Neural synchrony within the motor system: what have we learned so far?

Synchronization of neural activity is considered essential for information processing in the nervous system. Both local and inter-regional synchronization are omnipresent in different frequency regimes and relate to a variety of behavioral and cognitive functions. Over the years, many studies have sought to elucidate the question how alpha/mu, beta, and gamma synchronization contribute to motor control. Here, we review these studies with the purpose to delineate what they have added to our understanding of the neural control of movement. We highlight important findings regarding oscillations in primary motor cortex, synchronization between cortex and spinal cord, synchronization between cortical regions, as well as abnormal synchronization patterns in a selection of motor dysfunctions. The interpretation of synchronization patterns benefits from combining results of invasive and non-invasive recordings, different data analysis tools, and modeling work. Importantly, although synchronization is deemed to play a vital role, it is not the only mechanism for neural communication. Spike timing and rate coding act together during motor control and should therefore both be accounted for when interpreting movement-related activity

Brain Dynamics and Plastic Deformation of Self Circuitries in the Dementia Patient

Despite improved medical care that has resulted in greatly extended life expectancies, significant increases in numbers of individuals suffering age related cognitive defects is expected, making the improved understanding of normal and pathological aging an important priority. Current studies indicating that brain activity requires a dynamical architecture to preserve functional order in the face of persistent and extraneous activity suggests that cognitive impairments are likely to be closely linked to dysfunctional dynamical activity of brain systems. Cognitive impairments such as those introduced by Alzheimer’s dementia (AD), that affect fundamental operational constructs like the self, are thus likely to implicate global dynamics that oversee whole brain operation. This paper explores plastic events associated with dynamical elements used in the normal construction of the self percept and the etiology of their deconstruction in the course of AD. It is proposed that the evolution of the disease involves the increasing impairment of a global dynamical operation that is normally engaged in forming a stable and coherent self image needed to flexibly engage task related, motor plans and effectors

The Cortex and the Critical Point

How the cerebral cortex operates near a critical phase transition point for optimum performance. Individual neurons have limited computational powers, but when they work together, it is almost like magic. Firing synchronously and then breaking off to improvise by themselves, they can be paradoxically both independent and interdependent. This happens near the critical point: when neurons are poised between a phase where activity is damped and a phase where it is amplified, where information processing is optimized, and complex emergent activity patterns arise. The claim that neurons in the cortex work best when they operate near the critical point is known as the criticality hypothesis. In this book John Beggs—one of the pioneers of this hypothesis—offers an introduction to the critical point and its relevance to the brain. Drawing on recent experimental evidence, Beggs first explains the main ideas underlying the criticality hypotheses and emergent phenomena. He then discusses the critical point and its two main consequences—first, scale-free properties that confer optimum information processing; and second, universality, or the idea that complex emergent phenomena, like that seen near the critical point, can be explained by relatively simple models that are applicable across species and scale. Finally, Beggs considers future directions for the field, including research on homeostatic regulation, quasicriticality, and the expansion of the cortex and intelligence. An appendix provides technical material; many chapters include exercises that use freely available code and data sets

Constraints on coordination:Intrinsic dynamics, behavioral information and asymmetry in bimanual rhythmic coordination

Zonder oefening is het met pianospelen vrijwel onmogelijk om de handen onafhankelijk van elkaar te bewegen. De handbewegingen zijn op een bepaalde manier gekoppeld. Martine Verheul onderzocht hoe dat precies zit. Daarvoor liet ze haar proefpersonen met twee handen verschillende ritmes tikken. Naast persoonsgebonden verschillen blijken er ook taak-afhankelijke verschillen te zijn. Muzikale ervaring van de proefpersoon had een positief effect op de stabiliteit van tweehandige ritmische coördinatie. Daarna vergeleek Verheul links- en rechtshandigen bij het tikken van symmetrische en asymmetrische patronen. In tegenstelling tot taken waarbij de handen in verschillend tempo tikken blijkt bij het asymmetrisch tikken in een gelijk tempo de coördinatie even stabiel in beide handverdelingen. Verheul toont aan dat zowel de voorkeurshand als de niet-voorkeurshand de leidende rol op zich kan nemen. Die flexibiliteit vermindert echter bij het ouder worden. De coördinatieproblemen bij volwassenen met de ziekte van Parkinson komen niet voort uit de asymmetrische verdeling van symptomen over de twee lichaamshelften, maar zijn volgens Verheul het gevolg van centrale problemen met het koppelen van de ledematen.

