Correction: Data-driven analyses of motor impairments in animal models of neurological disorders.

[This corrects the article DOI: 10.1371/journal.pbio.3000516.].

Data-driven analyses of motor impairments in animal models of neurological disorders.

Behavior provides important insights into neuronal processes. For example, analysis of reaching movements can give a reliable indication of the degree of impairment in neurological disorders such as stroke, Parkinson disease, or Huntington disease. The analysis of such movement abnormalities is notoriously difficult and requires a trained evaluator. Here, we show that a deep neural network is able to score behavioral impairments with expert accuracy in rodent models of stroke. The same network was also trained to successfully score movements in a variety of other behavioral tasks. The neural network also uncovered novel movement alterations related to stroke, which had higher predictive power of stroke volume than the movement components defined by human experts. Moreover, when the regression network was trained only on categorical information (control = 0; stroke = 1), it generated predictions with intermediate values between 0 and 1 that matched the human expert scores of stroke severity. The network thus offers a new data-driven approach to automatically derive ratings of motor impairments. Altogether, this network can provide a reliable neurological assessment and can assist the design of behavioral indices to diagnose and monitor neurological disorders.

Does play shape hand use skill in rats?

Hand use is a widespread act in many vertebrate lineages and subserves behaviors including locomotion, predation, feeding, nest construction, and grooming. In order to determine whether hand use is similarly used in social behavior, the present paper describes hand use in the social play of rats. In the course of rough and tumble play sessions, rats are found to make as many as twenty different movements a minute with each hand for the purposes of manipulating a partner into a subordinate position or defending against a partner's attack. The hand movements comprise signaling movements of touching, offensive manipulating of a partner to control a play engagement, and defensive hand movements directed toward blocking, pushing and pulling to parry an attack. For signaling, attack and defense, hand movements have a structure that is similar to the structure of hand movements used for other purposes including eating, but in their contact points on an opponent, they are tailored for partner control. Given the time devoted to play by rats, play likely features the social rat behavior with the most extensive use of hand movements. This extensive use of hand movements for social play is discussed in relation to the ubiquity of hand use in adaptive behavior, the evolution of hand use in the play of mammals, and in relation to extending the multifunctional theory of the purposes of play to include the education of skilled hand movements for various adult functions including as feeding.

Human string-pulling with and without a string: movement, sensory control, and memory.

String-pulling is a behavior that is allied to many daily acts and is an easily performed action featuring hand-over-hand movements to reel in a string (or rope). String-pulling has been used as a test of perceptual and cognitive functions in many animal species, including human children, but its movements and sensory control have not been characterized. Male and female university students (n = 68) performed target-based or memory-based string-pulling in which they pulled down a string suspended on an overhead pulley and immediately afterwards attempted to make the same movement in a memory-based test. Frame-by-frame video scoring was used to describe movements, eye-tracking and visual occluding glasses were used to assess sensory control, and a Matlab video-analysis procedure was used to describe kinematics. The string was advanced using five arm/hand movements: with lift and advance comprising fast up movements, and grasp, pull and push comprising slow down movements. Fingers closed 5 (pinky) through 1 (thumb) to make a whole-hand grasp and release in target-based string pulling but moved in a reverse sequence for the memory-based task. Target-based string pulling was not visually guided unless participants were instructed to grasp at a cue, and then vision featured eye-tracking of the target and pupil dilation with the grasp, but there was no relation between eye events for memory-based string-pulling. For target-based string-pulling the left and right hands advanced the string with both independent and concurrent movement but only independent movements were featured in a more symmetrical memory-based movement. The results are discussed in relation to the sensory control of hand movements, contemporary theories of the neural control of hand movements, and species differences in string-pulling.

Gaze anchoring guides real but not pantomime reach-to-grasp: support for the action-perception theory.

