Assessment of mental chronometry (MC) in healthy subjects

Differences in Motor Imagery Ability between People with Parkinson's Disease and Healthy Controls, and Its Relationship with Functionality, Independence and Quality of Life

Motor imagery (MI) has been shown to be effective for the acquisition of motor skills; however, it is still unknown whether similar benefits can be achieved in neurological patients. Previous findings of differences in MI ability between people with Parkinson's disease (PwPD) and healthy controls (HCs) are mixed. This study examined differences in the ability to both create and maintain MI as well as investigating the relationship between the ability to create and maintain MI and motor function, independence and quality of life (QoL). A case-control study was conducted (31 PwPD and 31 HCs), collecting gender, age, dominance, socio-demographic data, duration and impact of the disease. MI intensity (MIQ-RS and KVIQ-34) and temporal accuracy of MI (imagined box and block test [iBBT], imagined timed stand and walk test [iTUG]) were assessed. Functional and clinical assessments included upper limb motor function, balance, gait, independence in activities of daily living and quality of life measures. Statistically significant differences in temporal accuracy were observed and partial and weak relationships were revealed between MI measures and functioning, independence and QoL. PwPD retain the ability to create MI, indicating the suitability of MI in this population. Temporal accuracy might be altered as a reflection of bradykinesia on the mentally simulated actions.

Relationship between Corticospinal Excitability While Gazing at the Mirror and Motor Imagery Ability

Mirror therapy (MT) helps stroke survivors recover motor function. Previous studies have reported that an individual's motor imagery ability is related to the areas of brain activity during motor imagery and the effectiveness of motor imagery training. However, the relationship between MT and motor imagery ability and between corticospinal tract excitability during mirror gazing, an important component of MT, and motor imagery ability is unclear. This study determined whether the motor-evoked potential (MEP) amplitude while gazing at the mirror relates to participants' motor imagery abilities. Twenty-four healthy right-handed adults (seven males) were recruited. Transcranial magnetic stimulation was performed while gazing at the mirror, and MEP of the first dorsal interosseous muscle of the right hand were measured. Motor imagery ability was measured using the Kinesthetic and Visual Imagery Questionnaire (KVIQ), which assesses the vividness of motor imagery ability. Additionally, a mental chronometry (MC) task was used to assess time aspects. The results showed a significant moderate correlation between changes in MEP amplitude values while gazing at the mirror, as compared with resting conditions, and assessment scores of KVIQ. This study shows that corticospinal excitability because of mirror gazing may be related to the vividness of motor imagery ability.

Imagined Timed Up and Go test (iTUG) in people with Parkinson's Disease: test-retest reliability and validity

PURPOSE

To determine the test-retest reliability and validity of the Imagined Timed Up and Go Test (iTUG) as a Motor Imagery measure of temporal accuracy in people with Parkinson's Disease (PD).

MATERIALS AND METHODS

A descriptive study was conducted following the GRRAS recommendations. Thirty-two people with idiopathic, mild to moderate PD (Hoehn and Yahr I-III), without cognitive impairment (MMSE ≥ 24), were assessed twice (7-15 days apart) with the iTUG. The absolute unadjusted difference in seconds, and the absolute adjusted difference as percentage of estimation error, between real and imagined TUG times, were calculated as outcome measures. Test-retest reliability was assessed using a two-way mixed-effects model of the ICC. Construct validity was tested with the Imagined Box and Blocks Test (iBBT) and convergent validity with clinical characteristics of PD, using the Spearman's rank correlation coefficient.

RESULTS

The ICC for the unadjusted and adjusted measures of the iTUG was ICC = 0.61 and ICC = 0.55, respectively. Correlations between iTUG and iBBT were not statistically significant. The iTUG was partially correlated to clinical characteristics of PD.

CONCLUSIONS

Test-retest reliability of the iTUG was moderate. Construct validity between iTUG and iBBT was poor, so caution should be taken when using them concurrently to assess imagery's temporal accuracy.

Extrinsic feedback facilitates mental chronometry abilities in stroke patients

BACKGROUND

Motor imagery (MI) can serve as a treatment for stroke rehabilitation. MI abilities can be assessed by testing mental chronometry (MC) as the degree of conformity between imagined and real performance of a task. A good MC performance is supposed to indicate good MI capacities.

