Feedback and feedforward adaptation to visuomotor delay during reaching and slicing movements

It has been suggested that the brain and in particular the cerebellum and motor cortex adapt to represent the environment during reaching movements under various visuomotor perturbations. It is well known that significant delay is present in neural conductance and processing; however, the possible representation of delay and adaptation to delayed visual feedback has been largely overlooked. Here we investigated the control of reaching movements in human subjects during an imposed visuomotor delay in a virtual reality environment. In the first experiment, when visual feedback was unexpectedly delayed, the hand movement overshot the end‐point target, indicating a vision‐based feedback control. Over the ensuing trials, movements gradually adapted and became accurate. When the delay was removed unexpectedly, movements systematically undershot the target, demonstrating that adaptation occurred within the vision‐based feedback control mechanism. In a second experiment designed to broaden our understanding of the underlying mechanisms, we revealed similar after‐effects for rhythmic reversal (out‐and‐back) movements. We present a computational model accounting for these results based on two adapted forward models, each tuned for a specific modality delay (proprioception or vision), and a third feedforward controller. The computational model, along with the experimental results, refutes delay representation in a pure forward vision‐based predictor and suggests that adaptation occurred in the forward vision‐based predictor, and concurrently in the state‐based feedforward controller. Understanding how the brain compensates for conductance and processing delays is essential for understanding certain impairments concerning these neural delays as well as for the development of brain–machine interfaces.     

Neural correlates of state estimation in visually guided movements: an event-related fMRI study

State estimation of self-movement, based on both motor commands and sensory feedback, has been suggested as essential to human movement control to compensate for inherent feedback delays in sensorimotor loops. The present study investigated the neural basis for state estimation of human movement using event-related functional magnetic resonance imaging (fMRI). Participants traced visually presented curves with a computer mouse, and an artificial delay was introduced to visual feedback. Motor performance and brain activities during movements were measured. Experiment 1 investigated brain activations that were significantly correlated with visual feedback delay and motor error by parametrically manipulating visual feedback delay. Activation of the right posterior parietal cortex (PPC) was positively correlated with motor error, whereas activation of the right temporo-parietal junction (TPJ) was observed only in the group with a smaller increase in motor error with increased visual feedback delay. Experiment 2 involved parametric analysis of motor performance while controlling mouse movement speed during the task. Activity in the right TPJ showed a significant positive correlation with motor performance under the delayed visual feedback condition. In addition, activity of the PPC was greater when motor error was presented visually. These results suggest that the PPC plays a significant role in evaluating visuomotor prediction error, while the TPJ is involved in state estimation of self-movement during visually guided movements.     

The rate of visuomotor adaptation correlates with cerebellar white‐matter microstructure

Convergent experimental evidence points to the cerebellum as a key neural structure mediating adaptation to visual and proprioceptive perturbations. In a previous study, we have shown that activity in the anterior cerebellum varies with the rate of learning, with fast learners exhibiting more activity in this region than slow learners. Here, we investigated whether this variability in behavior may partly reflect inter‐individual differences in the structural properties of cerebellar white‐matter output tracts. For this purpose, we used diffusion‐weighted magnetic resonance imaging to estimate fractional anisotropy (FA), and correlated the FA with the rate of adaptation to an optical rotation in 11 subjects. We found that FA in a region consistent with the superior cerebellar peduncle (SCP), containing fibers connecting the cerebellar cortex with motor and premotor cortex, was positively correlated with the rate of adaptation but not with the general level of performance or the initial deviation. The same pattern was observed in a region of the lateral posterior cerebellum. In contrast, FA in the angular gyrus of the posterior parietal cortex correlated positively both with the rate of adaptation and the overall level of performance. Our results show that the rate of learning a visuomotor task is associated with FA of cerebellar pathways. Hum Brain Mapp, 2009. © 2009 Wiley‐Liss, Inc.     

