Cortico-Cortical Connectivity between Right Parietal and Bilateral Primary Motor Cortices during Imagined and Observed Actions: A Combined TMS/tDCS Study

Previous transcranial magnetic stimulation (TMS) studies showed functional connections between the parietal cortex (PC) and the primary motor cortex (M1) during tasks of different reaching-to-grasp movements. Here, we tested whether the same network is involved in cognitive processes such as imagined or observed actions. Single pulse TMS of the right and left M1 during rest and during a motor imagery and an action observation task (i.e., an index–thumb pinch grip in both cases) was used to measure corticospinal excitability changes before and after conditioning of the right PC by 10 min of cathodal, anodal, or sham transcranial direct current stimulation (tDCS). Corticospinal excitability was indexed by the size of motor-evoked potentials (MEPs) from the contralateral first dorsal interosseous (FDI; target) and abductor digiti minimi muscle (control) muscles. Results showed selective ipsilateral effects on the M1 excitability, exclusively for motor imagery processes: anodal tDCS enhanced the MEPs’ size from the FDI muscle, whereas cathodal tDCS decreased it. Only cathodal tDCS impacted corticospinal facilitation induced by action observation. Sham stimulation was always uneffective. These results suggest that motor imagery, differently from action observation, is sustained by a strictly ipsilateral parieto-motor cortex circuits. Results might have implication for neuromodulatory rehabilitative purposes

Is a ‘quiet eye’ all it takes to be successful? Comment on Vickers

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Cortico-spinal modularity in the parieto-frontal system: a new perspective on action control

: Classical neurophysiology suggests that the motor cortex (MI) has a unique role in action control. In contrast, this review presents evidence for multiple parieto-frontal spinal command modules that can bypass MI. Five observations support this modular perspective: (i) the statistics of cortical connectivity demonstrate functionally-related clusters of cortical areas, defining functional modules in the premotor, cingulate, and parietal cortices; (ii) different corticospinal pathways originate from the above areas, each with a distinct range of conduction velocities; (iii) the activation time of each module varies depending on task, and different modules can be activated simultaneously; (iv) a modular architecture with direct motor output is faster and less metabolically expensive than an architecture that relies on MI, given the slow connections between MI and other cortical areas; (v) lesions of the areas composing parieto-frontal modules have different effects from lesions of MI. Here we provide examples of six cortico-spinal modules and functions they subserve: module 1) arm reaching, tool use and object construction; module 2) spatial navigation and locomotion; module 3) grasping and observation of hand and mouth actions; module 4) action initiation, motor sequences, time encoding; module 5) conditional motor association and learning, action plan switching and action inhibition; module 6) planning defensive actions. These modules can serve as a library of tools to be recombined when faced with novel tasks, and MI might serve as a recombinatory hub. In conclusion, the availability of locally-stored information and multiple outflow paths supports the physiological plausibility of the proposed modular perspective

