Spontaneous forelimb grasping in free feeding by rats: motor cortex aids limb and digit positioning

The relationship between distal trunk morphology and object grasping in the African savannah elephant (Loxodonta africana)

Background

During reach-to-grasp movements, the human hand is preshaped depending on the properties of the object. Preshaping may result from learning, morphology, or motor control variability and can confer a selective advantage on that individual or species. This preshaping ability is known in several mammals (i.e., primates, carnivores and rodents). However, apart from the tongue preshaping of lizards and chameleons, little is known about preshaping of other grasping appendages. In particular, the elephant trunk, a muscular hydrostat, has impressive grasping skills and thus is commonly called a hand. Data on elephant trunk grasping strategies are scarce, and nothing is known about whether elephants preshape their trunk tip according to the properties of their food.

Methods

To determine the influence of food sizes and shapes on the form of the trunk tip, we investigated the morphology of the distal part of the trunk during grasping movements. The influence of food item form on trunk tip shape was quantified in six female African savannah elephants (Loxodonta africana). Three food item types were presented to the elephants (elongated, flat, and cubic), as well as three different sizes of cubic items. A total of 107 ± 10 grips per individual were video recorded, and the related trunk tip shapes were recorded with a 2D geometric morphometric approach.

Results

Half of the individuals adjusted the shape of the distal part of their trunk according to the object type. Of the three elephants that did not preshape their trunk tip, one was blind and another was subadult.

Discussion and perspectives

We found that elephants preshaped their trunk tip, similar to the preshaping of other species' hands or paws during reach-to-grasp movements. This preshaping may be influenced by visual feedback and individual learning. To confirm these results, this study could be replicated with a larger sample of elephants.

The neural mechanisms of manual dexterity

The hand endows us with unparalleled precision and versatility in our interactions with objects, from mundane activities such as grasping to extraordinary ones such as virtuoso pianism. The complex anatomy of the human hand combined with expansive and specialized neuronal control circuits allows a wide range of precise manual behaviours. To support these behaviours, an exquisite sensory apparatus, spanning the modalities of touch and proprioception, conveys detailed and timely information about our interactions with objects and about the objects themselves. The study of manual dexterity provides a unique lens into the sensorimotor mechanisms that endow the nervous system with the ability to flexibly generate complex behaviour.

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.

Training in a cooperative bimanual skilled reaching task, the popcorn retrieval task, improves unimanual function after motor cortical infarcts in rats

Disuse of the paretic hand after stroke is encouraged by compensatory reliance on the nonparetic hand, to exacerbate impairment and potentially constrain motor rehabilitation efficacy. Rodent stroke model findings support that learning new unimanual skills with the nonparetic forelimb diminishes functional improvements that can be driven by rehabilitative training of the paretic forelimb. The influence of learning new ways of skillfully using the two hands together on paretic side function is much less clear. To begin to explore this, we developed a new cooperative bimanual skilled reaching task for rats, the Popcorn Retrieval Task. After motor cortical infarcts impaired an established unimanual reaching skill in the paretic forelimb, rats underwent a 7 week period of de novo bimanual training (BiT) or no-training control procedures (Cont). Probes of paretic forelimb unimanual performance revealed significant improvements during and after the training period in BiT vs. Cont. We additionally observed a striking change in the bimanual task strategy over training days: a switch from the paretic to the nonparetic forelimb for initiating reach-to-grasp sequences. This motivated another study to test whether rats that established the bimanual skill prior to the infarcts would similarly switch handedness, which they did not, though paretic paw use for manipulative movements diminished. These results indicate that unimanual function of the paretic side can be improved by novel bimanual skill practice, even when it involves compensatory reliance on the nonparetic hand. They further support the suitability of the Popcorn Retrieval Task for studying bimanual skill learning effects in rats.

Mouse Arm and hand movements in grooming are reaching movements: Evolution of reaching, handedness, and the thumbnail

Grooming in the mouse features hand licking and symmetric and asymmetric arm and hand "strokes" over the face and body to maintain pelage. Grooming is syntactically organized but the structure of individualized movements of the arm, hand, and tongue have not been examined. Here spontaneous and water-induced grooming was video recorded in free-moving and head-fixed mice and subject to frame-by-frame video inspection and kinematic analysis using Physics Tracker. All groom arm and hand movements had a structure similar to that described for reach-to-eat movements. The movement included the hand lifting from the floor to supinate with the digits flexing and closed to a collect position, an aim position directed to a groom target, an advance to the target during which the fingers extend and open and the hand pronates, a grasp of a target on the snout, nose, or vibrissae, and a withdraw to the mouth where licking occurs, or a return to the starting position. This structure was present in individual unilateral forelimb groom strokes, in bilateral symmetric, or asymmetric groom strokes, and comprised the individuated components of a sequence of groom movements. Reach-to-groom movements could feature an ulnar adduction that positions the ulnar portion of the hand including and the thumb across the eye and nose, a movement that aids Hardarian fluid spreading. It is proposed that the mouse thumb nail is an anatomical feature that minimizes damage to the eye or nose that might be incurred by a claw. This analysis of the reach-to-groom movement provides insights into the flexibility of hand use in adaptive behavior, the evolution of skilled reaching movements, the neural control of reaching movements and the presence of the thumb nail in the mouse.

Manual dexterity of mice during food-handling involves the thumb and a set of fast basic movements

The small first digit (D1) of the mouse's hand resembles a volar pad, but its thumb-like anatomy suggests ethological importance for manipulating small objects. To explore this possibility, we recorded high-speed close-up video of mice eating seeds and other food items. Analyses of ethograms and automated tracking with DeepLabCut revealed multiple distinct microstructural features of food-handling. First, we found that mice indeed made extensive use of D1 for dexterous manipulations. In particular, mice used D1 to hold food with either of two grip types: a pincer-type grasp, or a "thumb-hold" grip, pressing with D1 from the side. Thumb-holding was preferentially used for handling smaller items, with the smallest items held between the two D1s alone. Second, we observed that mice cycled rapidly between two postural modes while feeding, with the hands positioned either at the mouth (oromanual phase) or resting below (holding phase). Third, we identified two highly stereotyped D1-related movements during feeding, including an extraordinarily fast (~20 ms) "regrip" maneuver, and a fast (~100 ms) "sniff" maneuver. Lastly, in addition to these characteristic simpler movements and postures, we also observed highly complex movements, including rapid D1-assisted rotations of food items and dexterous simultaneous double-gripping of two food fragments. Manipulation behaviors were generally conserved for different food types, and for head-fixed mice. Wild squirrels displayed a similar repertoire of D1-related movements. Our results define, for the mouse, a set of kinematic building-blocks of manual dexterity, and reveal an outsized role for D1 in these actions.

