Motor Long-term Memory Research Articles

Disruption of Primary Motor Cortex before Learning Impairs Memory of Movement Dynamics

Although multiple lines of evidence implicate the primary motor cortex (M1) in motor learning, the precise role of M1 in the adaptation to novel movement dynamics and in the subsequent consolidation of a memory of those dynamics remains unclear. Here we used repetitive transcranial magnetic stimulation (rTMS) to dissociate the contribution of M1 to these distinct aspects of motor learning. Subjects performed reaching movements in velocity-dependent force fields over three epochs: a null-field baseline epoch, a clockwise-field learning epoch (15 min after the baseline epoch), and a clockwise-field retest epoch (24 h after the learning epoch). Half of the subjects received 15 min of 1 Hz rTMS to M1 between the baseline and learning epochs. Subjects given rTMS performed identically to control subjects during the learning epoch. However, control subjects performed with significantly less error than rTMS subjects in the retest epoch on the following day. These results suggest that M1 is not critical to the network supporting motor adaptation per se but that, within this network, M1 may be important for initiating the development of long-term motor memories.

When practice does not make perfect: well-practiced handwriting interferes with the consolidation phase gains in learning a movement sequence

Practice on a novel sequence of movements can lead to two expressions of procedural memory consolidation: delayed performance gains evolving hours after training, and a decrease in the susceptibility of the training-related gains to interference by subsequent experience. It has been assumed that behavioral interference occurs only if a critical overlap between the representations of the two tasks exists, and that such overlap is more likely when the two tasks are novel, competing for general resources for their execution. We investigated whether the delayed gains in the simple finger-opposition sequence (FOS) learning task are more prone to interference by well practiced than by less practiced complex hand movements. Participants were trained on the FOS task in a baseline (no interference) and an interference training condition. In the Interference condition, after FOS practice, participants wrote Hebrew common words in Hebrew (native script) or a Latin script (Heblatin). Native script writing but not the less practiced Heblatin, interfered with FOS learning, with significantly reduced delayed gains. Our results show that interference can occur even when two tasks share little or no kinematic or dynamic features and indicate that the representation of complex but well-practiced movement sequences may overlap with the representation of simpler ones. This result is in line with the notion that well-practiced complex movement sequences come to be represented as simpler ones in long-term motor memory.

Reading depends on writing, in Chinese

Language development entails four fundamental and interactive abilities: listening, speaking, reading, and writing. Over the past four decades, a large body of evidence has indicated that reading acquisition is strongly associated with a child's listening skills, particularly the child's sensitivity to phonological structures of spoken language. Furthermore, it has been hypothesized that the close relationship between reading and listening is manifested universally across languages and that behavioral remediation using strategies addressing phonological awareness alleviates reading difficulties in dyslexics. The prevailing view of the central role of phonological awareness in reading development is largely based on studies using Western (alphabetic) languages, which are based on phonology. The Chinese language provides a unique medium for testing this notion, because logographic characters in Chinese are based on meaning rather than phonology. Here we show that the ability to read Chinese is strongly related to a child's writing skills and that the relationship between phonological awareness and Chinese reading is much weaker than that in reports regarding alphabetic languages. We propose that the role of logograph writing in reading development is mediated by two possibly interacting mechanisms. The first is orthographic awareness, which facilitates the development of coherent, effective links among visual symbols, phonology, and semantics; the second involves the establishment of motor programs that lead to the formation of long-term motor memories of Chinese characters. These findings yield a unique insight into how cognitive systems responsible for reading development and reading disability interact, and they challenge the prominent phonological awareness view.

Changes in Brain Activation during the Acquisition of a Multifrequency Bimanual Coordination Task: From the Cognitive Stage to Advanced Levels of Automaticity

Little is known about activation changes reflecting overlearning, i.e., extensive motor training beyond asymptotic performance. Here we used functional magnetic resonance imaging to trace the neural shifts from an initial to a skilled (learning) and finally overlearned stage (automatization). Scanning occurred before training (PRE) and after 1 (MID) and 2 weeks (POST) of intensive practice on a new bimanual coordination task (>10,500 cycles). Kinematics revealed major improvements between PRE and MID sessions, whereas MID to POST session performance leveled off, indicative of learning and automatization, respectively. Imaging findings showed that activation decreased in bilateral opercular areas, bilateral ventrolateral prefrontal cortex, the right ventral premotor and supramarginal gyrus, and the anterior cingulate sulcus during the learning stage and in the supplementary motor area during the automatization stage. These changes are hypothesized to reflect decreases in attention-demanding sensory processing, as well as suppression of preferred coordination tendencies as a prelude to acquiring new coordination modes. Conversely, learning-related increases were observed in the primary motor cortex (M1), posterior cingulate zone (PCZ), putamen, and right anterior cerebellum. Importantly, both M1 and PCZ activation decreased again to initial level (PRE) during automated performance (POST). Only the putamen and anterior cerebellum remained more activated across both learning and automatization stages, supporting their crucial role in long-term motor memory formation for coordination tasks.

