Ipsilateral M1 Activation Research Articles

The role of ipsilateral motor network in upper limb movement.

The execution of voluntary movements is primarily governed by the cerebral hemisphere contralateral to the moving limb. Previous research indicates that the ipsilateral motor network, comprising the primary motor cortex (M1), supplementary motor area (SMA), and premotor cortex (PM), plays a crucial role in the planning and execution of limb movements. However, the precise functions of this network and its interplay in different task contexts have yet to be fully understood. Twenty healthy right-handed participants (10 females, mean age 26.1 ± 4.6years) underwent functional MRI scans while performing biceps brachii representations such as bilateral, unilateral flexion, and bilateral flexion-extension. Ipsilateral motor evoked potentials (iMEPs) were obtained from the identical set of participants in a prior study using transcranial magnetic stimulation (TMS) targeting M1 while employing the same motor tasks. The voxel time series was extracted based on the region of interest (M1, SMA, ventral PM and dorsal PM). Directed functinal connectivity was derived from the extracted time series using time-resolved partial directed coherence. We found increased connectivity from left-PMv to both sides M1, as well as right-PMv to both sides SMA, in unilateral flexion compared to bilateral flexion. Connectivity from left M1 to left-PMv, and left-SMA to right-PMd, also increased in both unilateral flexion and bilateral flexion-extension compared to bilateral flexion. However, connectivity between PMv and right-M1 to left-PMd decreased during bilateral flexion-extension compared to unilateral flexion. Additionally, during bilateral flexion-extension, the connectivity from right-M1 to right-SMA had a negative relationship with the area ratio of iMEP in the dominant side. Our results provide corroborating evidence for prior research suggesting that the ipsilateral motor network is implicated in the voluntary movements and underscores its involvement in cognitive processes such as movement planning and coordination. Moreover, ipsilateral connectivity from M1 to SMA on the dominant side can modulate the degree of ipsilateral M1 activation during bilateral antagonistic contraction.

Evaluating the Abnormality of Bilateral Motor Cortex Activity in Subacute Stroke Patients Executing a Unimanual Motor Task With Increasing Demand on Precision

Abnormal contralesional M1 activity is consistently reported in patients with compromised upper limb and hand function after stroke. The underlying mechanisms and functional implications of this activity are not clear, which hampers the development of treatment strategies targeting this brain area. The goal of the present study was to determine the extent to which contralesional M1 activity can be explained by the demand of a motor task, given recent evidence for increasing ipsilateral M1 activity with increasing demand in healthy age-matched controls. We hypothesized that higher activity in contralesional M1 is related to greater demand on precision in a hand motor task. fMRI data were collected from 19 patients with ischemic stroke affecting hand function in the subacute recovery phase and 31 healthy, right-handed, age-matched controls. The hand motor task was designed to parametrically modulate the demand on movement precision. Electromyography data confirmed strictly unilateral task performance by all participants. Patients showed significant impairment relative to controls in their ability to perform the task in the fMRI scanner. However, patients and controls responded similarly to an increase in demand for precision, with better performance for larger targets and poorer performance for smaller targets. Patients did not show evidence of elevated ipsilesional or contralesional M1 blood oxygenation level-dependent (BOLD) activation relative to healthy controls and mean BOLD activation levels were not elevated for patients with poorer performance relative to patients with better task performance. While both patients and healthy controls showed demand-dependent increases in BOLD activation in both ipsilesional/contralateral and contralesional/ipsilateral hemispheres, patients with stroke were less likely to show evidence of a linear relationship between the demand on precision and BOLD activation in contralesional M1 than healthy controls. Taken together, the findings suggest that task demand affects the BOLD response in contralesional M1 in patients with stroke, though perhaps less strongly than in healthy controls. This has implications for the interpretation of reported abnormal bilateral M1 activation in patients with stroke because in addition to contralesional M1 reorganization processes it could be partially related to a response to the relatively higher demand of a motor task when completed by patients rather than by healthy controls.

