, it is now clear that cortical areas are also involved, updating motor commands based on the state of the body and environment.

The study of animal locomotion is a branch of biology that investigates and quantifies how animals move.

Proprioception refers to the sensory information relayed from muscles, tendons, and skin that allows for the perception of the body in space. This feedback allows for more fine control of movement. In the brain, proprioceptive integration occurs in the somatosensory cortex, and motor commands are generated in the motor cortex. In the spinal cord, sensory and motor signals are integrated and modulated by motor neuron pools called central pattern generators (CPGs). At the base level, sensory input is relayed by muscle spindles in the muscle and Golgi tendon organs (GTOs) in tendons, alongside cutaneous sensors in the skin.

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