Neural correlates of lower limbs proprioception: An fMRI study of foot position matching

Little is known about the neural correlates of lower limbs position sense, despite the impact that proprioceptive deficits have on everyday life activities, such as posture and gait control. We used fMRI to investigate in 30 healthy right‐handed and right‐footed subjects the regional distribution of brain activity during position matching tasks performed with the right dominant and the left nondominant foot. Along with the brain activation, we assessed the performance during both ipsilateral and contralateral matching tasks. Subjects had lower errors when matching was performed by the left nondominant foot. The fMRI analysis suggested that the significant regions responsible for position sense are in the right parietal and frontal cortex, providing a first characterization of the neural correlates of foot position matching.     

Sensory feedback contributes to early movement-evoked fields during voluntary finger movements in humans

Neuromagnetic field changes accompanying voluntary movement in humans (`movement-evoked fields' or MEFs) were recorded over the scalp using a whole-head MEG system during the performance of self-paced finger movements in order to determine the contribution of sensory feedback to the generation of these brain responses. It was found that cooling the subject's arm resulted in delays of 8 ms or more in the latency of the early movement-evoked field component (MEFI). These delays were attributed to increases in conduction times in the afferent pathways as confirmed by electrically evoked somatosensory responses and suggest a peripheral origin of the MEFI. In a second experiment, we demonstrated the effects of sensory input to the contralateral hand during a simple button pressing task in 4 subjects. The results indicated that responses over the hemisphere ipsilateral to the side of movement which resembled previously reported ipsilateral MEFs can be elicited by the spread of mechanical stimulation to opposite side of the body when a mechanical trigger is used. These experiments provide further evidence that early movement-evoked fields produced by unilateral finger movements are observed primarily over the contralateral somatosensory cortex and represent sensory feedback to the somatosensory cortex from the periphery.     

The effects of digital anaesthesia on predictive grip force adjustments during vertical movements of a grasped object

Grip force adjustments to fluctuations of inertial loads induced by vertical arm movements with a grasped object were analysed during normal and impaired finger sensibility. Normally grip force is modulated in a highly economical way in parallel with fluctuations of load force. Two subjects performed vertical up and down movements of a grasped object, both with normal finger sensibility and then cutaneously anaesthetized finger sensibility. Short breaks were taken in between single movements, during which the object was held stationary. After digital anaesthesia was applied to the grasping fingers, both subjects substantially increased the grip force. The grip force amplitude and timing still anticipated changes in load force, although the established grip force had already overcome movement-induced load force peaks. This implies that the increase of grip force and consequently the elevated force ratio between maximum grip and maximum load force are not processed to alter the feedforward system of grip force control. Cutaneous afferent information from the grasping digits appears to be necessary for economic scaling of the grip force level, but it plays a subordinate role in the precise anticipatory temporal coupling of grip and load forces during voluntary object manipulation.     

Differential force scaling of fine‐graded power grip force in the sensorimotor network

Force scaling in the sensorimotor network during generation and control of static or dynamic grip force has been the subject of many investigations in monkeys and human subjects. In human, the relationship between BOLD signal in cortical and subcortical regions and force still remains controversial. With respect to grip force, the modulation of the BOLD signal has been mostly studied for forces often reaching high levels while little attention has been given to the low range for which electrophysiological neuronal correlates have been demonstrated. We thus conducted a whole‐brain fMRI study on the control of fine‐graded force in the low range, using a power grip and three force conditions in a block design. Participants generated on a dynamometer visually guided repetitive force pulses (ca. 0.5 Hz), reaching target forces of 10%, 20%, and 30% of maximum voluntary contraction. Regions of interest analysis disclosed activation in the entire cortical and subcortical sensorimotor network and significant force‐related modulation in several regions, including primary motor (M1) and somatosensory cortex, ventral premotor and inferior parietal areas, and cerebellum. The BOLD signal, however, increased monotonically with force only in contralateral M1 and ipsilateral anterior cerebellum. The remaining regions were activated with force in various nonlinear manners, suggesting that other factors such as visual input, attention, and muscle recruitment also modulate the BOLD signal in this visuomotor task. These findings demonstrate that various regions of the sensorimotor network participate differentially in the production and control of fine‐graded grip forces. Hum Brain Mapp 2009. © 2009 Wiley‐Liss, Inc.     

