Precise oculomotor correlates of visuospatial mental rotation and circular motion imagery

Visual imagery is a basic form of cognition central to activities such as problem solving or creative thinking. Phenomena such as mental rotation, in which mental images undergo spatial transformations, and motion imagery, in which we imagine objects in motion, are very elusive. For example, although several aspects of visual imagery and mental rotation have been reconstructed through mental chronometry, their instantaneous evolution has never been directly observed. We paired mental chronometry to eye movement recording in subjects performing a visuospatial mental rotation task and an instructed circular motion imagery task. In both tasks, sequences of spontaneous saccades formed curved trajectories with a regular spatio-temporal evolution. In the visuospatial mental rotation task, saccadic amplitude decreased progressively within each sequence, resulting in an average gaze rotation with a bell-shaped asymmetrical angular velocity profile whose peak and mean increased with the amount of the to-be-performed rotation, as in reaching movements. In the second task, the average gaze rotation reproduced faithfully the to-be-imagined constant-velocity circular motion, thus excluding important distortions in the oculomotor performance. These findings show for the first time the instantaneous spatio-temporal evolution of mental rotation and motion imagery. Moreover, the fact that visuospatial mental rotation is modeled as a reaching act suggests that reaching pertains to the realm of visuospatial thinking, rather than being restricted to the motor domain. This approach based on eye movement recording can be profitably coupled to methods such as event-related potentials, transcranial magnetic stimulation, or functional magnetic resonance to study the precise neuronal dynamics associated with an ongoing mental activity.     

Assessment of motor imagery in cerebral palsy via mental chronometry: The case of walking

Recent studies show varying results on whether motor imagery capacity is compromised in individuals with cerebral palsy (CP). Motor imagery studies in children predominantly used the implicit hand laterality task. In this task participants judge the laterality of displayed hand stimuli. A more explicit way of studying motor imagery is mental chronometry. This paradigm is based on the comparison between the movement durations of actually performing a task and imagining the same task. The current study explored motor imagery capacity in CP by means of mental chronometry of a whole body task. Movement durations of 20 individuals with CP (mean age = 13 years, SD = 3.6) were recorded in two conditions: actual walking and imagined walking. Six unique trajectories were used that varied in difficulty via manipulation of walking distance and path width. We found no main effect of condition (actual walking versus imagining) on movement durations. Difficulty of the walking trajectory did affect movement durations. In general, this was expressed by an increase in movement durations with increasing difficulty of the task. No interaction between task difficulty and movement condition was found. Our results show that task difficulty has similar effects on movement durations for both actual walking and imagined walking. These results exemplify that the tested individuals were able to use motor imagery in an explicit task involving walking. Previous studies using the implicit hand laterality task showed varying results on motor imagery capacity in CP. We therefore conclude that motor imagery capacity is task dependent and that an explicit paradigm as the one used in this study may reveal the true motor imagery capacity. The implications of these findings for the use of motor imagery training are discussed.     

Is the rhythm of physiological tremor involved in cortico‐cortical interactions?

The function of low-frequency oscillations as correlates of physiological tremor in supplementary motor area (SMA) and M1 remains unclear. In epicortical recordings from M1 and SMA and surface electromyographic (EMG) recordings in an epileptic patient we found reproducibly significant coherence between all three recording sites in the 6- to 15-Hz band. The partial coherence between SMA and muscle, however, was not significant. There was a constant phase shift between SMA and M1 indicating synchronized activity. We conclude that the cortical correlates of physiological tremor may be involved in linking different cortical motor centers and might therefore play a role in cortical motor planning.     

The eyes as a mirror of our thoughts: quantification of motor imagery of goal-directed movements through eye movement registration

It has been suggested that motor imagery possesses a range of useful applications in sport as well as in rehabilitation. Until now, research in this field has been hampered by the lack of an objective method to monitor the subjects' participation in the task. In this present study, a new approach to quantifying motor imagery of goal-directed hand movements by means of eye movement registration is examined. Eye movements of 15 right-handed subjects were recorded using EOG during both physical execution and visual motor imagery of a cyclical aiming task, performed at three different inter-target distances. We found that 89% of subjects made task-related eye movements during imagery with the eyes open and 84% of participants also did so during imagery with the eyes closed. Both the number and amplitude of the eye movements during imagery closely resembled those of eye movements made during physical execution of the task. This indicates that the coupling between neural patterns for eye and hand movements remains intact when hand movements are merely imagined as opposed to being physically executed. Therefore, eye movement recordings may be used as an objective technique to evaluate subjects' compliance, motor imagery ability, and spatial accuracy.     

