.<\/p>\n
The motor memory we use everyday-for sport, playing a musical . The motor memory we use everyday-for sport, playing a musical instrument and even typing-is acquired through repeated practice and stored in the brain. New motor skills can be learned through practice, but often those skills can be all but lost by the following day. This loss of motor skills can be attributed to the … <\/p>\n
\n instrument and even typing-is acquired through repeated practice
\n and stored in the brain. New motor skills can be learned through
\npractice, but often those skills can be all but lost by the following
\nday. This loss of motor skills can be attributed to the storage of
\nnewly learned motor skills in short-term memory. By repeating
\nthe exercises on a daily basis, however, these skills become stored in
\n long-term memory. In 2006, a team led by Soichi Nagao, head of the
\n Laboratory for Motor Learning Control at the RIKEN Brain Science
\n Institute (BSI), discovered that short-term motor memory is transferred
\nto a different site to become long-term memory, and that brain activity
\nwhile the body is at rest is important for creating long-term memory-
\nmore so than the brain activity while the body is working. With this
\ndiscovery, research into the mechanism of motor memory is now
\nbreaking new ground. A 40-year debate
\n.
\nThe mechanism of memory was originally attributed to changes in the transmission
\nefficiency of synapses in the brain. Around 1970, it was proposed that motor memory
\n specifically was created within the neural network of the cerebellum. One of the
\nadvocates of this theory was Masao Ito, senior advisor to the BSI. In 1982, Ito
\nexperimentally discovered the phenomenon of 'long-term depression', by which
\nthe transmission efficiency in the cerebellum is depressed over a long period of
\n time.
\n.
\nIn 1983, Nagao started work as a laboratory lecturer for Ito, who was then in the Faculty
\nof Medicine at The University of Tokyo. "Since then, I have continued my studies to
\nverify and develop the theoretical hypothesis proposed by Dr Ito and other researchers,"
\nsays Nagao.
\n.
\nThe process of eye movement is a good illustration of how the hypothesis proposed by Ito
\n works). Command signals that control eye movement are transmitted to the vestibular
\nnucleus in the medulla oblongata over two routes: one direct and the other indirect
\npassway via the parallel fibers and Purkinje cells of the cerebellar cortex. The vestibular
\n nucleus processes the command signals transmitted over both routes and outputs the
\n processed signals to the motor nerves, which in turn, control the movement of the eye.
\n.
\nA single Purkinje cell is connected to up to 200,000 parallel fibers, through which
\nommand signals to control movements are transmitted to the Purkinje cell. A single
\nclimbing fiber is connected to the Purkinje cell, and when an eye fails to move properly,
\n error signals are transmitted from the eye to the Purkinje cell through an inferior olivary
\nnucleus and the climbing fiber. This process triggers long-term depression, suppressing
\nthe transmission efficiency of the command signals at the synapses connecting the parallel
\n fibers to the Purkinje cell. When the eye moves properly, no long-term depression is
\n triggered because the error signals are low. In this way, command signals from the
\nPurkinje cell to the vestibular nucleus can change dynamically because of the long-term
\ndepression induced in response to eye movement. "Command signals from the vestibular
\nnucleus to the motor nerves are controlled so that the eye can move properly," says Nagao.
\n "In other words, Dr Ito's theory states that motor memory is created in Purkinje cells in the
\ncerebellar cortex through long-term depression."
\n.
\nPurkinje cells in the evolutionarily oldest region of the cerebellar cortex-the vestibulocerebellum-
\nhave axons that extend to the vestibular nuclei, whereas Purkinje cells in the newer region-the
\narchicerebellum and neocerebellum-have axons that extend to the deep cerebellar nuclei to
\n form neural circuits.
\n.
\n"Doctor Ito's hypothesis is controversial and has been debated for about 40 years. A
\ntypical argument runs as follows: it is true that Purkinje cells are capable of transmitting
\nthe information necessary for motor memory, but the memory is created in the vestibular
\nor cerebellar nuclei."
\n.
\nThe long-term motor memory<\/strong>
\n.