Neuronal correlates of perceptual stability during eye movements

We are usually unaware of retinal image motion resulting from our own movement. For instance, during slow-tracking eye movements the world around us remains perceptually stable despite the retinal image slip induced by the eye movement. It is commonly held that this example of perceptual invariance is achieved by subtracting an internal reference signal, reflecting the eye movement, from the retinal motion signal. If the two cancel each other, visual objects, which do not move, will also be perceived as non-moving. If, however, the reference signal is too small or too large, a false eye movement-induced motion of the external world, the Filehne illusion, will be perceived. We have exploited our ability to manipulate the size of the reference signal in an attempt to identify neurons in the visual cortex of monkeys, influenced by the percept of self-induced visual motion or the reference signal rather than the retinal motion signal. We report here that such 'percept-related' neurons can already be found in the primary visual cortex area, although few in numbers. They become more frequent in areas middle temporal and medial superior temporal in the superior temporal sulcus, and comprise almost 50% of all neurons in area visual posterior sylvian (VPS) in the posterior part of the lateral sulcus. In summary, our findings suggest that our ability to perceive a visual world, which is stable despite self-motion, is based on a neuronal network, which culminates in the VPS located in the lateral sulcus below the classical dorsal stream of visual processing.     

Neural correlates of exemplar novelty processing under different spatial attention conditions

The detection of novel events and their identification is a basic prerequisite in a rapidly changing environment. Recently, the processing of novelty has been shown to rely on the hippocampus and to be associated with activity in reward‐related areas. The present study investigated the influence of spatial attention on neural processing of novel relative to frequently presented standard and target stimuli. Never‐before‐seen Mandelbrot‐fractals absent of semantic content were employed as stimulus material. Consistent with current theories, novelty activated a widespread network of brain areas including the hippocampus. No activity, however, could be observed in reward‐related areas with the novel stimuli absent of a semantic meaning employed here. In the perceptual part of the novelty‐processing network a region in the lingual gyrus was found to specifically process novel events when they occurred outside the focus of spatial attention. These findings indicate that the initial detection of unexpected novel events generally occurs in specialized perceptual areas within the ventral visual stream, whereas activation of reward‐related areas appears to be restricted to events that do possess a semantic content indicative of the biological relevance of the stimulus. Hum Brain Mapp, 2009. © 2009 Wiley‐Liss, Inc.     

The performance of mouse pointing and selecting for pupils with and without intellectual disabilities

The purpose of this study was to compare the performance of mouse pointing and selecting in the tasks with different index of difficulty between 20 pupils with intellectual disabilities and 21 pupils without disabilities. A mouse proficiency assessment software was utilized to collect data. Pupils with intellectual disabilities executed tasks more correctly in bigger target even in tasks with the same index of difficulty. The group with intellectual disabilities performed worse in cursor control even when only those correctly completed tasks were used for comparison. However, a similar pattern was observed in the performance of the group without disabilities.     

Characterization of oculomotor and visual activities in the primate pedunculopontine tegmental nucleus during visually guided saccade tasks

The pedunculopontine tegmental nucleus (PPTN) has anatomical connections with numerous visuomotor areas including the basal ganglia, thalamus, superior colliculus and frontal eye field. Although many anatomical and physiological studies suggest a role for the PPTN in the control of conditioned behavior and associative learning, the detailed characteristics of saccade‐ and visual‐related activities of PPTN neurons remain unclear. We recorded the activity of PPTN neurons in monkeys (Macaca fuscata ) during visually guided saccade tasks, and examined the response properties of saccade‐ and visual‐related activities such as time course, direction selectivity and contextual modulation. Saccade‐related activity occurred either during saccade execution or after saccade end. The preferred directions of the neuronal activity were biased toward the contralateral and upward sides. Half of the saccade‐related neurons showed activity modulation only for task saccades and not for spontaneous saccades outside the task. Visually‐responsive neurons responded with short latencies. Some responded to the appearance of the visual stimulus in a directionally selective manner, and others responded to both the appearance and disappearance of the visual stimulus in a directionally non‐selective manner. Many of these neurons exhibited distinct visual responses to the appearance of two different stimuli presented under different stages of the task, whereas a population of the neurons responded equally to the disappearance of the two stimuli. Thus, many PPTN neurons exhibited context‐dependent activity related to the visuomotor events, consistent with a role in controlling conditioned behavior.     

