Dexterous Hand Movements and Their Recovery After Central Nervous System Injury

Implication of regional selectivity of dopamine deficits in impaired suppressing of involuntary movements in Parkinson's disease

To improve the initiation and speed of intended action, one of the crucial mechanisms is suppressing unwanted movements that interfere with goal-directed behavior, which is observed relatively aberrant in Parkinson's disease patients. Recent research has highlighted that dopamine deficits in Parkinson's disease predominantly occur in the caudal lateral part of the substantia nigra pars compacta (SNc) in human patients. We previously found two parallel circuits within the basal ganglia, primarily divided into circuits mediated by the rostral medial part and caudal lateral part of the SNc dopamine neurons. We have further discovered that the indirect pathway in caudal basal ganglia circuits, facilitated by the caudal lateral part of the SNc dopamine neurons, plays a critical role in suppressing unnecessary involuntary movements when animals perform voluntary goal-directed actions. We thus explored recent research in humans and non-human primates focusing on the distinct functions and networks of the caudal lateral part of the SNc dopamine neurons to elucidate the mechanisms involved in the impairment of suppressing involuntary movements in Parkinson's disease patients.

Evolution, biomechanics, and neurobiology converge to explain selective finger motor control

Humans use their fingers to perform a variety of tasks, from simple grasping to manipulating objects, to typing and playing musical instruments, a variety wider than any other species. The more sophisticated the task, the more it involves individuated finger movements, those in which one or more selected fingers perform an intended action while the motion of other digits is constrained. Here we review the neurobiology of such individuated finger movements. We consider their evolutionary origins, the extent to which finger movements are in fact individuated, and the evolved features of neuromuscular control that both enable and limit individuation. We go on to discuss other features of motor control that combine with individuation to create dexterity, the impairment of individuation by disease, and the broad extent of capabilities that individuation confers on humans. We comment on the challenges facing the development of a truly dexterous bionic hand. We conclude by identifying topics for future investigation that will advance our understanding of how neural networks interact across multiple regions of the central nervous system to create individuated movements for the skills humans use to express their cognitive activity.

Reorganization of Corticospinal Projections after Prominent Recovery of Finger Dexterity from Partial Spinal Cord Injury in Macaque Monkeys

We investigated morphologic changes in the corticospinal tract (CST) to understand the mechanism underlying recovery of hand function after lesion of the CST at the C4/C5 border in seven macaque monkeys. All monkeys exhibited prominent recovery of precision grip success ratio within a few months. The trajectories and terminals of CST from the contralesional (n = 4) and ipsilesional (n = 3) hand area of primary motor cortex (M1) were investigated at 5-29 months after the injury using an anterograde neural tracer, biotinylated dextran amine (BDA). Reorganization of the CST was assessed by counting the number of BDA-labeled axons and bouton-like swellings in the gray and white matters. Rostral to the lesion (at C3), the number of axon collaterals of the descending axons from both contralesional and ipsilesional M1 entering the ipsilesional and contralesional gray matter, respectively, were increased. Caudal to the lesion (at C8), axons originating from the contralesional M1, descending in the preserved gray matter around the lesion, and terminating in ipsilesional Laminae VI/VII and IX were observed. In addition, axons and terminals from the ipsilesional M1 increased in the ipsilesional Lamina IX after recrossing the midline, which were not observed in intact monkeys. Conversely, axons originating from the ipsilesional M1 and directed toward the contralesional Lamina VII decreased. These results suggest that multiple reorganizations of the corticospinal projections to spinal segments both rostral and caudal to the lesion originating from bilateral M1 underlie a prominent recovery in long-term after spinal cord injury.