Coordination dynamics in the sensorimotor loop

The last two decades have witnessed radical changes of perspective about the nature of intelligence and cognition, leaving behind some of the assumptions of computational functionalism. From the myriad of approaches seeking to substitute the old rule-based symbolic perception of mind, we are especially interested in two of them. The first is Embodied and Situated Cognition, where the advances in modeling complex adaptive systems through computer simulations have reconfigured the way in which mechanistic, embodied and interactive explanations can conceptualize the mind. We are particularly interested in the concept of sensorimotor loop, which brings a new perspective about what is needed for a meaningful interaction with the environment, emphasizing the role of the coordination of effector and sensor activities while performing a concrete task. The second one is the framework of Coordination Dynamics, which has been developed as a result of the increasing focus of neuroscience on self-organized oscillatory brain dynamics. It provides formal tools to study the mechanisms through which complex biological systems stabilize coordination states under conditions in which they would otherwise become unstable. We will merge both approaches and define coordination in the sensorimotor loop as the main phenomena behind the emergence of cognitive behavior. At the same time, we will provide methodological tools and concepts to address this hypothesis. Finally, we will present two case studies based on the proposed approach: 1. We will study the phenomenon known as “intermittent behavior”, which is observed in organisms at different levels (from microorganisms to higher animals). We will propose a model that understands intermittent behavior as a general strategy of biologica organization when an organism has to adapt to complex changing environments, and would allow to establish effective sensorimotor loops even in situations of instable engagement with the world. 2. We will perform a simulation of a phonotaxis task performed by an agent with an oscillator network as neural controller. The objective will be to characterize robust adaptive coupling between perceptive activity and the environmental dynamics just through phase information processing. We will observe how the robustness of the coupling crucially depends of how the sensorimotor loop structures and constrains both the emergent neural and behavioral patterns. We will hypothesize that this structuration of the sensorimotor space, in which only meaningful behavioral patterns can be stabilized, is a key ingredient for the emergence of higher cognitive abilities

Toward More Versatile and Intuitive Cortical Brain–Machine Interfaces

Brain–machine interfaces have great potential for the development of neuroprosthetic applications to assist patients suffering from brain injury or neurodegenerative disease. One type of brain–machine interface is a cortical motor prosthetic, which is used to assist paralyzed subjects. Motor prosthetics to date have typically used the motor cortex as a source of neural signals for controlling external devices. The review will focus on several new topics in the arena of cortical prosthetics. These include using: recordings from cortical areas outside motor cortex; local field potentials as a source of recorded signals; somatosensory feedback for more dexterous control of robotics; and new decoding methods that work in concert to form an ecology of decode algorithms. These new advances promise to greatly accelerate the applicability and ease of operation of motor prosthetics

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

Cortical activations underlying human bipedal balance control

Human bipedal balance is a complex sensorimotor task controlled by the central nervous system. Balance impairments, caused by aging or neuromuscular diseases, often lead to falls which are one of the leading causes of injury and subsequent increases in health care costs. Hence, understanding the mechanisms underlying human bipedal balance control has many functional and clinical implications. Traditionally, it was believed that balance control is mediated by subcortical structures. However, evidence from research in the past few decades has shown that the cerebral cortex plays a major role in bipedal balance control. Nevertheless, the cortical contributions in balance control are still unclear. Hence, the purpose of this thesis was to extend the understanding of cortical involvement in human bipedal balance control. Specifically, the two overarching goals of this thesis were to examine evidence of a cortical network involvement and its generalizability across reactive and predictive balance control. These two overarching goals were addressed through four different studies. Study 1 explored the frequency characteristics and mechanisms underlying the generation of perturbation-evoked potentials. Study 2 investigated cortical activity linked to ‘automatic’ balance reactions that occur continuously while standing still and its dependence on the amplitude of these balance reactions. Study 3 examined the cortical activations related to the preparation and execution of anticipatory postural adjustments that precede a step and whether the activations are dependent on the context of control. Study 4 was designed to examine the functional connectivity in balance control and whether similar networks underlie reactive and predictive balance control. Studies were conducted on young healthy adults and cortical activations were acquired using electroencephalography during feet-in-place balance reactions, standing still, and voluntary stepping. Overall, the findings of these studies provided direct and indirect evidence for the involvement of a cortical network in balance control and its generalizability across different classes of balance control. This work reinforces the view that cortical networks likely play an important role in the control of stability. It is proposed that the synchronized activation of neural assemblies distributed across the cortex might have contributed to the balance-related cortical activations. The findings of this thesis extend the understanding of cortical control of human bipedal balance that may help to inform future, more precise models of the cortical contributions to balance control. This, in turn, can inform future diagnostic and therapeutic approaches to improve mobility among those with balance impairments