Neural correlates of atomoxetine improving inhibitory control and visual processing in Drug‐naïve adults with attention‐deficit/hyperactivity disorder

Atomoxetine improves inhibitory control and visual processing in healthy volunteers and adults with attention‐deficit/hyperactivity disorder (ADHD). However, little is known about the neural correlates of these two functions after chronic treatment with atomoxetine. This study aimed to use the counting Stroop task with functional magnetic resonance imaging (fMRI) and the Cambridge Neuropsychological Test Automated Battery (CANTAB) to investigate the changes related to inhibitory control and visual processing in adults with ADHD. This study is an 8‐week, placebo‐controlled, double‐blind, randomized clinical trial of atomoxetine in 24 drug‐naïve adults with ADHD. We investigated the changes of treatment with atomoxetine compared to placebo‐treated counterparts using the counting Stroop fMRI and two CANTAB tests: rapid visual information processing (RVP) for inhibitory control and delayed matching to sample (DMS) for visual processing. Atomoxetine decreased activations in the right inferior frontal gyrus and anterior cingulate cortex, which were correlated with the improvement in inhibitory control assessed by the RVP. Also, atomoxetine increased activation in the left precuneus, which was correlated with the improvement in the mean latency of correct responses assessed by the DMS. Moreover, anterior cingulate activation in the pre‐treatment was able to predict the improvements of clinical symptoms. Treatment with atomoxetine may improve inhibitory control to suppress interference and may enhance the visual processing to process numbers. In addition, the anterior cingulate cortex might play an important role as a biological marker for the treatment effectiveness of atomoxetine. Hum Brain Mapp 38:4850–4864, 2017. © 2017 Wiley Periodicals, Inc.     

Somatosensory evoked potentials during the ideation and execution of individual finger movements

Scalp somatosensory evoked potentials (SEPs) were recorded in 10 volunteers after median nerve stimulation, in four experimental conditions of hand movements performance/ideation, and compared with the baseline condition of full relaxation. The experimental conditions were (a) self-improvised hand-finger sequential movements; (b) the same movements according to a read sequence of numbers; (c) mental ideation of finger movements; and (d) passive displacement of fingers in complete relaxation. Latencies and amplitudes of the parietal (N20, P25, N33, and P45) and frontal peaks (P20–22, N30, and P40) were analyzed. Latencies did not vary in any of the paradigms. Among the parietal complexes, only the P25-N33 amplitude was significantly reduced in (a), (b), (c), and (d) and the N20-P25 was reduced in (a) and (d); among frontal waves, N30 and P40 were significantly reduced (20–75%) in (a) and (b). Coronal electrodes showed amplitude decrements maximal at the frontal-rolandic positions contralateral to the stimulated side. © 1996 John Wiley & Sons, Inc.     

Neural correlates of preparatory and regulatory control over positive and negative emotion

This study used functional magnetic resonance imaging to investigate brain activation during preparatory and regulatory control while participants (N = 24) were instructed either to simply view or decrease their emotional response to, pleasant, neutral or unpleasant pictures. A main effect of emotional valence on brain activity was found in the right precentral gyrus, with greater activation during positive than negative emotion regulation. A main effect of regulation phase was evident in the bilateral anterior prefrontal cortex (PFC), precuneus, posterior cingulate cortex, right putamen and temporal and occipital lobes, with greater activity in these regions during preparatory than regulatory control. A valence X regulation interaction was evident in regions of ventromedial PFC and anterior cingulate cortex, reflecting greater activation while regulating negative than positive emotion, but only during active emotion regulation (not preparation). Conjunction analyses revealed common brain regions involved in differing types of emotion regulation including selected areas of left lateral PFC, inferior parietal lobe, temporal lobe, right cerebellum and bilateral dorsomedial PFC. The right lateral PFC was additionally activated during the modulation of both positive and negative valence. Findings demonstrate significant modulation of brain activity during both preparation for, and active regulation of positive and negative emotional states.     