Visualizing advances in the future of primate neuroscience research

Future neuroscience and biomedical projects involving non-human primates (NHPs) remain essential in our endeavors to understand the complexities and functioning of the mammalian central nervous system. In so doing, the NHP neuroscience researcher must be allowed to incorporate state-of-the-art technologies, including the use of novel viral vectors, gene therapy and transgenic approaches to answer continuing and emerging research questions that can only be addressed in NHP research models. This perspective piece captures these emerging technologies and some specific research questions they can address. At the same time, we highlight some current caveats to global NHP research and collaborations including the lack of common ethical and regulatory frameworks for NHP research, the limitations involving animal transportation and exports, and the ongoing influence of activist groups opposed to NHP research.

Phylogenetic view of the compensatory mechanisms in motor and sensory systems after neuronal injury

Through phylogeny, novel neural circuits are added on top of ancient circuits. Upon injury of a novel circuit which enabled fine control, the ancient circuits can sometimes take over its function for recovery; however, the recovered function is limited according to the capacity of the ancient circuits. In this review, we discuss two examples of functional recovery after neural injury in nonhuman primate models. The first is the recovery of dexterous hand movements following damage to the corticospinal tract. The second is the recovery of visual function after injury to the primary visual cortex (V1). In the former case, the functions of the direct cortico-motoneuronal pathway, which specifically developed in higher primates for the control of fractionated digit movements, can be partly compensated for by other descending motor pathways mediated by rubrospinal, reticulospinal, and propriospinal neurons. However, the extent of recovery depends on the location of the damage and which motor systems take over its function. In the latter case, after damage to V1, which is highly developed in primates, either the direct pathway from the lateral geniculate nucleus to extrastriate visual cortices or that from the midbrain superior colliculus-pulvinar-extrastriate/parietal cortices partly takes over the function of V1. However, the state of visual awareness is no longer the same as in the intact state, which might reflect the limited capacity of the compensatory pathways in visual recognition. Such information is valuable for determining the targets of neuromodulatory therapies and setting treatment goals after brain and spinal cord injuries.

Influence of Intervertebral Level of Stenosis on Neurological Recovery and Reduction of Neck Pain After Posterior Decompression Surgery for Cervical Spondylotic Myelopathy: A Retrospective Multicenter Study with Propensity Scoring

STUDY DESIGN

Retrospective multicenter study.

OBJECTIVE

To identify the impact of the intervertebral level of stenosis on surgical outcomes of posterior decompression for cervical spondylotic myelopathy (CSM).

SUMMARY OF BACKGROUND DATA

As the upper affected cervical levels in elderly patients result from degenerative changes in the lower cervical levels with aging, it is usually difficult to determine the influence of the upper affected cervical levels on surgical outcomes after posterior decompression for CSM in older age.

METHODS

This study involved 636 patients with CSM who underwent posterior decompression. According to the most stenotic intervertebral level, patients were divided into upper (n = 343, the most stenotic intervertebral level was C2/3, C3/4, or C4/5) and lower (n = 293, the most stenotic intervertebral level was C5/6, C6/7, or C7/T1) cervical stenosis groups. Propensity score matching of the baseline factors (characteristics, comorbidities, and neurological function) was performed to compare surgical outcomes, the Japanese Orthopaedic Association (JOA) scores, and visual analog scale (VAS) for neck pain between the upper (n = 135) and lower (n = 135) cervical stenosis groups.

RESULTS

Before propensity score matching, age at surgery was older and pre- and postoperative JOA scores were lower in the upper cervical stenosis group (P < 0.001, P < 0.001, and P < 0.001, respectively). Following matching, baseline factors were comparable between the groups. Postoperative JOA scores, preoperative-to-postoperative changes in the JOA scores, and the JOA score recovery rate were not significantly different between the groups (P = 0.866, P = 0.825, and P = 0.753, respectively). No differences existed in postoperative VAS for neck pain and preoperative-to-postoperative changes in VAS for neck pain between the groups (P = 0.092 and P = 0.242, respectively).

CONCLUSION

The intervertebral level of stenosis did not affect surgical outcomes after posterior decompression for CSM.Level of Evidence: 3.