Decoding motor intentions from human brain activity

“You read my mind.” Although this simple everyday expression implies ‘knowledge or understanding’ of another’s thinking, true ‘mind-reading’ capabilities implicitly seem constrained to the domains of Hollywood and science-fiction. In the field of sensorimotor neuroscience, however, significant progress in this area has come from mapping characteristic changes in brain activity that occur prior to an action being initiated. For instance, invasive neural recordings in non-human primates have significantly increased our understanding of how highly cognitive and abstract processes like intentions and decisions are represented in the brain by showing that it is possible to decode or ‘predict’ upcoming sensorimotor behaviors (e.g., movements of the arm/eyes) based on preceding changes in the neuronal output of parieto-frontal cortex, a network of areas critical for motor planning. In the human brain, however, a successful counterpart for this predictive ability and a similar detailed understanding of intention-related signals in parieto-frontal cortex have remained largely unattainable due to the limitations of non-invasive brain mapping techniques like functional magnetic resonance imaging (fMRI). Knowing how and where in the human brain intentions or plans for action are coded is not only important for understanding the neuroanatomical organization and cortical mechanisms that govern goal-directed behaviours like reaching, grasping and looking – movements critical to our interactions with the world – but also for understanding homologies between human and non-human primate brain areas, allowing the transfer of neural findings between species. In the current thesis, I employed multi-voxel pattern analysis (MVPA), a new fMRI technique that has made it possible to examine the coding of neural information at a more fine-grained level than that previously available. I used fMRI MVPA to examine how and where movement intentions are coded in human parieto-frontal cortex and specifically asked the question: What types of predictive information about a subject\u27s upcoming movement can be decoded from preceding changes in neural activity? Project 1 first used fMRI MVPA to determine, largely as a proof-of-concept, whether or not specific object-directed hand actions (grasps and reaches) could be predicted from intention-related brain activity patterns. Next, Project 2 examined whether effector-specific (arm vs. eye) movement plans along with their intended directions (left vs. right) could also be decoded prior to movement. Lastly, Project 3 examined exactly where in the human brain higher-level movement goals were represented independently from how those goals were to be implemented. To this aim, Project 3 had subjects either grasp or reach toward an object (two different motor goals) using either their hand or a novel tool (with kinematics opposite to those of the hand). In this way, the goal of the action (grasping vs. reaching) could be maintained across actions, but the way in which those actions were kinematically achieved changed in accordance with the effector (hand or tool). All three projects employed a similar event-related delayed-movement fMRI paradigm that separated in time planning and execution neural responses, allowing us to isolate the preparatory patterns of brain activity that form prior to movement. Project 1 found that the plan-related activity patterns in several parieto-frontal brain regions were predictive of different upcoming hand movements (grasps vs. reaches). Moreover, we found that several parieto-frontal brain regions, similar to that only previously demonstrated in non-human primates, could actually be characterized according to the types of movements they can decode. Project 2 found a variety of functional subdivisions: some parieto-frontal areas discriminated movement plans for the different reach directions, some for the different eye movement directions, and a few areas accurately predicted upcoming directional movements for both the hand and eye. This latter finding demonstrates -- similar to that shown previously in non-human primates -- that some brain areas code for the end motor goal (i.e., target location) independent of effector used. Project 3 identified regions that decoded upcoming hand actions only, upcoming tool actions only, and rather interestingly, areas that predicted actions with both effectors (hand and tool). Notably, some of these latter areas were found to represent the higher-level goals of the movement (grasping vs. reaching) instead of the specific lower-level kinematics (hand vs. tool) necessary to implement those goals. Taken together, these findings offer substantial new insights into the types of intention-related signals contained in human brain activity patterns and specify a hierarchical neural architecture spanning parieto-frontal cortex that guides the construction of complex object-directed behaviors

Estudio mediante estimulación magnética transcraneal de las cortezas somatosensorial primaria y parietal posterior en la enfermedad de Parkinson

Texto completo descargado desde TeseoLa enfermedad de parkinson (ep) es la segunda enfermedad neurodegenerativa más frecuente detrás de la enfermedad de alzheimer. La pérdida de las neuronas dopaminérgicas de la sustancia negra pars compacta conlleva la degeneración de la vía dopaminérgica nigroestriatal con una alteración funcional de los ganglios basales y de la corteza cerebral. Protocolos de pulsos apareados de estimulación magnética transcraneal (emt) pueden ser usados para el estudio de los circuitos intracorticales y de las interacciones que diferentes áreas cerebrales presentan con la corteza motora. Estos protocolos permiten medir el efecto modulador que un primer estímulo magnético ejerce sobre la respuesta de un segundo estímulo magnético a diferentes intervalos entre ambos. Estudios de emt en pacientes con ep han demostrado la existencia de alteraciones en circuitos intracorticales de la corteza motora (m1) así como alteraciones en la conectividad de diferentes áreas corticales con m1. El objetivo de este trabajo fue estudiar, mediante el uso de emt, los circuitos intracorticales de la corteza somatosensorial primaria (s1) y la conectividad entre la corteza parietal posterior (cpp) y la m1 ipsilateral en pacientes con ep; así como su modulación por fámacos dopaminérgicos. Para el estudio de s1, se utilizó un protocolo de pulsos apareados dónde ambos estímulos se realizan sobre la corteza s1. Para el estudio de conectividad entre la cpp y m1 ipsilateral se utilizó un protocolo similar al anterior; aunque en este caso el primer estímulo se realiza sobre la cpp y el segundo sobre m1 con dos bobinas de estimulación diferentes. Los resultados del presente trabajo muestran que en la ep no existe una alteración de los circuitos intracorticales de s1, si bien estos circuitos sí se afectan por la presencia de la medicación dopaminérgica. Por otro lado, en la ep existe una alteración de la conectividad entre la cpp y m1, que mejora parcialmente con la presencia de la medicación dopaminérgica, y se correlaciona con la bradicinesia de los pacientes estudiados. Estos resultados demuestran que en la ep existe una alteración cortical funcional que se extiende más allá de m1, aportando nuevos conocimientos en el proceso fisiopatológico de la EP.Parkinsons disease (pd) is the second most common neurodegenerative disease after alzheimers disease. The loss of dopaminergic neurons within the substantia nigra pars compacta leads to the degeneration of the dopaminergic nigrosgtriatal pathway. This degeneration produces a functional impairment of the basal ganglia circuit and the cerebral cortex. Paired-pulse protocols of transcranial magnetic stimulation (tms) can be used to study intracortical circuits and intercortical connections of different cortical areas with the motor cortex. These protocols allow us to evaluate the modulatory effect of a first magnetic stimulus in the effect of a second magnetic stimulus at different interstimuli intervals between them. Tms investigations with pd patients have shown different intracortical circuit impairment within the primary motor cortex (m1), as well as in the connectivity of different cortical areas with m1. The objective of the present study was evaluate, using tms, intracortical circuits in the primary somatosensory cortex (s1) and the connectivity between the posterior parietal cortex (ppc) and ipsilateral m1 in pd patients and their modulation by dopaminergic treatment. To study s1, a paired-pulse tms protocol was used and both stimuli were delivered over s1. To study ipsilateral ppc to m1 connectivity, a similar protocol was used but this time using two different coils to each stimulus. The first magnetic stimulus was delivered over the ppc and the second magnetic stimulus was delivered over m1 using a different coil. The results obtained in this study showed that in pd there are not a impairment of s1 intracortical circuits, but that these circuits are affected by the presence of dopaminergic treatment in pd patients. On the other hand, there is a ppc to m1 connectivity impairment in pd patients that is partially improved by the dopaminergic treatment. This impairment was related to bradykinesia observed in pd studied patients. Overall, these results demonstrate that in pd there is a functional cortical impairment involving more tan m1 area, thus providing new knowledge in the pathophysiological process of pd