Mental chronometry in the study of individual and group differences

The papers in this issue are excellent examples of the many uses of measuring reaction time in the exploration of nervous system pathologies. In our commentary we consider mental chronometry as a field that seeks to measure the time course of mental operations in the human nervous system. We draw upon diverse methods such as neuroimaging, electrical recording and reaction time to illustrate the use of chronometry in conjunction with anatomy and genetics to approach both normal individual differences and pathologies. The goal is to examine general and specific changes in neural networks that underlie both variations in normal function and changes due to pathology. Although much remains to be done along these lines, it is now possible to see how the various chronometric contributions outlined in this special issue can converge to provide a basis for improved understanding of the genetic and experiential basis of cognitive and emotional processes.     

Mental Chronometry in the Study of Individual and Group Differences

The papers in this issue are excellent examples of the many uses of measuring reaction time in the exploration of nervous system pathologies. In our commentary we consider mental chronometry as a field that seeks to measure the time course of mental operations in the human nervous system. We draw upon diverse methods such as neuroimaging, electrical recording and reaction time to illustrate the use of chronometry in conjunction with anatomy and genetics to approach both normal individual differences and pathologies. The goal is to examine general and specific changes in neural networks that underlie both variations in normal function and changes due to pathology. Although much remains to be done along these lines, it is now possible to see how the various chronometric contributions outlined in this special issue can converge to provide a basis for improved understanding of the genetic and experiential basis of cognitive and emotional processes.     

Brain activity during visual versus kinesthetic imagery: an fMRI study

Although there is ample evidence that motor imagery activates similar cerebral regions to those solicited during actual movements, it is still unknown whether visual (VI) and kinesthetic imagery (KI) recruit comparable or distinct neural networks. The present study was thus designed to identify, through functional magnetic resonance imaging at 3.0 Tesla in 13 skilled imagers, the cerebral structures implicated in VI and KI. Participants were scanned in a perceptual control condition and while physically executing or focusing during motor imagery on either the visual or kinesthetic components of an explicitly known sequence of finger movements. Subjects' imagery abilities were assessed using well-established psychological, chronometric, and new physiological measures from the autonomic nervous system. Compared with the perceptual condition, physical executing, VI, and KI resulted in overlapping (albeit non-identical) brain activations, including motor-related regions and the inferior and superior parietal lobules. By contrast, a divergent pattern of increased activity was observed when VI and KI were compared directly: VI activated predominantly the occipital regions and the superior parietal lobules, whereas KI yielded more activity in motor-associated structures and the inferior parietal lobule. These results suggest that VI and KI are mediated through separate neural systems, which contribute differently during processes of motor learning and neurological rehabilitation.     

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.     

Autonomic nervous system activities during motor imagery in elite athletes.

Motor imagery (MI), a mental simulation of voluntary motor actions, has been used as a training method for athletes for many years. It is possible that MI techniques might similarly be useful as part of rehabilitative strategies to help people regain skills lost as a consequence of diseases or stroke. Mental activity and stress induce several different autonomic responses as part of the behavioral response to movement (e.g., motor anticipation) and as part of the central planning and preprogramming of movement. However, the interrelationships between MI, the autonomic responses, and the motor system have not yet been worked out. The authors compare a number of autonomic responses (respiration, heart rate, electro skin resistance) and motoneuron excitability (soleus H-reflex) in elite and nonelite speed skaters during MI. In contrast to the nonelite athletes, MI of elite speed skaters is characterized by larger changes in heart rate and respiration, a greater reliance on an internal perspective for MI, a more vivid MI, a more accurate correspondence between the MI and actual race times, and decreased motoneuron excitability. Two observations suggest that the changes in the autonomic responses and motoneuron excitability for the elite speed skaters are related to the effects of central motor programming: (1) there was no correlation between the autonomic responses for MI and those recorded during mental arithmetic; and (2) mental arithmetic did not significantly alter motoneuron activity. It is suggested that in elite speed skaters, the descending neural mechanisms that reduce motoneuron excitability are activated even when full, vivid MI is performed internally. These inhibitory responses of the motor system may enhance actual motor performance under conditions of remarkably high mental stress, such as that which occurs in the Olympic games.     

Imagery about suicide in depression—“Flash-forwards”?

Suicide is a significant world health problem, with more deaths by suicide globally than by war. We need to better understand the cognitive processes underlying suicidal thinking for improved treatment development. Cognitive psychology indicates that mental imagery can be causal in determining future behavior, yet the occurrence of suicide-related imagery has not previously been investigated. Interviews with 15 depressed and formerly suicidal patients in remission found that all patients reported experiencing detailed mental imagery in addition to verbal thoughts when at their most despairing, for example images of making a future suicide attempt. A clinical measure of the severity of suicidal ideation was associated with both preoccupation with suicide-related imagery and perceived imagery realness. Echoing flashbacks in posttraumatic stress disorder, the current images appeared like “flash-forwards” to suicide. These results provide the first data to our knowledge on the existence of mental imagery in suicidality, opening a promising new avenue for research.