Para-Sports can Promote Functional Reorganization in the Ipsilateral Primary Motor Cortex of Lower Limbs Amputee

Background. Drastic functional reorganization was observed in the ipsilateral primary motor cortex (M1) of a Paralympic long jumper with a unilateral below-knee amputation in our previous study. However, it remains unclear whether long-term para-sports are associated with ipsilateral M1 reorganization since only 1 athlete with amputation was investigated. Objective. This study aimed to investigate the relationship between the long-term para-sports and ipsilateral M1 reorganization after lower limb amputation. Methods. Lower limb rhythmic muscle contraction tasks with functional magnetic resonance imaging and T1-weighted structural imaging were performed in 30 lower limb amputees with different para-sports experiences in the chronic phase. Results. Brain activity in the ipsilateral primary motor and somatosensory areas (SM1) as well as the contralateral dorsolateral prefrontal cortex, SM1, and inferior temporal gyrus showed a positive correlation with the years of routine para-sports participation (sports years) during contraction of the amputated knee. Indeed, twelve of the 30 participants who exhibited significant ipsilateral M1 activation during amputated knee contraction had a relatively longer history of para-sports participation. No significant correlation was found in the structural analysis. Conclusions. Long-term para-sports could lead to extensive reorganization at the brain network level, not only bilateral M1 reorganization but also reorganization of the frontal lobe and visual pathways. These results suggest that the interaction of injury-induced and use-dependent cortical plasticity might bring about drastic reorganization in lower limb amputees.

Increased Ipsilateral M1 Activation after Incomplete Spinal Cord Injury Facilitates Motor Performance.

Incomplete spinal cord injury (SCI) may result in muscle weakness and difficulties with force gradation. Although these impairments arise from the injury and subsequent changes at spinal levels, changes have also been demonstrated in the brain. Blood-oxygen-level dependent (BOLD) imaging was used to investigate these changes in brain activation in the context of unimanual contractions with the first dorsal interosseous muscle. BOLD- and force data were obtained in 19 individuals with SCI (AISA Impairment Scale [AIS] C/D, level C4-C8) and 24 able-bodied controls during maximal voluntary contractions (MVCs). To assess force modulation, participants performed 12 submaximal contractions with each hand (at 10, 30, 50, and 70% MVC) by matching their force level to a visual target. MVCs were weaker in the SCI group (both hands p < 0.001), but BOLD activation did not differ between SCI and control groups. For the submaximal contractions, force (as %MVC) was similar across groups. However, SCI participants showed increased activity of the ipsilateral motor cortex and contralateral cerebellum across all contractions, with no differential effect of force level. Activity of ipsilateral M1 was best explained by force of the target hand (vs. the non-target hand). In conclusion, the data suggest that after incomplete cervical SCI, individuals remain capable of producing maximal supraspinal drive and are able to modulate this drive adequately. Activity of the ipsilateral motor network appears to be task related, although it remains uncertain how this activity contributes to task performance and whether this effect could potentially be harnessed to improve motor functioning.

Role of kinaesthetic motor imagery in mirror-induced visual illusion as intervention in post-stroke rehabilitation.

Mirror-induced visual illusion obtained through mirror therapy is widely used to facilitate motor recovery after stroke. Activation of primary motor cortex (M1) ipsilateral to the moving limb has been reported during mirror-induced visual illusion. However, the mechanism through which the mirror illusion elicits motor execution processes without movements observed in the mirrored limb remains unclear. This study aims to review evidence based on brain imaging studies for testing the hypothesis that neural processes associated with kinaesthetic motor imagery are attributed to ipsilateral M1 activation. Four electronic databases were searched. Studies on functional brain imaging, investigating the instant effects of mirror-induced visual illusion among stroke survivors and healthy participants were included. Thirty-five studies engaging 78 stroke survivors and 396 healthy participants were reviewed. Results of functional brain scans (n = 20) indicated that half of the studies (n = 10, 50%) reported significant changes in the activation of ipsilateral M1, which mediates motor preparation and execution. Other common neural substrates included primary somatosensory cortex (45%, kinaesthesia), precuneus (40%, image generation and self-processing operations) and cerebellum (20%, motor control). Similar patterns of ipsilateral M1 activations were observed in the two groups. These neural substrates mediated the generation, maintenance, and manipulation of motor-related images, which were the key processes in kinaesthetic motor imagery. Relationships in terms of shared neural substrates and mental processes between mirror-induced visual illusion and kinaesthetic motor imagery generate new evidence on the role of the latter in mirror therapy. Future studies should investigate the imagery processes in illusion training for post-stroke patients.

