When a given motor pattern is computed by cortical motor areas, it is first conveyed to the basal ganglia via glutamatergic projections with the purpose of releasing the intended movement and suppressing the unintended ones. Along with the initial signal to the striatum, the cerebral cortex suppresses surrounding or competing motor patterns.
When excited by the glutamatergic inputs of the cerebral cortex, striatal D2 receptors allow the cells of the striatal matrix to send inhibitory signals to the GPe which normally exerts a tonic GABAergic inhibition on the STN.
This latter view is supported by the fact that cortical neurons projecting to GPe appear to be in a different group than those projecting to STN Kita and Kita, The following inhibition of the thalamocortical projections suggests therefore a major role of the hyperdirect pathway in holding back movements Wessel et al. A possible electrophysiological correlate of basal ganglia activity in the human brain is the Bereitschaft potential, also known as readiness potential RP , a slow negative electroencephalographic EEG activity that usually precedes self-paced movements Shibasaki and Hallett, The RP has been initially considered as an electrical phenomenon originating from cortical activity which occurs before both simple and complex motor tasks Rektor et al.
However different evidences suggest that RP may be recorded also from subcortical structures such as striatum and thalamic nuclei ventral intermediate nucleus VIM, ventroposterior nucleus VP; Rektor et al.
In particular, latencies of RP recorded in the putamen precedes those recorded by electrodes implanted in cortical motor areas Rektor et al. Following investigations conducted on patients implanted in caudate nucleus, putamen and GPi demonstrated that these regions are potential substrates for RP generation Rektor et al. Moreover, a P3-like activity has been recorded in basal ganglia and in cortical motor and premotor areas during a multimodal evoked related potential ERP stimulation paradigm aimed at investigating electrical activity related to cognitive processing of sensorial stimuli Rektor et al.
This suggests a possible interplay of cortical areas and basal ganglia during cognitive processing. One of the main aims of the present review is to widen the current perspective on basal ganglia connectomics providing a new challenging, comprehensive and integrated basal ganglia model. As previously mentioned, most of our knowledge on the basal ganglia is mainly based on invasive tract-tracing studies conducted on animals, whilst the available data on humans come from clinical evidences of patients with movement disorders and from pioneering neuroimaging studies.
The last 10 years have been characterized by the growing idea that, in addition to the direct, indirect and hyperdirect pathways, several other feedback and reverberating circuits can contribute to modulate basal ganglia output. Numerous studies have indeed pointed out that the basal ganglia directly integrate signals from widespread cortical areas and are part of an extensive network involving also the cerebellum Figure 2. Figure 2. Schematic illustration of the recently demonstrated anatomical connections in the basal ganglia network.
The figure reports the three direct systems running between the cerebral cortex and the basal ganglia STN, GPi and SNr, shaded gray boxes , providing a fast route of connection by passing the striatum and the thalamus. Recent studies have also demonstrated that the basal ganglia communicate with the cerebellum. Retrograde transneuronal transport of rabies virus in monkeys revealed a disynaptic pathway from the STN passing through the pontine nuclei to the granule cells of the cerebellar cortex.
Additional findings suggest the existence of reciprocal cerebellar output on the basal ganglia via the dentate nucleus. Indeed, it has been demonstrated both in animals and humans that the dentate nucleus is connected with the GPi and SNr thus directly influencing the output stations of the basal ganglia in the timing of actions as well as in action selection. The dashed lines represent the cerebral cortex output on the basal ganglia and the information flow from the basal ganglia to the cerebellum.
The solid lines instead represent the cerebellar output on the output nuclei of the basal ganglia which in turn communicates with the cerebral cortex. Cortico-caudatal and cortico-putaminal fibers are indicated together as cortico-striatal pathway: they are less than cortico-pallidal fibers. The cortico-pallidal fibers are prevalently but not exclusively cortico-fugal efferent. Over the subsequent decades, the cortico-pallidal fibers almost disappeared from the literature.
Early degeneration studies have described the possible existence of a direct cortico-pallidal projection in monkeys Leichnetz and Astruc, , leaving an open window to provide more conclusive evidences on the topic. By using BDA anterograde tract-tracing in rodents, Naito and Kita showed for the first time the existence of direct, topographically-organized connections between the medial and lateral precentral cortices and the GPe Naito and Kita, Although it could be argued that these projections could represent passing fibers that it is well known to be massively present in the GP , it is worthy to note that the BDA approach used in the study labeled with great precision fine fibers and boutons thus allowing to disentangle them from pallidal passing fibers.