Investigation of the electrophysiological correlates of negative BOLD response during intermittent photic stimulation: An EEG‐fMRI study

Although the occurrence of concomitant positive BOLD responses (PBRs) and negative BOLD responses (NBRs) to visual stimuli is increasingly investigated in neuroscience, it still lacks a definite explanation. Multimodal imaging represents a powerful tool to study the determinants of negative BOLD responses: the integration of functional Magnetic Resonance Imaging (fMRI) and electroencephalographic (EEG) recordings is especially useful, since it can give information on the neurovascular coupling underlying this complex phenomenon. In the present study, the brain response to intermittent photic stimulation (IPS) was investigated in a group of healthy subjects using simultaneous EEG‐fMRI, with the main objective to study the electrophysiological mechanisms associated with the intense NBRs elicited by IPS in extra‐striate visual cortex. The EEG analysis showed that IPS induced a desynchronization of the basal rhythm, followed by the instauration of a novel rhythm driven by the visual stimulation. The most interesting results emerged from the EEG‐informed fMRI analysis, which suggested a relationship between the neuronal rhythms at 10 and 12 Hz and the BOLD dynamics in extra‐striate visual cortex. These findings support the hypothesis that NBRs to visual stimuli may be neuronal in origin rather than reflecting pure vascular phenomena. Hum Brain Mapp 37:2247–2262, 2016. © 2016 Wiley Periodicals, Inc.     

Neural correlates underlying the attentional spotlight in human parietal cortex independent of task difficulty

Changes in the size of the attentional focus and task difficulty often co‐vary. Nevertheless, the neural processes underlying the attentional spotlight process and task difficulty are likely to differ from each other. To differentiate between the two, we parametrically varied the size of the attentional focus in a novel behavioral paradigm while keeping visual processing difficulty either constant or not. A behavioral control experiment proved that the present behavioral paradigm could indeed effectively manipulate the size of the attentional focus per se, rather than affecting purely perceptual processes or surface processing. Imaging results showed that neural activity in a dorsal frontoparietal network, including right superior parietal cortex (SPL), was positively correlated with the size of the attentional spotlight, irrespective of whether task difficulty was constant or varied across different sizes of attentional focus. In contrast, neural activity in the ventral frontoparietal network, including the right inferior parietal cortex (IPL), was positively correlated with increasing task difficulty. Data suggest that sub‐regions in parietal cortex are differentially involved in the attentional spotlight process and task difficulty: while SPL was involved in the attentional spotlight process independent of task difficulty, IPL was involved in the effect of task difficulty independent of the attentional spotlight process. Hum Brain Mapp 38:4996–5018, 2017. © 2017 Wiley Periodicals, Inc.     

A lesion of the posterior parietal cortex disrupts on-line adjustments during aiming movements

It is long known that the posterior parietal cortex (PPC) is critically involved in goal-directed movements. Nevertheless, there are still some controversies about its specific functions. Although most published studies have emphasised the role of PPC in sensorimotor planning processes, it has been recently suggested that PPC can also participate to on-line movement control. We studied kinematics of hand movements in a patient with a bilateral PPC lesion who exhibited no deficit in planning of her grasping movements in central vision. She was instructed to reach and grasp a cylinder presented at different locations and her motor performance was compared to that of four healthy control subjects. To address on-line control specifically, the cylinder was quickly and unexpectedly jumped, on a few trials, at movement onset, to a new location some 10° (of apparent visual angle) from the original location. The patient could easily grasp stationary objects seen in foveal vision, exhibiting the same kinematic pattern as controls. Therefore, she could plan movements accurately. In response to the object jump, unlike the controls, the patient was unable to amend her ongoing movement. In this situation, she completed two distinct movements, a first one toward the initial object location and a second one toward the final object location. These results support the hypothesis that beyond a role in movement planning, PPC plays a major role in the on-line control of reach-to-grasp movements.     

