Elsevier

Brain Research Reviews

Volume 50, Issue 2, 15 December 2005, Pages 387-397
Brain Research Reviews

Review
Contribution from neurophysiological and psychological methods to the study of motor imagery

https://doi.org/10.1016/j.brainresrev.2005.09.004Get rights and content

Abstract

This paper reviews studies on neurophysiological and behavioral methods used to evaluate motor imagery accuracy. These methods can be used when performed in the field and are based on recordings of peripheral indices such as autonomic nervous system or electromyographic activities, mental chronometry and psychological tests. Providing physiological signs that correlate to these types of mental processes may be considered an objective approach for motor imagery analysis. However, although autonomic nervous system activity recording has been shown to match motor imagery in real time, to evaluate its accuracy qualitatively and the individual ability to form mental images, the relationship between physiological responses and mental processes remains an inference. Moreover, electromyographic recordings may be associated with postural control data, but due to inconsistent results, they remain insufficient to solely evaluate motor imagery accuracy. Other techniques traditionally used in psychology and cognitive psychology are questionnaires, “debriefing” with subjects and mental chronometry. Although such methods lead to interesting results, there remains an important part of subjectivity as subjects perform an autoevaluation of motor imagery accuracy. Similarly, mental chronometry gives information on the ability to preserve temporal organization of movement but does not allow the evaluation of the vividness of mental images. Thus, several methods should be combined to analyze motor imagery accuracy in greater detail. Neurophysiological recordings cannot therefore be considered an alternative but rather a complementary technique to behavioral and psychological methods. The advantages and inconvenient of each technique and the hypotheses that could be tested are discussed.

Introduction

Motor Imagery (MI) is defined as a mental representation of movement without any body movement. MI may involve the whole body or be limited to part of the body, thus requiring body representation as the generator of acting forces and not only of the effects of these forces on the external world [70]. MI is known to improve motor task performance, combination of mental and physical practice being more efficient than, or at least equal to physical execution, when there is no decrease in total physical performance time [37], [41]. However, athletes have to respect several rules of mental work to improve its efficiency. For example, Roure et al. [112] provided evidence that the characteristics of mental training should be close to those related to execution. In a volleyball task, they observed that MI led to improved performance, but that the benefit of mental training was not transferred, even in a close (but different) motor skill. Several types of imagery may be used, according to each sensory modality. Visual and kinesthetic imagery are often performed by athletes to simulate motor performance. Visual imagery requires self-visualization of movement, whereas kinesthetic imagery requires to “feel” the movement, i.e., to mentally perceive muscle contractions, the latter being however beneficial only with an adequate degree of expertise [60]. MI may be studied through several techniques. Behavioral and psychological tools are very useful in field studies and lead to the evaluation of individual ability to either imagine an event accurately or preserve temporal characteristics of movement during MI. However, psychological tests include an important part of subjectivity and mental chronometry gives no information about MI accuracy, but only the characteristic of time preservation. As it is now well known that common neural substrate underlie motor performance and MI [92], understanding the neural correlates of goal-directed action, whether executed or imagined, has been an important aim of cognitive brain research since the advent of functional imaging studies using for example positron emission tomography and functional magnetic resonance imaging. Such brain mapping techniques have therefore provided converging evidence that imagined and executed movements share the same neural substrate [84], [92]. Results suggest overlapping of neural networks in motor and premotor cortices, including supplementary motor area, were activated during MI and motor performance [29], [30], [96], [105], [111], although the primary motor cortex was not always found to be activated [30]. These studies also emphasized the involvement of several parietal areas [95], [116], [130] and subcortical structures such as the cerebellum and the basal ganglia [26], [82], [96]. Neuroimaging data have also provided evidence that cerebral plasticity occurring during incremental acquisition of a motor task was reflected in the same brain regions during MI [80], and that specific cerebral structures were activated while distinguishing MI in a first-person process from MI of another person acting with an object [114]. Such results may be of interest to better understand agency disorders in both neurological and psychopathological patients and to investigate the potential therapeutic effects of MI. Indeed, the use of MI for the rehabilitation of patients with cerebral motor impairments to facilitate the future execution of specific movements is currently one of the most actual growing topics of MI research [35], [36], [69], [72], [83], [85], [86], [100], [103], [124], [135]. However, such neuroimaging techniques cannot be used in the field as they are non-ambulatory methods, and the type and amplitude of movements are limited. Autonomic nervous system (ANS) effectors are activated by MI, and their activities can be measured continuously by non-invasive sensors associated with portable instrumentation. Although the relationships between physiological responses and central mental processes are inferred, data brought by peripheral recordings paralleled those obtained by central nervous system investigation and thus appear to be well-adapted to study MI. Therefore, both central and peripheral methods may be useful to evaluate MI quality, in reference to both direct and indirect data.

Section snippets

Recording of autonomic nervous system activity during motor imagery

Higher brain functions may be studied through ANS effector activity at a peripheral level [63]. Central operations (planning and programming) are paralleled by ANS responses which anticipate and accompany behavior, thus representing non-conscious physiological mechanisms of central mental processes [14], [104], [117]. According to Jeannerod [70], monitoring vegetative functions during motor preparation and MI is an interesting way to compare the two situations: as ANS escapes voluntary control

Changes in muscular activity during motor imagery

The psychoneuromuscular theory is one of the first that attempted to explain the effects of MI in motor performance. Since the early works by Jacobson [66], [67], Shaw [118], [119] and McGuigan [90], it has been presumed that a subliminal activity of the same muscles occurs during MI and during overt movement execution. The Golgi tendon organs are thought to be stimulated and thereby generate neuromuscular feedback [115]. Motor performance enhancement may result from such neuromuscular effects

Behavioral and psychological techniques

MI effects on forthcoming performance have been extensively studied in experimental and cognitive psychology. Several techniques are used to analyze the effects on motor performance, motor learning, evaluation of MI accuracy and vividness, and to understand why, where and when MI is performed. Among the various validated questionnaires, the most frequently used are the Vividness of Visual Imagery Questionnaire [87], the Movement Imagery Questionnaire [55] or its revised version [54], the

Conclusion

At this time, EMG activity during MI cannot bring reliable information to evaluate MI accuracy, and experimental investigation on postural control when mentally simulating a movement remains also necessary. By contrast, ANS activity recording has been shown to match MI in real time and to evaluate qualitatively MI accuracy and individual ability to form mental images. Moreover, a good correlation was obtained in good imagers between four autonomic indices and performance improvement [113]: (i)

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