Using Dual-Site Transcranial Magnetic Stimulation to Probe Connectivity between the Dorsolateral Prefrontal Cortex and Ipsilateral Primary Motor Cortex in Humans.

Dual-site transcranial magnetic stimulation to the primary motor cortex (M1) and dorsolateral prefrontal cortex (DLPFC) can be used to probe functional connectivity between these regions. The purpose of this study was to characterize the effect of DLPFC stimulation on ipsilateral M1 excitability while participants were at rest and contracting the left- and right-hand first dorsal interosseous muscle. Twelve participants were tested in two separate sessions at varying inter-stimulus intervals (ISI: 4, 5, 6, 7, 8, 9, 10, 11, 12, 15, and 20 ms) at two different conditioning stimulus intensities (80% and 120% of resting motor threshold). No significant effect on ipsilateral M1 excitability was found when applying a conditioning stimulus over DLPFC at any specific inter-stimulus interval or intensity in either the left or right hemisphere. Our findings suggest neither causal inhibitory nor faciliatory influences of DLPFC on ipsilateral M1 activity while participants were at rest or when performing an isometric contraction in the target hand muscle.

Cortical Activation Changes in Hirayama Disease After Anterior Cervical Decompression and Fusion

Spinal cord injury may cause cortical reconstruction. We, therefore explored the changes in cortical activation before and after anterior cervical decompression and fusion surgery in patients with Hirayama disease (HD). In total, 17 cases with HD underwent anterior cervical decompression and fusion surgery. Blood oxygenation level-dependent functional magnetic resonance imaging scan was performed preoperatively, 3 months, 6 months, and 1 year after surgery. Activated voxels were compared between both hands after adjusting for head motion, slice timing, spatial normalization, and image smoothing. Grip strength also was tested in both hands. A retrospective review indicated that the grip strength of the asymptomatic hand was significantly stronger than the symptomatic hand at the time point before the surgery, 3 months after surgery, 6 months after surgery, and 1 year after surgery (P < 0.001). The grip strength of both symptomatic and asymptomatic hands continuously increased within 6 months after surgery (P < 0.05), but it stopped at 1 year after the surgery. The symptomatic limb tends to produce bilateral activation in the primary motor area (M1) during motor tasks. Both contralateral and ipsilateral M1 activation were stronger in symptomatic hand tasks preoperatively (P < 0.05). Both contralateral and ipsilateral activation in M1 during symptomatic hand tasks began to reduce after surgery, and statistical significance was observed 6 months after surgery (P<0.05). Contralateral activation was relatively even over 6 months of the surgery (P > 0.05). After surgery, pathologic reconstruction may have occurred in the primary motor cortex. Recovery of motor function in the symptomatic limb was accompanied by decreased ipsilateral and contralateral M1 activation, as well as symptom improvement. These findings suggested that postoperative cortical activation changes may reflect functional recovery in HD.

Demand on skillfulness modulates interhemispheric inhibition of motor cortices.