Reach-to-grasp movements feature the integration of a reach directed by the extrinsic (location) features of a target and a grasp directed by the intrinsic (size, shape) features of a target. The action-perception theory suggests that integration and scaling of a reach-to-grasp movement, including its trajectory and the concurrent digit shaping, are features that depend upon online action pathways of the dorsal visuomotor stream. Scaling is much less accurate for a pantomime reach-to-grasp movement, a pretend reach with the target object absent. Thus, the action-perception theory proposes that pantomime movement is mediated by perceptual pathways of the ventral visuomotor stream. A distinguishing visual feature of a real reach-to-grasp movement is gaze anchoring, in which a participant visually fixates the target throughout the reach and disengages, often by blinking or looking away/averting the head, at about the time that the target is grasped. The present study examined whether gaze anchoring is associated with pantomime reaching. The eye and hand movements of participants were recorded as they reached for a ball of one of three sizes, located on a pedestal at arms' length, or pantomimed the same reach with the ball and pedestal absent. The kinematic measures for real reach-to-grasp movements were coupled to the location and size of the target, whereas the kinematic measures for pantomime reach-to-grasp, although grossly reflecting target features, were significantly altered. Gaze anchoring was also tightly coupled to the target for real reach-to-grasp movements, but there was no systematic focus for gaze, either in relation with the virtual target, the previous location of the target, or the participant's reaching hand, for pantomime reach-to-grasp. The presence of gaze anchoring during real vs. its absence in pantomime reach-to-grasp supports the action-perception theory that real, but not pantomime, reaches are online visuomotor actions and is discussed in relation with the neural control of real and pantomime reach-to-grasp movements.

Organization of the reach and grasp in head-fixed vs freely-moving mice provides support for multiple motor channel theory of neocortical organization.

Multiple motor channel (MMC) theory of neocortical organization proposes that complex movements, such as reaching for a food item to eat, are produced by the coordinated action of separate neural channels. For example, the human reach-to-grasp act is mediated by two visuo-parieto-motor cortex channels, one for the reach and one for the grasp. The present analysis asked whether there is a similar organization of reach-and-grasp movements in the mouse. The reach-to-eat movements of the same mice were examined from high-shutter speed, frame-by-frame video analysis in three tasks in which the mice obtained equivalent success scores: when freely-moving reaching for food pellets, when head-fixed reaching for food pellets, and when head-fixed reaching for pieces of pasta. To reach, the mice used egocentric cues to vary upper arm movements in a task-appropriate manner to place an open hand on the food or to locate the food using a "touch-release-grasp" strategy. Although mice could not hand-shape offline when reaching, they could hand-shape using online touch-related cues from the mouth to manipulate the food at the mouth. That the reach can be performed offline in relation to egocentric cues whereas hand shaping for the grasp requires online cues supports the idea that for the mouse, as for primates, the reach and grasp are separate acts. The results are further discussed in relation to the use of the head-fixed behavioral procedure to identify the independent neural substrates of the reach and the grasp using mesoscale stimulation/imaging methods.

The mane effect in the horse (Equus ferus caballus): Right mane dominance enhanced in mares but not associated with left and right manoeuvres in a reining competition.

A human physical asymmetry is the near 90% clockwise occipitoparietal scalp hair-whorl direction in Europeans, an incidence that approximates the left lateralization of speech and right-handedness. Hair-whorl direction is also asymmetric in horses, Equus ferus caballus and placement is proposed to be related to temperament and lateralized skill in equitation manoeuvres. We describe a hair-whorl asymmetry in the horse, mane direction. Of 526, 3-year-old American Quarter horses, 69% of horses had mane directed to the right and 31% had mane directed to the left. The bias was larger in females, with 74% of females vs. 65% of males having mane directed to the right. Mane direction was unrelated to coat colour. The behavioural significance of mane asymmetry was investigated using judges' scores from a reining competition requiring symmetrical maneuvers of spin, circle and roll-back to either the left or to the right. There was no relation between mane asymmetry and overall reining performance and no relation between mane direction and scores for left or right manoeuvres. The results are discussed in relation to the significance of morphological asymmetries, neural function and the influence of planar cell polarity genes, such as Frizzled, that influence epidermal hair cell patterning.

Synchrony of the Reach and the Grasp in pantomime reach-to-grasp.