Neural correlates of retrieval processing in the prefrontal cortex during recognition and exclusion tasks

Event-related fMRI was employed to contrast the neural activity elicited in prefrontal cortex during recognition memory and exclusion tests. The study phases preceding each memory test were identical, involving the presentation of study items (visually presented words) in one of two study contexts. For the recognition test subjects were required to respond positively to all old items regardless of study context, and to respond negatively to new items. For the exclusion task, positive responses were required to old items presented in one of the study contexts only; negative responses were required both to unstudied items and studied items from the alternative context (non-targets). No prefrontal region demonstrated greater activity for new items in the exclusion task. Thus, there was no evidence that retrieval cues were processed differently according to the specificity of the sought-for information. In several regions, most notably bilateral anterior prefrontal cortex, activity was greater for old than for new items regardless of task. Activity in right dorsolateral prefrontal cortex was also greater for old than for new items; these effects however were larger in the exclusion task. The findings are consistent with previous reports that activity in anterior prefrontal cortex elicited by recognition retrieval cues is sensitive to retrieval success, and extend these findings to the exclusion task. The findings for the right dorsolateral cortex add further weight to the proposal that this region supports post-retrieval monitoring of retrieved information.     

EEG correlates of finger movements with different inertial load conditions as revealed by averaging techniques.

OBJECTIVE: The present study was aimed to further address the general empirical question regarding the sensitivity of EEG correlates toward specific kinematic and/or kinetic movement parameters. In particular, we examined whether adding different inertial loads to the index finger, while a subject produced various amplitudes of discrete finger movements, influenced the movement-related potentials (MRP). METHODS: Our experimental design systematically controlled the angular displacement, velocity and acceleration (kinematic) profiles of finger movement while torque (kinetics) was varied by adding different external loads opposing finger flexion movement. We applied time-domain averaging of EEG single trials in order to extract three movement-related potentials (BP-600 to -500 BP-100 to 0 and N0 to 100) preceding and accompanying 25, 50 and 75 degrees unilateral finger movements with no inertial load, small (100 g) and large (200 g) loading. RESULTS: It was shown that both inertial load and the degree of angular displacement of index finger flexion increased the amplitude of late components of MRP (BP-100 to 0 and N0 to 100) over frontal and precentral areas. In contrast, the external load and movement amplitude manipulations did not influence the earlier component of the MRP (BP- 600 to -500). CONCLUSIONS: Overall, the data demonstrate that adding inertial load to the finger with larger angular displacements involves systematic increase in activation across frontal and precentral areas that are related to movement initiation as reflected in BP-100 to 0 and N0 to 100.     

Independent on-line control of the two hands during bimanual reaching

Many studies on bimanual coordination have shown that people exhibit a preference for mirror-symmetric movements. We demonstrate that this constraint is absent when bimanual reaching movements are made to visual targets. We investigated the ability of humans to make on-line adjustments during such movements when one or both targets were displaced during the initial phase of the movements. Adjustments were as efficient during bimanual as unimanual movements, even when two adjustments had to be made simultaneously. When one target was displaced in the bimanual condition, the hand reaching to that target adjusted efficiently to the displacement. However, a small transient perturbation in the trajectory of the other hand was also observed. This perturbation was in the same direction as the displacement, rather than in mirror-symmetric direction. A control experiment demonstrated that these perturbations could be elicited by visual information alone, but that they were also influenced by whether an adjustment was required in the trajectory of the other hand. Our results demonstrate near independent control of the two arms during visually guided reaching. The subtle interference observed between the arms reflects interactions between target-related representations in visual coordinates rather than between movement-related representations in joint- or muscle-coordinates.