The role of primary motor cortex (M1) in the control of hand movements is still unclear. Functional magnetic resonance imaging (fMRI) studies of unimanual performance reported a relationship between level of precision of a motor task and additional ipsilateral M1 (iM1) activation. In the present study, we determined whether the demand on accuracy of a movement influences the magnitude of the inhibitory effect between primary motor cortices (IHI). We used transcranial magnetic stimulation (TMS) to measure active IHI (aIHI) of the iM1 on the contralateral M1 (cM1) in the premovement period of a left-hand motor task. Ten healthy participants manipulated a joystick to point to targets of two different sizes. For aIHI, the conditioning stimulus (CS) was applied to iM1, and the test stimulus (TS) to cM1, with an interstimulus interval of 10 ms. The amount of the inhibitory effect of the CS on the motor-evoked potential (MEP) of the subsequent TS was expressed as percentage of the mean MEP amplitude evoked by the single TS. Across different time points of aIHI measurements in the premovement period, there was a significant effect for target size on aIHI. Preparing to point to small targets was associated with weaker aIHI compared with pointing to large targets. The present findings suggest that, during the premovement period, aIHI from iM1 on cM1 is modulated by the demand on accuracy of the motor task. This is consistent with task fMRI findings showing bilateral M1 activation during high-precision movements but only unilateral M1 activity during low-precision movements.

Voltage-sensitive dye imaging of primary motor cortex activity produced by ventral tegmental area stimulation.

The primary motor cortex (M1) receives dopaminergic projections from the ventral tegmental area (VTA) through the mesocortical dopamine pathway. However, few studies have focused on changes in M1 neuronal activity caused by VTA activation. To address this issue, we used voltage-sensitive dye imaging (VSD) to reveal the spatiotemporal dynamics of M1 activity induced by single-pulse stimulation of VTA in anesthetized rats. VSD imaging showed that brief electrical stimulation of unilateral VTA elicited a short-latency excitatory-inhibitory sequence of neuronal activity not only in the ipsilateral but also in the contralateral M1. The contralateral M1 response was not affected by pharmacological blockade of ipsilateral M1 activity, but it was completely abolished by corpus callosum transection. Although the VTA-evoked neuronal activity extended throughout the entire M1, we found the most prominent activity in the forelimb area of M1. The 6-OHDA-lesioned VTA failed to evoke M1 activity. Furthermore, both excitatory and inhibitory intact VTA-induced activity was entirely extinguished by blocking glutamate receptors in the target M1. When intracortical microstimulation of M1 was paired with VTA stimulation, the evoked forelimb muscle activity was facilitated or inhibited, depending on the interval between the two stimuli. These findings suggest that VTA neurons directly modulate the excitability of M1 neurons via fast glutamate signaling and, consequently, may control the last cortical stage of motor command processing.

Motor demand-dependent activation of ipsilateral motor cortex.

The role of ipsilateral primary motor cortex (M1) in hand motor control during complex task performance remains controversial. Bilateral M1 activation is inconsistently observed in functional (f)MRI studies of unilateral hand performance. Two factors limit the interpretation of these data. As the motor tasks differ qualitatively in these studies, it is conceivable that M1 contributions differ with the demand on skillfulness. Second, most studies lack the verification of a strictly unilateral execution of the motor task during the acquisition of imaging data. Here, we use fMRI to determine whether ipsilateral M1 activity depends on the demand for precision in a pointing task where precision varied quantitatively while movement trajectories remained equal. Thirteen healthy participants used an MRI-compatible joystick to point to targets of four different sizes in a block design. A clustered acquisition technique allowed simultaneous fMRI/EMG data collection and confirmed that movements were strictly unilateral. Accuracy of performance increased with target size. Overall, the pointing task revealed activation in contralateral and ipsilateral M1, extending into contralateral somatosensory and parietal areas. Target size-dependent activation differences were found in ipsilateral M1 extending into the temporal/parietal junction, where activation increased with increasing demand on accuracy. The results suggest that ipsilateral M1 is active during the execution of a unilateral motor task and that its activity is modulated by the demand on precision.