Altered Recruitment of Motor Cortex Neuronal Activity During the Grasping Phase of Skilled Reaching in a Chronic Rat Model of Unilateral Parkinsonism

Parkinson's disease causes prominent difficulties in the generation and execution of voluntary limb movements, including regulation of distal muscles and coordination of proximal and distal movement components to achieve accurate grasping. Difficulties with manual dexterity have a major impact on activities of daily living. We used extracellular single neuron recordings to investigate the neural underpinnings of parkinsonian movement deficits in the motor cortex of chronic unilateral 6-hydroxydopamine lesion male rats performing a skilled reach-to-grasp task the. Both normal movements and parkinsonian deficits in this task have striking homology to human performance. In lesioned animals there were several differences in the activity of cortical neurons during reaches by the affected limb compared with control rats. These included an increase in proportions of neurons showing rate decreases, along with increased amplitude of their average rate-decrease response at specific times during the reach, suggesting a shift in the balance of net excitation and inhibition of cortical neurons; a significant increase in the duration of rate-increase responses, which could result from reduced coupling of cortical activity to specific movement components; and changes in the timing and incidence of neurons with pure rate-increase or biphasic responses, particularly at the end of reach when grasping would normally be occurring. The changes in cortical activity may account for the deficits that occur in skilled distal motor control following dopamine depletion, and highlight the need for treatment strategies targeted toward modulating cortical mechanisms for fine distal motor control in patients.SIGNIFICANCE STATEMENT We show for the first time in a chronic lesion rat model of Parkinson's disease movement deficits that there are specific changes in motor cortex neuron activity associated with the grasping phase of a skilled motor task. Such changes provide a possible mechanism underpinning the problems with manual dexterity seen in Parkinson's patients and highlight the need for treatment strategies targeted toward distal motor control.

The temporal choreography of the yo-yo movement of getting spaghetti into the mouth by the head-fixed mouse

There is debate over whether single-handed eating movements, reaching for food and withdrawing the hand to place the food in the mouth, originated in the primate lineage or whether they originated in phylogenetically-earlier Euarchontoglires. Most spontaneous hand use in eating by the laboratory mouse (Mus domestica) involves both hands, and a central question is the extent to which the movements are symmetric. Here we describe an asymmetry of spontaneous single hand use by the head-fixed mouse in making the yo-yo hand movement of removing and replacing a piece of pasta (spaghetti) in the mouth for eating. We also describe the problem/solution of placing into the mouth the end of a held item that protrudes at some distance from the hand. Pasta-eating proceeds in bouts, and a bout starts with raising the hands, which are holding a piece of pasta, to place one end of the pasta in the mouth for biting. A bout ends with lowering the hands, still holding the pasta stem, while the pasta morsel that has been bitten off is chewed. Hand-lowering after the pasta is removed from the mouth is slow, concurrent and symmetric, both when the pasta is held by both hands and when it is held in one hand. Hand-raising to place the pasta in the mouth is fast, consecutive and asymmetric, both when the pasta is held in both hands and when it is held in one hand. Frame-by-frame analyses of the video record combined with kinematic analyses show that a preferred single hand not only directs one end of the pasta to the mouth but also readjusts the trajectory of the pasta if it misses the mouth. The specialized use of a single hand by the mouse, even when the hands are bilaterally engaged, and the corrective asymmetric movements with which one hand adjusts the pasta's trajectory with the other hand playing a supporting role, is discussed in relation to the idea that hand preference, specialization, and dexterity have somatosensory and preprimate origins.

A kinematic study of skilled reaching movement in rat

BACKGROUND

In the rat, the single-pellet reaching task includes orienting, reaching, grasping and retracting movements. It has previously been described by notation techniques, high-speed video and cineradiographic recordings. Recently, high-definition cameras have been used to track paw and digit movements with DeepLabCut, a machine-learning algorithm for markerless estimation of paw position.

NEW METHOD

Our new approach consists of positioning three high-speed infrared digital cameras to track the full motion of markers on the rat's body. This provided a previously unavailable 3D recording of skilled reaching kinematics in the rat moving freely in the reaching box, which were analysed by Qualisys Track Manager software and MATLAB.

RESULTS

This method enabled description of kinematic parameters unobtainable without motion tracking and provided insight into the spatiotemporal metrics of movements used to perform skilled reaching. It revealed that orientation features three steps and reaching has two bimodal start-point distributions, one along the horizontal axis and one along the vertical axis. At the end of reaching, the wrist/paw occupies the same position as the nose at the end of orienting. In grasping, averaging trajectories confirmed the marker lowering and target approaching.

COMPARISON WITH EXISTING METHODS

Our method required significantly reduced time to label data and obviates the need for off-line manual marking of videos. It provides an efficient means of capturing volumes containing the entire range of marker movements.

CONCLUSIONS

This study validated a new and efficient approach for quantifying rat movement kinematics, useful for comparing preclinical and clinical conditions.

A mouse's spontaneous eating repertoire aids performance on laboratory skilled reaching tasks: A motoric example of instinctual drift with an ethological description of the withdraw movements in freely-moving and head-fixed mice

Rodents display a spontaneous "order-common" pattern of food eating: they pick up food using the mouth, sit on their haunches, and transfer the food to the hands for handling/chewing. The present study examines how this pattern of behaviour influences performance on "skilled-reaching" tasks, in which mice purchase food with a single hand. Here five types of withdraw movement, the retraction of the hand, in three reaching tasks: freely-moving single-pellet, head-fixed single-pellet, and head-fixed pasta-eating is described. The withdraw movement varied depending upon whether a reach was anticipatory, no food present, or was unsuccessful or successful with food present. Ease of withdraw is dependent upon the extent to which animals used order-common movements. For freely-moving mice, a hand-to-mouth movement was assisted by a mouth-to-hand movement and food transfer to the mouth depended upon a sitting posture and using the other hand to assist food holding, both order-common movements. In the head-fixed single-pellet task, with postural and head movements prevented, withdraw was made with difficulty and tongue protrude movements assisted food transfer to the mouth once the hand reached the mouth. Only when a head-fixed mouse made a bilateral hand-to-mouth movement, a component of order-common eating, was the withdraw movement made with ease. The results are discussed with respect to the use of order-common movements in skilled-reaching tasks and with respect to the optimal design of tasks used to assess rodent skilled hand movement.

The syntactic organization of pasta-eating and the structure of reach movements in the head-fixed mouse

Mice are adept in the use of their hands for activities such as feeding, which has led to their use in investigations of the neural basis of skilled-movements. We describe the syntactic organization of pasta-eating and the structure of hand movements used for pasta manipulation by the head-fixed mouse. An ethogram of mice consuming pieces of spaghetti reveals that they eat in bite/chew bouts. A bout begins with pasta lifted to the mouth and then manipulated with hand movements into a preferred orientation for biting. Manipulation involves many hand release-reach movements, each with a similar structure. A hand is advanced from a digit closed and flexed (collect) position to a digit extended and open position (overgrasp) and then to a digit closed and flexed (grasp) position. Reach distance, hand shaping, and grasp patterns featuring precision grasps or whole hand grasps are related. To bite, mice display hand preference and asymmetric grasps; one hand (guide grasp) directs food into the mouth and the other stabilizes the pasta for biting. When chewing after biting, the hands hold the pasta in a symmetric resting position. Pasta-eating is organized and features structured hand movements and so lends itself to the neural investigation of skilled-movements.