The existence of such fibers of passage could furthermore explain why retrograde tract-tracing techniques are not able to the show the presence of this cortico-pallidal pathway. Supporting evidences for the existence of such direct pattern of connectivity come from recent studies showing cholinergic and GABAergic neurons within the GPe that in turn send direct signals to the cerebral cortex Chen et al. More recently, evidence supporting the likely existence of a direct cortico-pallidal pathway was provided by Milardi et al.
More recently, Cacciola et al. These findings have been further corroborated by other diffusion tractography studies da Silva et al. Indirect evidences supporting a tight interplay between GP and frontal cortex in humans come also from PET studies in patients with focal lesions of the GP which have demonstrated reduced metabolism in frontal cortical areas as well as psychiatric symptoms reminiscent of patients with frontotemporal lobe damage.
Taken together these findings strongly indicate a disrupted functional interaction between the GP and the frontal lobe Laplane et al. In particular, MEG-LFP coherence analysis revealed oscillatory pallidal connectivity with the temporal cortex in the theta band 4—7 Hz , with the sensorimotor regions in the beta band 10—30 Hz and with the cerebellum in the alpha band 6—13 Hz. Therefore, the oscillatory drive of information flow between the motor-related areas and the GPi could be gathered either indirectly via the corticostriatal pathway or through a direct cortico-pallidal connection.
The cortico-pallidal pathway could represent a possible anatomical substrate of the robust beta-band oscillatory activity in the cerebral-basal ganglia feedback loops involved in motor control Cacciola et al.
Figure 3. Highlight the newly identified connections between the cerebral cortex, GPi, GPe and SN as well as the complementary circuits between the dentate nucleus and such nuclei as described in recent tractographic studies in humans. In addition, it has been reported in dystonic implanted patients, that single-pulse GPi-DBS may modulate motor cortical excitability at a relatively short latency suggesting the possibility of a direct cortical-GPi connection in humans Cacciola et al.
Recently, Cacciola et al. In particular, the topographical organization of the cortico-pallidal pathway within the GP resulted in an antero-dorsal associative region and a posterior sensorimotor region, despite it was not possible to identify a well-defined limbic territory, thus suggesting that the cortico-pallidal fibers may provide only a relative contribution to the limbic territories in the GP.
On the other hand, the most represented connectivity patterns to the GPi derived from sensorimotor regions suggesting a possible role of such pathway in sensorimotor integration.
Although the direct and indirect evidences on the possible existence of a monosynaptic pathway between the cerebral cortex and the GPi are continuously growing, its exact functional meaning is still not clear and speculative Cacciola et al.
Along with the GPi, the SNr is a key hub of the basal ganglia circuitry, involved in motor control Friend and Kravitz, , cognition Simpson et al. GABAergic neurons located in the SNr mainly target the peduncolopontine nucleus and the superior colliculi, thus suggesting SNr involvement in eyes, head and neck movements. In addition, SNr sends GABAergic inputs to the thalamic intralaminar nuclei that in turn send back projections to the striatum as well as to nuclei that send inputs to the cerebral cortex.
In rodents, the ventromedial and paralaminar medial dorsal thalamic nuclei are the main target of GABAergic SNr inputs and in turn provide widespread projections to frontal cortical areas, including the equivalent eye field areas in primates. On the other hand, the principal targets of the SNr are the ventral anterior and paralaminar medial dorsal nuclei which instead project to more discrete organized frontal areas Bentivoglio et al.
By contrast, both in rodents and in primates, SNc provides extensive dopaminergic innervation to dorsal and ventral striatum Beckstead et al.
Therefore, both the SNc and SNr receive disynaptic inhibitory and excitatory inputs from the cerebral cortex via the neostriatum and STN respectively. In addition, several anatomical studies have indicated a direct connection between the cortex and the SN Figure 3.
Although the majority of these studies have clearly shown the existence of a direct cortico-SN pathway, the topographical arrangement, the extent of the cortical regions involved in the projection and the morphological characteristics of the fibers and boutons were not well clarified until the mid-nineties. In an anterograde tracing study with BDA in rats, Naito and Kita addressed this issue by showing that the SNc received orderly arranged, but sparse connections from the entire prefrontal cortex; the density of boutons in SNc was much less than the ones of the striatum.
