Abnormal projection of corticospinal tracts in a patient with congenital mirror movements

Facilitative effects of use-dependent learning on interlimb transfer of visuomotor adaptation in a person with congenital mirror movements

It has been shown that use-dependent learning can facilitate interlimb transfer of motor learning in neurologically intact individuals. However, it is unknown whether it can also facilitate interlimb transfer in individuals with neurological impairment. In this case study, we examined the effect of use-dependent learning on interlimb transfer of visuomotor adaptation in a person with congenital mirror movements, DB, who showed no interlimb transfer in our previous studies (Bao, Morgan, Lei, & Wang, 2020; Javidialsaadi, & Wang, 2021). DB first performed reaching movements with the right arm repeatedly while adapting to a visuomotor rotation condition with the left arm (training session), and then adapted to the same rotation condition with the right arm (transfer session). DB's right arm performance in the transfer session was significantly better than that observed in our previous studies, indicating interlimb transfer of visuomotor adaptation. The percentage of transfer was over 90%, which is similar to that observed in healthy young adults previously. These findings suggest that interlimb transfer of visuomotor adaptation can occur by involving model-based learning, which is effector independent, and/or use-dependent (or model-free) learning, which is effector specific; and also that the relative contribution of use-dependent learning to interlimb transfer of visuomotor adaptation can be as large as that of model-based learning.

Congenital Mirror Movements Associated With Brain Malformations

BACKGROUND

Congenital mirror movements are involuntary movements of a side of the body imitating intentional movements on the opposite side, appearing in early childhood and persisting beyond 7 years of age. Congenital mirror movements are usually idiopathic but have been reported in association with various brain malformations.

METHODS

We describe clinical, genetic, and radiologic features in 9 individuals from 5 families manifesting congenital mirror movements.

RESULTS

The brain malformations associated with congenital mirror movements were: dysplastic corpus callosum in father and daughter with a heterozygous p.Met1* mutation in DCC; hypoplastic corpus callosum, dysgyria, and malformed vermis in a mother and son with a heterozygous p.Thr312Met mutation in TUBB3; dysplastic corpus callosum, dysgyria, abnormal vermis, and asymmetric ventricles in a father and 2 daughters with a heterozygous p.Arg121Trp mutation in TUBB; hypoplastic corpus callosum, dysgyria, malformed basal ganglia and abnormal vermis in a patient with a heterozygous p.Glu155Asp mutation in TUBA1A; hydrocephalus, hypoplastic corpus callosum, polymicrogyria, and cerebellar cysts in a patient with a homozygous p.Pro312Leu mutation in POMGNT1.

CONCLUSION

DCC, TUBB3, TUBB, TUBA1A, POMGNT1 cause abnormal axonal guidance via different mechanisms and result in congenital mirror movements associated with brain malformations.

Uncrossed corticospinal tract in health and genetic disorders: Review, case report, and clinical implications

BACKGROUND AND PURPOSE

Crossing pathologies of the corticospinal tract (CST) are rare and often associated with genetic disorders. However, they can be present in healthy humans and lead to ipsilateral motor deficits when a lesion to motor areas occurs. Here, we review historical and current literature of CST crossing pathologies and present a rare case of asymmetric crossing of the CST.

METHODS

Description of the case and systematic review of the literature were based on the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. The PubMed database was searched for peer-reviewed articles in English since 1950. All articles on ipsilateral stroke, uncrossed CST, and associated neurologic disorders were screened. Furthermore, a literature review between the years 1850 and 1980 including articles in other languages, books, opinions, and case studies was conducted.

RESULTS

Only a few descriptions of CST crossing pathologies exist in healthy humans, whereas they seem to be more common in genetic disorders such as horizontal gaze palsy with progressive scoliosis or congenital mirror movements. Our patient presented with aphasia and left-sided hemiparesis. Computed tomographic (CT) scan revealed a perfusion deficit in the left middle cerebral artery territory, which was confirmed by diffusion-weighted magnetic resonance imaging (MRI), so that thrombolysis was administered. Diffusion tensor imaging with fibre tracking revealed an asymmetric CST crossing.