Compensatory limb use and behavioral assessment of motor skill learning following sensorimotor cortex injury in a mouse model of ischemic stroke

Mouse models have become increasingly popular in the field of behavioral neuroscience, and specifically in studies of experimental stroke. As models advance, it is important to develop sensitive behavioral measures specific to the mouse. The present protocol describes a skilled motor task for use in mouse models of stroke. The Pasta Matrix Reaching Task functions as a versatile and sensitive behavioral assay that permits experimenters to collect accurate outcome data and manipulate limb use to mimic human clinical phenomena including compensatory strategies (i.e., learned non-use) and focused rehabilitative training. When combined with neuroanatomical tools, this task also permits researchers to explore the mechanisms that support behavioral recovery of function (or lack thereof) following stroke. The task is both simple and affordable to set up and conduct, offering a variety of training and testing options for numerous research questions concerning functional outcome following injury. Though the task has been applied to mouse models of stroke, it may also be beneficial in studies of functional outcome in other upper extremity injury models.

Different evolutionary origins for the reach and the grasp: an explanation for dual visuomotor channels in primate parietofrontal cortex

The Dual Visuomotor Channel Theory proposes that manual prehension consists of two temporally integrated movements, each subserved by distinct visuomotor pathways in occipitoparietofrontal cortex. The Reach is mediated by a dorsomedial pathway and transports the hand in relation to the target's extrinsic properties (i.e., location and orientation). The Grasp is mediated by a dorsolateral pathway and opens, preshapes, and closes the hand in relation to the target's intrinsic properties (i.e., size and shape). Here, neuropsychological, developmental, and comparative evidence is reviewed to show that the Reach and the Grasp have different evolutionary origins. First, the removal or degradation of vision causes prehension to decompose into its constituent Reach and Grasp components, which are then executed in sequence or isolation. Similar decomposition occurs in optic ataxic patients following cortical injury to the Reach and the Grasp pathways and after corticospinal tract lesions in non-human primates. Second, early non-visual PreReach and PreGrasp movements develop into mature Reach and Grasp movements but are only integrated under visual control after a prolonged developmental period. Third, comparative studies reveal many similarities between stepping movements and the Reach and between food handling movements and the Grasp, suggesting that the Reach and the Grasp are derived from different evolutionary antecedents. The evidence is discussed in relation to the ideas that dual visuomotor channels in primate parietofrontal cortex emerged as a result of distinct evolutionary origins for the Reach and the Grasp; that foveated vision in primates serves to integrate the Reach and the Grasp into a single prehensile act; and, that flexible recombination of discrete Reach and Grasp movements under various forms of sensory and cognitive control can produce adaptive behavior.

Beyond the silence: bilateral somatosensory stimulation enhances skilled movement quality and neural density in intact behaving rats

It is thought that a close dialogue between the primary motor (M1) and somatosensory (S1) cortices is necessary for skilled motor learning. The extent of the relative S1 contribution in producing skilled reaching movements, however, is still unclear. Here we used anodal transcranial direct current stimulation (tDCS), which is able to alter polarity-specific excitability in the S1, to facilitate skilled movement in intact behaving rats. We hypothesized that the critical role of S1 in reaching performance can be enhanced by bilateral tDCS. Pretrained rats were assigned to control or stimulation conditions: (1) UnAno: the unilateral application of an anodal current to the side contralateral to the paw preferred for reaching; (2) BiAno1: bilateral anodal current; (3) BiAno2: a bilateral anodal current with additional 30ms of 65μA pulses every 5s. Rats received tDCS (65μA; 10min/rat) to the S1 during skilled reach training for 20 days (online-effect phase). After-effect assessment occurred for the next ten days in the absence of electrical stimulation. Quantitative and qualitative analyses of online-effects of tDCS showed that UnAno and BiAno1 somatosensory stimulation significantly improve skilled reaching performance. Bilateral BiAno1 stimulation was associated with greater qualitative functional improvement than unilateral UnAno stimulation. tDCS-induced improvements were not observed in the after-effects phase. Quantitative cytoarchitectonic analysis revealed that somatosensory tDCS bilaterally increases cortical neural density. The findings emphasize the central role of bilateral somatosensory feedback in skill acquisition through modulation of cortico-motor excitability.

Post-stroke protection from maladaptive effects of learning with the non-paretic forelimb by bimanual home cage experience in C57BL/6 mice

Behavioral experience, in the form of skilled limb use, has been found to impact the structure and function of the central nervous system, affecting post-stroke behavioral outcome in both adaptive and maladaptive ways. Learning to rely on the less-affected, or non-paretic, body side is common following stroke in both humans and rodent models. In rats, it has been observed that skilled learning with the non-paretic forelimb following ischemic insult leads to impaired or delayed functional recovery of the paretic limb. Here we used a mouse model of focal motor cortical ischemic injury to examine the effects of non-paretic limb training following unilateral stroke. In addition, we exposed some mice to increased bimanual experience in the home cage following stroke to investigate the impact of coordinated dexterous limb use on the non-paretic limb training effect. Our results confirmed that skilled learning with the non-paretic limb impaired functional recovery following stroke in C56BL/6 mice, as it does in rats. Further, this effect was avoided when the skill learning of the non-paretic limb was coupled with increased dexterous use of both forelimbs in the home cage. These findings further establish the mouse as an appropriate model in which to study the neural mechanisms of recovery following stroke and extend previous findings to suggest that the dexterous coordinated use of the paretic and non-paretic limb can promote functional outcome following injury.

Oral hapsis guides accurate hand preshaping for grasping food targets in the mouth

Preshaping the digits and orienting the hand when reaching to grasp a distal target is proposed to be optimal when guided by vision. A reach-to-grasp movement to an object in one's own mouth is a natural and commonly used movement, but there has been no previous description of how it is performed. The movement requires accuracy but likely depends upon haptic rather than visual guidance, leading to the question of whether the kinematics of this movement are similar to those with vision or whether the movement depends upon an alternate strategy. The present study used frame-by-frame video analysis and linear kinematics to analyze hand movements as participants reached for ethologically relevant food targets placed either at a distal location or in the mouth. When reaching for small and medium-sized food items (blueberries and donut balls) that had maximal lip-to-target contact, hand preshaping was equivalent to that used for visually guided reaching. When reaching for a large food item (orange slice) that extended beyond the edges of the mouth, hand preshaping was suboptimal compared to vision. Nevertheless, hapsis from the reaching hand was used to reshape and reorient the hand after first contact with the large target. The equally precise guidance of hand preshaping under oral hapsis is discussed in relation to the idea that hand preshaping, and its requisite neural circuitry, may have originated under somatosensory control, with secondary access by vision.

The emergence of somatotopic maps of the body in S1 in rats: the correspondence between functional and anatomical organization

Most of what we know about cortical map development and plasticity comes from studies in mice and rats, and for the somatosensory cortex, almost exclusively from the whisker-dominated posteromedial barrel fields. Whiskers are the main effector organs of mice and rats, and their representation in cortex and subcortical pathways is a highly derived feature of murine rodents. This specialized anatomical organization may therefore not be representative of somatosensory cortex in general, especially for species that utilize other body parts as their main effector organs, like the hands of primates. For these reasons, we examined the emergence of whole body maps in developing rats using electrophysiological recording techniques. In P5, P10, P15, P20 and adult rats, multiple recordings were made in the medial portion of S1 in each animal. Subsequently, these functional maps were related to anatomical parcellations of S1 based on a variety of histological stains. We found that at early postnatal ages (P5) medial S1 was composed almost exclusively of the representation of the vibrissae. At P10, other body part representations including the hindlimb and forelimb were present, although these were not topographically organized. By P15, a clear topographic organization began to emerge coincident with a reduction in receptive field size. By P20, body maps were adult-like. This study is the first to describe how topography of the body develops in S1 in any mammal. It indicates that anatomical parcellations and functional maps are initially incongruent but become tightly coupled by P15. Finally, because anatomical and functional specificity of developing barrel cortex appears much earlier in postnatal life than the rest of the body, the entire primary somatosensory cortex should be considered when studying general topographic map formation in development.