The Dual Visuomotor Channel theory of reaching proposes that a reach-to-grasp act integrates a Reach, directed toward the extrinsic properties of the target (location), and a Grasp, directed toward the intrinsic properties of the target (size and shape). Previous studies of reach-to-grasp report that the Grasp is altered in pantomime tasks made from a starting position with digit 1 and digit 2 closed and proximal to the target. The present study extends the analysis of real versus pantomime reaching to a task that featured both a Reach and a Grasp, having a starting position with the hand open and proximal to the body. For a real reach, seated participants reached for a doughnut ball (food item) located on a pedestal at arms distance, with the intent of bringing the doughnut ball to the mouth for eating. Participants also made four pantomime reaches with: (1) the doughnut ball removed from the pedestal, (2) the doughnut ball and pedestal moved to the side of the reach location, (3) the doughnut ball and pedestal absent, and (4) the participants wearing vision-occluding glasses. There were two main findings. First, the presence of task-related cues, platform, doughnut ball, and room influenced the kinematics of the Reach and Grasp. Second, the compound structure of a real reach, in which flexion/extension of the arm featured in the Reach and flexion/extension of the digits featured in the Grasp are out of phase, changed in pantomime such that these features of Reach and Grasp became in phase. The results show that pantomime reaching is influenced not only by task-related percepts but also by central mechanisms ordinarily related to integrating the Reach and the Grasp.

Dissociation of the Reach and the Grasp in the destriate (V1) monkey Helen: a new anatomy for the dual visuomotor channel theory of reaching.

Dual visuomotor channel theory proposes that reaching depends on two neural pathways that extend from visual cortex (V1) to motor cortex via the parietal lobe. The Reach pathway directs the hand to the target's location and the Grasp pathway shapes the hand and digits for purchase. Sighted human participants integrate the Reach and the Grasp, but without vision they dissociate the movements to capitalize on tactile cues. They use a Reach with a relatively open hand to locate the target and then they use touch cues to shape the fingers to Grasp. After a V1 lesion, the rhesus monkey, Helen, learned to make near-normal visual discriminations based on size and brightness but displayed visual agnosia. She also learned to reach for food with her mouth and her hands. The present analysis of film of her reaching behavior shows that she dissociated the Reach and the Grasp, as do unsighted human participants reaching for a food target at a fixed location. Her rapid and direct Reach was made with an open hand and extended fingers to contact the food with the palm whereas her Grasp was initiated after she touched the food. She also visually fixated the target during the Reach and visually disengaged after target contact, as do sighted human participants. In contrast, Helen did integrate the Reach and the Grasp to take food from her mouth, demonstrating that she could integrate the movements using online tactile cues. The finding that extrastriate pathways can direct the hand toward extrinsic target properties (location) but not intrinsic target properties (size and shape) is discussed as a novel addition to dual visuomotor channel theory.

Construction of a global pain systems network highlights phospholipid signaling as a regulator of heat nociception.

The ability to perceive noxious stimuli is critical for an animal's survival in the face of environmental danger, and thus pain perception is likely to be under stringent evolutionary pressure. Using a neuronal-specific RNAi knock-down strategy in adult Drosophila, we recently completed a genome-wide functional annotation of heat nociception that allowed us to identify α2δ3 as a novel pain gene. Here we report construction of an evolutionary-conserved, system-level, global molecular pain network map. Our systems map is markedly enriched for multiple genes associated with human pain and predicts a plethora of novel candidate pain pathways. One central node of this pain network is phospholipid signaling, which has been implicated before in pain processing. To further investigate the role of phospholipid signaling in mammalian heat pain perception, we analysed the phenotype of PIP5Kα and PI3Kγ mutant mice. Intriguingly, both of these mice exhibit pronounced hypersensitivity to noxious heat and capsaicin-induced pain, which directly mapped through PI3Kγ kinase-dead knock-in mice to PI3Kγ lipid kinase activity. Using single primary sensory neuron recording, PI3Kγ function was mechanistically linked to a negative regulation of TRPV1 channel transduction. Our data provide a systems map for heat nociception and reinforces the extraordinary conservation of molecular mechanisms of nociception across different species.

Absence of population asymmetry in the American Quarter Horse (Equus ferus caballus) performing skilled left and right manoeuvres in reining competition.