More recently, Frankle et al. In this regard, by using dMRI and tractography, Cacciola et al. In addition, in line with previous findings, the same authors demonstrated that the SN is extensively connected with many sensorimotor and associative cortical areas as well as with subcortical structures, including the cerebellum Cacciola et al.
In conclusion, the basal ganglia connectome seems to be more complex than expected; non-canonical pathways such as the cortico-pallidal and cortico-nigral pathways may have a role in basal ganglia physiology and pathophysiology of basal ganglia disorders. However, their functions remain speculative and need more investigation to be completely understood.
Along with the fundamental role in motor control, the cerebellum and basal ganglia are involved in several aspects of behavior, from cognition to emotion Middleton and Strick, ; Schmahmann and Caplan, The involvement of the cerebellum in so many functions could be explained by taking into account that it works in strict connection with the cerebral cortex and the basal ganglia, which in turn play both a pivotal role in a variety of motor and non-motor functions.
According to the traditional view, the cerebellum and basal ganglia interact at the level of the cerebral cortex. However, the last decades have been characterized by increasing evidences showing a direct cerebello-basal ganglia interplay forming an integrated building block involved in several complex tasks.
Anterograde and retrograde studies demonstrated that neurons of the central lateral nucleus of thalamus, which projects both to motor cortex and to laterodorsal part of the striatum, receive inputs from the lateral cerebellar nucleus Ichinohe et al.
These findings were extended to non-human primates in a study conducted on macaques by means of retrograde transneuronal transport of rabies virus Hoshi et al. Labeled neurons in the dentate nucleus belonged both to its motor and non-motor domains Dum et al.
A few years later, Bostan et al. The retrograde transport revealed that first-order neurons were located in the pedunculopontine nucleus while second-order neurons were found to be topographically organized in the STN Figure 3.
These fascinating studies provided new insights on the roles of basal ganglia and cerebellum showing that their interplay may be more complex than expected. Virus tracing is not the only technique which has been employed to study connectivity between these two subcortical structures.
Converging evidences coming from electrophysiological experiments and human neuroimaging studies will be discussed below. Electrophysiological investigations, conducted on anesthetized cats to assess the latency of basal ganglia-cerebellum activation, failed in finding strong evidences of a rapid-gated cerebellum-basal ganglia communication.
The long latencies 50— ms found made the hypothesis of rapidly funneling stimuli from cerebellum to basal ganglia neglectable Ratchetson and Li, This assumption has been recently challenged by Chen et al. Moreover, when the electrical stimulation of dentate nucleus is delivered simultaneously to high frequency stimulation of cerebral cortex, the overall result is a direction change of synaptic plasticity, reverting long term depression LTD in long term potentiation LTP; Chen et al.
These findings do provide new insight on the role of basal ganglia-cerebellum communication in learning phenomena. The synergic role of cerebellum and basal ganglia in learning processes is not new considering the pioneer studies of the early showing that the cerebral cortex, cerebellum and basal ganglia are involved in specific learning paradigms: unsupervised, error-based supervised and reward-based learning Doya, , The recent anatomical findings of the two- and tri-synaptic pathways linking the cerebellum and basal ganglia, together with the evidence of a short latency communication, led Caligiore et al.
The possible computational role of the dento-thalamo-striatal pathway is to convey the predicted outcome of a candidate action, processed in the cerebellum to the striatum where the outcome itself is evaluated forward model.
On the other hand, the computational role of the subthalamic-ponto-cerebellar pathway is not clear at all; nevertheless, considering the involvement of the subthalamic nucleus in the indirect pathway and aversive learning phenomena, it is tempting to speculate that it would prevent the new forward models to be conveyed to the striatum Caligiore et al.
In addition to the dento-thalamo-striatal and subthalamo-ponto-cerebellar pathways, Milardi et al. Although its physiological meaning is still unknown, the dento-nigral pathway, reconstructed in human by means of dMRI and tractography, could represent the phylogenetical equivalent of the pathway observed via tract-tracing in cats and rats Snider et al. In addition, release of dopamine in caudate nucleus and incremented dopamine production in substantia nigra were found after unilateral stimulation of the dentate nucleus in cats Nieoullon et al.