Sensorimotor adaptation in young and elderly humans

Our brain's capacity for adaptation allows us to interact meaningfully with an ever-changing environment. Experimental evidence suggests that the time course of sensorimotor adaptation is preserved or only moderately degraded in old age, and that seniors benefit from a previous adaptive experience even more than younger subjects. However, experimental evidence suggests that sensorimotor adaptation seems to be associated with a higher computational load in the elderly. We discuss two possible explanations for this pattern of findings: Older adults may take longer to consolidate newly gained information into long-term motor memory, or they may have problems to utilize supplementary (e.g. cognitive) strategies. In any case, the age-related deficits were relatively mild. If these deficits are related to an increased computational load, it should be possible to reduce them by extended practice on adaptation tasks.

Adaptation of postural control to perturbations--a process that initiates long-term motor memory.

The objective was to investigate postural control adaptation during daily repeated posturography with vibratory calf stimulation. The posturography was performed with eyes open and closed daily for 5 days and after 90 days on 12 healthy subjects. The postural control adaptation could be described as two separate processes, a rapid adaptation during the test progress and a long-term habituation between consecutive test days. The adaptive improvements gained during the 5 days consecutive testing, largely remained 90 days later but seemed restricted to the same test situation. The findings suggest that balance rehabilitation should include a variety of repeated exercises, which are sufficiently long to induce habituation.

Functional Stages in the Formation of Human Long-Term Motor Memory

Previous research has demonstrated that the primate CNS has the ability to learn and store multiple and conflicting visuo-motor maps. Here we studied the ability of human subjects to learn to make reaching movements while interacting with one of two conflicting mechanical environments as produced by a robotic manipulandum. We demonstrate that two motor maps may be learned and retained, but only if the training sessions in the tasks are separated by an interval of approximately 5 hr. If the interval is shorter, learning of the second map begins with an internal model appropriate for the first task and performance in the second task is significantly impaired. Analysis of the after-effects suggests that with a short temporal distance, learning of the second task leads to an unlearning of the internal model for the first. With the longer temporal distance, learning of the second task starts with an unbiased internal model, and performance approaches that of naives. Furthermore, the memory of the consolidated skill lasts for at least 5 months after training. These results argue for a distinct change in the state of resistance of motor memory (to disruption) within a few hours after acquisition. We suggest that motor practice results in memories that have at least two functional components: soon after completion of practice, one component fades while another is strengthened. A further experiment suggests that the hypothetical first stage is not merely a gateway to long-term memory, but also temporary storage for items of information, whether new or old, for use in the near-term. Our results raise the possibility that there are distinct neuronal mechanisms for representation of the two functional stages of motor memory.

Covert Rehearsal and Motor Long-Term Memory

This was a preliminary study of the effects of covert rehearsal, i.e., mental practice, on retention of movement in motor long-term memory. Rehearsal has been recognized as one of the most important factors in experiments on human memory ( 1 ) . There have been many studies of rehearsal in motor short-term memory (2), however, most studies of motor long-term memory concerning the role of covert rehearsal have been atheoretical (3). If rehearsal is necessary for retention beyond the typical short-term memory period of a few minutes, it follows that preventing rehearsal should produce poorer retention of movement information than conditions in which rehearsal is allowed. In the present study 18 right-handed subjects participated in a study of a linear positioning task. In the first phase three movement lengths, 10, 15, 25 cm, were used. A movement length was assigned to one of three rehearsal conditions: immediate recall, recall after 20 sec. of rehearsal, recall after 20 sec. interpolated activity (backward counting by threes). Rehearsal intervals were counterbalanced between subjects, and subjects received both distance and location information cues. For each trial subjects moved the slide carriage from right to left until a stop was reached. Following the appropriate rehearsal interval the stop was removed and the subject attempted to reproduce the movement three times. This procedure was followed for all three rehearsal intervals. Following the completion of this phase subjects received a word-analogy test. After a 10-min. period subjects received a surprise recall test, in which they attempted to reproduce each movement three times in the same serial order as presented in the initial phase. Movement error was recorded in centimeters. Since the movement lengths were used simply to provide a repertoire of movements to remember, errors were collapsed over movement lengths. Errors were also collapsed over reproduction attempts within rehearsal condirions. Analysis of absolute error2 indicated there was no significant effect for rehearsal condirions in the initial phase. However, there was a significant effect for rehearsal in the second phase (F = 4.04, p < .05). The cell means were 4.5, 2.8, 4.9 cm for 0, 20, and 20 sec. filled, respectively. Subsequent analysis (Tukey HSD = 1.9) indicated a significant difference between 20 sec. filled and 20 sec. rehearsal but not between 0-sec. and 20-sec. rehearsal groups. The separate analysis was performed for each phase because recall in the first phase is sequential whereas recall in the second phase is serial. These findings provide preliminary evidence that covert rehearsal increases the retention of movement in motor long-term memory. The rehearsal condition (20 sec.) led to superlor retention of movement compared to the noor block-rehearsal conditions. The data suggest study of rehearsal in motor long-term memory is warranted.

Note on Absence of Proactive Interference in Motor Long-Term Memory

3 groups of 10 subjects made and recalled a linear arm-positioning movement after a 10-min. retention interval. One of the groups made and recalled four similar movements immediately prior to the last movement (a Brown-Peterson proactive design) and another learned all five movements and then recalled them in reverse order after the retention interval. The control group made and recalled only one movement. Significant forgetting was evident for all groups in terms of absolute error, but there was no significant difference between the groups in either absolute, constant, or variable errors.