The neural network involved in a bimanual tactile-tactile matching discrimination task: a functional imaging study at 3 T

Involvement of the intrinsic functional network of the red nucleus in complex behavioral processing

Previous studies suggested the possibility that the red nucleus (RN) is involved in other cognitive functions than motion per se, even though such functions have yet to be clarified. We investigated the activation of RN during several tasks and its intrinsic functional network associated with social cognition and musical practice. The tasks included finger tapping, n-back, and memory recall tasks. Region of interest for RN was identified through those tasks, anatomical information of RN, and a brain atlas. The intrinsic functional network was identified for RN by an analysis of connectivity between RN and other regions typically involved in seven known resting state functional networks with RN used as the seed region. Association of the RN network with a psychological trait of the interpersonal reactivity index and musical training years revealed subnetworks that included empathy related regions or music practice related regions. These social or highly coordinated motor activity represent the most complex functions ever known to involve the RN, adding further evidence for the multifunctional roles of RN. These discoveries may lead to a new direction of investigations to clarify probable novel roles for RN in high-level human behavior.

Red nucleus structure and function: from anatomy to clinical neurosciences

The red nucleus (RN) is a large subcortical structure located in the ventral midbrain. Although it originated as a primitive relay between the cerebellum and the spinal cord, during its phylogenesis the RN shows a progressive segregation between a magnocellular part, involved in the rubrospinal system, and a parvocellular part, involved in the olivocerebellar system. Despite exhibiting distinct evolutionary trajectories, these two regions are strictly tied together and play a prominent role in motor and non-motor behavior in different animal species. However, little is known about their function in the human brain. This lack of knowledge may have been conditioned both by the notable differences between human and non-human RN and by inherent difficulties in studying this structure directly in the human brain, leading to a general decrease of interest in the last decades. In the present review, we identify the crucial issues in the current knowledge and summarize the results of several decades of research about the RN, ranging from animal models to human diseases. Connecting the dots between morphology, experimental physiology and neuroimaging, we try to draw a comprehensive overview on RN functional anatomy and bridge the gap between basic and translational research.

The cortico-rubral and cerebello-rubral pathways are topographically organized within the human red nucleus

The Red Nucleus (RN) is a large nucleus located in the ventral midbrain: it is subdivided into a small caudal magnocellular part (mRN) and a large rostral parvocellular part (pRN). These distinct structural regions are part of functionally different networks and show distinctive connectivity features: the mRN is connected to the interposed nucleus, whilst the pRN is mainly connected to dentate nucleus, cortex and inferior olivary complex. Despite functional neuroimaging studies suggest RN involvement in complex motor and higher order functions, the pRN and mRN cannot be distinguished using conventional MRI. Herein, we employ high-quality structural and diffusion MRI data of 100 individuals from the Human Connectome Project repository and constrained spherical deconvolution tractography to perform connectivity-based segmentation of the human RN. In particular, we tracked connections of RN with the inferior olivary complex, the interposed nucleus, the dentate nucleus and the cerebral cortex. We found that the RN can be subdivided according to its connectivity into two clusters: a large ventrolateral one, mainly connected with the cerebral cortex and the inferior olivary complex, and a smaller dorsomedial one, mainly connected with the interposed nucleus. This structural topography strongly reflects the connectivity patterns of pRN and mRN respectively. Structural connectivity-based segmentation could represent a useful tool for the identification of distinct subregions of the human red nucleus on 3T MRI thus allowing a better evaluation of this subcortical structure in healthy and pathological conditions.

The centre of the brain: topographical model of motor, cognitive, affective, and somatosensory functions of the basal ganglia

The basal ganglia have traditionally been viewed as motor processing nuclei; however, functional neuroimaging evidence has implicated these structures in more complex cognitive and affective processes that are fundamental for a range of human activities. Using quantitative meta-analysis methods we assessed the functional subdivisions of basal ganglia nuclei in relation to motor (body and eye movements), cognitive (working-memory and executive), affective (emotion and reward) and somatosensory functions in healthy participants. We document affective processes in the anterior parts of the caudate head with the most overlap within the left hemisphere. Cognitive processes showed the most widespread response, whereas motor processes occupied more central structures. On the basis of these demonstrated functional roles of the basal ganglia, we provide a new comprehensive topographical model of these nuclei and insight into how they are linked to a wide range of behaviors.

Multivariate pattern analysis reveals common neural patterns across individuals during touch observation

In a recent study we found that multivariate pattern analysis (MVPA) of functional magnetic resonance imaging (fMRI) data could predict which of several touch-implying video clips a subject saw, only using voxels from primary somatosensory cortex. Here, we re-analyzed the same dataset using cross-individual MVPA to locate patterns of information that were common across participants' brains. In this procedure a classifier learned to distinguish the neural patterns evoked by each stimulus based on the data from a sub-group of the subjects and was then tested on data from an individual that was not part of that sub-group. We found prediction performance to be significantly above chance both when using voxels from the whole brain and when only using voxels from the postcentral gyrus. SVM voxel weight maps established based on the whole-brain analysis as well as a separate searchlight analysis suggested foci of especially high information content in medial and lateral occipital cortex and around the intraparietal sulcus. Classification across individuals appeared to rely on similar brain areas as classification within individuals. These data show that observing touch leads to stimulus-specific patterns of activity in sensorimotor networks and that these patterns are similar across individuals. More generally, the results suggest that cross-individual MVPA can succeed even when applied to restricted regions of interest.