Double viral vector intersectional approaches for pathway-selective manipulation of motor functions and compensatory mechanisms

Selective manipulation of particular subcomponent of neural circuits is crucial for understanding the functional architecture of neural systems and for development of the future therapeutic strategies against neurological disorders. In this article, I review how the intersectional approaches with double viral vector technique was introduced for the pathway-selective manipulation of spinal circuits. In this technique, a retrograde gene transfer vector is injected into the terminal area of the targeted neurons and an anterograde vector is injected at the location of their somata. Either by using the Tet-transactivator or Cre-loxP system, the experimenter can chemogenetically or optogenetically manipulate the transmission of the target pathway originated from the double-infected neurons. This technique was first developed for manipulation of spinal cord interneurons in the macaque monkeys by selective expression of tetanus neurotoxin and successfully affected the dexterous hand movements. Currently, this technique is widely used on a variety of neural pathways both in rodents and primates in combination with a variety of retrograde vectors and a variety of optogenetic and chemogenetic tools. The advantage of this technique is that it is not necessary to generate transgenic animals. Knowledge of the cell-type specific promotors is not needed. Manipulation is achieved primarily by injection of two viral vectors based on the anatomical knowledge and it is applicable in a variety of animal species including primates. The pros, cons and future direction of this technique are discussed.

When Spinal Neuromodulation Meets Sensorimotor Rehabilitation: Lessons Learned From Animal Models to Regain Manual Dexterity After a Spinal Cord Injury

Electrical neuromodulation has strongly hit the foundations of spinal cord injury and repair. Clinical and experimental studies have demonstrated the ability to neuromodulate and engage spinal cord circuits to recover volitional motor functions lost after the injury. Although the science and technology behind electrical neuromodulation has attracted much of the attention, it cannot be obviated that electrical stimulation must be applied concomitantly to sensorimotor rehabilitation, and one would be very difficult to understand without the other, as both need to be finely tuned to efficiently execute movements. The present review explores the difficulties faced by experimental and clinical neuroscientists when attempting to neuromodulate and rehabilitate manual dexterity in spinal cord injured subjects. From a translational point of view, we will describe the major rehabilitation interventions employed in animal research to promote recovery of forelimb motor function. On the other hand, we will outline some of the state-of-the-art findings when applying electrical neuromodulation to the spinal cord in animal models and human patients, highlighting how evidences from lumbar stimulation are paving the path to cervical neuromodulation.

Long-term rehabilitation reduces task error variability in cervical spinal cord contused rats

To promote skilled forelimb function following a spinal cord injury, we have evaluated whether long-term voluntary sensorimotor rehabilitation can promote substantial reaching and grasping recovery. Long-Evans rats were trained to reach single pellets and then received a moderate 100 kdyn contusion to the C5 lateral funiculi. During the first eight months post-injury, a group of animals was enrolled in daily skilled reaching rehabilitation consisting of grabbing and manipulating seeds from the bottom of a grid. Single-pellet reaching and grasping recovery was tested biweekly throughout the functional follow-up and the recovery was compared to a second group of contused but non-rehabilitated animals. Following the injury, reaching and grasping success dropped to zero in both groups and remained absent for three months post-injury, followed by a slight recovery that remained constant until the end of the follow-up. No differences in reaching success were found between groups. Nevertheless, the type of gesture errors in the failed attempts were categorized and scored. The errors ranged from the animal's inability to lift the paw and initiate the movement to the final stage of the attempt, in which the pellet falls during grasping and retraction of the paw towards the mouth. Both groups of animals exhibited similar types of errors but the animals with rehabilitation showed less error variability and those that occurred at the latest stages of the attempt predominated compared to those performed by the non-trained animals. Histological examination of the injury showed that injury severity was similar between groups and that the damage was circumscribed to the site of impact, affecting mainly the dorsal and medial region of the lateral funiculi, with preservation of the dorsal component of the corticospinal tract and the interneurons and motoneurons of the spinal segments beyond the site of injury. The results indicate that activity-dependent plasticity driven by voluntary rehabilitation decreases task error variability and drives the recovery of the movement gestures. However, the plasticity achieved is insufficient to attain full functional recovery to successfully reach, grasp and release the pellets in the mouth, indicating the necessity for additional interventional therapies to promote repair.