\nIn 2006, Nagao published an article that finally settled the dispute over where motor
\n memory is created: in Purkinje cells in the cerebellar cortex, or in the vestibular or
\ncerebellar nuclei? The achievement came just two years after he established the
\nLaboratory for Motor Learning Control at the RIKEN BSI in 2004. Nagao and his
\nlaboratory members developed a new experimental system using mice to examine the
\nmemory of eye movement. One of the mechanisms of eye movement allows us to track
\nobjects reflexively, like when watching the passing view from a train window. If this
\n mechanism, known as optokinetic eye movement response, is working properly, the
\n view is clear and we can see passing objects. The memory function of the optokinetic
\neye movement response can be evaluated by placing a checkered screen in front of a
\n mouse and moving it in a wave-like manner. "The mouse will get used to the
\nmovement in about an hour of exercise and will be able to follow the movement of
\n the checkered screen by moving its eyes in a wave-like motion. This is because
\nmotor memory has been created, and the eye movement efficiency of the mouse
\nhas improved. However, when the mouse is kept in a dark room after the exercise,
\nand when the eye movement efficiency is examined the next day, you will find the
\nefficiency has returned to the initial state."
\n.
\nEven when motor memory has been established after one day of exercise, most
\nmemory is lost within several hours. This is because only short-term memory is
\n created in the first instance, but this can be improved. "A mouse can gradually
\n improve its eye movement efficiency when we get the mouse to do exercises on
\na daily basis. A mouse that has done such exercises for one week can maintain
\n its eye movement efficiency at a higher level than before it started, even after the
\nexercises have been terminated. This means that long-term memory has been
\nestablished."
\n.
\nHowever, it was still unknown whether these short- and long-term motor memories
\nare created in Purkinje cells in the cerebellar cortex or somewhere else. "To stop the
\nfunction of the cerebellar cortex, we administered local anesthesia to the cerebellar
\ncortex of a mouse that had repeated specific exercises for four days and examined
\n the eye movement efficiency of the mouse. We found that the efficiency remained
\nat the same level as when the exercise was started on the fourth day. In other
\n words, the previous three days had contributed to improving the eye movement
\nefficiency and the efficiency then remained at that level, indicating that long-term
\nmemory was created at a site other than in the cerebellar cortex." The exercise on
\nthe fourth and subsequent days, on the other hand, did not add to improving the
\neye movement efficiency, indicating that short-term memory was created in Purkinje
\ncells in the cerebellar cortex.
\n.
\nNagao and his team then conducted experiments to confirm whether long-term memory
\n is created in the vestibular nucleus. "We discovered that no motor memory is created in
\n either the cerebellar cortex or the vestibular nucleus alone, but that short- and long-term
\nmemories are created at different sites: short-term memory in Purkinje cells in the
\ncerebellar cortex and long-term memory in the vestibular nucleus. Around the time we
\n published these experimental results, other research groups also reported similar
\nresults using different models. That is how we succeeded in settling the 40-year debate."
\n.
\nNeither short- nor long-term memory is created when the functioning of the cerebellar
\ncortex is impeded. "Motor memory is initiated by short-term memory by long-term depression
\n in Purkinje cells in the cerebellar cortex. Short-term memory becomes long-term memory
\nwhen it is transferred in one way or another to the vestibular nucleus, into which axons
\nextend from the Purkinje cells. Long-term memory is considered to be created in neural
\ncircuits in the vestibular or cerebellar nuclei, into which axons extend from the Purkinje
\ncells.
\n.
\nNot made for sophisticated motion<\/strong>
\n.
\nIt is thought that information that can be expressed verbally, such as experienced events
\nand the spelling of English words, is stored in the hippocampus, deep in the cerebrum, as
\nshort-term memory, and is later transferred to the cerebral cortex to become long-term
\nmemory. "The short-term memory of effable information is not immediately transferred
\nto the cerebral cortex, but stays in the hippocampus for a few weeks. We have clarified
\nthat short-term motor memory created in Purkinje cells in the cerebellar cortex is trans
\nferred to the vestibular or cerebellar nuclei in as little as several hours or as long as
\n several days."
\n.
