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The Info List - Muscle Memory


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MUSCLE MEMORY has been used synonymously with motor learning , which is a form of procedural memory that involves consolidating a specific motor task into memory through repetition. When a movement is repeated over time, a long-term muscle memory is created for that task, eventually allowing it to be performed without conscious effort. This process decreases the need for attention and creates maximum efficiency within the motor and memory systems. Examples of muscle memory are found in many everyday activities that become automatic and improve with practice, such as riding a bicycle, typing on a keyboard, typing in a PIN , playing a musical instrument, or Poker
Poker
martial arts or even dancing.

CONTENTS

* 1 History

* 1.1 Retention

* 2 Physiology

* 2.1 Motor behavior * 2.2 Muscle
Muscle
memory encoding * 2.3 Muscle
Muscle
memory consolidation * 2.4 Strength training and adaptations

* 3 Fine motor memory

* 3.1 Music memory * 3.2 Puzzle cube memory

* 4 Gross motor memory

* 4.1 Learning in childhood * 4.2 Effect of Alzheimer\'s disease

* 5 Impairment

* 5.1 Consolidation deficit * 5.2 Dysgraphia
Dysgraphia
for the alphabet

* 6 See also * 7 References

HISTORY

The origins of research for the acquisition of motor skills stem from philosophers such as Plato
Plato
, Aristotle
Aristotle
and Galen
Galen
. After the break from tradition of the pre-1900s view of introspection , psychologists emphasized research and more scientific methods in observing behaviours. Thereafter, numerous studies exploring the role of motor learning were conducted. Such studies included the research of handwriting, and various practice methods to maximize motor learning.

RETENTION

The retention of motor skills, now referred to as muscle memory, also began to be of great interest in the early 1900s. Most motor skills are thought to be acquired through practice; however, mere observation of the skill has led to learning as well. Research suggests we do not start off with a blank slate with regard to motor memory although we do learn most of our motor memory repertoire during our lifetime. Movements such as facial expressions, which are thought to be learned, can actually be observed in children who are blind; thus there is some evidence for motor memory being genetically pre-wired.

In the early stages of empirical research of motor memory Edward Thorndike , a leading pioneer in the study of motor memory, was among the first to acknowledge learning can occur without conscious awareness. One of the earliest and most notable studies regarding the retention of motor skills was by Hill, Rejall, and Thorndike, who showed savings in relearning typing skills after a 25-year period with no practice. Findings related to the retention of learned motor skills have been continuously replicated in studies, suggesting that through subsequent practice, motor learning is stored in the brain as memory. This is why performing skills such as riding a bike or driving a car are effortlessly and 'subconsciously' executed, even if someone had not performed these skills in a long period of time.

PHYSIOLOGY

MOTOR BEHAVIOR

When first learning a motor task, movement is often slow, stiff and easily disrupted without attention. With practice, execution of motor task becomes smoother, there is a decrease in limb stiffness, and muscle activity necessary to the task is performed without conscious effort.

MUSCLE MEMORY ENCODING

The neuroanatomy of memory is widespread throughout the brain ; however, the pathways important to motor memory are separate from the medial temporal lobe pathways associated with declarative memory . As with declarative memory, motor memory is theorized to have two stages: a short-term memory encoding stage, which is fragile and susceptible to damage, and a long-term memory consolidation stage, which is more stable.

The memory encoding stage is often referred to as motor learning , and requires an increase in brain activity in motor areas as well as an increase in attention. Brain
Brain
areas active during motor learning include the motor and somatosensory cortices; however, these areas of activation decrease once the motor skill is learned. The prefrontal and frontal cortices are also active during this stage due to the need for increased attention on the task being learned.

The main area involved in motor learning is the cerebellum . Some models of cerebellar-dependent motor learning, in particular the Marr-Albus model, propose a single plasticity mechanism involving the cerebellar long-term depression (LTD) of the parallel fiber synapses onto Purkinje cells
Purkinje cells
. These modifications in synapse activity would mediate motor input with motor outputs critical to inducing motor learning. However, conflicting evidence suggests that a single plasticity mechanism is not sufficient and a multiple plasticity mechanism is needed to account for the storage of motor memories over time. Regardless of the mechanism, studies of cerebellar-dependent motor tasks show that cerebral cortical plasticity is crucial for motor learning, even if not necessarily for storage.

The basal ganglia also play an important role in memory and learning, in particular in reference to stimulus-response associations and the formation of habits. The basal ganglia-cerebellar connections are thought to increase with time when learning a motor task.

MUSCLE MEMORY CONSOLIDATION

Muscle
Muscle
memory consolidation involves the continuous evolution of neural processes after practicing a task has stopped. The exact mechanism of motor memory consolidation within the brain is controversial. However, most theories assume that there is a general redistribution of information across the brain from encoding to consolidation. Hebb\'s rule states that "synaptic connectivity changes as a function of repetitive firing." In this case, that would mean that the high amount of stimulation coming from practicing a movement would cause the repetition of firing in certain motor networks, presumably leading to an increase in the efficiency of exciting these motor networks over time.