Bimanual digit training improves right-hand dexterity in older adults by reactivating declined ipsilateral motor-cortical inhibition

Improving deteriorated sensorimotor functions in older individuals is a social necessity in a super-aging society. Previous studies suggested that the declined interhemispheric sensorimotor inhibition observed in older adults is associated with their deteriorated hand/finger dexterity. Here, we examined whether bimanual digit exercises, which can train the interhemispheric inhibitory system, improve deteriorated hand/finger dexterity in older adults. Forty-eight healthy, right-handed, older adults (65–78 years old) were divided into two groups, i.e., the bimanual (BM) digit training and right-hand (RH) training groups, and intensive daily training was performed for 2 months. Before and after the training, we evaluated individual right hand/finger dexterity using a peg task, and the individual state of interhemispheric sensorimotor inhibition by analyzing ipsilateral sensorimotor deactivation via functional magnetic resonance imaging when participants experienced a kinesthetic illusory movement of the right-hand without performing any motor tasks. Before training, the degree of reduction/loss of ipsilateral motor-cortical deactivation was associated with dexterity deterioration. After training, the dexterity improved only in the BM group, and the dexterity improvement was correlated with reduction in ipsilateral motor-cortical activity. The capability of the brain to inhibit ipsilateral motor-cortical activity during a simple right-hand sensory-motor task is tightly related to right-hand dexterity in older adults.

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.

Functional networks in non-human primate spinal cord and the effects of injury

Spontaneous fluctuations of Blood Oxygenation-Level Dependent (BOLD) MRI signal in a resting state have previously been detected and analyzed to describe intrinsic functional networks in the spinal cord of rodents, non-human primates and human subjects. In this study we combined high resolution imaging at high field with data-driven Independent Component Analysis (ICA) to i) delineate fine-scale functional networks within and between segments of the cervical spinal cord of monkeys, and also to ii) characterize the longitudinal effects of a unilateral dorsal column injury on these networks. Seven distinct functional hubs were revealed within each spinal segment, with new hubs detected at bilateral intermediate and gray commissure regions in addition to the bilateral dorsal and ventral horns previously reported. Pair-wise correlations revealed significantly stronger connections between hubs on the dominant hand side. Unilateral dorsal-column injuries disrupted predominantly inter-segmental rather than intra-segmental functional connectivities as revealed by correlation strengths and graph-theory based community structures. The effects of injury on inter-segmental connectivity were evident along the length of the cord both below and above the lesion region. Connectivity strengths recovered over time and there was revival of inter-segmental communities as animals recovered function. BOLD signals of frequency 0.01-0.033 Hz were found to be most affected by injury. The results in this study provide new insights into the intrinsic functional architecture of spinal cord and underscore the potential of functional connectivity measures to characterize changes in networks after an injury and during recovery.

Contralateral and Ipsilateral Interactions in the Somatosensory Pathway in Healthy Humans

