Safe and effective navigation of the world's oceans and waterways relies on maritime education and training. This involves the learning of motor, procedural and verbal components of complex skills. Motor learning theory evaluates training variables, such as instructions, feedback and scheduling, to determine best practices for long-term retention of such skills. Motor learning theory has come a long way from focusing primarily on underlying cognitive processes to now including individual and contextual characteristics in making predictions about instructional strategies and their role in performance and learning. A remaining challenge in applying recent motor learning theory to maritime education and training is a lack of empirical testing of complex vocational skills, such as simulation scenarios, with delayed retention and transfer tests. Incorporating theory-based understanding of beneficial instructional practices, through both cognitive approaches and those considering context and environment, task complexity and learner characteristics is a fruitful way forward in advancing maritime education and training.

Objectives: Although motor adaptation is a highly relevant process for both everyday life as well as rehabilitation many details of this process are still unresolved. To evaluate the contribution of primary motor (M1), parietal and cerebellar areas to motor adaptation processes transcranial direct current stimulation (tDCS) has been applied. We hypothesized that anodal stimulation of the cerebellum and the M1 improves the learning process in mirror drawing, a task involving fine grained and spatially well-organized hand movements. Methods: High definition tDCS (HD-tDCS) allows a focal stimulation to modulate brain processes. In a single-session double-blind study, we compared the effects of different anodal stimulation procedures. The groups received stimulation either at the cerebellum (CER), at right parietal (PAR), or at left M1, and a SHAM group was included. Participants (n=83) had to complete several mirror drawing tasks before, during, and after stimulation. They were instructed to re-trace a line in the shape of a pentagonal star as fast and accurate as possible. Tracing time (seconds) and accuracy (deviation in mm) have been evaluated. Results: The results indicated that cerebellar HD-tDCS can facilitate motor adaptation in a single session. The stimulation at M1 showed only a tendency to increase motor adaptation and these effects were visible only during the first part of the stimulation. Stimulating the right parietal area, relevant for visuospatial processing did not lead to increased performance. Conclusions: Our results suggest that motor adaptation relies to a great extent on cerebellar functions and HD-tDCS can speed up this process. (JINS, 2016, 22, 928–936)

Within the NIMH Research Domain Criteria (RDoC) framework, dimensions of behavior are investigated across diagnoses with the goal of developing a better understanding of their underlying neural substrates. Currently, this framework includes five domains: cognitive, social, arousal/regulatory, negative, and positive valence systems. We argue that the inclusion of a motor systems domain is sorely needed as well. Independent of medication, distinct areas of motor dysfunction (e.g. motor planning/inhibition/learning/coordination, involuntary movements) commonly appear across a number of mental disorders (e.g. schizophrenia, bipolar disorder, autism, attention deficit hyperactivity disorder, Alzheimer's disease, depression) as well as neurological disorders accompanied by significant psychological symptoms (e.g. Parkinson's disease). In addition, motor systems are amenable to study across multiple levels of analysis from the cellular molecular level focusing on cytoarchitechtonics and neurotransmitter systems, to networks and circuits measured using neuroimaging, and finally at the level of overt behavioral performance. Critically, the neural systems associated with motor performance have been relatively well defined, and different circuits have been linked to distinct aspects of motor behavior. As such, they may also be differentially associated with symptoms and motor dysfunction across diagnoses, and be uniquely informative about underlying etiology. Importantly, motor signs can change across stages of illness; they are also often present in the prodromal phases of disease and closely linked with course, suggesting that these behaviors represent a core feature reflective of pathogenic processes. The inclusion of a motor domain would allow researchers to better understand psychopathology more broadly, and may also reveal important contributions to disease processes across diagnoses.