The vermicelli and capellini handling tests: simple quantitative measures of dexterous forepaw function in rats and mice

Previous characterizations of rodent eating behavior have revealed that they use coordinated forepaw movements to manipulate food pieces. We have extended upon this work to develop a simple quantitative measure of forepaw dexterity that is sensitive to lateralized impairments and age-dependent changes. Rodents learn skillful forepaw and digit movements to manage thin pasta pieces, which they eagerly consume. We have previously described methods for quantifying vermicelli handling in rats and showed that the measures are very sensitive to forelimb impairments resulting from unilateral ischemic lesions, middle cerebral artery occlusions and unilateral striatal dopamine depletion [Allred, R.P., Adkins, D.L., Woodlee, M.T., Husbands, L.C., Maldonado M.A., Kane, J.R., Schallert, T. & Jones, T.A. The Vermicelli Handling Test: a simple quantitative measure of dexterous forepaw function in rats. J. Neurosci. Methods 170, 229-244 (2008)]. Here we present a more detailed protocol for this test in rats and compare it with a newly developed version for mice, the Capellini Handling Test. Rats and mice are videotaped while handling short lengths of uncooked vermicelli or capellini pasta, respectively, with a camera positioned to optimize the view of paw movements. Slow motion video playback allows for the identification of forepaw adjustments, defined as any distinct removal and replacement of the paw, or of any number of digits, on the pasta piece after eating commences. Forepaw adjustments per piece are averaged over trials per each testing session. Repeated testing permits sensitive quantitative analysis of changes in forepaw dexterity over time. Protocols for pre-testing habituation and handling practice, as well as procedures for characterizing atypical handling patterns, are described. Because rats and mice perform the pasta handling tests slightly differently, species-specific differences in administration and scoring of these tests are highlighted. All animal use was in accordance with protocols approved by the University of Texas at Austin Animal Care and Use Committee.

Rats' learning of a new motor skill: insight into the evolution of motor sequence learning

Recent behavioral and neural evidence has suggested that ethologically relevant sub-movements (movement primitives) are used by primates for more complex motor skill learning. These primitives include extending the hand, grasping an object, and holding food while moving it toward the mouth. In prior experiments with rats performing a reach-to-grasp-food task, we observed that especially during early task learning, rats appeared to have movement primitives similar to those seen in primates. Unlike primates, however, during task learning the rats performed these sub-movements in a disordered manner not seen in humans or macaques, e.g. with the rat chewing before placing the food pellet in its mouth. Here, in two experiments, we tested the hypothesis that for rats, learning this ecologically relevant skill involved learning to concatenate the sub-movements in the correct order. The results confirmed our initial observations, and suggested that several aspects of forepaw/hand use, taken for granted in primate studies, must be learned by rats to perform a logically connected and seemingly ecologically important series of sub-movements. We discuss our results from a comparative and evolutionary perspective.

Motor cortex stroke impairs individual digit movement in skilled reaching by the rat

Over 30 years ago, Castro [(1972) Brain Res., 37, 173-185] proposed that motor cortex (MtCx) ablation produced deficits in digital usage that contributed to the rat's impairments in a reach-to-eat task, but the impairment was not directly documented. The present study examined digit use in control rats and rats with MtCx lesions using high-speed (1000 f/s) video recording. Temporal and spatial characteristics of individual digits were evaluated by digitizing the tip of the digits and digital joints using the motion measurement system Peak Motus. Control rats displayed differential digital use during grasping actions and MtCx damage reduced individual digit movement, both as the paw was pre-shaped for grasping and in the grasping action itself. The findings show that although grasping is retained following MtCx damage, MtCx is essential for dexterous movement. The results are discussed in relation to the idea that rodent MtCx is not only necessary for rotatory movements of the limb, but also for digital control and in relation to the similarities of rodent digit use to that described for primates.

The vermicelli handling test: a simple quantitative measure of dexterous forepaw function in rats

Loss of function in the hands occurs with many brain disorders, but there are few measures of skillful forepaw use in rats available to model these impairments that are both sensitive and simple to administer. Whishaw and Coles previously described the dexterous manner in which rats manipulate food items with their paws, including thin pieces of pasta [Whishaw IQ, Coles BL. Varieties of paw and digit movement during spontaneous food handling in rats: postures, bimanual coordination, preferences, and the effect of forelimb cortex lesions. Behav Brain Res 1996;77:135-48]. We set out to develop a measure of this food handling behavior that would be quantitative, easy to administer, sensitive to the effects of damage to sensory and motor systems of the CNS and useful for identifying the side of lateralized impairments. When rats handle 7 cm lengths of vermicelli, they manipulate the pasta by repeatedly adjusting the forepaw hold on the pasta piece. As operationally defined, these adjustments can be easily identified and counted by an experimenter without specialized equipment. After unilateral sensorimotor cortex (SMC) lesions, transient middle cerebral artery occlusion (MCAO) and striatal dopamine depleting (6-hydroxydopamine, 6-OHDA) lesions in adult rats, there were enduring reductions in adjustments made with the contralateral forepaw. Additional pasta handling characteristics distinguished between the lesion types. MCAO and 6-OHDA lesions increased the frequency of several identified atypical handling patterns. Severe dopamine depletion increased eating time and adjustments made with the ipsilateral forepaw. However, contralateral forepaw adjustment number most sensitively detected enduring impairments across lesion types. Because of its ease of administration and sensitivity to lateralized impairments in skilled forepaw use, this measure may be useful in rat models of upper extremity impairment.

A qualitative and quantitative analysis of skilled forelimb reaching impairment following intracerebral hemorrhage in rats

The Montoya staircase test is commonly used to measure skilled forelimb reaching ability in a number of brain injury and disease models, but little has been done to characterize the precise nature of the impairments observed after stroke. The present study used slow motion video-recording to analyze staircase reaching performance both qualitatively and quantitatively, and to precisely determine the components of fine forelimb motor function that are disturbed in the collagenase model of hemorrhagic stroke. Male Sprague-Dawley rats were trained to reach for pellets in the staircase task, and subjected to either striatal hemorrhage induced by microinjections of bacterial collagenase or sham surgery. Reaching performance was recorded and examined before surgery, and 2 and 4 weeks later. Impaired animals made fewer attempts and retrieved less pellets than did shams, especially from the lower steps. Interestingly, impaired animals were less able to retrieve a pellet even when the forepaw made contact with it. Detailed qualitative analysis determined that significant disturbances were most prominent in components of skilled reaching that involved fine manipulation of the distal muscles, especially the wrist and digits. While some components of the reaching impairment were found to partially recover at 4 weeks post-surgery, the impairments in these distal motor movements persisted and there was no significant improvement in overall success. These results suggest that the collagenase model of intracerebral hemorrhage produces a functional impairment that most severely affects fine control of the distal forelimb and paw.