Recent evidences of a direct route connecting dentate nucleus to globus pallidus, on human side, comes from a MEG-LFP study Neumann et al. In addition, it was also found a negative correlation between the alpha band of coherence and symptoms severity as measured by Toronto Western Spasmodic Torticollis Rating Scale suggesting a compensatory role of the cerebellum in dystonic patients. These direct connections between the dentate nucleus and GPi and SNr are very intriguing considering the presence of a direct cortico-pallidal and cortico-SN pathways bypassing the striatum in humans Milardi et al.
Hence, it is tempting to speculate on the existence of 3 direct systems running between the cortex, the basal ganglia STN, GPi and SNr and the cerebellum, providing a fast route of connection bypassing the striatum and the thalamus Figure 4. These considerations are not necessarily in conflict with the consensus position of Caligiore et al. This new fast system would be necessary to support the manual dexterity which is an exquisite feature of human specimens.
Figure 4. Cerebellum-basal ganglia interplay. This panel shows the connections between the cerebellum and basal ganglia as revealed by retrograde tracing studies in monkeys. Red lines indicate the output of the cerebellum on the basal ganglia via the dentate-thalamo-striatal pathway as well as the control of basal ganglia on the cerebellum via the STN-ponto-cerebellar cortex pathway. The basal ganglia and the cerebellum have been often conceived separately as structures involved in different neurological syndromes.
However, evidences concerning the co-operation of cerebellum and basal ganglia in movement disorders are currently growing. Thus, the above-described scenario could open an entirely new perspective into the pathophysiology of basal ganglia and cerebellum disorders Coenen et al. Different aspects of movement disorders could be gathered by cerebellum-basal ganglia interface. Cerebellum and basal ganglia have been involved in time computation: the former should be accounted for millisecond-range intervals whilst the latter would work mainly on the second-ranges Ivry, ; Buhusi and Meck, ; Wiener et al.
This would suggest an involvement of cerebello-basal ganglia circuits in motor and perceptual timing alterations, that are typical of PD. Although the involvement of basal ganglia in the pathophysiology of dystonia is indisputable, the mechanisms producing dystonia are incompletely understood, with recent evidence pointing to the involvement of a variety of brain areas including the cerebellum Quartarone and Hallett, ; Jinnah et al.
As it is possible that the etiological heterogeneity of dystonias reflects the relative importance of different nodes in this extended motor network, one major challenge is determining first, the role and contribution of the different brain regions in the various forms of dystonia with a comprehensive model; second, if there is a final common pathway for all dystonias Quartarone and Ruge, Anomalies in the cerebellum and basal ganglia have been widely investigated in both animal and human studies of dystonia Filip et al.
In a murine model of cerebellar-induced dystonia, a cerebellar outflow interruption has been causally linked to burst firing activity in basal ganglia, which is a prominent feature of dystonia Chen et al. Moreover, also primary dystonia, such as cervical dystonia has also been conceptualized as deriving from alterations in neural integration for head and eye movements, involving cerebellum and basal ganglia in association with oculomotor structures Shaikh et al.
In line with this hypothesis, in a fMRI study during a visuospatial task, Filip et al. In particular, STN pathological activity, characterized by burst activity and higher firing rates, may in turn be responsible for hyperactivity of cerebellar cortex leading to alterations in the cerebello-thalamo-cortical circuits Bostan et al.
Supporting this hypothesis, a recent fMRI study on 20 PD patients implanted with DBS of the STN found that functional connectivity between active contact and contralateral cerebellum is strongly predictive of improvement in motor learning de Almeida Marcelino et al. It would be tempting to speculate that suppression of STN aberrant activity, promoted by DBS, could lead to improved cerebellar function and, by consequence, to improvement in motor learning.
In conclusion, further experimental and challenging studies should be fostered to characterize the full extent of the interplay between the cerebral cortex, the basal ganglia and the cerebellum. However, several evidences have already suggested that the system is more intricated than initially assumed.
In the present review, we discussed the invasive and non-invasive techniques to investigate the anatomy and the extrinsic and intrinsic connections of the basal ganglia network. We illustrated the neuroanatomical findings obtained in non-human species that have inspired a paradigmatic shift in this scenario, providing evidences that the cortico-basal ganglia circuits constitute a complex system.
Finally, we provide further support coming from neuroimaging studies that these pathways may exist in humans and may exert a meaningful role in basal ganglia disorders. Taken together, these observations suggest that the cerebral cortex, the basal ganglia and the cerebellum form an integrated and segregated network acting on multiple motor and non-motor functions.