Hemispheric asymmetry of ipsilateral motor cortex activation in motor skill learning

In this study, we investigated how ipsilateral motor cortex (M1) activation during unimanual hand movements and hemispheric asymmetry changed after motor skill learning. Eleven right-handed participants preformed a two-ball-rotation motor task with the right and the left hand, separately, in all experimental sessions. Before and after exercise sessions, the degree of ipsilateral M1 activation during brief execution of the motor task was measured as changes in the size of motor-evoked potentials (MEPs) of the thenar and the first dorsal interosseous muscle of the nontask hand using transcranial magnetic stimulation. Before exercise, MEPs of the nontask hand were significantly facilitated on both sides during the motor task. After exercise, facilitation of MEPs of the nontask hand during the motor task was significantly reduced for the right hand (thenar: P=0.014, first dorsal interosseous: P=0.022) but not for the left hand. We conclude that ipsilateral M1 activation, associated with a complex motor task, is first symmetrical in both hemispheres. However, on exercise, ipsilateral activation is reduced only in left M1, indicating a stronger learning-dependent modification of motor networks within the left hemisphere.

The activity of the primary motor cortex ipsilateral to the exercising hand decreases during repetitive handgrip exercise

The brain function controlling muscle force production is not yet fully understood. The purpose of this study was to examine bilateral primary motor cortex (M1) oxygenation during static-handgrip exercises performed with the right hand (60% maximal voluntary contraction; 10 s exercise/75 s rest; five sets). Twelve healthy, right-handed male subjects participated in this study. Near-infrared spectroscopy probes were positioned over the bilateral M1 to measure cortical oxygenation during handgrip exercises. The maximum values of the changes in concentrations of oxyhemoglobin (HbO2) and deoxyhemoglobin (Hb) across the trials (i) did not change significantly during the contralateral M1 activation (p > 0.05), whereas (ii) in the case of the ipsilateral M1 activation a significant (p < 0.05) decrease in HbO2 and a significant (p < 0.01) decrease in Hb could be measured. The activation in ipsilateral M1 at the fifth trial was significantly decreased compared with that in the first trial (HbO2: p < 0.001; Hb: p < 0.001). The present results suggest that the ipsilateral M1 is recruited during the motor task in compensation for the contralateral M1 and the habituation to motor task might alter the efficiency for interaction of the ipsilateral M1 to the contralateral M1. The interhemispheric interaction might change due to habituation to motor task.

Involvement of the Primary Motor Cortex in Controlling Movements Executed with the Ipsilateral Hand Differs between Left- and Right-handers

Unimanual motor tasks, specifically movements that are complex or require high forces, activate not only the contralateral primary motor cortex (M1) but evoke also ipsilateral M1 activity. This involvement of ipsilateral M1 is asymmetric, such that the left M1 is more involved in motor control with the left hand than the right M1 in movements with the right hand. This suggests that the left hemisphere is specialized for movement control of either hand, although previous experiments tested mostly right-handed participants. In contrast, research on hemispheric asymmetries of ipsilateral M1 involvement in left-handed participants is relatively scarce. In the present study, left- and right-handed participants performed complex unimanual movements, whereas TMS was used to disrupt the activity of ipsilateral M1 in accordance with a "virtual lesion" approach. For right-handed participants, more disruptions were induced when TMS was applied over the dominant (left) M1. For left-handed participants, two subgroups could be distinguished, such that one group showed more disruptions when TMS was applied over the nondominant (left) M1, whereas the other subgroup showed more disruptions when the dominant (right) M1 was stimulated. This indicates that functional asymmetries of M1 involvement during ipsilateral movements are influenced by both hand dominance as well as left hemisphere specialization. We propose that the functional asymmetries in ipsilateral M1 involvement during unimanual movements are primarily attributable to asymmetries in the higher-order areas, although the contribution of transcallosal pathways and ipsilateral projections cannot be completely ruled out.