Subcortical middle cerebral artery ischemia abolishes the digit flexion and closing used for grasping in rat skilled reaching

That rats reach for and grasp a food item using a single paw has prompted their use in neurobiological studies of skilled movements and modeling neural injury including middle cerebral artery stroke. Although motor system lesions have been shown to disrupt various qualitative aspects of the transport of a limb to a food target and withdrawal of the limb with the food, no lesion has been found to abolish digit flexion for grasping. Here, rats received unilateral transient middle cerebral artery ischemia that was restricted mainly to subcortical tissue of the forebrain (caudate-putamen, globus pallidus, and associated fibers) or a sham operation. Both paws were later trained and evaluated on skilled reaching using a rating scale for digit use. Middle cerebral artery rats did not flex and close their digits to grasp food when using their contralateral-to-lesion limb. The grasp impairment was not due to a failure to learn the task as middle cerebral artery rats used the ipsilateral limb as successfully as control rats and they were reinforced for reaching by raking food into the reaching box using an open paw. The impairment was also not due to an inability to move the digits, as they were flexed and closed in other phases of the reach. The paradigm should prove useful for further studies of rehabilitation in relation to the idea that digit closure may be controlled by the joint action of a number of neural systems that converge in the basal ganglia.

Bilateral alteration in stepping pattern after unilateral motor cortex injury: a new test strategy for analysis of skilled limb movements in neurological mouse models

Mice are becoming increasingly popular to model neurological disease and motor system dysfunction. For evaluation of discrete, chronic motor impairments, skilled limb movements represent a valuable extension of standard mouse test batteries. This study introduces an efficient and sensitive test strategy for comprehensive assessment of skilled fore- and hind-limb stepping in mice. Adult C57BL/6 mice were trained and video-recorded in two walking tasks, the widely used rotorod test and a new ladder rung task. The animals then received a unilateral ischemic lesion in the motor cortex forelimb and hind limb area and were video-recorded on days 12 and 26 post-lesion. Forelimb and hind limb stepping movements were rated using a combination of endpoint measures and qualitative assessment. The results showed that while animals maintained a weight-supported gait, posture and stepping movements were abnormal at both post-operative intervals. The rotorod analysis revealed stepping deficits in both forelimbs that led to adoption of compensatory movement strategies. The ladder rung task revealed stepping errors in ipsi- and contralateral fore- and hind-limbs. The findings demonstrate that this test strategy provides comprehensive assessment of motor impairments in mice and that qualitative movement analysis is a valuable tool for elaborating subtle motor disturbances.

Unilateral frontal lobe contusion and forelimb function: chronic quantitative and qualitative impairments in reflexive and skilled forelimb movements in rats

Traumatic brain injury induced by mechanical impacts of the head can be modeled in rats in order to investigate acute and chronic therapy. Because frontal lobe contusion affects the neural representation of the forelimb in both the neocortex and basal ganglia, the purpose of the present experiments was to examine the chronic changes in reflexive and skilled forelimb induced by the injury. Contusions produced a cavity in the sensorimotor cortex, accompanied by shrinkage of the pyramidal tract, loss of cells in the dorsolateral striatum, and enlargement of the lateral ventricle. There were substantial individual differences in lesion size despite use of two different contusion forces, but all rats receiving contusions displayed chronic forelimb deficits. Reflexive tests of forelimb use (limb posture, placing, and support) indicated that impairments were most pronounced in the forelimb contralateral to the lesion. Tests of limb preference indicated that the contusion rats displayed a forelimb asymmetry: they were more likely to lean on their ipsilateral-to-lesion forelimb for support when rearing in a test cylinder, and this impairment was amplified in a home cage test. They also displayed a preference for the forelimb ipsilateral to the lesion when reaching for food, although both forelimbs were equally impaired on measures of success when reaching for food from a tray and reaching for a single food pellet on a shelf. A qualitative analysis from frame-by-frame video records indicated that when reaching for single pellets, impairments in forelimb use primarily affected the contralateral-to-lesion limb, especially limb aiming, supination, and food pellet release. Impairments in the ipsilateral-to-lesion forelimb were generally, but not exclusively, secondary to postural abnormalities. The wide range of chronic impairments in forelimb use following contusion injuries are discussed in relation to the anatomical and behavioral origins of the impairments and the potential use of forelimb tests in the assessment of therapy for traumatic brain injury to the frontal cortex.

Did a change in sensory control of skilled movements stimulate the evolution of the primate frontal cortex?

The classical view of the evolution of such skilled movements as use of the hand and digits for reaching and grasping posited that these movements had their origin in the primate lineage. The hypothesis was that the permissive influence of adaptations to an arboreal environment led to the evolution and elaboration of these skills. Associated with skilled movements were increases in the size of the frontal lobe, temporal lobe, and cerebellum and the elaboration of new connections between these structures and other cortical regions, the brainstem, and spinal cord. The classical view saw rodents as phylogenetically old and relatively unrelated animals, displaying no skilled movements, and whose normal repertoire of behavior had little dependence on the frontal lobes. Here, evidence is reviewed that shows that the classical view of the origins of skilled movements is incorrect. Skilled movements are phylogenetically old, evolved in relation to food handling, and are especially well developed in rodents. Behavioral evidence also shows that the skilled movements of rodents are dependent upon the function of the frontal cortex. Nevertheless, there are difference in the sensory control of skilled movement in primates and rodents. Skilled movements are largely directed by vision in primates but are directed by hapsis/olfaction in rodents. This difference in sensory control suggests that at a dividing point between primates and rodents, there was a profound behavior/brain transformation. Primates retained the skilled movements exemplified in rodents, but brought these movements under visual control. Correspondingly, along with many other anatomical changes, the primate frontal cortex became relatively larger and move complex under visual influence.

Quantitative and qualitative impairments in skilled reaching in the mouse (Mus musculus) after a focal motor cortex stroke

BACKGROUND AND PURPOSE

Skilled reaching movements are an important aspect of human motor behavior but are impaired after motor system stroke. The purpose of this study was to document skilled movements in mice before and after a focal motor cortex stroke for the purpose of developing a mouse model of human stroke.

METHODS

Male C57/BL6 mice were trained to reach with a forelimb for food pellets and then given a motor cortex stroke, induced by pial stripping, contralateral to their preferred reaching limb. Reaching success and the movements used in reaching were analyzed by frame-by-frame inspection of presurgical and postsurgical video records.

RESULTS

Reaching success was severely impaired after the stroke. Improvement in success over 2 postsurgical weeks was moderate. Analysis of 10 movement components comprising reaches pre- and postsurgically indicated that most of the rotatory movements of the limb used for aiming, advancing, pronating, and supinating the paw were impaired. When successful reaches did occur, body movements that compensated for the impairments in limb rotatory movements aided them.

CONCLUSIONS

The results indicate that skilled reaching in the mouse is impaired by focal motor cortex stroke and they suggest that the mouse, and the skilled reaching task, provides an excellent model for studying impairments, compensation, and recovery after motor system stroke.

