Jörn Munzert

Cognitive motor processes. The role of motor imagery in the study of motor representations

Motor imagery is viewed as a window to cognitive motor processes and particularly to motor control. Mental simulation theory [Jeannerod, M., 2001. Neural simulation of action: a unifying mechanism for motor cognition. NeuroImage 14, 103-109] stresses that cognitive motor processes such as motor imagery and action observation share the same representations as motor execution. This article presents an overview of motor imagery studies in cognitive psychology and neuroscience that support and extend predictions from mental simulation theory. In general, behavioral data as well as fMRI and TMS data demonstrate that motor areas in the brain play an important role in motor imagery. After discussing results on a close overlap between mental and actual performance durations, the review focuses specifically on studies reporting an activation of primary motor cortex during motor imagery. This focus is extended to studies on motor imagery in patients. Motor imagery is also analyzed in more applied fields such as mental training procedures in patients and athletes. These findings support the notion that mental training procedures can be applied as a therapeutic tool in rehabilitation and in applications for power training.

The embodied nature of motor imagery: the influence of posture and perspective

It is assumed that imagining oneself from a first-person perspective (1PP) is more embodied than a third-person perspective (3PP). Therefore, 1PP imagery should lead to more activity in motor and motor-related structures, and the postural configuration of one’s own body should be particularly relevant in 1PP simulation. The present study investigated whether proprioceptive information on hand position is integrated similarly in 1PP and 3PP imagery of hand movements. During functional magnetic resonance imaging (fMRI) scanning, 20 right-handed female college students watched video sequences of different hand movements with their right hand in a compatible versus incompatible posture and subsequently performed 1PP or 3PP imagery of the movement. Results showed stronger activation in left hemisphere motor and motor-related structures, especially the inferior parietal lobe, on 1PP compared with 3PP trials. Activation in the left inferior parietal lobe (parietal operculum, SII) and the insula was stronger in 1PP trials with compatible compared with incompatible posture. Thus, proprioceptive information on actual body posture is more relevant for 1PP imagery processes. Results support the embodied nature of 1PP imagery and indicate possible applications in athletic training or rehabilitation.

Differential activation of pre-SMA and SMA proper during action observation: Effects of instructions

Many neurophysiological studies give evidence for a matching system between action observation and imitation. We used functional MRI to investigate the effects of different instructions for observing identical stimuli of whole-body gymnastics movements. The imitative-like observation mode asked normal human participants to observe the sequence containing repetitive parts and to subsequently imagine the observed movements in the first-person perspective. The evaluative observation mode asked the participants to carefully observe and judge movement accuracy and consistency in the repetitive sequence. We hypothesized that the supplementary motor area would be specifically involved in performing the observational tasks. Results indicate that the SMA proper is generally activated during observation of whole-body gymnastic movements and shows pronounced activation in imitative-like observation mode. Pre-SMA activity can be differentially modulated by instructions related to the observation task.

Activation of the parieto-premotor network is associated with vivid motor imagery - a parametric FMRI study

The present study examined the neural basis of vivid motor imagery with parametrical functional magnetic resonance imaging. 22 participants performed motor imagery (MI) of six different right-hand movements that differed in terms of pointing accuracy needs and object involvement, i.e., either none, two big or two small squares had to be pointed at in alternation either with or without an object grasped with the fingers. After each imagery trial, they rated the perceived vividness of motor imagery on a 7-point scale. Results showed that increased perceived imagery vividness was parametrically associated with increasing neural activation within the left putamen, the left premotor cortex (PMC), the posterior parietal cortex of the left hemisphere, the left primary motor cortex, the left somatosensory cortex, and the left cerebellum. Within the right hemisphere, activation was found within the right cerebellum, the right putamen, and the right PMC. It is concluded that the perceived vividness of MI is parametrically associated with neural activity within sensorimotor areas. The results corroborate the hypothesis that MI is an outcome of neural computations based on movement representations located within motor areas.

Motor imagery and its implications for understanding the motor system.

In the neurosciences, motor imagery (MIm) has not just been a topic of basic research. It has also attracted attention in applied research as a therapeutic tool. MIm is conceptualized as an internal simulation of motor acts that generates images on the basis of motor representations. Therefore, MIm is associated with neural activation of the cortical and subcortical motor system. The resulting concept of functional equivalence between MIm and execution opens a window to study the organization of motor processes and, more generally, to understand the neural plasticity of the motor system.