OBJECTIVE

To explore if MC abilities can be modified by extrinsic feedback in stroke patients.

METHODS

60 subacute stroke patients were randomized into three groups. MC was evaluated by executing a modified version of the Box and Block Test (BBT) mentally and in real before and after a training session. For Groups 1 and 2 the training consisted of repeated performance of the BBT in a mental and then a real version. The time needed to complete each task was measured. Only participants of Group 1 received feedback about how well mental and real performance matched. Group 3 executed the same number of BBTs but without MI.

RESULTS

MC ability only improved in Group 1. The improvement lasted for at least 24 hours. In all groups, BBT real performance was improved post-training.

CONCLUSION

External feedback was able to enhance MC capability which might be an approach for improving MI abilities.

Using crutches during walking possibly reduces gait imagery accuracy among healthy young and older adults

[Purpose] Although crutches are widely used in the field of rehabilitation to improve gait performance, patients usually have difficulties using them, and this may increase their risks for falls. This study aimed to define the accuracy of gait imagery during walking with and without crutches, in healthy young and older adults, using the mental chronometry method. [Participants and Methods] Overall, 99 healthy young (mean age, 20.2 ± 1.0 years) and 39 healthy older adults (mean age, 71.3 ± 2.9 years) performed the imagery and execution tasks, which involved walking through a distance of 10 meters both with and without crutches. Using the mental chronometry method, the accuracy of the motor imagery was defined as the difference between the imagery time and the actual execution time. Two-way analysis of variance and one-sample t-tests were performed to evaluate the accuracy of the gait imagery. [Results] Both the young and older adults significantly overestimated their gait speeds when using crutches; the overestimation was larger among the older adults. [Conclusion] The overestimations indicate that participants estimated their gait speeds with crutches to be faster than their actual speeds. Therefore, using crutches decreased the accuracy of gait imagery and might therefore increase an individual’s risk of falling during walking.

Motor Imagery of Walking in People Living with and without Multiple Sclerosis: A Cross-Sectional Comparison of Mental Chronometry

Motor imagery represents the ability to simulate anticipated movements mentally prior to their actual execution and has been proposed as a tool to assess both individuals’ perception of task difficulty as well as their perception of their own abilities. People with multiple sclerosis (pwMS) often present with motor and cognitive dysfunction, which may negatively affect motor imagery. In this cross-sectional study, we explored differences in motor imagery of walking performance between pwMS (n = 20, age = 57.1 (SD = 8.6) years, 55% female) and age- and sex-matched healthy controls (n = 20, age = 58.1 (SD = 7.0) years, 60% female). Participants underwent mental chronometry assessments, a subset of motor imagery, which evaluated the difference between imagined and actual walking times across four walking tasks of increasing difficulty (i.e., large/narrow-width walkway with/without obstacles). Raw and absolute mental chronometry (A-MC) measures were recorded in single- (ST) and dual-task (DT) conditions. In ST conditions, pwMS had higher A-MC scores across all walking conditions (p ≤ 0.031, η² ≥ 0.119), indicating lower motor imagery ability compared to healthy controls. During DT, all participants tended to underestimate their walking ability (3.38 ± 6.72 to 5.63 ± 9.17 s). However, after physical practice, pwMS were less able to adjust their imagined walking performance compared to healthy controls. In pwMS, A-MC scores were correlated with measures of balance confidence (ρ = −0.629, p < 0.01) and the self-reported expanded disability status scale (ρ = 0.747, p < 0.01). While the current study revealed that pwMS have lower motor imagery of walking performance compared to healthy individuals, further work is necessary to examine how the disassociation between mental chronometry and actual performance relates to quality of life and well-being.

Effects of a single mental chronometry training session in subacute stroke patients - a randomized controlled trial

Background

Motor imagery training might be helpful in stroke rehabilitation. This study explored if a single session of motor imagery (MI) training induces performance changes in mental chronometry (MC), motor execution, or changes of motor excitability.