CONCLUSIONS

The knowledge of CST crossing pathologies is essential if a motor deficit occurs ipsilateral to the lesion side. An ipsilateral deficit should not lead to exclusion or delay of therapeutic options in patients with suspected stroke. Here, a combined evaluation of CT perfusion imaging and MRI diffusion imaging may be of advantage.

Lack of interlimb transfer following visuomotor adaptation in a person with congenital mirror movements despite the awareness of the visuomotor perturbation

There is a controversy regarding whether visuomotor adaptation heavily involves both implicit and explicit learning processes or not. Likewise, another controversy exists regarding whether interlimb transfer of visuomotor adaptation is related to explicit processes or not. To address the latter issue, we examined interlimb transfer of visuomotor adaptation in an individual with congenital mirror movements, 'DB'. DB has been tested previously using an experimental paradigm in which neurologically intact individuals demonstrated substantial transfer. DB, however, showed no transfer due to impaired interhemispheric communications. In that study, DB was unaware of the visuomotor perturbation. Here, we informed him of the perturbation prior to the experiment to determine whether providing the information would increase interlimb transfer. DB first adapted to a visuomotor rotation with the left arm, then with the right arm during reaching movements. Data from the present study were compared against those from our previous study. Results indicate no transfer across the arms despite the fact that he was aware of the perturbation. Considering overall findings in the literature, we suggest that interlimb transfer does not depend on one's awareness, although its extent can increase when individuals rely on cognitive strategies to deal with perturbations (c.f., Werner et al., 2019).

Ipsilateral motor evoked potentials in a patient with unihemispheric cortical atrophy due to Rasmussen encephalitis

The role of the ipsilaterally descending motor pathways in the recovery mechanisms after unilateral hemispheric damage is still poorly understood. Motor output reorganization was investigated in a 56-year-old male patient with acquired unilateral hemispheric atrophy due to Rasmussen encephalitis. In particular, the ipsilateral corticospinal pathways were explored using focal transcranial magnetic stimulation. In the first dorsal interosseous and wrist extensors muscles, the median amplitudes of the ipsilateral motor evoked potentials induced by transcranial magnetic stimulation in the patient were higher than those of 10 age-matched healthy control subjects. In the biceps brachii muscle, the median amplitudes of the ipsilateral motor evoked potentials were the second largest in the patient compared to the controls. This study demonstrated a reinforcement of ipsilateral motor projections from the unaffected motor cortex to the hemiparetic hand in a subject with acquired unihemispheric cortical damage.

DCC mutation update: Congenital mirror movements, isolated agenesis of the corpus callosum, and developmental split brain syndrome

The deleted in colorectal cancer (DCC) gene encodes the netrin-1 (NTN1) receptor DCC, a transmembrane protein required for the guidance of commissural axons. Germline DCC mutations disrupt the development of predominantly commissural tracts in the central nervous system (CNS) and cause a spectrum of neurological disorders. Monoallelic, missense, and predicted loss-of-function DCC mutations cause congenital mirror movements, isolated agenesis of the corpus callosum (ACC), or both. Biallelic, predicted loss-of-function DCC mutations cause developmental split brain syndrome (DSBS). Although the underlying molecular mechanisms leading to disease remain poorly understood, they are thought to stem from reduced or perturbed NTN1 signaling. Here, we review the 26 reported DCC mutations associated with abnormal CNS development in humans, including 14 missense and 12 predicted loss-of-function mutations, and discuss their associated clinical characteristics and diagnostic features. We provide an update on the observed genotype-phenotype relationships of congenital mirror movements, isolated ACC and DSBS, and correlate this to our current understanding of the biological function of DCC in the development of the CNS. All mutations and their associated phenotypes were deposited into a locus-specific LOVD (https://databases.lovd.nl/shared/genes/DCC).