Use of the right hand by humans for speech-related hand gestures, writing and throwing exemplifies motoric asymmetry. There are reports of asymmetry in many other animal species, including reports of left preference in emotional responsivity, spontaneous behaviour and the trained performance of the horse, Equus ferus caballus. The present study used the novel approach of using judges' scores to examine asymmetry in an equestrian event. The study analysed the scores of five judges evaluating the reining performance of 482, three-year-old American Quarter Horses competing in a major competition. Reining requires that the horses perform the manoeuvres of spin, circle and stop directed to either the left or right and symmetrical performance is featured in the judging criteria. The scores were sensitive to performance level, sex and manoeuvre, but there was no evidence of a population asymmetry in the left vs. right direction of the manoeuvres. The results are discussed in relation to need of using a large number of subjects in measuring asymmetry, the expression of individual vs. population asymmetry as a function of morphological and behavioural measures, and the influence of behavioural training on asymmetry.

Haptic grasping configurations in early infancy reveal different developmental profiles for visual guidance of the Reach versus the Grasp.

The Dual Visuomotor Channel theory posits that reaching consists of two movements mediated by separate but interacting visuomotor pathways that project from occipital to parietofrontal cortex. The Reach transports and orients the hand to the target while the Grasp opens and closes the hand for target purchase. Adults rely on foveal vision to synchronize the Reach and the Grasp so that the hand orients, opens, and largely closes by the time it gets to the target. Young infants produce discrete preReach and preGrasp movements, but it is unclear how these movements become synchronized under visual control throughout development. High-speed 3-D video recordings and linear kinematics were used to analyze reaching components, hand orientation, hand aperture, and grasping strategy in infants aged 4-24 months compared with adults who reached with and without vision. Infants aged 4-8 months resembled adults reaching without vision; in that, they delayed both Reach orientation and Grasp closure until after target contact, suggesting that they relied primarily on haptic cues to guide reaching. Infants aged 9-24 months oriented the Reach prior to target contact, but continued to delay the majority of Grasp closure until after target contact, suggesting that they relied on vision for the Reach versus haptics for the Grasp. Changes in sensorimotor control were associated with sequential Reach and Grasp configurations in early infancy versus partially synchronized Reach and Grasp configurations in later infancy. The results argue that (1) haptic inputs likely contribute to the initial development of separate Reach and Grasp pathways in parietofrontal cortex; (2) the Reach and the Grasp are adaptively uncoupled during development, likely to capitalize on different sensory inputs at different developmental stages; and (3) the developmental transition from haptic to visual control is asymmetrical with visual guidance of the Reach preceding that of the Grasp.

Reach and Grasp reconfigurations reveal that proprioception assists reaching and hapsis assists grasping in peripheral vision.

The dual visuomotor channel theory proposes that prehension consists of a Reach that transports the hand in relation to an object's extrinsic properties (e.g., location) and a Grasp that shapes the hand to an object's intrinsic properties (e.g., size and shape). In central vision, the Reach and the Grasp are integrated but when an object cannot be seen, the movements can decompose with the Reach first used to locate the object and the Grasp postponed until it is assisted by touch. Reaching for an object in a peripheral visual field is an everyday act, and although it is reported that there are changes in Grasp aperture with target eccentricity, it is not known whether the configuration of the Reach and the Grasp also changes. The present study examined this question by asking participants to reach for food items at 0° or 22.5° and 45° from central gaze. Participants made 15 reaches for a larger round donut ball and a smaller blueberry, and hand movements were analyzed using frame-by-frame video inspection and linear kinematics. Perception of targets was degraded as participants could not identify objects in peripheral vision but did recognize their differential size. The Reach to peripheral targets featured a more dorsal trajectory, a more open hand, and less accurate digit placement. The Grasp featured hand adjustments or target manipulations after contact, which were associated with a prolonged Grasp duration. Thus, Grasps to peripheral vision did not consist only of a simple modification of visually guided reaching but included the addition of somatosensory assistance. The kinematic and behavioral changes argue that proprioception assists the Reach and touch assists the Grasp in peripheral vision, supporting the idea that Reach and Grasp movements are used flexibly in relation to sensory guidance depending upon the salience of target properties.

Adaptive forgetting of place/object memory for dung in the domestic horse (Equus ferus caballus): Memory for a day.

