Autonomic nervous system correlates in movement observation and motor imagery

Abstract

The purpose of the current article is to provide a comprehensive overview of the literature offering a better understanding of the autonomic nervous system (ANS) correlates in motor imagery (MI) and movement observation. These are two high brain functions involving sensori-motor coupling, mediated by memory systems. How observing or mentally rehearsing a movement affect ANS activity has not been extensively investigated. The links between cognitive functions and ANS responses are not so obvious. We will first describe the organization of the ANS whose main purposes are controlling vital functions by maintaining the homeostasis of the organism and providing adaptive responses when changes occur either in the external or internal milieu. We will then review how scientific knowledge evolved, thus integrating recent findings related to ANS functioning, and show how these are linked to mental functions. In turn, we will describe how movement observation or MI may elicit physiological responses at the peripheral level of the autonomic effectors, thus eliciting autonomic correlates to cognitive activity. Key features of this paper are to draw a step-by step progression from the understanding of ANS physiology to its relationships with high mental processes such as movement observation or MI. We will further provide evidence that mental processes are co-programmed both at the somatic and autonomic levels of the central nervous system (CNS). We will thus detail how peripheral physiological responses may be analyzed to provide objective evidence that MI is actually performed. The main perspective is thus to consider that, during movement observation and MI, ANS activity is an objective witness of mental processes.

Keywords: autonomic nervous system activity; motor imagery; movement observation.

Figure 1

Illustrative recording from a participant showing a 2-min sequence of static handgrip at 30% maximal voluntary contraction [Adapted with permission from Vissing et al. (1991), Circulation Research]. Muscle and skin sympathetic nerve activity are recorded from left and right peroneal nerves. Static handgrip markedly increased both skin and muscle sympathetic nerve activity. However, skin ANS increased rapidly and anticipated the onset of handgrip, whereas muscle ANS increased much more slowly with a latency of almost 1 min from the onset of handgrip to the onset of sympathetic activation.

Figure 2

Example of two normalized skin conductance responses during a series of three consecutive MI repetitions of a finger sequence in skilled (SC_Good, dark brown) and unskilled imagers (SC_Poor, light brown). Each vertical bar represents the starting of MI and is paralleled by electrodermal response onset. In the skilled group, electrodermal response duration is comparable to that of the actual finger sequence, thus indicating a close relationship between MI and actual movement durations. Electrodermal tonic values remained at a constant level (around 1), thus attesting that general arousal remained stable and favored general attention. In the unskilled group, electrodermal response is shorter than that of actual movement, thus indicating temporal discrepancy between actual and imagined movement durations. Normalized electrodermal tonic values decreased (from 1.00 to about 0.65), indicating a decrease of general arousal, likely to impair sustained attention. These data suggest that the participant encountered difficulty at keeping arousal at a level that is compatible with efficient cognitive processing. Skin conductance could thus distinguish between MI abilities.