Redundant information encoding in primary motor cortex during natural and prosthetic motor control

Redundant encoding of information facilitates reliable distributed information processing. To explore this hypothesis in the motor system, we applied concepts from information theory to quantify the redundancy of movement-related information encoded in the macaque primary motor cortex (M1) during natural and neuroprosthetic control. Two macaque monkeys were trained to perform a delay center-out reaching task controlling a computer cursor under natural arm movement (manual control, 'MC'), and using a brain-machine interface (BMI) via volitional control of neural ensemble activity (brain control, 'BC'). During MC, we found neurons in contralateral M1 to contain higher and more redundant information about target direction than ipsilateral M1 neurons, consistent with the laterality of movement control. During BC, we found that the M1 neurons directly incorporated into the BMI ('direct' neurons) contained the highest and most redundant target information compared to neurons that were not incorporated into the BMI ('indirect' neurons). This effect was even more significant when comparing to M1 neurons of the opposite hemisphere. Interestingly, when we retrained the BMI to use ipsilateral M1 activity, we found that these neurons were more redundant and contained higher information than contralateral M1 neurons, even though ensembles from this hemisphere were previously less redundant during natural arm movement. These results indicate that ensembles most associated to movement contain highest redundancy and information encoding, which suggests a role for redundancy in proficient natural and prosthetic motor control.

Network Dynamics Mediating Ipsilateral Motor Cortex Activity during Unimanual Actions

Executing difficult actions with the left hand results in bilateral activity of motor areas along the precentral gyrus. Using TMS and fMRI, we explored the functional relationship between primary (M1) and premotor areas during unimanual actions, focusing on M1 activity in the ipsilateral hemisphere. Single-pulse TMS revealed that the amplitude of motor-evoked potentials (MEPs), elicited in the stationary right-hand muscles following left M1 stimulation, fluctuated with the state of homologous muscles in the moving left hand. This ipsilateral excitability was pronounced when the left-hand movements were more complex. We used fMRI to visualize the cortical dynamics during unimanual actions. Trial-by-trial fluctuations in ipsilateral M1 activity were correlated with contralateral M1 responses and this correlation increased with movement complexity. Consistent with previous studies, the left caudal precentral premotor area (pcPM) was engaged during movements of either hand. Following low-frequency rTMS over left pcPM, the correlation between the activity level in the two M1s increased. This finding indicates that left pcPM may regulate the unintentional mirroring of motor commands in M1 during unilateral movement.

Bi-directional interhemispheric inhibition during unimanual sustained contractions

BackgroundThe interaction between homologous muscle representations in the right and left primary motor cortex was studied using a paired-pulse transcranial magnetic stimulation (TMS) protocol known to evoke interhemispheric inhibition (IHI). The timecourse and magnitude of IHI was studied in fifteen healthy right-handed adults at several interstimulus intervals between the conditioning stimulus and test stimulus (6, 8, 10, 12, 30, 40, 50 ms). IHI was studied in the motor dominant to non-dominant direction and vice versa while the right or left hand was at rest, performing isometric contraction of the first dorsal interosseous (FDI) muscle, and isometric contraction of the FDI muscle in the context of holding a pen.ResultsCompared with rest, IHI was reduced at all ISIs during contraction of either type (with or without the context of pen). IHI was reduced bi-directionally without evidence of hemispheric dominance. Further, contraction of the hand contralateral to the conditioning and test pulse yielded similar reductions in IHI.ConclusionThese data provide evidence for bi-directional reduction of IHI during unimanual contractions. During unimanual, sustained contractions of the hand, the contralateral and ipsilateral motor cortices demonstrate reduced inhibition. The data suggest that unimanual movement decreases inhibition bi-directionally across motor hemispheres and offer one explanation for the observation of ipsilateral M1 activity during hand movements.

Comparison of unilateral and bilateral complex finger tapping‐related activation in premotor and primary motor cortex