Although such complex interplay has not yet been explored in detail, we hope it will be a focus of new-generation optogenetic, physiologic, behavioral and neuroimaging studies. The proposed scenario, with the presence of parallel direct and indirect projections running between the cortex, basal ganglia and cerebellum, complements new ideas that view movement disorders as disorders of a complex motor network rather than a limited disruption of individual nuclei in the basal ganglia.
DM: writing of the first draft of the manuscript, conception, organization, and execution of the research project, data analysis and interpretation, literature research, and critically revised the manuscript. AQ: writing of the first draft of the manuscript, conception, organization, and execution of the research project, data analysis and interpretation, literature research, critically revised the manuscript, and Guarantor and supervisor of the research project.
GA: conception, organization, and execution of the research project, data interpretation, critically revised the manuscript, Guarantor and supervisor of the research project. AC: conception, organization, and execution of the research project, data analysis and interpretation, writing of the first draft and revision of the final version of the manuscript, and Guarantor and supervisor of the research project.
GC: data analysis and interpretation, revised the manuscript and literature research. GR and DB: data analysis and interpretation and literature research. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Afifi, A. The cortico-nigral fibre tract. An experimental Fink-Heimer study in cats. PubMed Abstract Google Scholar. Focal limb dystonia in a patient with a cerebellar mass. Albin, R. The functional anatomy of basal ganglia disorders. Trends Neurosci. Alexander, G. Brain Res. Alexander, A. Diffusion tensor imaging of the brain. Neurotherapeutics 4, — Arrigo, A.
Brain Imaging Behav. Aston-Jones, G. Use of pseudorabies virus to delineate multisynaptic circuits in brain: opportunities and limitations. Methods , 51— Basser, P. MR diffusion tensor spectroscopy and imaging. Beach, T. Tract-tracing with horseradish peroxidase in the postmortem human brain.
Beckstead, R. Efferent connections of the substantia nigra and ventral tegmental area in the rat. Bentivoglio, M. The organization of the efferent projections of the substantia nigra in the rat. A retrograde fluorescent double labeling study. Bostan, A. The basal ganglia communicate with the cerebellum. U S A , — The basal ganglia and the cerebellum: nodes in an integrated network. Buhusi, C. What makes us tick? Functional and neural mechanisms of interval timing.
Cacciola, A. Enlarged Virchow-Robin spaces in a young man: a constrained spherical deconvolution tractography study. Acta Biomed. A connectomic analysis of the human basal ganglia network. Constrained spherical deconvolution tractography reveals cerebello-mammillary connections in humans. Cerebellum 16, — A direct cortico-nigral pathway as revealed by constrained spherical deconvolution tractography in humans.
Role of cortico-pallidal connectivity in the pathophysiology of dystonia. Brain e Cortico-pallidal connectivity: lessons from patients with dystonia. Structural connectivity-based topography of the human globus pallidus: implications for therapeutic targeting in movement disorders. Calamuneri, A. White matter tissue quantification at low b-values within constrained spherical deconvolution framework. Caligiore, D. Consensus paper: towards a systems-level view of cerebellar function: the interplay between cerebellum, basal ganglia, and cortex.
Carter, D. The projections of the entopeduncular nucleus and globus pallidus in rat as demonstrated by autoradiography and horseradish peroxidase histochemistry. Catani, M.
Atlas of Human Brain Connections. Google Scholar. Perisylvian language networks of the human brain. Chen, C. Short latency cerebellar modulation of the basal ganglia. Chen, M.
Identification of a direct GABAergic pallidocortical pathway in rodents. Chevalier, G. Disinhibition as a basic process in the expression of striatal functions. Chowdhury, R. Parcellation of the human substantia nigra based on anatomical connectivity to the striatum. Neuroimage 81, — Chung, H.
Principles and limitations of computational algorithms in clinical diffusion tensor MR tractography. Coenen, V. Individual fiber anatomy of the subthalamic region revealed with diffusion tensor imaging: a concept to identify the deep brain stimulation target for tremor suppression. Neurosurgery 68, — Neuroimage , 83— Brain , — DeLong, M. Circuits and circuit disorders of the basal ganglia. Update on models of basal ganglia function and dysfunction. Dick, J.