Although there is increasing agreement that the cerebellum plays an important role in motor learning, the basic substance of what constitutes motor learning has been difficult to define. Unless motor learning is somehow radically different from other forms of learning, it must involve relatively simple stimulus-stimulus and stimulus-response associations. All forms of learning, including purely sensory associations and cognitive learning as well as motor learning, effect changes in behavior. However, a singular characteristic of motor learning is that it adjusts joint and limb mechanics by altering the neural input to muscles through practice and mental rehearsal. The hypothesis proposed here is that the cerebellum plays an important role in motor learning by forming and storing associated muscle activation patterns for the time-varying control of limb mechanics. By modulating the cocontraction of agonist-antagonist muscles through adjustments in the timing and amplitude of muscle activity, the viscoelastic properties of joints can be appropriately regulated throughout Movement and adapted for transitions between postures and movements. Optimal control of joint viscoelastic properties cannot be achieved by online corrections initiated by reflex feedback because of the delays and consequent instabilities incurred. Instead, strategies for optimizing muscle activation patterns or synergies must be learned from the temporal association of proprioceptive stimuli signaling muscle lengths and forces and the rates of changes in these parameters, with reinforcement occurring when the movement achieves its objective. Such strategies would involve varying degrees of cocontraction or reciprocal inhibition of agonist-antagonist muscles that ultimately contribute to joint and limb stiffness. Evidence from neural recordings and clinical and experimental lesion studies are presented, suggesting that the cerebellum uses teleceptive and proprioceptive feedback as feedforward conditioned stimuli for specific muscle activation patterns contributing to joint stiffness (i.e., agonist-antagonist muscle synergies) for particular tasks and postures. A wide variety of observations are thought to be consistent with such a role for the cerebellum, but ultimately additional experiments could confirm or disconfirm this hypothesis.

Brindley proposed that we initially generate movements “consciously”, under higher cerebral control. As the movement is practiced, the cerebellum learns to link within itself the context in which the movement is made to the lower level movement generators. Marr and Albus proposed that the linkage is established by a special input from the inferior olive, which plays upon an input-output element within the cerebellum during the period of the learning. When the linkage is complete, the occurrence of the context (represented by a certain input to the cerebellum) will trigger (through the cerebellum) the appropriate motor response. The “learned” movement is distinguished from the “unlearned” conscious movement by its now being automatic, rapid, and stereotyped. The idea is still controversial, but has been supported by a variety of animal studies and, as reviewed here, is consistent with the results of a number of human PET and ablation studies. I have added to the idea of context-response linkage what I think is another important variable: novel combinations of downstream elements. With regard to the motor system and the muscles, this could explain how varied combinations of muscles may become active in precise time-amplitude specifications so as to produce coordinated movements appropriate to specific contexts. In this target article, I have further extended this idea to the premotor parts of the brain and their role in cognition. These areas receive influences from the cerebellum; they are active both in planning movements that are to be executed and in thinking about movements that are not to be executed. From recent evidence, the cerebellar output extends even to what has been characterized as the ultimate frontal planning area, the “prefrontal” cortex, area 46. The cerebellum thus may be involved in context-response linkage, and response combination even at these higher levels. The implication would be that, through practice, an experiential context would automatically evoke a certain mental action plan. The plan would be in the realm of thought, and could – but need not – lead to execution. The specific cerebellar contribution would be one of the context linkage and the shaping of the response, through trial and error learning. The prefrontal and premotor areas could still plan without the help of the cerebellum, but not so automatically, rapidly, stereotypically, so precisely linked to context, or so free of error. Nor would their activities improve optimally with mental practice.