Pre-movement planning processes in people with congenital mirror movements

OBJECTIVE

Pre-movement processes were investigated in people with Congenital mirrormovement (CMM), a rare disorder in which bilateral movement (mirroring) occurs in the upper distal extremities (primarily the hands and fingers) during intended unilateral movements. Abnormal density of ipsilateral corticospinal projections is an established hallmark of CMM. This study tested whether the Lateralised Readiness Potential (LRP), which reflects movement planning and readiness, is also abnormal in people with CMM.

METHODS

Twenty-eight neurologically-normal controls and 8 people with CMM were tested on a unimanual Go/No-go task while electroencephalography (EEG) was recorded to assess the LRP.

RESULTS

No significant group differences were found in reaction time (RT). However, significantly smaller LRP amplitudes were found, on average, in the CMM group compared to Controls at central-motor (C3,C4) sites in stimulus-locked and response-locked epochs; similar group differences were also found at further frontal sites (F3,F4) during response-locked epochs.

CONCLUSIONS

Abnormal brain activity in pre-movement processes associated with response planning and preparation is present in people with CMM.

SIGNIFICANCE

Aberrant bilateral activity during pre-movement processes is clearly implicated; whether part of the etiology of CMM, or as a mechanism of neuro-compensation, is not yet known.

Non cell-autonomous role of DCC in the guidance of the corticospinal tract at the midline

DCC, a NETRIN-1 receptor, is considered as a cell-autonomous regulator for midline guidance of many commissural populations in the central nervous system. The corticospinal tract (CST), the principal motor pathway for voluntary movements, crosses the anatomic midline at the pyramidal decussation. CST fails to cross the midline in Kanga mice expressing a truncated DCC protein. Humans with heterozygous DCC mutations have congenital mirror movements (CMM). As CMM has been associated, in some cases, with malformations of the pyramidal decussation, DCC might also be involved in this process in human. Here, we investigated the role of DCC in CST midline crossing both in human and mice. First, we demonstrate by multimodal approaches, that patients with CMM due to DCC mutations have an increased proportion of ipsilateral CST projections. Second, we show that in contrast to Kanga mice, the anatomy of the CST is not altered in mice with a deletion of DCC in the CST. Altogether, these results indicate that DCC controls CST midline crossing in both humans and mice, and that this process is non cell-autonomous in mice. Our data unravel a new level of complexity in the role of DCC in CST guidance at the midline.

The corticospinal tract: Evolution, development, and human disorders

The corticospinal tract (CST) plays a major role in cortical control of spinal cord activity. In particular, it is the principal motor pathway for voluntary movements. Here, we discuss: (i) the anatomic evolution and development of the CST across mammalian species, focusing on its role in motor functions; (ii) the molecular mechanisms regulating corticospinal tract formation and guidance during mouse development; and (iii) human disorders associated with abnormal CST development. A comparison of CST anatomy and development across mammalian species first highlights important similarities. In particular, most CST axons cross the anatomical midline at the junction between the brainstem and spinal cord, forming the pyramidal decussation. Reorganization of the pattern of CST projections to the spinal cord during evolution led to improved motor skills. Studies of the molecular mechanisms involved in CST formation and guidance in mice have identified several factors that act synergistically to ensure proper formation of the CST at each step of development. Human CST developmental disorders can result in a reduction of the CST, or in guidance defects associated with abnormal CST anatomy. These latter disorders result in altered midline crossing at the pyramidal decussation or in the spinal cord, but spare the rest of the CST. Careful appraisal of clinical manifestations associated with CST malformations highlights the critical role of the CST in the lateralization of motor control. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 810-829, 2017.

Egocentric and allocentric constraints in the expression of patterns of interlimb coordination

Tasks that are easy when performed in isolation become difficult when performed simultaneously in the upper and/or lower limbs. This observation points to basic CNS constraints in the organization of patterns of interlimb coordination. The present studies provide evidence for the existence of two basic coordinative constraints whose effects may be additive under certain conditions. On one hand, the egocentric constraint denotes a general preference for moving the limbs toward or away from the longitudinal axis of the body in a symmetrical fashion and is of primary importance during the coordination of homologous limbs. On the other hand, the allocentric constraint refers to a general preference to move the limbs in the same direction in extrinsic space and pertains to the coordination of nonhomologous limbs (eg., various combinations of the upper and lower limbs). In the present context, constraints are considered as expressions of basic features of CNS operation that give way to preferred coordination patterns to which the system is naturally drawn or biased. The identification and description of these constraints is considered of critical importance to obtain a better understanding of the control of coordination patterns.