The domestic horse (Equus ferus caballus) makes dung deposits to form "stud-piles" and compulsively examines dung droppings, suggesting that dung contains species-relevant information. The present study investigates horses' use of location (place), odor (object) and memory for dung sniff encounters. Horses were video recorded in 2 indoor and 4 outdoor riding arenas as they were taken at different time intervals to experimenter-determined objects or dung deposits that they could sniff. Frame-by-frame video analysis measured approaches, sniff duration, nostril use, ear position and blinking associated with dung investigation. Horses approached and sniffed dung-deposits for longer duration than non-dung objects in all test locations. They made head movements across the extent of dung-deposits when sniffing, showed no nostril or ear preference directed to the target, and blinked as they disengage from sniffing. Reduced approach probability and sniff duration showed that they displayed good place/object memory for dung previously visited at similar and different locations on the same day but poor memory for dung visited on a previous day. Adaptive forgetting of object/place memory for dung after a previous day's dung visit may optimizes risk assessment, including the possibility of premature interruption of foraging by conspecifics.

Nonvisual learning of intrinsic object properties in a reaching task dissociates grasp from reach.

The Dual Visuomotor Channel theory proposes that skilled reaching is composed of a Reach that directs the hand in relation to the extrinsic properties of an object (e.g., location) and a Grasp that opens and closes the hand in relation to the intrinsic properties of an object (e.g., size). While Reach and Grasp movements are often guided by vision, they can also be performed without vision when reaching for a body part or an object on one's own body. Memory of a recently touched but unseen object can also be used to guide Reach and Grasp movements although the touch-response memory durations described are extremely brief (Karl et al. in Exp Brain Res 219:59-74, 2012a). The purpose of the present study was to determine whether repeated nonvisual reaching for a consistent object could calibrate Reach and Grasp movements in a way similar to those guided by vision. The nonvision group wore vision-occluding goggles and reached for fifty consecutive trials for a round donut ball placed on a pedestal. The control group performed the same task with vision. Frame-by-frame video analysis and linear kinematics revealed that nonvision participants consistently used an elevated Reach trajectory, in which the hand, rather than being directed toward the target in the horizontal plane, was first elevated above the target before being lowered to touch and locate it. First contact was established with the dorsal surface of the target, and thus, adjustments in contact locations were often required for purchase. Although nonvision participants initially used an open and extended hand during transport, with practice they began to scale digit aperture to object size with an accuracy and temporal relation similar to vision participants. The different ways in which the Reach and Grasp movements respond to nonvisual learning are discussed in relation to support for the dual channel theory of reaching and to the idea that the Reach and Grasp channels may be differentially dependent on online visual guidance.

Precocious hand use preference in reach-to-eat behavior versus manual construction in 1- to 5-year-old children.

The variation in hand use as a function of task and developmental age poses a problem for understanding how and when "handedness," preferred use of one hand, develops. The present cross-section study is the first to contrast hand preference use for the natural and frequently used reach-to-eat movement with a constructional task that requires a very similar reach-to-grasp movement. Thirty children between the ages of 1 and 3 years completed an eating task, in which they grasped small food items (Cheerios™ or Froot Loops™) that they brought to the mouth for eating. Thirty children between the ages of 3 and 5 years completed the construction task, in which they grasped LEGO® pieces to construct 3D models. Hand use preference for grasping in the eating and construction tasks was calculated by comparing the percentage of grasps made by the right hand and by the left hand. There were two main findings: First, right hand preference for grasping in the eating task is present as early as 1 year of age, whereas right hand preference for grasping in the construction task does not develop until 4 years of age. Second, right hand preference for grasping is greater in the eating than in the construction task. The results are discussed in relation to the idea that a consideration for task constraints (e.g., unimanual vs. bimanual; eating vs. construction; natural vs. praxic) should be incorporated into the experimental design when measuring hand use in children.

Hippocampal conjunctive and complementary CA1 populations relate sensory events to movement.