\nHowever, it has become clear that not all information in short-term motor memory becomes
\n long-term motor memory. Nagao and his team used monkeys to investigate how
\nsophisticated motion is memorized. In the experiment, the speed of a moving ball is
\n suddenly increased for a fifth to a tenth of a second. "In this experiment, monkeys are
\n required to follow the complex motion of the ball, called 'smooth-pursuit eye movement'.
\n Monkeys usually get used to the motion only after the exercise has been repeated a few
\n dozen times, moving their eyes based on their prediction of the change in the speed of
\n the ball. However, sophisticated motor memory of this kind is easily lost in just ten to 15
\nminutes. In other words, the memory of sophisticated motion is stored quickly but also lost
\nquickly. One major advantage in terms of short-time memory in the cerebellar cortex is that
\nsophisticated motion can be memorized very quickly." For example, a baseball batter will
\n be able to hit a curve ball after the movement of the ball has been observed several
\n times and memorized. Unfortunately, however, it has become clear that sophisticated
\nmotor memory of this kind hardly ever becomes long-term memory because only the
\n broad information in short-time memory is transferred to long-term memory.
\n.
\n"It is said that skills that are learned physically cannot really be forgotten. For example,
\n once you have learned how to ride a bicycle, you will be able to ride a bicycle again with
\na little practice even after a long period without riding. We can consider long-term motor
\nmemory to be robust and difficult to forget. However, we should respect the importance of
\n 'a little practice' because long-term motor memory only holds rough or broad information.
\n We need to activate the functions of the cerebellar cortex by memorizing sophisticated
\nmovement to get the 'feel' for the movement. I do not think that any professional musicians
\nwould be able to show their abilities at a concert without practicing beforehand."
\n.
\nThere are evolutionary reasons why short- and long-term memories are created at different
\n sites in the brain. "Keeping specific sophisticated motor information in the cerebellar cortex
\n for a long time would make it difficult to adapt movements quickly in response to
\nenvironmental changes. I think that transferring only basic motor information to the vestibular
\nor cerebellar nuclei as long-term memory ensures that sophisticated movements will always
\n be stored in the cerebellar cortex and remain adaptable in response to changing situations."
\n All vertebrate animals, from fish to mammals, have the same mechanism of short- and
\nlong-term motor memory storage at different sites. Invertebrate animals, however, are known
\n to store short- and long-term motor memories at the same site in their neural circuits.
\n "This difference is one of the features that differentiate vertebrate animals from invertebrates."
\n.
\nInterval training for long-term memory<\/strong>
\n.
\nThe mechanism of how short-term memory in the cerebellar cortex is transferred to the
\nvestibular or cerebellar nuclei to become long-term memory is still open for debate. "Making
\nuse of a variety of techniques, we are working towards answering the question." Recently,
\nNagao and his team discovered that short-term memory is transferred efficiently to long-term
\nmemory when experiments on motor memorization using animals are conducted with
\n intervals between the exercises rather than conducting the experiment continuously.
\n "For example, a one-hour experiment can be divided into four short 15-minute exercises
\n with intervals of 30 minutes between them for higher transfer efficiency. We also discovered
\nthat no long-term memory is created irrespective of the number of repeated exercises if the
\nfunctions of the cerebellar cortex are deactivated during those intervals."
\n.
\nThese findings suggest that the activities of the cerebellar cortex during periods of inactivity
\nare important in creating long-term memory. This presents the question of what happens in the
\ncerebellar cortex during the intervals to cause long-term memory to be created in the vestibular
\n or cerebellar nuclei. "We have not yet obtained experimental data that can lead us to a
\nconclusion. However, we are beginning to collect important data that suggest the importance
\n of 'long-term potentiation', which enhances the transmission efficiency of synapses, for
\n long-term memory creation."
\n.
\nCoachly advice<\/strong>
\n.
\nNagao's research provides some valuable pointers as to how to improve sporting and
\nperformance skills. "The key is to repeat exercises, with intervals, on a daily basis. Top
\n athletes and musicians will be more talented than ordinary people in creating short-term
\nand long-term memories. Motor memory, however, is not created without repeated exercise.
\n I think even someone who is thought of as a genius needs to continue daily exercises
\nbecause motor information on sophisticated movements is difficult to establish as
\n long-term memory."
\n.<\/p>\n","protected":false},"excerpt":{"rendered":"