Interhemispheric control of unilateral movement

To perform strictly unilateral movements, the brain relies on a large cortical and subcortical network. This network enables healthy adults to perform complex unimanual motor tasks without the activation of contralateral muscles. However, mirror movements (involuntary movements in ipsilateral muscles that can accompany intended movement) can be seen in healthy individuals if a task is complex or fatiguing, in childhood, and with increasing age. Lateralization of movement depends on complex interhemispheric communication between cortical (i.e., dorsal premotor cortex, supplementary motor area) and subcortical (i.e., basal ganglia) areas, probably coursing through the corpus callosum (CC). Here, we will focus on transcallosal interhemispheric inhibition (IHI), which facilitates complex unilateral movements and appears to play an important role in handedness, pathological conditions such as Parkinson's disease, and stroke recovery.

Association between schizophrenia and genetic variation in DCC: a case-control study

Schizophrenia is a highly heritable neurodevelopmental disorder associated with alterations in synaptic connectivity. Deleted in colorectal cancer (DCC), a receptor for the guidance cue netrin-1, plays a pivotal role in organizing neuronal circuitry by guiding growing axons and dendrites to their correct targets and by influencing synaptic connectivity. Results from experiments we previously conducted in dcc-heterozygous mice show that DCC plays a critical role in the developmental organization of the mesocorticolimbic dopamine (DA) circuitry. Furthermore we have shown that reduced expression of DCC during development and/or throughout life confers resilience to the development of schizophrenia-like DA and behavioural abnormalities. Importantly, this "protective" phenotype only emerges after puberty. Here we assess whether DCC may contribute to the risk of schizophrenia. We examined single nucleotide polymorphisms (SNPs) located in the DCC gene for association with schizophrenia using a case-control sample consisting of 556 unrelated schizophrenic patients and 208 healthy controls. We found one SNP, rs2270954, to be nominally associated with schizophrenia; patients were less likely to be heterozygous at this locus and more likely to be homozygous for the minor allele (χ(2)=9.84, df=2, nominal p=0.0071). Intriguingly, this SNP is located within the 3' untranslated region, an area known to contain a number of regulatory sequences that determine the stability and translation efficacy of mRNA. These results, together with our previous findings from studies in rodents, point at DCC as a promising novel candidate gene that may contribute to the genetic basis behind individual differences in susceptibility to schizophrenia.

Mirror movements in movement disorders: a review

BACKGROUND

Mirror movements (MM) are involuntary movements of homologous muscles during voluntary movements of contralateral body regions. While subtle mirroring can be present in otherwise healthy adults, overt MM may be common in many movement disorders. Examining these collective findings may further our understanding of MM and help define their usefulness as a clinical sign.

METHODS

We sought to review English language research articles examining the presence, clinical significance, and/or pathophysiology of MM in Parkinson's disease (PD), corticobasal syndrome (CBS), essential tremor (ET), focal hand dystonia, Creutzfeldt-Jakob's disease (CJD), and Huntington's disease. When available, MM in these disorders were compared with those of healthy age-matched controls and congenital disorders such as Klippel-Feil syndrome and X-linked Kallman's syndrome.

RESULTS

Clinical presentation of MM is common in asymmetric parkinsonian disorders (early PD, CBS) and manifests differently depending on the side affected (less affected hand in PD, more affected hand in CBS, either hand in ET, and both hands in healthy adults and congenital disorders), stage of disease (early, asymmetric PD and CJD), and presence of concomitant mirror-like overflow phenomena (focal dystonia and CBS-associated alien hand). In general, uncrossed descending corticospinal projections (congenital MM) and/or abnormal activation of the motor cortex ipsilateral to the voluntary task (most acquired MM), i.e., activation of the normal crossed corticospinal pathway, are required for the generation of MM.