Cortical and subcortical lesions impair skilled walking in the ladder rung walking test: a new task to evaluate fore- and hindlimb stepping, placing, and co-ordination

The ladder rung walking test is a new task to assess skilled walking and measure both forelimb and hindlimb placing, stepping, and inter-limb co-ordination. Rats spontaneously walk from a starting location to a goal along a horizontal ladder. The spacing between the rungs of the ladder is variable and can be changed to prevent the animal from learning either the absolute or relative location of the rungs. The testing procedure requires minimal training and allows detailed quantitative and qualitative analysis using video recording. The utility of the test is described with postoperative data obtained from animals with unilateral neocortical strokes produced by pial stripping over the motor cortex, neonatal and adult unilateral corticospinal tract lesions produced by tract section at the pyramids, and unilateral dopamine depletions produced by injection of 6-hydroxydopamine into the nigrostriatal bundle. In addition, a group of aged rats was examined. Deficits in limb placing, stepping and co-ordination displayed by the animals demonstrate that this test can discriminate between lesions of the motor system or age-associated impairments. The test is useful for assessing loss and recovery of function due to brain or spinal cord injury, the effectiveness of treatment therapies, as well as compensatory processes through which animals adapt to nervous system injury.

Cognitive and behavioral assessment in experimental stroke research: will it prove useful?

Stroke in humans is associated with deficits in sensorimotor and cognitive function. Consequently, many stroke researchers recently have expanded their techniques to assess cognitive and behavioral correlates of histologically-determined stroke damage in animal models. Although the incorporation of functional outcome assessment represents an important step forward in stroke research, reports of middle cerebral artery occlusion (MCAO) induced behavioral deficits often conflict, and a significant correlation between post-stroke histology and behavior has been reported in few stroke studies. Discrepancies in behavioral outcomes among studies may be due to several factors, such as method of MCAO, duration of occlusion, strain, the timing and method of the behavioral testing and the laboratory environment. Furthermore, proper experimental and control groups, necessary to rule out potential confounding factors during cognitive testing, often are not incorporated. The goal of this review is: (1) to provide a description of the techniques most commonly employed to assess functional outcome after (MCAO) in rodents and (2) to identify potential confounding factors that may interfere with a clear interpretation of the behavioral data.

Skilled reaching an action pattern: stability in rat (Rattus norvegicus) grasping movements as a function of changing food pellet size

Many animals in different mammalian orders display skilled forelimb use for prehension, but there has been little study of the rules underlying skilled forelimb use that may provide insight into its neural organization. Inflexibility of movement would imply an underlying fixed neural control characteristic of innate action pattern, whereas flexibility of movement would imply more plastic neural control. In the present study, rat reaching was examined by analyzing movements used to obtain nine different sized food pellets, weighing between 20 and 1000 mg. The prediction was that if the rats' reaching movements were flexible, then systematic modifications in reaching would occur as food pellet size changed; whereas if reaching was inflexible, disruptions should occur for extreme food pellet sizes. Reaching was filmed using normal (30 frames/s) and high-speed (60 frames/s) video-recording procedures. Behavior was scored in terms of successful reaches and, in addition, a new rating scale, derived from Eshkol-Wachman Movement Notation, was used to evaluate the qualitative aspects of movement. Reaching success was stable across smaller food pellet sizes but dropped sharply for larger food pellets sizes. Qualitative analysis of limb movements revealed that animals were unable to change their typical movement sequence to obtain the larger pellets. This result indicates that rat skilled reaching is relatively inflexible, supporting the position that it is produced by a complex, relatively fixed neural circuitry. This finding is discussed in relation to the evolution of skilled reaching, the modifications of skilled reaching that are observed after motor cortex and other nervous system injuries, and comparative differences in reaching in rats and primates.

Complete compensation in skilled reaching success with associated impairments in limb synergies, after dorsal column lesion in the rat

Each of the dorsal columns of the rat spinal cord conveys primary sensory information, by way of the medullary dorsal column nucleus, to the ventrobasal thalamus on the contralateral side; thus the dorsal columns are an important source of neural input to the sensorimotor cortex. Damage to the dorsal columns causes impairments in synergistic proximal or whole-body movements in cats and distal limb impairments in primates, particularly in multiarticulated finger movements and tactile foviation while handling objects, but the behavioral effects of afferent fiber lesions in the dorsal columns of rodents have not been described. Female Long-Evans rats were trained to reach with a forelimb for food pellets and subsequently received lesions of the dorsomedial spinal cord at the C2 level, ipsilateral to their preferred limb. Reaching success completely recovered within a few days of dorsal column lesion. Nevertheless, a detailed analysis of high-speed video recordings revealed that rotatory limb movements (aiming, pronation, supination, etc.) were irreversibly impaired. Compensation was achieved with whole-body and alternate limb movements. These results indicate the following: (1) in the absence of the dorsal columns, other sensorimotor pathways support endpoint success in reaching; (2) sensory input conveyed by the dorsal columns is important for both proximal and distal limb movements used for skilled reaching; and (3) detailed behavioral analyses in addition to endpoint measures are necessary to completely describe the effects of dorsal column lesions.

Neuronal activity in rat red nucleus during forelimb reach-to-grasp movements

The activity of 259 task-related red nucleus neurons was recorded using chronic electrophysiological methods in free moving rats. Modulations in activity were analysed in relation to onset (first detected wrist movement) and end (arrival of the paw over the food) of a reach-to-grasp movement. Excitatory peaks were found to begin before, during and after the reach, but there were clear peaks in the distribution of onset times after reach-onset and before reach-end, reflecting the fact that one third of all peaks began specifically during the reach, although this occupied only a small fraction of the analysis time. Both excitations and inhibitions showed a strong tendency to end in close temporal association with reach-end. Analysis of excitatory modulation amplitudes showed that the largest peaks were formed when data was aligned to reach-end, and that these largest peaks nearly all began during the reach and ended precisely at the time the paw would have been about to grasp the food. The spread of neural activation onset times throughout the course of the complex reach-to-grasp movement is consistent with a relationship of individual neurons in the rat red nucleus with movements of all parts of the forelimb, as would be expected if all limb muscle groups are represented in the nucleus. On the other hand the disproportionate number of modulations that occur during the reach and their strong alignment with time of reach-end suggests there is a bias in red nucleus function towards the control of distal motions associated with accurate grasp, consistent with the result of recent lesion studies. This provides indirect evidence that functionally the rat red nucleus may be organized in a similar way to that of monkeys, in which an important role in control of accurate distal movements is well established. The possibility is discussed that red nucleus offers a timing signal for co-ordination of movements across joints, in particular the precise distal-proximal binding normally seen in accurate reach-to-grasp movements.

