Deep brain activation patterns involved in virtual gait without and with a doorway: An fMRI study.

The human gait program involves many brain areas such as motor cortices, cerebellum, basal ganglia, brainstem, and spinal cord. The mesencephalic locomotor region (MLR), which contains the pedunculopontine (PPN) and cuneiform (CN) nuclei, is thought to be one of the key supraspinal gait generators. In daily life activities, gait primarily occurs in complex conditions, such as through narrow spaces, or while changing direction or performing motor or cognitive tasks. Here, we aim to explore the activity of these subcortical brain areas while walking through narrow spaces, using functional MRI in healthy volunteers and designing a virtual reality task mimicking walking down a hallway, without and with an open doorway to walk through. As a control, we used a virtual moving walkway in the same environment. Twenty healthy volunteers were scanned. Fifteen subjects were selected for second level analysis based on their ability to activate motor cortices. Using the contrast Gait versus Walkway, we found activated clusters in motor cortices, cerebellum, red nucleus, thalamus, and the left MLR including the CN and PPN. Using the contrast Gait with Doorway versus Walkway with Doorway, we found activated clusters in motor cortices, left putamen, left internal pallidum, left substantia nigra, right subthalamic area, and bilateral MLR involving the CN and PPN. Our results suggest that unobstructed gait involves a motor network including the PPN whereas gait through a narrow space requires the additional participation of basal ganglia and bilateral MLR, which may encode environmental cues to adapt locomotion.

Disruption in cerebellar and basal ganglia networks during a visuospatial task in cervical dystonia.

BACKGROUND: Although dystonia is traditionally conceptualized as a basal ganglia disorder, increasing interest has been directed at a different neural network node, the cerebellum, which may play a significant role in the pathophysiology of dystonia. Abnormal sensorimotor processing and disturbed motor schemes, possibly attributable to cerebellar changes, remain unclear. METHODS: We sought to characterize the extent of cerebellar dysfunction within the motor network using functional MRI activation analysis, connectivity analysis, and voxel-based morphometry in cervical dystonia patients (n = 25, 15 women, mean age 45.8 years) and healthy volunteers (n = 25, 15 women, mean age 44.7 years) in a visuospatial task requiring predictive motor timing. RESULTS: Cervical dystonia patients showed decreased activation in the posterior cerebellar lobules as well as in the premotor areas, the associative parietal cortex, and visual regions. Patients also had decreased cerebellar connectivity with bilateral basal ganglia structures and the dorsolateral prefrontal cortex. CONCLUSIONS: This promotes the view that dystonia results from miscommunication between the basal ganglia and cerebellar loops, thus providing new insights into the brain regions essential for the development of cervical dystonia. © 2017 International Parkinson and Movement Disorder Society.

Pedunculopontine network dysfunction in Parkinson's disease with postural control and sleep disorders.

BACKGROUND: The objective of this study was to investigate pedunculopontine nucleus network dysfunctions that mediate impaired postural control and sleep disorder in Parkinson's disease. METHODS: We examined (1) Parkinson's disease patients with impaired postural control and rapid eye movement sleep behavior disorder (further abbreviated as sleep disorder), (2) Parkinson's disease patients with sleep disorder only, (3) Parkinson's disease patients with neither impaired postural control nor sleep disorder, and (4) healthy volunteers. We assessed postural control with clinical scores and biomechanical recordings during gait initiation. Participants had video polysomnography, daytime sleepiness self-evaluation, and resting-state functional MRIs. RESULTS: Patients with impaired postural control and sleep disorder had longer duration of anticipatory postural adjustments during gait initiation and decreased functional connectivity between the pedunculopontine nucleus and the supplementary motor area in the locomotor network that correlated negatively with the duration of anticipatory postural adjustments. Both groups of patients with sleep disorder had decreased functional connectivity between the pedunculopontine nucleus and the anterior cingulate cortex in the arousal network that correlated with daytime sleepiness. The degree of dysfunction in the arousal network was related to the degree of connectivity in the locomotor network in all patients with sleep disorder, but not in patients without sleep disorder or healthy volunteers. CONCLUSIONS: These results shed light on the functional neuroanatomy of pedunculopontine nucleus networks supporting the clinical manifestation and the interdependence between sleep and postural control impairments in Parkinson's disease. © 2016 International Parkinson and Movement Disorder Society.

The dark side of self-focus: brain activity during self-focus in low and high brooders.