Methods

Subacute stroke patients (n = 33) participated in two training sessions. The order was randomized. One training consisted of a mental chronometry task, the other training was a hand identification task, each lasting 30 min. Before and after the training session, the Box and Block Test (BBT) was fully executed and also performed as a mental version which served as a measure of MC. A subgroup analysis based on the presence of sensory deficits was performed. Patients were allocated to three groups (no sensory deficits, moderate sensory deficits, severe sensory deficits). Motor excitability was measured by transcranial magnetic stimulation (TMS) pre and post training. Amplitudes of motor evoked potentials at rest and during pre-innervation as well as the duration of cortical silent period were measured in the affected and the non-affected hand.

Results

Pre-post differences of MC showed an improved MC after the MI training, whereas MC was worse after the hand identification training. Motor execution of the BBT was significantly improved after mental chronometry training but not after hand identification task training. Patients with severe sensory deficits performed significantly inferior in BBT execution and MC abilities prior to the training session compared to patients without sensory deficits or with moderate sensory deficits. However, pre-post differences of MC were similar in the 3 groups. TMS results were not different between pre and post training but showed significant differences between affected and unaffected side.

Conclusion

Even a single training session can modulate MC abilities and BBT motor execution in a task-specific way. Severe sensory deficits are associated with poorer motor performance and poorer MC ability, but do not have a negative impact on training-associated changes of mental chronometry. Studies with longer treatment periods should explore if the observed changes can further be expanded.

Trial registration

DRKS, DRKS00020355, registered March 9th, 2020, retrospectively registered

Imagery Ability and Imagery Perspective Preference: A Study of Their Relationship and Age- and Gender-Related Changes

This study examined if imagery ability (i.e., vividness and temporal congruence between imagined and executed knee extensions) and imagery perspective preference were affected by ageing and gender. Ninety-four participants, 31 young, 43 intermediate, and 20 older adults completed the Vividness of Movement Imagery Questionnaire-2 and a knee extension temporal congruence test to reflect on their imagery ability and an imagery perspective preference test. Male participants had a better imagery ability than the female participants (F (4, 85) = 2.84, p = .029, η² = .118). However, significant age-related changes in imagery ability were not found in the three age groups. Change in imagery perspective preference with a trend towards an external imagery perspective was observed with ageing (F (3, 89) = 3.16, p = .028, η² = .096) but not between male and female. The results suggest that imagery ability may be preserved with ageing. As individuals age, their preference for using an imagery perspective shifts from a more internal to a more external perspective. This understanding is important when designing future imagery research and real-life application or clinical intervention.

Disruption of motor imagery performance following inhibition of the left inferior parietal lobe

The left inferior parietal lobe (IPL), a brain region localized to the ventro-dorsal stream, is known to be critical to motor imagery (MI) performance. Yet its specific role in processes underlying MI, namely the generation, maintenance, manipulation, and controllability of motor images, is conflicting in the literature. To determine the specific role of the left IPL in MI, the current study sought to examine the effect inhibition of the left IPL has on performance on two disparate measures thought to probe different MI processes within the same participants. Participants (N = 31) completed the hand laterality judgment task (HLJT), employed to probe processes related to manipulation and controllability, and mental chronometry, employed to probe processes related to generation and maintenance, after receiving either inhibitory transcranial magnetic stimulation to the left IPL (Active-TMS group), or with the coil angled away from the scalp (Sham group). Impaired performance on the HLJT was observed following active TMS relative to sham. Similar mental chronometry performance resulted regardless of left IPL inhibition. In showing that inhibition of the left IPL selectively disrupted performance on the HLJT but not mental chronometry, our findings indicate that the left IPL is specifically involved in image manipulation and controllability during MI. Ultimately, the current study extends our understanding of the role of the left IPL in MI.

Descriptive pilot study of vividness and temporal equivalence during motor imagery training after quadriplegia

BACKGROUND

Motor imagery (MI) training is often used to improve physical practice (PP), and the functional equivalence between imagined and practiced movements is widely considered essential for positive training outcomes.

OBJECTIVE

We previously showed that a 5-week MI training program improved tenodesis grasp in individuals with C6-C7 quadriplegia. Here we investigated whether functional equivalence changed during the course of this training program.