Evidence for rodent-common and species-typical limb and digit use in eating, derived from a comparative analysis of ten rodent species

Order Rodentia comprises a vast portion of mammalian species (1814 species), which occupy extremely diverse habitats requiring very distinct motor specializations (e.g. burrowing, hopping, climbing, flying and swimming). Although early classification of paw use ability suggests rodents are impoverished relative to primates and make little use of their paws, there have been no systematic investigations of paw use in rodents. The present study was undertaken to describe limb/paw movements in a variety of common rodents. The movements used for handling sunflower seeds and other foods were videorecorded and analyzed in the guinea pig (Cavia porcellus), Mongolian gerbil (Meriones unguiculatus), Syrian hamster (Mesocricetus auratus), laboratory mouse (Mus musculus), laboratory rat (Rattus norvegicus), gray squirrel (Sciurus carolinensis), red squirrel (Tamiasciurus hudsonicus), Richardson's ground squirrel (Spermophilus richardsonni), prairie dog (Cynomus parvidens), and Canadian beaver (Castor americanus). The results suggested five order-common movements of food handling: (1) locating food by sniffing, (2) grasping food by mouth, (3) sitting back on the haunches to eat, (4) grasping the food using an elbow-in movement, and (5) manipulate the food with the digits. Different species displayed species-typical specializations including (1) bilateral grasping with the paws (gerbil), (2) unilateral grasping with a paw (beaver), (3) unilateral holding (ground squirrels), (4) various grip and digit postures (all species), (5) unilateral object removal from the mouth (gerbil), (6) bilateral thumb holding (squirrels), and (7) simultaneous holding/manipulation of two objects (squirrels). Only the guinea pig did not handle food with its paws, suggesting its behavior is regressive. The existence of a core pattern of paw and digit use in rodents suggests that skilled limb and paw movements originate at least with the common ancestors of the rodent, and likely the common ancestor to rodent and primate lineages, while species-typical movements suggest specialization/regression of limb use has occurred in a number of mammalian orders.

The ground reaction forces of postural adjustments during skilled reaching in unilateral dopamine-depleted hemiparkinson rats

Rats with unilateral dopamine (DA) depletions (hemiParkinson analogue rats) produced by intracerebral 6-hydroxydopamine injection are impaired in using the contralateral (bad) limbs for postural adjustments. This article examines whether the bad limbs are impaired in applying the forces required to initiate postural adjustments that anticipate and accompany voluntary movements. The rats were trained to reach for food using their good paw while standing on small platforms, each of which measured force changes produced by an individual limb. In one condition the force platforms were aligned to support the limb placement of normal rats and in the second they were aligned to permit the DA-depleted rats to use a compensatory reaching stance. It was found that the bad limbs of the DA-depleted rats produced normal supporting reactions but did not initiate adjustments in posture. Postural adjustments were initiated with the good limbs and preceded rather than accompanied the reaching movements. When constrained to use the posture of normal rats, the DA-deplete rats could not reach successfully, but when allowed to adjust their stance to increase reliance on the good limbs, reaching performance improved. Measures of ground reaction forces confirm that DA-depleted rats can support posture but cannot initiate postural adjustments with their impaired limbs.

Blockade of basic fibroblast growth factor retards recovery from motor cortex injury in rats

The endogenous expression of basic fibroblast growth factor (bFGF) was blocked by neutralizing antibodies following unilateral suction lesions of the motor cortex. Rats with control treatment (saline, goat IgG) after motor cortex lesions showed slow recovery of forelimb manipulatory abilities. Rats with blockade of bFGF expression showed little recovery. Anatomically, the control-treated lesioned rats showed an acute increase in bFGF and glial fibrillary acidic protein (GFAP) reactivity, and chronically they had normal dendritic arborization and spine density in layer V pyramidal cells in the remaining motor cortex. In contrast, rats treated with antibodies to bFGF showed little bFGF reactivity, normal GFAP reactivity, and atrophy of dendritic arbor and decreased spine density in layer V pyramidal cells. These results demonstrate the importance of endogenous bFGF release in processes related to functional recovery after cortical injury.

Impairments and compensation in mouth and limb use in free feeding after unilateral dopamine depletions in a rat analog of human Parkinson's disease

Rats depleted unilaterally of dopamine (DA) with the neurotoxin 6-hydroxydopamine (6-OHDA) have contralateral sensorimotor deficits. These include pronounced impairments in using the contralateral limbs (bad limbs) for skilled movements in tests of reaching and bar pressing. There has been no systematic examination of the changes that take place in movements of spontaneous food handling. This was the purpose of the present study. Rats were filmed as they picked up and ate pieces of angel hair pasta (Capelli d'Angelo), a food item that challenges the rats to use delicate and bilaterally coordinated limb and paw movements. Control rats picked up the food with their incisors, transferred it to their paws, and manipulated it using a variety of bilaterally coordinated limb and paw movements. The DA-depleted rats were impaired in both their mouth and paw movements. They seemed unable to use their teeth to grasp the food and so used their tongue. They did not use the bad side of their mouth to chew and relied upon the good side of their mouth. The bad paw was impaired in grasping the food, grasped only with a whole paw grip, did not make manipulatory movements, and did not open to release the food or open to regain support once the food was eaten. Although the rats improved over a 30-day recovery period, much of the improvement was due to compensatory adjustments. That unilateral DA-depletion results in profound contralateral impairments of the mouth and limb with improvements due mainly to compensatory adjustments confirms a role for dopaminergic systems in motor control. Additionally, the behavioral tests described here could provide important adjuncts for assessing therapies in this animal analog of human Parkinson's disease.

Skilled forelimb movements in prey catching and in reaching by rats (Rattus norvegicus) and opossums (Monodelphis domestica): relations to anatomical differences in motor systems

Traditional anatomical/behavioral classifications suggest that rats and opossums have simple motor systems and are impoverished with respect to their ability to make prehensile movements. Nevertheless, the motor system in rats and opossums represent extremes in relative size and complexity suggesting that a behavioral analysis of the movement competencies of these species will provide insights into the significance of such anatomical differences. This paper examines the movements that the two species use in catching crickets and in reaching for food items. Both species could use a single limb to reach out and grasp prey during prey catching and both could use a single limb to take food from a shelf. Both species could transport the food to the mouth by using a single paw. The food handling behavior of the rats was more complex than that of the opossums, however. They used a variety of prey catching movements and extensively manipulated the prey to remove the legs and wings before eating only the head and body. Additionally the rats made rotatory limb movements of aiming, pronation, and supination, when reaching. For both cricket catching and reaching, they used their digits more than did the opossums. The suggestion also emerged from the results that the movements of the opossums were more fixed and species-typical whereas those of the rats were more plastic and individualistic. Thus, the skilled movements of both species are more complex than is generally recognized and the greater complexity of the rat movements parallels their more complex motor system. These results are discussed in relation to anatomical differences in the motor system and, specifically, to differences in the terminal fields of the pyramidal tract. It is concluded that the motor abilities of nonprimate mammals have been vastly underrated.

An endpoint, descriptive, and kinematic comparison of skilled reaching in mice (Mus musculus) with rats (Rattus norvegicus)

The forelimb and paw movements of mice were compared with those of rats in two skilled reaching for food tasks. Both species could use a single forelimb to reach for food, as measured in two different tasks, although performance was better and more consistent in rats than in mice. Both species located the food using olfaction, and moved from a diagonal supporting pattern in which support and postural adjustments came mainly from the contralateral to reaching forelimb and the ipsilateral to reaching hindlimb. Forelimb movements in both species could be divided into 3 components: (1) a transport component in which the limb is lifted, aimed, advanced, and pronated over the food using mainly movements of the upper limb; (2) a manipulatory component in which the digits are pronated over the food in an arpeggio movement and in which the digits grasp the food using grips that are scaled to the size of the food; and (3) a withdrawal component, in which the paw is supinated by adduction by the upper arm and by a movement about the wrist, as the food is withdrawn and presented to the mouth. Kinematic measures showed that the initial velocity of reaching in mice was slower than for rats, but otherwise the shape of the velocity curve and the trajectory of the limb movement, above and beyond the food pellet, were similar in both species. The results suggest that the motor control of reaching in the two rodent species is almost the same despite an evolutionary divergence that occurred about 20 million years ago. This profile of movement could be useful for investigating motor systems in normal mice and it could be applied to the analysis of motor systems in mutant and transgenic mice suspected of having motor abnormalities.