There are two distinct modes of self-focus: analytical self-focus is abstract, general and evaluative whereas experiential self-focus is concrete, specific and non-evaluative. Using functional magnetic resonance imaging (fMRI), we investigated the neural bases of these two modes of self-focus in relation with brooding, the maladaptive form of rumination. Forty-one French-speaking right-handed healthy young adults (10 men, mean age ± s.d.: 21.8 ± 2.3 years) engaged in analytical and experiential self-focus triggered by verbal stimuli during fMRI. Brooding was measured with the 22-item Rumination Response Style scale. Individuals with lower brooding scores showed greater activation of the posterior cingulate cortex/precuneus during analytical than experiential self-focus, whereas individuals with higher brooding scores did not. This is consistent with the hypothesis that brooding is associated with less control over the nature of the self-focus engaged. These findings may help to refine our understanding of how rumination promotes depression through maladaptive self-focus.

Contribution of corticospinal tract and functional connectivity in hand motor impairment after stroke.

BACKGROUND: Motor outcome after stroke is associated with reorganisation of cortical networks and corticospinal tract (CST) integrity. However, the relationships between motor severity, CST damage, and functional brain connectivity are not well understood. Here, the main objective was to study the effect of CST damage on the relationship between functional motor network connectivity and hand motor function in two groups of stroke patients: the severely (n=8) and the mildly impaired (n=14). METHODS: Twenty-two carotid stroke patients with motor deficits were studied with magnetic resonance imaging (MRI) at 3 weeks, at 3 and 6 months. Healthy subjects (n=28) were scanned once. The CST injury was assessed by fractional anisotropy values. Functional connectivity was studied from a whole-hand grip task fMRI in a cortical and cerebellar motor network. Functional connectivity indexes were computed between these regions at each time point. The relationship between hand motor strength, ipsilesional CST damage and functional connectivity from the primary motor cortex (M1) was investigated using global and partial correlations. FINDINGS: In mildly impaired patients, cortico-cortical connectivity was disturbed at three weeks but returned to a normal pattern after 3 months. Cortico-cerebellar connectivity was still decreased at 6 months. In severely impaired patients, the cortico-cortical connectivity tended to return to a normal pattern, but the cortico-cerebellar connectivity was totally abolished during the follow-up. In the entire group of patients, the hand motor strength was correlated to the ipsilesional functional connectivity from M1. Partial correlations revealed that these associations were not anymore significant when the impact of CST damage was removed, except for the ipsilesional M1-contralateral cerebellum connectivity. CONCLUSION: Functional brain connectivity changes can be observed, even in severely impaired patients with no recovery. Upper limb function is mainly explained by the CST damage and by the ipsilesional cortico-cerebellar connectivity.

RAD51 deficiency disrupts the corticospinal lateralization of motor control.

Mirror movements are involuntary symmetrical movements of one side of the body that mirror voluntary movements of the other side. Congenital mirror movement disorder is a rare condition characterized by mirror movements that persist throughout adulthood in subjects with no other clinical abnormalities. The affected individuals have mirror movements predominating in the muscles that control the fingers and are unable to perform purely unimanual movements. Congenital mirror movement disorder thus provides a unique paradigm for studying the lateralization of motor control. We conducted a multimodal, controlled study of patients with congenital mirror movements associated with RAD51 haploinsufficiency (n = 7, mean age 33.3 ± 16.8 years) by comparison with age- and gender-matched healthy volunteers (n = 14, mean age 33.9 ± 16.1 years). We showed that patients with congenital mirror movements induced by RAD51 deficiency had: (i) an abnormal decussation of the corticospinal tract; (ii) abnormal interhemispheric inhibition and bilateral cortical activation of primary motor areas during intended unimanual movements; and (iii) an abnormal involvement of the supplementary motor area during both unimanual and bimanual movements. The lateralization of motor control thus requires a fine interplay between interhemispheric communication and corticospinal wiring. This fine interplay determines: (i) the delivery of appropriate motor plans from the supplementary motor area to the primary motor cortex; (ii) the lateralized activation of the primary motor cortex; and (iii) the unilateral transmission of the motor command to the limb involved in the intended movement. Our results also unveil an unexpected function of RAD51 in corticospinal development of the motor system.

Assessment of corticospinal tract (CST) damage in acute stroke patients: comparison of tract-specific analysis versus segmentation of a CST template.

PURPOSE: To compare two techniques to assess corticospinal tract (CST) damage in stroke patients: tract-specific analysis by probabilistic tractography and segmentation using a CST template. MATERIALS AND METHODS: We extracted fractional anisotropy (FA) values, the FA ratio, and mean diffusivity (MD) in 18 stroke patients and 21 healthy volunteers matched for age and sex. We compared the two methods in order to determine their ability to detect 1) differences between diffusion tensor imaging (DTI) parameters of healthy volunteers and stroke patients, 2) the correlation between DTI parameters and clinical scores, and 3) the correlation between DTI parameters and blood oxygen level-dependent (BOLD) signals in a fist-closure task. RESULTS: FA values were higher with the tractography approach than with the segmentation method, but differences between the ipsilesional CST and the homologous region in healthy subjects were detected using both methods. In patients, clinical scores were significantly correlated with FA values and FA ratios with both methods. The BOLD signal was positively correlated with FA values for CST with the segmentation but not with the tractography approach. CONCLUSION: CST damage in stroke patients can be assessed by either probabilistic tractography or segmentation of a CST template. Although each method has advantages and limitations, both are sensitive enough to detect differences among stroke patients and identify specific correlations with clinical scores.