Sixteen healthy right-handed subjects performed a complex finger-tapping task that broadly activates the motor and premotor regions, including primary motor (M1), ventral premotor (PMv), and dorsal premotor (PMd) cortex. This task was performed with the right hand only, left hand only and both hands simultaneously. Behavioral performance and the possibility of mirror movements were controlled through the use of MRI-compatible gloves to monitor finger movements. Using spatially normalized ROIs from the Human Motor Area Template (HMAT), comparisons were made of the spatial extent and location of activation in the left and right motor regions between all three tasks. During unilateral right and left hand tapping, ipsilateral precentral gyrus activation occurred in all subjects, mainly in the PMv and PMd. Ipsilateral M1 activation was less consistent and shifted anteriorly within M1, towards the border of M1 and premotor cortex. Regions of ipsilateral activation were also activated during contralateral and bilateral tasks. Overall, 83%/70%/58% of the ipsilaterally activated voxels in M1/PMd/PMv were also activated during contralateral and bilateral tapping. The mean percent signal change of spatially overlapping activated voxels was similar in PMv and PMd between all three tasks. However, the mean percent signal change of spatially overlapping M1 activation was significantly less during ipsilateral tapping compared with contra- or bilateral tapping. Results suggest that the ipsilateral fMRI activation in unilateral motor tasks may not be inhibitory in nature, but rather may reflect part of a bilateral network involved in the planning and/or execution of tapping in the ipsilateral hand.

Investigation of the normal proximal somatomotor system using magnetoencephalography

The role of the ipsilateral cortex in proximal muscle control in normal human subjects is still under debate. One clinical finding, rapid recovery of proximal muscle relative to distal muscle use following stroke, has led to the suggestion that the ipsilateral as well as the contralateral motor cortex may be involved in normal proximal muscle control. The primary goal of this project was to identify contralateral and ipsilateral motor cortex activation associated with proximal muscle movement in normal subjects using magnetoencephalography (MEG). We developed protocols for a self-paced bicep motor task and a deltoid, electrical-stimulation somatosensory task. The MEG data were analyzed using automated multi-dipole spatiotemporal modeling techniques to localize the sources and characterize the associated timing of these sources. Reliable contralateral primary motor and somatosensory sources localized to areas consistent with the homunculus. Ipsilateral M1 activation was only found in 2/12 hemispheres. Robust contralateral motor cortex activation and sparse ipsilateral motor cortex activation suggest that the ipsilateral motor cortex is not involved in normal proximal muscle control. The results suggest that proximal and distal muscle control is similar in normal subjects in the sense that proximal muscle control is primarily governed by the contralateral motor cortex.

Somatotopy in the ipsilateral primary motor cortex.

Conflicting reports exist about the occurrence, reliability and localization of activation in the ipsilateral primary motor cortex (M1). We re-examined this issue with functional magnetic resonance imaging in 12 volunteers performing right hand, finger, wrist, elbow, foot and tongue movements in two separate sessions. Ipsilateral M1 activation was inconsistently and non-reliably present during all movements: in 54% of all hand, 50% elbow, 46% finger, 33% wrist, and in 17% of all foot experiments. When compared to contralateral M1, the volumes and maximum t-values were always smaller. The ipsilateral M1 body representation was somatotopically organized with coordinates similar to the contralateral M1. Finally, the presence of ipsilateral M1 activation depended on the global activation level in other motor-related areas, which was significantly increased, when ipsilateral M1 activation was detected.

Mirror movements in X-linked Kallmann's syndrome. II. A PET study.

To investigate the mechanism of mirror movements seen in X-linked Kallmann's syndrome, we measured changes of regional cerebral blood flow with H2 15O-PET. We studied six right-handed Kallmann male subjects and six matched, right-handed control subjects during an externally paced finger opposition task. The analyses were done both on a single subject and a group basis. The Kallmann group showed a strong primary motor cortex (M1) activation contralateral to the voluntarily moved hand, but there was also a significant degree of M1 activation ipsilateral to the voluntarily moved hand, i.e. contralateral to the mirroring hand. However, when comparing contralateral to ipsilateral M1 activation, the M1 activation contralateral to the voluntarily moved hand was significantly stronger. In the controls, significant increases in rCBF were seen in the contralateral M1 during voluntary movement of either hand; a small ipsilateral M1 activation was found in two out of six normal subjects when they moved their left hand. In a second experiment it was shown that, in two out of two Kallmann subjects, passive movements of the right hand resulted in left M1 activation that was similar to the activation in the left M1 when subjects made mirror movements with their right hand. This suggests, but does not prove, that the small but significant activation of the ipsilateral M1 in Kallmann's subjects may be due to sensory feedback from the involuntarily mirroring hand.