In vivo structural and functional imaging of the human rubral and inferior olivary nuclei: A mini-review

Few imaging studies have been devoted to the structural and functional connectivity of the red and inferior olivary nuclei although these two nuclei represent two main targets of the cerebellum within the brainstem. However, the RN is anatomically and functionally related to a widespread sensorimotor, limbic, and executive brain network. It projects massively onto the principal olive with which it contributes to a cerebello-rubro-olivo-cerebellar loop modulated by cortical and subcortical afferents. Despite a minor role in planning and execution of rhythmic movements, the red nucleus in conjunction with the inferior olive, more specifically involved in the detection of "unexpected" events, contributes to sensorimotor, sensory and, likely, cognitive higher functions.

Cognitive disturbances in primary blepharospasm

The common belief that primary dystonia is a purely motor disorder with no anatomical substrate and no other accompanying neurological dysfunction has recently been challenged. In addition, there is increasing evidence that the basal ganglia besides motor control, plays a role in cognitive functioning. However, no systematic cognitive performance evaluation has been carried out in patients with primary blepharospasm (BS), one of the most common forms of adult dystonia. We evaluated a series of 20 patients with primary BS and a group of 17 controls matched by severity of mood symptoms, age, and sex. BS patients performed significantly worse on the Luria sequencing test, Purdue pegboard test, reciprocal coordination, tactile denomination, and reverse visuospatial span and the differences persisted after correction for age, duration of disease, severity of BS, and degree of depression. The Wisconsin card sorting test showed no statistical difference, but BS patients made more errors and more perseverative answers than expected according to population means, whereas the control group performed poorly but within normal parameters. Our findings suggest broad cortical involvement in focal dystonia that is not correlated with the severity or duration of dystonia.

Dissociation of the neural networks recruited during a haptic object-recognition task: complementary results with a tensorial independent component analysis

BACKGROUND AND PURPOSE

The cerebral and cerebellar networks involved in bimanual object recognition were assessed by blood oxygen level-dependent functional MR imaging by using multivariate model-free analysis, because conventional univariate model-based analysis, such as the general linear model (GLM), does not allow investigation of resting, background, and transiently task-related brain activities.

MATERIALS AND METHODS

Data from 14 healthy right-handed volunteers, scanned while successively performing bilateral finger movements and a bimanual tactile-tactile matching discrimination task were analyzed by using tensor-independent component analysis (TICA), which computes statistically independent spatiotemporal processes (P > .7) thought to reflect specific and distinct anatomofunctional neural networks. These results were compared with the network obtained in a previous study by using the same paradigm based on GLM to evaluate the advantages of TICA.

RESULTS

TICA characterized and distinguished the following: 1) resting-state networks such as the default-mode networks, 2) networks transiently synchronized with the beginning and end of the task, such as temporo-pericentral and temporo-pericentral-occipital networks, and 3) task-related networks such as cerebello-fronto-parietal, cerebello-prefrontocingulo-insular, and cerebello-parietal networks.

CONCLUSION

Bimanual tactile-tactile matching discrimination specifically recruits a complex neural network, which can be dissociated into 3 distinct but cooperative neural subnetworks related to sensorimotor function, salience detection, executive control, and, possibly, sensory expectation. This tripartite network involved in bimanual object recognition could not be demonstrated by GLM. Moreover, TICA allowed monitoring of the temporal succession of the networks recruited during the resting phase, audition of the "go" and "stop" signals, and the tactile discrimination task.

Network activation during bimanual movements in humans

The coordination of movement between the upper limbs is a function highly distributed across the animal kingdom. How the central nervous system generates such bilateral, synchronous movements, and how this differs from the generation of unilateral movements, remain uncertain. Electrophysiologic and functional imaging studies support that the activity of many brain regions during bimanual and unimanual movement is quite similar. Thus, the same brain regions (and indeed the same neurons) respond similarly during unimanual and bimanual movements as measured by electrophysiological responses. How then are different motor behaviors generated? To address this question, we studied unimanual and bimanual movements using fMRI and constructed networks of activation using Structural Equation Modeling (SEM). Our results suggest that (1) the dominant hemisphere appears to initiate activity responsible for bimanual movement; (2) activation during bimanual movement does not reflect the sum of right and left unimanual activation; (3) production of unimanual movement involves a network that is distinct from, and not a mirror of, the network for contralateral unimanual movement; and (4) using SEM, it is possible to obtain robust group networks representative of a population and to identify individual networks which can be used to detect subtle differences both between subjects as well as within a single subject over time. In summary, these results highlight a differential role for the dominant and non-dominant hemispheres during bimanual movements, further elaborating the concept of handedness and dominance. This knowledge increases our understanding of cortical motor physiology in health and after neurological damage.

Neural correlates of simple unimanual discrete and continuous movements: a functional imaging study at 3 T

INTRODUCTION

The cerebral and cerebellar network involved in unimanual continuous and discrete movements was studied in blood oxygenation level-dependent functional magnetic resonance imaging (fMRI) at 3 T.

METHODS

Seven healthy right-handed volunteers were scanned (1) while drawing a circle with the tip of the right index finger (continuous motor task), and (2) while drawing a triangle with the tip of the right index finger (discrete motor task).

RESULTS

In both motor tasks, extensive activations were observed in the sensorimotor (M1/S1), parietal, prefrontal, insular, lateral occipital (LOC) and anterior cerebellar cortices. Subcortical activations within red, thalamic and lentiform nuclei were also detected. However, discrete movements were specifically followed by the recruitment of the left orbitofrontal cortex, right dentate nucleus and the second cerebellar homunculus (HVIII), and bilateral and stronger activation of the sensorimotor cortical areas, whereas continuous movements specifically activated the right prefrontal cortex and the lateral hemispherical part of the neocerebellum (crus 1).

CONCLUSION

We confirm the findings of previous studies showing partly distinct neural networks involved in monitoring continuous and discrete movements, but we found new differential neural relays within the prefrontal, insular and neocerebellar cortices.