Neural Encoding of Direction and Distance across Reference Frames in Visually Guided Reaching.

Goal-directed actions require transforming sensory information into motor plans defined across multiple parameters and reference frames. Substantial evidence supports the encoding of target direction in gaze- and body-centered coordinates within parietal and premotor regions. However, how the brain encodes the equally critical parameter of target distance remains less understood.

Repeated context-specific actions disrupt feedforward adjustments in motor commands in younger and older adults.

The flexibility of the motor system to adjust a planned action before or during the execution of the movement in response to sensory information is critical for preventing errors in motor control. As individuals age, this function declines, leading to an increased incidence of motor errors. Although sensory processing and cognitive decline are known contributors to this impairment, here, we test the hypothesis that repetition of context-specific planned actions interferes with the adjustment of feedforward motor commands.

Reorganization of sensorimotor representations of the intact limb after upper but not lower limb traumatic amputation.

It is becoming increasingly clear that limb loss induces wider spread reorganization of representations of the body that are nonadjacent to the affected cortical territory. Data from upper extremity amputees reveal intrusion of the representation of the ipsilateral intact limb into the former hand territory. Here we test for the first time whether this reorganization of the intact limb into the deprived cortex is specific to the neurological organization of the upper limbs or reflects large scale adaptation that is triggered by any unilateral amputation.

Visual information following object grasp supports digit position variability and swift anticipatory force control.

Anticipatory force control underlying dexterous manipulation has historically been understood to rely on visual object properties and on sensorimotor memories associated with previous experiences with similar objects. However, it is becoming increasingly recognized that anticipatory force control also relies on how an object is grasped. Experiments that allow unconstrained grasp contact points when preventing tilting an object with an off-centered mass show trial-to-trial variations in digit position and subsequent scaling of lift forces, all before feedback of object properties becomes available.

Overt and Covert Object Features Mediate Timing of Patterned Brain Activity during Motor Planning.

Humans are seamless in their ability to efficiently and reliably generate fingertip forces to gracefully interact with objects. Such interactions rarely end in awkward outcomes like spilling, crushing, or tilting given advanced motor planning. Here we combine multiband imaging with deconvolution- and Bayesian pattern component modeling of functional magnetic resonance imaging data and in-scanner kinematics, revealing compelling evidence that the human brain differentially represents preparatory information for skillful object interactions depending on the saliency of visual cues.

Motor adaptation via distributional learning.

. Both artificial and biological controllers experience errors during learning that are probabilistically distributed. We develop a framework for modeling distributions of errors and relating deviations in these distributions to neural activity.

Neural substrates of anticipatory motor adaptation for object lifting.

Anticipatory force control is a fundamental means by which humans stave off slipping, spilling, and tilting disasters while manipulating objects. This control must often be adapted due to changes in an object's dynamics (e.g.

Representational Neural Mapping of Dexterous Grasping Before Lifting in Humans.

The ability of humans to reach and grasp objects in their environment has been the mainstay paradigm for characterizing the neural circuitry driving object-centric actions. Although much is known about hand shaping, a persistent question is how the brain orchestrates and integrates the grasp with lift forces of the fingers in a coordinated manner. The objective of the current study was to investigate how the brain represents grasp configuration and lift force during a dexterous object-centric action in a large sample of male and female human subjects.

Neural Representations of Sensorimotor Memory- and Digit Position-Based Load Force Adjustments Before the Onset of Dexterous Object Manipulation.

Anticipatory load forces for dexterous object manipulation in humans are modulated based on visual object property cues, sensorimotor memories of previous experiences with the object, and, when digit positioning varies from trial to trial, the integrating of this sensed variability with force modulation. Studies of the neural representations encoding these anticipatory mechanisms have not considered these mechanisms separately from each other or from feedback mechanisms emerging after lift onset. Here, representational similarity analyses of fMRI data were used to identify neural representations of sensorimotor memories and the sensing and integration of digit position.

The Relationship Between Hand Function and Overlapping Motor Representations of the Hands in the Contralesional Hemisphere in Unilateral Spastic Cerebral Palsy.

Background: In many children with unilateral spastic cerebral palsy (USCP), the corticospinal tract to the affected hand atypically originates in the hemisphere ipsilateral to the affected hand. Such ipsilateral connectivity is on average a predictor of poor hand function. However, there is high variability in hand function in these children, which might be explained by the complexity of motor representations of both hands in the contralesional hemisphere.

Digit Position and Forces Covary during Anticipatory Control of Whole-Hand Manipulation.

Theoretical perspectives on anticipatory planning of object manipulation have traditionally been informed by studies that have investigated kinematics (hand shaping and digit position) and kinetics (forces) in isolation. This poses limitations on our understanding of the integration of such domains, which have recently been shown to be strongly interdependent. Specifically, recent studies revealed strong covariation of digit position and load force during the loading phase of two-digit grasping.

