The Control of Movements via Motor Gamma Oscillations

The ability to perform movements is vital for our daily life. Our actions are embedded in a complex environment where we need to deal efficiently in the face of unforeseen events. Neural oscillations play an important role in basic sensorimotor processes related to the execution and preparation of movements. In this review, I will describe the state of the art regarding the role of motor gamma oscillations in the control of movements. Experimental evidence from electrophysiological studies has shown that motor gamma oscillations accomplish a range of functions in motor control beyond merely signaling the execution of movements. However, these additional aspects associated with motor gamma oscillation remain to be fully clarified. Future work on different spatial, temporal and spectral scales is required to further understand the implications of gamma oscillations in motor control.

Spatially bivariate EEG-neurofeedback can manipulate interhemispheric rebalancing of M1 excitability

Human behavior requires interregional crosstalk to employ the sensorimotor processes in the brain. Although some external neuromodulation tools have been used to manipulate interhemispheric sensorimotor activity, a central controversy concerns whether this activity can be volitionally controlled. Experimental tools lack the power to up- or down-regulate the state of the targeted hemisphere over a large dynamic range and, therefore, cannot evaluate the possible volitional control of the activity. We overcame this difficulty by using the recently developed method of spatially bivariate electroencephalography (EEG)-neurofeedback to systematically enable participants to manipulate their bilateral sensorimotor activities. Herein, we report that bi-directional changes in ipsilateral excitability to the imagined hand (conditioning hemisphere) affect interhemispheric inhibition (IHI) assessed by paired-pulse transcranial magnetic stimulation paradigm. In addition, participants were able to robustly manipulate the IHI magnitudes. Further physiological analyses revealed that the self-manipulation of IHI magnitude reflected interhemispheric connectivity in EEG and TMS, which was accompanied by intrinsic bilateral cortical oscillatory activities. Our results provide clear neuroscientific evidence regarding the inhibitory interhemispheric sensorimotor activity and IHI manipulator, thereby challenging the current theoretical concept of recovery of motor function for neurorehabilitation.

KEEPING IN TOUCH WITH OUR HIDDEN SIDE

Previous studies have shown that the sensory modality used to identify the position of proprioceptive targets hidden from sight, but frequently viewed, influences the type of the body representation employed for reaching them with the finger. The question then arises as to whether this observation also applies to proprioceptive targets which are hidden from sight, and rarely, if ever, viewed. We used an established technique for pinpointing the type of body representation used for the spatial encoding of targets which consisted of assessing the effect of peripheral gaze fixation on the pointing accuracy. More precisely, an exteroceptive, visually dependent, body representation is thought to be used if gaze deviation induces a deviation of the pointing movement. Three light-emitting diodes (LEDs) were positioned at the participants' eye level at -25 deg, 0 deg and +25 deg with respect to the cyclopean eye. Without moving the head, the participant fixated the lit LED before the experimenter indicated one of the three target head positions: topmost point of the head (vertex) and two other points located at the front and back of the head. These targets were either verbal-cued or tactile-cued. The goal of the subjects (n=27) was to reach the target with their index finger. We analysed the accuracy of the movements directed to the topmost point of the head, which is a well-defined, yet out of view anatomical point. Based on the possibility of the brain to create visual representations of the body areas that remain out of view, we hypothesized that the position of the vertex is encoded using an exteroceptive body representation, both when verbally or tactile-cued. Results revealed that the pointing errors were biased in the opposite direction of gaze fixation for both verbal-cued and tactile-cued targets, suggesting the use of a vision-dependent exteroceptive body representation. The enhancement of the visual body representations by sensorimotor processes was suggested by the greater pointing accuracy when the vertex was identified by tactile stimulation compared to verbal instruction. Moreover, we found in a control condition that participants were more accurate in indicating the position of their own vertex than the vertex of other people. This result supports the idea that sensorimotor experiences increase the spatial resolution of the exteroceptive body representation. Together, our results suggest that the position of rarely viewed body parts are spatially encoded by an exteroceptive body representation and that non-visual sensorimotor processes are involved in the constructing of this representation.

The Human Cerebellum as a Hub of the Predictive Brain

Although the cerebellum has long been believed to be involved uniquely in sensorimotor processes, recent research works pointed to its participation in a wide range of cognitive predictive functions. Here, we review the available evidence supporting a generalized role of the cerebellum in predictive computation. We then discuss the anatomo-physiological properties that make the cerebellum the ideal hub of the predictive brain. We further argue that cerebellar involvement in cognition may follow a continuous gradient, with higher cerebellar activity occurring for tasks relying more on predictive processes, and outline the empirical scenarios to probe this hypothesis.

Concepts for which we need others more: The case of abstract concepts

The capability to form and use concepts is a core component of human cognition. While all concepts are grounded in sensorimotor processes, more abstract concepts (e.g. “phantasy”) collect more heterogeneous and perceptually dissimilar exemplars; thus, linguistic and social interaction are particularly crucial for their acquisition and use. Due to their indeterminacy, abstract concepts generate more uncertainty than more concrete concepts; hence they induce people to monitor their inner knowledge longer and then to revert to others to ask for information and negotiate the word meaning. We propose that abstract concepts are concepts for which we need others more – other people are essential to acquire, process, and use them. Conceiving them in these terms requires the employment of novel, interactive methods to investigate their representation in use.