Doya, K. What are the computations of the cerebellum, the basal ganglia and the cerebral cortex? Neural Netw. Complementary roles of basal ganglia and cerebellum in learning and motor control. Dum, R. Motor and nonmotor domains in the monkey dentate. N Y Acad. Functional imaging of the human dopaminergic midbrain.
Dyrby, T. Validation of in vitro probabilistic tractography. Neuroimage 37, — Ferrier, D. The Functions of the Brain. Filip, P. Disruption in cerebellar and basal ganglia networks during a visuospatial task in cervical dystonia. Dystonia and the cerebellum: a new field of interest in movement disorders? Frankle, W. Prefrontal cortical projections to the midbrain in primates: evidence for a sparse connection.
Neuropsychopharmacology 31, — Friend, D. Working together: basal ganglia pathways in action selection. Gerfen, C. The neostriatal mosaic: III. Biochemical and developmental dissociation of patch-matrix mesostriatal systems.
The neostriatal mosaic: II. Patch- and matrix-directed mesostriatal dopaminergic and non-dopaminergic systems. Grewal, S. Corticopallidal connectome of the globus pallidus externus in humans: an exploratory study of structural connectivity using probabilistic diffusion tractography.
Grillner, S. The basal ganglia over million years. Haber, S. Methods 23, 15— The place of dopamine in the cortico-basal ganglia circuit. Neuroscience , — Pfaff and N. Striatonigrostriatal pathways in primates form an ascending spiral from the shell to the dorsolateral striatum.
The reward circuit: linking primate anatomy and human imaging. Neuropsychopharmacology 35, 4— Hardman, C. Comparison of the basal ganglia in rats, marmosets, macaques, baboons and humans: volume and neuronal number for the output, internal relay, and striatal modulating nuclei. Hooks, B. Topographic precision in sensory and motor corticostriatal projections varies across cell type and cortical area. Hoover, J. Multiple output channels in the basal ganglia. Science , — The organization of cerebellar and basal ganglia outputs to primary motor cortex as revealed by retrograde transneuronal transport of herpes simplex virus type 1.
Hoshi, E. The cerebellum communicates with the basal ganglia. Neuroimaging 24, 45— The basal ganglia are a group of structures found deep within the cerebral hemispheres.
The structures generally included in the basal ganglia are the caudate , putamen , and globus pallidus in the cerebrum , the substantia nigra in the midbrain , and the subthalamic nucleus in the diencephalon. The word basal refers to the fact that the basal ganglia are found near the base, or bottom, of the brain.
The use of the word ganglia , however, is a bit of a misnomer according to contemporary neuroscience conventions. The word nucleus is generally used to describe clusters of neurons found in the central nervous system.
Thus, the basal ganglia might more accurately be considered nuclei. The separate nuclei of the basal ganglia all have extensive roles of their own in the brain, but they also are interconnected with one another to form a network that is thought to be involved in a variety of cognitive, emotional, and movement-related functions.
The basal ganglia are best-known, however, for their role in movement. The contributions of the basal ganglia to movement are complex and still not completely understood. In fact, the basal ganglia probably have multiple movement-related functions, ranging from choosing actions that are likely to lead to positive consequences to avoiding things that might be aversive.
But the basal ganglia are most often linked to the initiation and execution of movements. To understand how this might work, think about the action of reaching out to pick up a pencil.
Although it might seem like there would be very little movement-related activity going on in the brain at this point because you are sitting still , your brain is actually constantly at work to inhibit unwanted movements like jerking your hand involuntarily up in the air or suddenly turning your head to one side. The basal ganglia are hypothesized to play a critical role in this type of movement inhibition, as well as in the release of that inhibition when you do have a movement that you want to make reaching for the pencil in this case.
These thalamic neurons in turn project to the motor cortex an area of the brain where many voluntary movements originate and can stimulate movement via these connections. The basal ganglia, however, continuously inhibit the thalamic neurons, which stops them from communicating with the motor cortex—inhibiting movement in the process. Then, the signal follows a circuit in the basal ganglia known as the direct pathway , which leads to the silencing of neurons in the globus pallidus and substantia nigra.
This frees the thalamus from the inhibitory effects of the basal ganglia and allows movement to occur. There is also a circuit within the basal ganglia called the indirect pathway , which involves the subthalamic nucleus and leads to the increased suppression of unwanted movements.
It is thought that a balance between activity in these two pathways may facilitate smooth movement.
0コメント