Elucidating the neural circuitry underlying planning of internally-guided voluntary action.

In an attempt to elucidate the neural circuitry of planning of internally guided voluntary action, Ariani et al. (2015) used a delayed-movement design and multivariate pattern analysis of functional MRI data and found areas decoding internally elicited action plans, stimulus-elicited action plans, and both types of plans. In interpreting their results in the context of a heuristic decision model of voluntary action, encompassing "what" action to perform, "when" to perform it, and "whether" to perform it at all, we highlight at least some neural dissociation of these components.

Visual Cues of Object Properties Differentially Affect Anticipatory Planning of Digit Forces and Placement.

Studies on anticipatory planning of object manipulation showed initial task failure (i.e., object roll) when visual object shape cues are incongruent with other visual cues, such as weight distribution/density (e.

Generalization of Dexterous Manipulation Is Sensitive to the Frame of Reference in Which It Is Learned.

Studies have shown that internal representations of manipulations of objects with asymmetric mass distributions that are generated within a specific orientation are not generalizable to novel orientations, i.e., subjects fail to prevent object roll on their first grasp-lift attempt of the object following 180° object rotation.

The neural bases of different levels of action understanding.

Many have recently questioned whether all levels of actions understanding, from lower kinematic levels to the higher goal or intention levels of action understanding, are processed in the action observation network (a network of neurons that are active during action execution and observation). A recent study by Wurm and Lingnau (J Neurosci 35: 7727-7735, 2015) gave evidence to the contrary, by showing that higher levels of action understanding are processed in the lateral occipitotemporal cortex. An important next step is to differentiate between the role of the lateral occipitotemporal cortex in processing the visual form of an observed action and the goal of an observed action.

Voluntary control of facial musculature in Parkinson's disease.

Aside from being measured in the context of producing facial expressions of emotion, the ability to voluntarily control a range of facial muscles in Parkinson's disease (PD) has not been systematically measured. We used in three enrollment phases an adaptation of the Upper and Lower Face Apraxia test, a measure of the ability to make voluntary movements of the upper and lower face in PD patients and healthy controls. Errors were scored due to (1) pauses prior to movement initiation, (2) loss of individuation, (3) impoverished movement, (4) no movement at all, or (5) content errors (likened to ideational apraxia errors).

Discriminating facial expressions of emotion and its link with perceiving visual form in Parkinson's disease.

We investigated the link between the ability to perceive facial expressions of emotion and the ability to perceive visual form in Parkinson's disease (PD). We assessed in individuals with PD and healthy controls the ability to discriminate graded intensities of facial expressions of anger from neutral expressions and the ability to discriminate radial frequency (RF) patterns with modulations in amplitude from a perfect circle. Those with PD were, as a group, impaired relative to controls in discriminating graded intensities of angry from neutral expressions and discriminating modulated amplitudes of RF patterns from perfect circles; these two abilities correlated positively and moderately to highly, even after removing the variance that was shared with disease progression and general cognitive functioning.

Discrimination and recognition of facial expressions of emotion and their links with voluntary control of facial musculature in Parkinson's disease.

Objective: To explore perception of facial expressions of emotion and its link with voluntary facial musculature control in Parkinson's disease (PD).

Method: We investigated in 2 sets of experiments in PD patients and healthy controls the perceptual ability to discriminate (a) graded intensities of emotional from neutral expressions, (b) graded intensities of the same emotional expressions, (c) full-blown discrepant emotional expressions from 2 similar expressions and the more complex recognition ability to label full-blown emotional expressions. We tested an embodied simulationist account of emotion perception in PD, which predicts a link between the ability to perceive emotional expressions and facial musculature control.

Psychophysical measures of sensitivity to facial expression of emotion.

We report the development of two simple, objective, psychophysical measures of the ability to discriminate facial expressions of emotion that vary in intensity from a neutral facial expression and to discriminate between varying intensities of emotional facial expression. The stimuli were created by morphing photographs of models expressing four basic emotions, anger, disgust, happiness, and sadness with neutral expressions. Psychometric functions were obtained for 15 healthy young adults using the Method of Constant Stimuli with a two-interval forced-choice procedure.

Short-interval intracortical inhibition and manual dexterity in healthy aging.

Short-interval intracortical inhibition (SICI) acting on the first dorsal interosseus was measured using paired-pulse transcranial magnetic stimulation (interstimulus interval=2ms) in samples of young and healthy older subjects and correlated with manual dexterity measured with the Purdue Pegboard test and two isometric force-matching tasks. There was an age-related decrease in SICI and an age-related decline in all dexterity measures. The level of SICI was not correlated with any of the dexterity measures, but the appearance of atypical facilitation (rather than inhibition) in some subjects was associated with impaired pegboard performance but not force-matching performance.