Strength gains by motor imagery with different ratios of physical to mental practice

The purpose of this training study was to determine the magnitude of strength gains following a high-intensity resistance training (i.e., improvement of neuromuscular coordination) that can be achieved by imagery of the respective muscle contraction imagined maximal isometric contraction (IMC training). Prior to the experimental intervention, subjects completed a 4-week standardized strength training program. 3 groups with different combinations of real maximum voluntary contraction (MVC) and mental (IMC) strength training (M75, M50, M25; numbers indicate percentages of mental trials) were compared to a MVC-only training group (M0) and a control condition without strength training (CO). Training sessions (altogether 12) consisted of four sets of two maximal 5-s isometric contractions with 10 s rest between sets of either MVC or IMC training. Task-specific effects of IMC training were tested in four strength exercises commonly used in practical settings (bench pressing, leg pressing, triceps extension, and calf raising). Maximum isometric voluntary contraction force (MVC) was measured before and after the experimental training intervention and again 1 week after cessation of the program. IMC groups (M25, M50, M75) showed slightly smaller increases in MVC (3.0% to 4.2%) than M0 (5.1%), but significantly stronger improvements than CO (−0.2%). Compared to further strength gains in M0 after 1 week (9.4% altogether), IMC groups showed no “delayed” improvement, but the attained training effects remained stable. It is concluded that high-intensity strength training sessions can be partly replaced by IMC training sessions without any considerable reduction of strength gains.

Your mind's hand: Motor imagery of pointing movements with different accuracy

Jeannerod (2001) postulated that motor control and motor simulation states are functionally equivalent. If this is the case, the specifically relevant task parameters in online motor control should also be represented in motor imagery. We tested whether the different spatial accuracy demands of manual pointing movements are reflected on a neural level in motor imagery. During functional magnetic resonance imaging (fMRI) scanning, 23 participants imagined hand movements that differed systematically in terms of pointing accuracy needs (i.e., none, low, high). In a low-accuracy condition, two big squares were presented visually prior to the imagery phase. These squares had to be pointed at alternately on a mental level. In the high-accuracy condition, two little squares had to be hit. As expected on the basis of speed-accuracy trade-off principles, results showed that participants required more time when accuracy of the imagined movements increased. The fMRI results showed a stepwise increase in activation in the anterior cerebellum and the anterior part of the superior parietal lobe (SPL) with rising accuracy needs. Moreover, we found increased activation of the anterior part of the SPL and of the dorsal premotor cortex (dPMC) when imagery included a square (i.e., in the low- and high-accuracy conditions) compared to the no-square condition. These areas have also been discussed in relation to online motor control, suggesting that specific task parameters relevant in the domain of motor control are also coded in motor imagery. We suggest that the functional equivalence of action states is due mostly to internal estimations of the expected sensory feedback in both motor control and motor imagery.

Simulation during observation of human actions - Theories, empirical studies, applications

Historically, data from brain imaging and brain stimulation studies have supported the idea that the processing of observed actions recruits - among other areas - a distinct sub-set of brain sites in the sensory and motor cortices. These empirical findings have initially been linked with the thesis of direct matching as a mechanism of action understanding, i.e., the idea of motor resonance implemented by mirror neurons. In more recent approaches, it has been proposed that the mirror neuron system plays a role in minimizing prediction error when inferring the most likely cause of an observed action. According to these theories, motor resonance is thought to function as predictive coding. Other theoretical accounts suggest that action understanding might result from a hypothesis testing mechanism in which potential goals are continually fed into the system until the correct one is identified. In this review, we will explore the relationship of these theories to specific empirical findings. Finally, we will discuss the implications of these theoretical structures on action observation-based approaches to the optimization of skilled performance in athletes and patients.

The influence of motor expertise and motor experience on action and actor recognition

Two experiments examined whether different levels of motor and visual experience influence action perception and whether this effect depends on the type of perceptual task. Within an action recognition task (Experiment 1), professional basketball players and novice college students were asked to identify basketball dribbles from point-light displays. Results showed faster reaction times and greater accuracy in experts, but no advantage when observing either own or teammates’ actions compared with unknown expert players. Within an actor recognition task (Experiment 2), the same expert players were asked to identify the model actors. Results showed poor discrimination between teammates and players from another team, but a more accurate assignment of own actions to the own team. When asked to name the actor, experts recognised themselves slightly better than teammates. Results support the hypothesis that motor experience influences action recognition. They also show that the influence of motor experience on the perception of own actions depends on the type of perceptual task.

Neural Correlates of Attentional Focusing during Finger Movements: A fMRI Study

ABSTRACT One finding in recent motor control and learning research is that an external focus (i.e., attending to environmental aspects) improves performance, whereas an internal focus (i.e., controlling bodily movements) impedes it. Despite being replicated in behavioral studies, the neurophysiological basis of this phenomenon remains largely unknown. The present authors separate global attention to actions into an external and an internal focus. Using a between-participants design, participants were either trained to attend to moving their fingers (internal focus) or to the keys to be hit (external focus) during learning a finger sequence. Subsequently, they applied functional magnetic resonance imaging under focus (internal/external), dual task, and move-only conditions. Results revealed higher activation in primary somatosensory and motor cortex for an external compared to an internal focus. The authors conclude that external participants focused on the task-related environment (i.e., the keys) to enhance tactile input to somatosensory areas that closely connect to motor areas.