Cerebellar long-term depression (LTD) is a form of synaptic plasticity, first described by Ito and co-workers, in which simultaneous activation of two excitatory inputs to a Purkinje neuron, parallel fibers (PFs) and climbing fibers (CFs), results in a sustained depression of PF synaptic drive. The purpose of this target article is not to assess the possible role of this synaptic alteration in motor learning, an issue which is addressed by other authors in this volume, nor is it to provide a detailed summary of the work on cerebellar LTD to this point (see Linden & Connor 1993; Crépel et al. 1993 for review) or to place cerebellar LTD within the context of other forms of persistent synaptic depression that occur within the mammalian brain (see Linden 1994b). Rather, it is to discuss results obtained using a very reduced preparation for the study of LTD, embryonic Purkinje neurons grown in culture and stimulated with exogenous excitatory amino acids, and to consider some advantages and limitations of this approach. Recent work using this preparation has suggested that three processes are necessary for the induction of cerebellar LTD: Ca influx through voltage-gated channels, Na influx through AMPA receptor-associated channels or voltage-gated Na channels, and protein kinase C activation - which is dependent upon activation of the metabotropic glutamate receptor mGluRl. In addition, input-specific induction of LTD has been demonstrated in this preparation Under conditions where both spontaneous and evoked neurotransmitter release are reduced or eliminated, indicating that postsynaptic alterations are sufficient to confer this important computational property.

Cerebellar involvement in motor and non-motor sequence learning was examined with serial reaction time tasks (SRT). Our sample consisted of 8 children and adolescents who had undergone surgical removal of a benign posterior fossa tumor (PFT) during childhood. None of them had undergone chemotherapy or cranial radiation therapy (CRT). Ages ranged from 1–11 years at surgery and 9–17 years at testing. The children were tested not earlier than 2.5 years after surgery (M = 5.9 years), enabling brain plasticity and recovery of functions. Their performance was compared with a matched control sample. The PFT group was not impaired in the implicit learning of sequences, as reflected in their performance in blocks with a repeated sequence, both before and after a random block. However, in the perceptual task, their performance deteriorated more than that of the control group when a random block was introduced, suggesting that it was more difficult for the patients to respond flexibly or change their response set when encountering changing task demands. These results are in line with another study by our group on task switching with the same patients. (JINS, 2005, 11, 482–487.)

Cerebro–cerebellar interactions are becoming progressively more focused in their anatomical substrate but their functional meaning is still elusive. Here, we review current data on the cerebellar influence on cortical function, with special emphasis on the importance of the cerebellar input for cortical processing in primary motor and sensorimotor areas. Differences in the intracortical processing of cerebellar information are described and the possible role of the thalamus in controlling cerebro–cerebellar loops discussed.

To examine the hypothesis that abnormalities in those cognitive functions for which cerebellar components have been implicated contribute to the pathophysiology of autism, tests of judgment of explicit time intervals and procedural learning were administered to 11 participants with autism and 17 age-and-IQ-matched controls. Results indicated that the group with autism demonstrated significant impairments in procedural learning compared with the group of controls. No significant difference in judgment of explicit time intervals was found. The data suggest that deficits in procedural learning may contribute to the cognitive and behavioral phenotype of autism; these deficits may be secondary to abnormalities in cerebellar–frontal circuitry. (JINS, 2000, 6, 752–759.)

A total of 22 monozygotic (MZ) and 41 dizygotic (DZ) twin pairs were given 72 trials on a stabilometer balance task over six days to study the extent of the genetic contribution to learning and performance of a gross motor skill. The expectations that interindividual differences would be less for the MZ than for the DZ twins and that intraindividual variability would not be different between the two groups were supported. Intraclass correlations were used to provide estimates for the proportions of total phenotypic variance accounted for by heritability (h2), systematic environmental variance (E2), and nonsystematic environmental effects (e2). Heritability was found to be low during the early stages of learning, before it increased to stabilize at approximately 65% for the remaining practice. E2 was highest during these early stages (24%), then declined quickly to stabilize at half that level. Error variance (e2) constituted the remaining variance. Learning profiles of the twin pairs were also analyzed, with a greater intrapair resemblance being found for the MZ twins. The present findings indicate that, for gross motor skills, there is considerable potential for influencing both the levels of performance (and learning) and the differences between individuals by judicious use of systematic environmental effects.