METHODS

In this descriptive pilot study, we retrospectively analyzed data for 6 individuals with C6-C7 quadriplegia (spinal cord injured [SCI]) and 6 healthy age-matched controls who trained for 5 weeks in visual and kinesthetic motor imagery or visualization of geometric shapes (controls). Before training, we assessed MI ability by using the Kinesthetic and Visual Imagery Questionnaire (KVIQ). We analyzed functional equivalence by vividness measured on a visual analog scale (0-100) and MI/PP time ratios computed from imagined and physically practiced movement durations measured during MI training. These analyses were re-run considering that half of the participants with quadriplegia were good imagers and the other half were poor imagers based on KVIQ scores. To investigate generalization of training effects, we analyzed MI/PP ratios for an untrained pointing task before (3 baseline measures), immediately after, and 2 months after training.

RESULTS

During MI training, imagery vividness increased significantly. Only the good imagers evolved toward temporal equivalence during training. Good imagers were also the only participants who showed changes in temporal equivalence on the untrained pointing task.

CONCLUSION

This is the first study reporting improvement in functional equivalence during an MI training program that improved tenodesis grasp in individuals with C6-C7 quadriplegia. We recommend that clinical MI programs focus primarily on vividness and suggest that feedback about movement duration could potentially improve temporal equivalence, which could in turn lead to further improvement in PP.

Mental chronometry and mental rotation abilities in stroke patients with different degrees of sensory deficit

BACKGROUND

Motor imagery is used for treatment of motor deficits after stroke. Clinical observations suggested that motor imagery abilities might be reduced in patients with severe sensory deficits. This study investigated the influence of somatosensory deficits on temporal (mental chronometry, MC) and spatial aspects of motor imagery abilities.

METHODS

Stroke patients (n = 70; <6 months after stroke) were subdivided into 3 groups according to their somatosensory functions. Group 1 (n = 31) had no sensory deficits, group 2 (n = 27) had a mild to moderate sensory impairment and group 3 (n = 12) had severe sensory deficits. Patients and a healthy age-matched control group (n = 23) participated in a mental chronometry task (Box and Block Test, BBT) and a mental rotation task (Hand Identification Test, HIT). MC abilities were expressed as a ratio (motor execution time-motor imagery time/motor execution time).

RESULTS

MC for the affected hand was significantly impaired in group 3 in comparison to stroke patients of group 1 (p = 0.006), group 2 (p = 0.005) and healthy controls (p < 0.001). For the non-affected hand MC was similar across all groups. Stroke patients had a slower BBT motor execution than healthy controls (p < 0.001), and group 1 executed the task faster than group 3 (p = 0.002). The percentage of correct responses in the HIT was similar for all groups.

CONCLUSION

Severe sensory deficits impair mental chronometry abilities but have no impact on mental rotation abilities. Future studies should explore whether the presence of severe sensory deficits in stroke patients reduces the benefit from motor imagery therapy.

What Do Eye Gaze Metrics Tell Us about Motor Imagery?

Many of the brain structures involved in performing real movements also have increased activity during imagined movements or during motor observation, and this could be the neural substrate underlying the effects of motor imagery in motor learning or motor rehabilitation. In the absence of any objective physiological method of measurement, it is currently impossible to be sure that the patient is indeed performing the task as instructed. Eye gaze recording during a motor imagery task could be a possible way to "spy" on the activity an individual is really engaged in. The aim of the present study was to compare the pattern of eye movement metrics during motor observation, visual and kinesthetic motor imagery (VI, KI), target fixation, and mental calculation. Twenty-two healthy subjects (16 females and 6 males), were required to perform tests in five conditions using imagery in the Box and Block Test tasks following the procedure described by Liepert et al. Eye movements were analysed by a non-invasive oculometric measure (SMI RED250 system). Two parameters describing gaze pattern were calculated: the index of ocular mobility (saccade duration over saccade + fixation duration) and the number of midline crossings (i.e. the number of times the subjects gaze crossed the midline of the screen when performing the different tasks). Both parameters were significantly different between visual imagery and kinesthesic imagery, visual imagery and mental calculation, and visual imagery and target fixation. For the first time we were able to show that eye movement patterns are different during VI and KI tasks. Our results suggest gaze metric parameters could be used as an objective unobtrusive approach to assess engagement in a motor imagery task. Further studies should define how oculomotor parameters could be used as an indicator of the rehabilitation task a patient is engaged in.