Dissecting errors of the exogenously-driven and endogenously-driven saccadic tasks in the common marmoset

Various saccadic tasks traditionally used in oculomotor research, including both exogenously-driven and endogenously-driven saccades, have been proposed as clinical diagnostic for human movement disorders. Recently, common marmosets have been proven to be a good primate model for these movement disorders. However, whether similar saccadic measurements can be used for marmosets was not tested. Here, we trained three marmosets on the gap task, an exogenously-driven saccadic task, and the oculomotor delayed response (ODR) task, an endogenously-driven saccadic task. We demonstrated that with long-term training, they were able to learn and switch between the two tasks. The marmosets showed undershooting tendency in the gap and both under- and overshooting tendency in the ODR task when they made saccades to the target. We also categorized the error trails into distractive, impulsive, and visuomotor errors, depending on when a false saccade happened in relation to the task progression and interpreted possible causes of errors based on the saccade response time and the task history. Each error category may indicate specific failures in a particular aspect of cognitive or sensory-motor processes. Finally, and critically, we found that saccades from successful trials exhibited the highest saccade peak velocity and the shortest saccade duration comparing to the same saccade amplitude from error trials. Taken together, we showed the potential of training the same marmosets on conflicting oculomotor tasks simultaneously. We documented the baseline performance and compared successful and error trials in both gap and ODR tasks from the same animals. We propose that analyzing the error trials in sync with successful trials could provide a further understanding of the cognitive and sensorimotor processes of the marmosets, in both healthy and disease conditions.

Scanpath Theory in Virtual Reality

It has long been thought that visual perception is represented in sensorimotor processes that unfold over time. One prominent theory predicts that our memory for a scene consists of both the scene content and the motor commands (i.e., eye movements) used to explore that scene. This Scanpath Theory (Noton & Stark, Science 171 (1971) 308-311) has long been contested, with many studies providing evidence both for, and against it. That past work, however, has failed to account for the fact that visual perception is embodied within an active system of effectors, namely, that people routinely move both their eyes and head to explore visible space. In the present work we tested Scanpath Theory while observers were free to move within a 360-degree VR environment. Their task was to encode and later recognise panoramic scenes within this fully immersive world. During both encoding and recognition, we recorded their eye and head movements using a VR headset equipped with eye and head tracking. Our results reveal that eye and head movement patterns are diagnostic of memory performance; and that scene recognition improves when certain movements that had occurred during encoding are repeated. Finally, including head movement measures enhances performance prediction, strengthening the evidence for Scanpath Theory, and reinforcing the fact that the head moves in service of the eyes in allocating attention.

The Sensorimotor Dynamics of Joint Attention

Social interactions are composed of coordinated, multimodal behaviors with each individual taking turns and sharing attention. By the second year of life, infants are able to engage in coordinated interactions with their caregivers. Although research has focused on the social behaviors that enable parent-infant dyads to engage in joint attention, little work has been done to understand the sensorimotor mechanisms underlying coordination. Using wireless head-mounted eye trackers and motion sensing, we recorded 31 dyads as they played freely in a home-like laboratory. We identified moments of visual joint attention, when parent and infant were looking at the same object, and then measured the dyad’s head and hand movements during and around joint attention. We found evidence that both parents and infants still their bodies during joint attention. We also compared instances of joint attention that were led by the parent or by the infant and identified different sensorimotor pathways that support the two types of joint attention. These results provide the foundation for continued exploration of the critical role of sensorimotor processes on coordinated social behavior and its development.

EXPRESS: Short-term upper limb immobilization impairs grasp representation

The present experiment aimed to gain more information on the effect of limb nonuse on the cognitive level of actions and, more specifically, on the content of the motor program used for grasping an object. For that purpose, we used a hand-grasping laterality task that is known to contain concrete information on manipulation activity. Two groups participated in the experiment: an immobilized group, including participants whose right hand and arm were fixed with a rigid splint and an immobilization vest for 24 hours, and a control group, including participants who did not undergo the immobilization procedure. The main results confirmed a slowdown of sensorimotor processes, which is highlighted in the literature, with slower response times when the participants identified the laterality of hand images that corresponded to the immobilized hand. Importantly, the grip-precision effect, highlighted by slower response times for hands grasping a small sphere versus a large sphere, is impaired by 24 hours of limb nonuse. Overall, this study provided additional evidence of the disengagement of sensorimotor processes due to a short period of limb immobilization.

Oculomotor biomarkers of illness, risk, and pharmacogenetic treatment effects across the psychosis spectrum

Eye movements are used to assess alterations in brain systems involved in cognitive and sensorimotor processes in psychiatric disorders. This chapter summarizes findings comparing saccadic and smooth pursuit eye movement performance across psychotic proband and relative groups, with an emphasis on schizophrenia, schizoaffective disorder, and psychotic bipolar disorder. Inhibitory errors on the antisaccade task represent a robust and graded deficit across probands, with greatest impairment observed in schizophrenia, and among relatives, particularly those with elevated psychosis spectrum traits. Abnormalities in the use of early visual motion information during smooth pursuit is apparent among both probands and relatives, while deficient use of visual feedback for dynamical pursuit appears restricted to probands. Select eye movement measures appear differentially affected by glutamate and dopamine gene variants. Overall, research findings support eye movement measures as promising biomarkers of altered brain systems underlying select cognitive and sensorimotor processes across the psychosis spectrum.