DISCUSSION

MM are common motor phenomena and present differently in several acquired (mostly neurodegenerative) and congenital movement disorders. Future studies on MM will enhance the clinical diagnosis of selected movement disorders and contribute to our understanding of the normal physiology of bimanual coordination.

Ipsilateral corticospinal projections do not predict congenital mirror movements: a case report

Congenital mirror movements (CMMs) are involuntary, symmetric movements of one hand during the production of voluntary movements with the other. CMMs have been attributed to a range of physiological mechanisms, including excessive ipsilateral projections from each motor cortex to distal extremities. We examined this hypothesis with an individual showing pronounced CMMs. Mirror movements were characterized for a set of hand muscles during a simple contraction task. Transcranial magnetic stimulation (TMS) was then used to map the relative input to each muscle from both motor cortices. Contrary to our expectations, CMMs were most prominent for muscles with the strongest contralateral representation rather than in muscles that were activated by stimulation of either hemisphere. These findings support a bilateral control hypothesis whereby CMMs result from the recruitment of both motor cortices during intended unimanual movements. Consistent with this hypothesis, bilateral motor cortex activity was evident during intended unimanual movements in an fMRI study. To assess the level at which bilateral recruitment occurs, motor cortex excitability during imagined unimanual movements was assessed with TMS. Facilitory excitation was only observed in the contralateral motor cortex. Thus, the bilateral recruitment of the hemispheres for unilateral actions in individuals with CMMs appears to occur during movement execution rather than motor planning.

Separate ipsilateral and contralateral corticospinal projections in congenital mirror movements: Neurophysiological evidence and significance for motor rehabilitation

The neurophysiological hallmark of congenital mirror movements (MM) are fast-conducting corticospinal projections from the hand area of one primary motor cortex to both sides of the spinal cord. It is still unclear whether the abnormal ipsilateral projection originates through branching fibres from the normal contralateral projection or constitutes a separate ipsilateral projection. To clarify this question, we used focal paired-pulse transcranial magnetic stimulation to test task-related modulation of short-interval intracortical inhibition (SICI) in the abductor pollicis brevis (APB) muscles of a 15-year-old girl (Patient 1) and a 40-year-old woman (Patient 2) with congenital MM. In both patients, during intended unilateral APB contraction, SICI decreased markedly in the "task" APB but remained unchanged in the "mirror" APB when compared to muscle rest. In contrast, spinal excitability as tested with H reflexes increased similarly in the task and mirror flexor carpi radialis muscles. This dissociation of task-related SICI modulation strongly supports the existence of a separate ipsilateral fast-conducting corticospinal projection. In Patient 1, we tested the functional significance of this separate ipsilateral projection during 7 months of motor rehabilitation training, which was designed to facilitate unilateral finger movements. A marked reduction of MM was observed after training, suggesting that unwanted mirror activity in the ipsilateral pathway can be suppressed by learning.

Ipsilateral motor responses to focal transcranial magnetic stimulation in healthy subjects and acute-stroke patients

BACKGROUND AND PURPOSE

Prevalence and characteristics of ipsilateral upper limb motor-evoked potentials (MEPs) elicited by focal transcranial magnetic stimulation (TMS) were compared in healthy subjects and patients with acute stroke.

METHODS

Sixteen healthy subjects and 25 patients with acute stroke underwent focal TMS at maximum stimulator output over motor and premotor cortices. If present, MEPs evoked in muscles ipsilateral to TMS were analyzed for latency, amplitude, shape, and center of gravity (ie, preferential coil location to elicit them). In stroke patients, possible relationships between early ipsilateral responses and functional outcome at 6 months were sought.