The brain's dorsal route for speech represents word meaning: evidence from gesture.

The dual-route model of speech processing includes a dorsal stream that maps auditory to motor features at the sublexical level rather than at the lexico-semantic level. However, the literature on gesture is an invitation to revise this model because it suggests that the premotor cortex of the dorsal route is a major site of lexico-semantic interaction. Here we investigated lexico-semantic mapping using word-gesture pairs that were either congruent or incongruent. Using fMRI-adaptation in 28 subjects, we found that temporo-parietal and premotor activity during auditory processing of single action words was modulated by the prior audiovisual context in which the words had been repeated. The BOLD signal was suppressed following repetition of the auditory word alone, and further suppressed following repetition of the word accompanied by a congruent gesture (e.g. ["grasp" + grasping gesture]). Conversely, repetition suppression was not observed when the same action word was accompanied by an incongruent gesture (e.g. ["grasp" + sprinkle]). We propose a simple model to explain these results: auditory and visual information converge onto premotor cortex where it is represented in a comparable format to determine (in)congruence between speech and gesture. This ability of the dorsal route to detect audiovisual semantic (in)congruence suggests that its function is not restricted to the sublexical level.

Functional parcellation of the lateral mesencephalus.

The mesencephalic locomotor region (MLR), which includes the pedunculopontine nucleus (PPN) and the cuneiform nucleus (CN), has been recently identified as a key structure for locomotion and gait control in mammals. However, the function and the precise anatomy of the MLR remain unclear in humans. To study the lateral mesencephalus, we used fMRI in 15 right-handed healthy volunteers performing two tasks: imagine walking in a hallway and imagine an object moving along the same hallway. Both tasks were performed at two different speeds: normal and 30% faster. We identified two distinct networks of cortical activation: one involving motor/premotor cortices and the cerebellum for the walking task and the other involving posterior parietal and dorsolateral prefrontal cortices for the object moving task. In the lateral mesencephalus, we found that two different but anatomically connected parts of the MLR were activated during the fast condition of each task. The CN and the dorsal part of the PPN were activated during the fast imaginary walking task, whereas the ventral part of the PPN and the ventral part of the reticular formation were activated while subjects were imagining the object moving fast. Our data suggest that the lateral mesencephalus participates in different aspects of gait in humans, with the CN and dorsal PPN controlling motor aspects of locomotion and the ventral PPN being involved in integrating sensory information.

Brain-speech alignment enhances auditory cortical responses and speech perception.

Asymmetry in auditory cortical oscillations could play a role in speech perception by fostering hemispheric triage of information across the two hemispheres. Due to this asymmetry, fast speech temporal modulations relevant for phonemic analysis could be best perceived by the left auditory cortex, while slower modulations conveying vocal and paralinguistic information would be better captured by the right one. It is unclear, however, whether and how early oscillation-based selection influences speech perception. Using a dichotic listening paradigm in human participants, where we provided different parts of the speech envelope to each ear, we show that word recognition is facilitated when the temporal properties of speech match the rhythmic properties of auditory cortices. We further show that the interaction between speech envelope and auditory cortices rhythms translates in their level of neural activity (as measured with fMRI). In the left auditory cortex, the neural activity level related to stimulus-brain rhythm interaction predicts speech perception facilitation. These data demonstrate that speech interacts with auditory cortical rhythms differently in right and left auditory cortex, and that in the latter, the interaction directly impacts speech perception performance.

Reciprocal imitation: toward a neural basis of social interaction.

Social interaction is a coregulated coupling activity that involves at least 2 autonomous agents. Numerous methodological and technical challenges impede the production of natural social interaction within an Magnetic Resonance Imaging environment under controlled conditions. To overcome the obstacle, we chose a simple format of social interaction, namely "interactive imitation" through a double-video system. We registered blood oxygen level-dependent activity of 23 participants during 2 imitative conditions: free (F) and instructed (I) episodes of imitating (i) and of being imitated (bi). In addition to the areas classically reported in instructed imitation tasks, 2 activation patterns were found, which differentiate the subconditions. Firstly, brain areas involved during decisional and attentional processes (dorsolateral prefrontal cortex , dorsal part of anterior cingulate gyrus [dACC], pre-SMA) were activated during all conditions except for instructed imitation-classically used in neuroimaging studies of imitation. Second, a greater activation in dACC and insula combined with an increased deactivation in the default mode network was observed when subjects were imitated compared with when they imitated. We suggest that these 2 patterns reflect the anticipation of the other's behavior and the engagement with others required by social interaction.