Hippocampal CA1 neurons respond to sensory stimuli during enforced immobility, movement, and their transitions in a new conveyor belt task. Head-fixed mice were exposed to light flashes or air streams while at rest, spontaneously moving, or running a fixed distance. Two-photon calcium imaging of CA1 neurons revealed that 62% of 3341 imaged cells were active during one or more of 20 sensorimotor events. Of these active cells, 17% were active for any given sensorimotor event, with a higher proportion during locomotion. The study found two types of cells: Conjunctive cells that were active across multiple events, and complementary cells that were active only during individual events, encoding novel sensorimotor events or their delayed repetitions. The configuration of these cells across changing sensorimotor events may signify the role of hippocampus in functional networks integrating sensory information with ongoing movement making it suitable for movement guidance.

Impairments and compensation in string-pulling after middle cerebral artery occlusion in the rat.

Stroke is a leading cause of long-term disability in humans, and it is frequently associated with impairments in the skilled use of the arms and hands. Many human upper limb impairments and compensatory changes have been successfully modeled in rodent studies of neocortical stroke, especially those that evaluate single limb use in tasks, such as reaching for food. Humans also use their hands for bilaterally coordinated movements, dependent upon interhemispheric cortical projections, which are also compromised by unilateral stroke. This study describes middle cerebral artery occlusion (MCAO) dependent changes in the bilaterally dependent hand use behavior of string-pulling in the rat. The task involves making hand-over-hand movements to pull down a string that contains a food reward attached to its end. MCAO rats missed the string more often with both hands than Sham rats. When the string was missed on the contralateral to MCAO body side, rats continued to cycle through subcomponents of string-pulling behavior as if the string were grasped in the hand. Rats also failed to make a grasping motion with the contralateral to MCAO hand when the string was missed and instead, demonstrated an open-handed raking-like motions. Nevertheless, with repeated attempts, rats performed components of string-pulling well enough to obtain a reward on the end of the string. Thus, string-pulling behavior is sensitive to bilateral impairments but is achieved with compensatory adjustments following MCAO. These aspects of MCAO string-pulling provide a foundation for studies that investigate the efficacy of therapeutic intervention which might enhance neuroplasticity and recovery.

Cortical network and projection neuron types that articulate serial order in a skilled motor behavior.

Skilled motor behaviors require orderly coordination of multiple constituent movements with sensory cues towards achieving a goal, but the underlying brain circuit mechanisms remain unclear. Here we show that target-guided reach-grasp-to-drink (RGD) in mice involves the ordering and coordination of a set of forelimb and oral actions. Cortex-wide activity imaging of multiple glutamatergic projection neuron (PN) types uncovered a network, involving the secondary motor cortex (MOs), forelimb primary motor and somatosensory cortex, that tracked RGD movements. Photo-inhibition highlighted MOs in coordinating RGD movements. Within the MOs, population neural trajectories tracked RGD progression and single neuron activities integrated across constituent movements. Notably, MOs intratelencephalic, pyramidal tract, and corticothalamic PN activities correlated with action coordination, showed distinct neural dynamics trajectories, and differentially contributed to movement coordination. Our results delineate a cortical network and key areas, PN types, and neural dynamics therein that articulate the serial order and coordination of a skilled behavior.

Weak-hyperactive hippocampal CA1 neurons in the prodromal stage of Alzheimer's disease in hybrid AppNL-G-F/NL-G-F × Thy1-GCaMP6s+/- mice suggest disrupted plasticity.

This study investigated the impact of familial Alzheimer's disease (AD)-linked amyloid precursor protein (App) mutations on hippocampal CA1 neuronal activity and function at an early disease stage in AppNL-G-F/NL-G-F × Thy1-GCaMP6s+/- (A-TG) mice using calcium imaging. Longitudinal assessment of spatial behavior at 12 and 18 months of age identified an early disease stage at 12 months when there was significant amyloid beta pathology with mild behavioral deficits. Hippocampal CA1 neuronal activity and event-related encoding of distance and time were therefore assessed at 12 months of age in several configurations of an air-induced running task to assess the dynamics of cellular activity. Neurons in A-TG mice displayed diminished (weaker) and more frequent (hyperactive) neuronal firing that was more pronounced during movement compared to immobility. Responsive neurons showed configuration-specific deficits in distance and time encoding with impairment in adapting their responses to changing configurations. These results suggest that at an early stage of AD in the absence of full-blown behavioral deficits, weak-hyperactive neuronal activity may induce impairments in sensory perception of changing environments.