RESULTS

With relaxed or slightly contracting target muscle, maximal TMS over the motor cortex failed to elicit ipsilateral MEPs in the first dorsal interosseous (FDI) or biceps of any of 16 normal subjects. In 5 of 8 healthy subjects tested, ipsilateral MEPs with latencies longer than contralateral MEPs were evoked in FDI muscle (in biceps, 6 of 8 subjects) during strong (>50% maximum) contraction of the target muscle. In 15 of 25 stroke patients, ipsilateral MEPs in the unaffected relaxed FDI (in biceps, 6 of 25 stroke patients) were evoked by stimulation of premotor areas of the affected hemisphere. Their latencies were shorter than those that MEPs evoked in the same muscle by stimulation of the motor cortex of the contralateral unaffected hemisphere. Such responses were never obtained in normal subjects and were mostly observed in patients with subcortical infarcts. Patients harboring these responses had slightly better bimanual dexterity after 6 months.

CONCLUSIONS

Ipsilateral MEPs obtained in healthy individuals and stroke patients have different characteristics and probably different origins. In the former, they are probably conveyed via corticoreticulospinal or corticopropriospinal pathways, whereas in the latter, early ipsilateral MEPs could originate in hyperexcitable premotor areas.

Dissociation of the pathways mediating ipsilateral and contralateral motor-evoked potentials in human hand and arm muscles

1. Growing evidence points toward involvement of the human motor cortex in the control of the ipsilateral hand. We used focal transcranial magnetic stimulation (TMS) to examine the pathways of these ipsilateral motor effects. 2. Ipsilateral motor-evoked potentials (MEPs) were obtained in hand and arm muscles of all 10 healthy adult subjects tested. They occurred in the finger and wrist extensors and the biceps, but no response or inhibitory responses were observed in the opponens pollicis, finger and wrist flexors and the triceps. 3. The production of ipsilateral MEPs required contraction of the target muscle. The threshold TMS intensity for ipsilateral MEPs was on average 1.8 times higher, and the onset was 5.7 ms later (in the wrist extensor muscles) compared with size-matched contralateral MEPs. 4. The corticofugal pathways of ipsilateral and contralateral MEPs could be dissociated through differences in cortical map location and preferred stimulating current direction. 5. Both ipsi- and contralateral MEPs in the wrist extensors increased with lateral head rotation toward, and decreased with head rotation away from, the side of the TMS, suggesting a privileged input of the asymmetrical tonic neck reflex to the pathway of the ipsilateral MEP. 6. Large ipsilateral MEPs were obtained in a patient with complete agenesis of the corpus callosum. 7. The dissociation of the pathways for ipsilateral and contralateral MEPs indicates that corticofugal motor fibres other than the fast-conducting crossed corticomotoneuronal system can be activated by TMS. Our data suggest an ipsilateral oligosynaptic pathway, such as a corticoreticulospinal or a corticopropriospinal projection as the route for the ipsilateral MEP. Other pathways, such as branching of corticomotoneuronal axons, a transcallosal projection or a slow-conducting monosynaptic ipsilateral pathway are very unlikely or can be excluded.

Hand motor cortex activation in a patient with congenital mirror movements: a study of the silent period following focal transcranial magnetic stimulation

Motor evoked potentials (MEPs) to focal transcranial magnetic stimulation (TMS) have demonstrated that abnormal ipsilateral corticospinal projections are active in patients with congenital mirror movements. In addition, movement-related potentials and PET suggest that an abnormal pattern of motor cortex activation could be associated with an anomaly of the corticospinal tracts. In the present study the silent period (SP) following focal TMS was investigated in a woman with familial congenital mirror movements. Recordings were made from both abductor pollicis brevis (APB) muscles. When focal TMS was delivered during an intended contralateral APB muscle contraction, MEP and SP were bilaterally recorded and SP was significantly shorter than the contralateral SP observed in normal controls. An abnormal bilateral activation of the hand motor cortex can explain our findings. The non-stimulated motor cortex causes an early partial recovery of the background EMG activity when the stimulated motor cortex is still inhibited (beginning as soon as the transcallosal and the short-lasting segmental inhibition are both complete).