Varieties of paw and digit movement during spontaneous food handling in rats: postures, bimanual coordination, preferences, and the effect of forelimb cortex lesions

This study describes how rats use their paws and digits when handling a wide range of foodstuffs, including food pellets, grapes, sunflower seeds, shelled and unshelled peanuts, and different sized pastas, etc. Analysis of videorecordings show that the rats display digit postures that include variations in the spacing of the digits, differences in the relative use of different digits, and interlimb differences in paw and digit posture. The rats also display limb preferences in that one paw is used in a supporting function while the other rotates, flips, or pushes the food as is required by the shape of the item. There is a significant correlation between the paw used for manipulation and food items of similar shape but no correlation between the limb used for manipulation and that used for skilled reaching. Small unilateral lesions to the forepaw area of somatic sensorimotor cortex produced impairments in use of the paw contralateral to the lesions. These results: (1) reveal a surprising complexity in the way in which rats use their paws and digits in manipulating food; (2) show that rats have limb preferences in spontaneous food handling; and (3) show that manipulatory dexterity is dependent upon the integrity of the forelimb area of motor cortex. The results are discussed in relation to the evolution of motor skill, the use of rats for investigating questions of motor system organization, neural plasticity, and recovery of function after brain damage.

Morphology of identified corticospinal cells in the rat following motor cortex injury: absence of use-dependent change

After unilateral injury to the forelimb area of the motor cortex, rats are reported to show relatively increased use of the ipsilateral forelimb during exploratory behavior and a concomitant transient increase in dendritic growth in neurons in the undamaged motor cortex. To identify the specific population of cells in motor cortex that undergo such use-dependent change, we examined the morphology of corticospinal pyramidal cells in the intact hemisphere 18 days following unilateral motor cortex damage. Corticospinal neurons in the motor cortex were retrogradely labeled with injections of the fluorescent tracer, DiO, into the cervical enlargement of the spinal cord. Seven days later, the rats received a lesion in the forelimb area of the contralateral motor cortex and 18 days following the lesion, limb use was assessed in two behavioral tests after which the rats were sacrificed. Under fluorescent light, corticospinal cells were visualized and injected with a horseradish peroxidase-fluorescein conjugate that was then reacted with diaminobenzidine. The labeled cells were reconstructed and the number and centrifugal order of the branches were analyzed. The increased use of the paw contralateral to the intact motor cortex was not associated with an increase in dendritic arborization in corticospinal motor neurons in the intact motor cortex. The results are discussed in light of methodological and theoretical considerations relevant to the study of neural plasticity in the motor system.

Effects of complete and partial lesions of the dopaminergic mesotelencephalic system on skilled forelimb use in the rat

This study compares certain behavioural consequences of partial and complete unilateral lesions of the dopaminergic mesotelencephalic system. We investigated skilled forelimb use, rotations induced by apomorphine and amphetamine, and dopaminergic metabolism of the nigrostriatal system of rats that had received a unilateral injection of 6-hydroxydopamine into the medial forebrain bundle. The rats classified Apo(+), that rotated after the administration of apomorphine, had a complete lesion of the nigrostriatal system, whereas those classified Apo(-), that did not rotate after the administration of apomorphine, had a partial lesion of the nigrostriatal system. In the Apo(+) rats, 99.8% of the dopamine in the striatum was depleted, as was 85% of that in the substantia nigra. For the Apo(-) rats, 72% of the dopamine in the striatum was depleted as was 56% of that in the substantia nigra. When investigated with the staircase test, the animals with the most severe dopamine depletions were those most impaired in the paw reaching task. Complete and partial unilateral depletions of the dopaminergic mesotelencephalic system impaired the hierarchic phases of paw reaching differently. A complete dopamine depletion, but not a partial one, decreased the number of attempts made with the contralateral paw, and induced a bias towards the ipsilateral paw. A partial dopamine lesion impaired the sensorimotor co-ordination of both paws, whereas the complete dopamine lesion had a greater effect on the contralateral paw than on the ipsilateral paw. The mild paw reaching impairments observed in animals with moderate depletions of dopamine are proposed as a model of the early symptoms of Parkinson's disease that may be useful for the development of protective or restorative therapies.

Arpeggio and fractionated digit movements used in prehension by rats

Although it is well known that rats can use one limb to reach for and retrieve food, the way that the paw and digits are used to grasp the food has not been described. Using results obtained from a high speed videorecording procedure, the present study describes how small and large pieces of food are located by the paw and grasped with the digits in a reaching task. As the rat pronates a paw over food, the tips of digits 5 through 2 are successively placed and spread over the target area in an arpeggio movement. The target area is then palpated by downward movements of the palm. If food is not present, the paw is withdrawn without grasping. If food is contacted, the food is manipulated and grasped by the digits with grasp patterns that depend upon food size. Large food pellets are contacted with the pad of digit 3 and then grasped between digits 3 and 4. Small food pellets are first contacted with pad of digit 4 and are grasped between digits 4 and 5. Digit 5 can be partially flexed medially so that the food is held in a modified power grip between digits 4 and 5. The results show that rats use a whole paw movement to position the digits in an arpeggio fashion and they use fractionated digit movements to grasp food. The results are discussed in relation to the possible comparative and anatomical significance of the movements.

Proximal and distal impairments in rat forelimb use in reaching follow unilateral pyramidal tract lesions

Although it was once thought that the corticospinal (pyramidal) tract was the main substrate of voluntary movement, the extent to which it is involved in the control of proximal vs. distal musculature, independent finger movements, and movements characteristic of different species of animals now is unclear. The objective of this study was to examine the effects of pyramidal tract lesions on skilled forelimb use in rats. In addition, cell morphology in motor cortex following lesions was examined. Naive and trained rats received unilateral pyramidal sections just rostral to the pyramidal decussation. Performance was assessed and filmed on two reaching tasks. Measures of reaching consisted of success in obtaining food, kinematic analysis of limb trajectory and velocity, and qualitative evaluation of 10 movement components comprising a reach. Pyramidal tract lesions only impaired reaching for single food pellets. Almost all movements comprising a reach, except digit opening, were impaired, including lifting, aiming, pronating and supinating the limb, and releasing food. Although success in limb use was unchanged over the 180 day observation period, there were significant improvements in the qualitative features of limb use. Histologically, the morphology of pyramidal cells in the forelimb area ipsilateral to the lesion seemed normal. Rats with additional damage to adjacent structures, such as the medial lemniscus and olivary complex, were much more severely impaired on the reaching tasks, and displayed similar impairments as judged by qualitative and kinematic measures. The results demonstrate that a number of movements involved in independent limb use are chronically impaired by pyramidal tract lesions in the rat. Nevertheless, significant use of the limb is possible, due perhaps to both the contribution of extrapyramidal motor systems and the influence of the remaining pyramidal system through its extrapyramidal connections. The results not only show that the rat pyramidal tract supports functions very similar to those of primates and thus might provide a good model for some aspects of pyramidal tract dysfunctions, but also they argue that the pyramidal tract is involved in both proximal and distal limb movements.