Though the exact location of muscle memory storage is not known, studies have suggested that it is the inter-regional connections that play the most important role in advancing motor memory encoding to consolidation, rather than decreases in overall regional activity. These studies have shown a weakened connection from the cerebellum to the primary motor area with practice, it is presumed, because of a decreased need for error correction from the cerebellum. However, the connection between the basal ganglia and the primary motor area is strengthened, suggesting the basal ganglia play an important role in the motor memory consolidation process.

STRENGTH TRAINING AND ADAPTATIONS

See also: Muscle memory (strength training)

When participating in any sport, new motor skills and movement combinations are frequently being used and repeated. All sports require some degree of strength, endurance training, and skilled reaching in order to be successful in the required tasks. Muscle memory related to strength training involves elements of both motor learning, described below, and long-lasting changes in the muscle tissue.

Evidence has shown that increases in strength occur well before muscle hypertrophy , and decreases in strength due to detraining or ceasing to repeat the exercise over an extended period of time precede muscle atrophy . To be specific, strength training enhances motor neuron excitability and induces synaptogenesis , both of which would help in enhancing communication between the nervous system and the muscles themselves.

However, neuromuscular efficacy is not altered within a two-week time period following cessation of the muscle usage; instead, it is merely the neuron 's ability to excite the muscle that declines in correlation with the muscle's decrease in strength. This confirms that muscle strength is first influenced by the inner neural circuitry, rather than by external physiological changes in the muscle size.

Previously untrained muscles acquire newly formed nuclei by fusion of satellite cells preceding the hypertrophy. Subsequent detraining leads to atrophy but no loss of myo-nuclei. The elevated number of nuclei in muscle fibers that had experienced a hypertrophic episode would provide a mechanism for muscle memory, explaining the long-lasting effects of training and the ease with which previously trained individuals are more easily retrained.

On subsequent detraining, the fibers maintain an elevated number of nuclei that might provide resistance to atrophy; on retraining, a gain in size can be obtained by a moderate increase in the protein synthesis rate of each of these many nuclei, skipping the step of adding newly formed nuclei. This shortcut may contribute to the relative ease of retraining compared with the first training of individuals with no previous training history.

Reorganization of motor maps within the cortex are not altered in either strength or endurance training. However, within the motor cortex, endurance induces angiogenesis within as little as three weeks to increase blood flow to the involved regions. In addition, neurotropic factors within the motor cortex are upregulated in response to endurance training to promote neural survival.

Skilled motor tasks have been divided into two distinct phases: a fast-learning phase, in which an optimal plan for performance is established, and a slow-learning phase, in which longer-term structural modifications are made on specific motor modules. Even a small amount of training may be enough to induce neural processes that continue to evolve even after the training has stopped, which provides a potential basis for consolidation of the task. In addition, studying mice while they are learning a new complex reaching task, has found that "motor learning leads to rapid formation of dendritic spines (spinogenesis) in the motor cortex contralateral to the reaching forelimb". However, motor cortex reorganization itself does not occur at a uniform rate across training periods. It has been suggested that the synaptogenesis and motor map reorganization merely represent the consolidation, and not the acquisition itself, of a specific motor task. Furthermore, the degree of plasticity in various locations (namely motor cortex versus spinal cord) is dependent on the behavioural demands and nature of the task (i.e., skilled reaching versus strength training).

Whether strength or endurance related, it is plausible that the majority of motor movements would require a skilled moving task of some form, whether it be maintaining proper form when paddling a canoe, or bench pressing a heavier weight. Endurance training assists the formation of these new neural representations within the motor cortex by up regulating neurotropic factors that could enhance the survival of the newer neural maps formed due to the skilled movement training. Strength training results are seen in the spinal cord well before any physiological muscular adaptation is established through muscle hypertrophy or atrophy. The results of endurance and strength training, and skilled reaching, therefore, combine to help each other maximize performance output.

FINE MOTOR MEMORY

Fine motor skills are often discussed in terms of transitive movements, which are those done when using tools (which could be as simple as a tooth brush or pencil). Transitive movements have representations that become programmed to the premotor cortex , creating motor programs that result in the activation of the motor cortex and therefore the motor movements. In a study testing the motor memory of patterned finger movements (a fine motor skill) it was found that retention of certain skills is susceptible to disruption if another task interferes with one's motor memory. However, such susceptibility can be reduced with time. For example, if a finger pattern is learned and another finger pattern is learned six hours later, the first pattern will still be remembered. But attempting to learn two such patterns one immediately after the other could cause the first one to be forgotten. Furthermore, the heavy use of computers by recent generations has had both positive and negative effects. One of the main positive effects is an enhancement of children's fine motor skills. Repetitive behaviors, such as typing on a computer from a young age, can enhance such abilities. Therefore, children who learn to use computer keyboards at an early age could benefit from the early muscle memories.

MUSIC MEMORY

Playing the piano requires complex actions

Fine motor skills are very important in playing musical instruments. It was found that muscle memory is relied on when playing the clarinet, specifically to help create special effects through certain tongue movements when blowing air into the instrument.

Certain human behaviours, especially actions like the finger movements in musical performances, are very complex and require many interconnected neural networks where information can be transmitted across multiple brain regions. It has been found that there are often functional differences in the brains of professional musicians, when compared to other individuals. This is thought to reflect the musician's innate ability, which may be fostered by an early exposure to musical training. An example of this is bimanual synchronized finger movements, which play an essential role in piano playing. It is suggested that bimanual coordination can come only from years of bimanual training, w