FMRI resting slow fluctuations correlate with the activity of fast cortico-cortical physiological connections

Recording of slow spontaneous fluctuations at rest using functional magnetic resonance imaging (fMRI) allows distinct long-range cortical networks to be identified. The neuronal basis of connectivity as assessed by resting-state fMRI still needs to be fully clarified, considering that these signals are an indirect measure of neuronal activity, reflecting slow local variations in de-oxyhaemoglobin concentration. Here, we combined fMRI with multifocal transcranial magnetic stimulation (TMS), a technique that allows the investigation of the causal neurophysiological interactions occurring in specific cortico-cortical connections. We investigated whether the physiological properties of parieto-frontal circuits mapped with short-latency multifocal TMS at rest may have some relationship with the resting-state fMRI measures of specific resting-state functional networks (RSNs). Results showed that the activity of fast cortico-cortical physiological interactions occurring in the millisecond range correlated selectively with the coupling of fMRI slow oscillations within the same cortical areas that form part of the dorsal attention network, i.e., the attention system believed to be involved in reorientation of attention. We conclude that resting-state fMRI ongoing slow fluctuations likely reflect the interaction of underlying physiological cortico-cortical connections

Sensory-motor integration in focal dystonia.

Traditional definitions of focal dystonia point to its motor component, mainly affecting planning and execution of voluntary movements. However, focal dystonia is tightly linked also to sensory dysfunction. Accurate motor control requires an optimal processing of afferent inputs from different sensory systems, in particular visual and somatosensory (e.g., touch and proprioception). Several experimental studies indicate that sensory-motor integration - the process through which sensory information is used to plan, execute, and monitor movements - is impaired in focal dystonia. The neural degenerations associated with these alterations affect not only the basal ganglia-thalamic-frontal cortex loop, but also the parietal cortex and cerebellum. The present review outlines the experimental studies describing impaired sensory-motor integration in focal dystonia, establishes their relationship with changes in specific neural mechanisms, and provides new insight towards the implementation of novel intervention protocols. Based on the reviewed state-of-the-art evidence, the theoretical framework summarized in the present article will not only result in a better understanding of the pathophysiology of dystonia, but it will also lead to the development of new rehabilitation strategies

Using in vivo probabilistic tractography to reveal two segregated dorsal 'language-cognitive' pathways in the human brain

Primate studies have recently identified the dorsal stream as constituting multiple dissociable pathways associated with a range of specialized cognitive functions. To elucidate the nature and number of dorsal pathways in the human brain, the current study utilized in vivo probabilistic tractography to map the structural connectivity associated with subdivisions of the left supramarginal gyrus (SMG). The left SMG is a prominent region within the dorsal stream, which has recently been parcellated into five structurally-distinct regions which possess a dorsal–ventral (and rostral-caudal) organisation, postulated to reflect areas of functional specialisation. The connectivity patterns reveal a dissociation of the arcuate fasciculus into at least two segregated pathways connecting frontal-parietal-temporal regions. Specifically, the connectivity of the inferior SMG, implicated as an acoustic-motor speech interface, is carried by an inner/ventro-dorsal arc of fibres, whilst the pathways of the posterior superior SMG, implicated in object use and cognitive control, forms a parallel outer/dorso-dorsal crescent