Hyper-adaptability, the ability to adapt to changes in the internal environment caused by neurological disorders, is necessary to recover from various disabilities, such as motor paralysis and sensory impairment. In the recovery from motor paralysis, the pre-existing neural pathway of the ipsilateral descending pathway, which is normally suppressed and preserved in the course of development, is activated to contribute to the motor control of the paretic limb. Conversely, in sensory pathways, it remains unclear whether there are compensatory pathways which are beneficial for the recovery of sensory impairment due to damaged unilateral somatosensory pathways, such as thalamic hemorrhage. Here, we investigated the interaction between the left and right somatosensory pathways in healthy humans using paired median nerve somatosensory evoked potentials (SEPs). Paired median nerve SEPs were recorded at CP3 and CP4 with a reference of Fz in the International 10–20 System. The paired median nerve stimulation with different interstimulus intervals (ISIs; 1, 2, 3, 5, 10, 20, 40, 60, and 100 ms) was performed to test the influence of the first stimulus (to the right median nerve) on the P14, P14/N20, and N20/P25 components induced by the second stimulus (left side). Results showed that the first stimulation had no effect on SEP amplitudes (P14, P14/N20, and N20/P25) evoked by the second stimulation in all ISI conditions, suggesting that there might not be a neural connectivity formed by a small number of synapses in the left–right interaction of the somatosensory pathway. Additionally, the somatosensory pathway may be less diverse in healthy participants.

The motor deficit of ALS reflects failure to generate muscle synergies for complex motor tasks, not just muscle strength

Customarily the motor deficits that develop in ALS are considered in terms of muscle weakness. Functional rating scales used to assess ALS in terms of functional decline do not measure the deficits when performing complex motor tasks, that make up the human skilled motor repertoire, best exemplified by tasks requiring skilled hand and finger movement. This repertoire depends primarily upon the strength of direct corticomotoneuronal (CM) connectivity from primary motor cortex to the motor units subserving skilled movements. Our review prompts the question: if accumulating evidence suggests involvement of the CM system in the early stages of ALS, what kinds of motor deficit might be expected to result, and is current methodology able to identify such deficits? We point out that the CM system is organized not in "commands" to individual muscles, but rather encodes the building blocks of complex and intricate movements, which depend upon synergy between not only the prime mover muscles, but other muscles that stabilize the limb during skilled movement. Our knowledge of the functional organization of the CM system has come both from invasive studies in non-human primates and from advanced imaging and neurophysiological techniques in humans, some of which are now being applied in ALS. CM pathology in ALS has consequences not only for muscle strength, but importantly in the failure to generate complex motor tasks, often involving elaborate muscle synergies. Our aim is to encourage innovative methodology specifically directed to assessing complex motor tasks, failure of which is likely a very early clinical deficit in ALS.

Importance of the Primary Motor Cortex in Development of Human Hand/Finger Dexterity

Hand/finger dexterity is well-developed in humans, and the primary motor cortex (M1) is believed to play a particularly important role in it. Here, we show that efficient recruitment of the contralateral M1 and neuronal inhibition of the ipsilateral M1 identified by simple hand motor and proprioceptive tasks are related to hand/finger dexterity and its ontogenetic development. We recruited healthy, right-handed children (n = 21, aged 8–11 years) and adults (n = 23, aged 20–26 years) and measured their brain activity using functional magnetic resonance imaging during active and passive right-hand extension–flexion tasks. We calculated individual active control-related activity (active–passive) to evaluate efficient brain activity recruitment and individual task-related deactivation (neuronal inhibition) during both tasks. Outside the scanner, participants performed 2 right-hand dexterous motor tasks, and we calculated the hand/finger dexterity index (HDI) based on their individual performance. Participants with a higher HDI exhibited less active control-related activity in the contralateral M1 defined by the active and passive tasks, independent of age. Only children with a higher HDI exhibited greater ipsilateral M1 deactivation identified by these tasks. The results imply that hand/finger dexterity can be predicted by recruitment and inhibition styles of the M1 during simple hand sensory–motor tasks.

Coordinated increase of reliable cortical and striatal ensemble activations during recovery after stroke

Skilled movements rely on a coordinated cortical and subcortical network, but how this network supports motor recovery after stroke is unknown. Previous studies focused on the perilesional cortex (PLC), but precisely how connected subcortical areas reorganize and coordinate with PLC is unclear. The dorsolateral striatum (DLS) is of interest because it receives monosynaptic inputs from motor cortex and is important for learning and generation of fast reliable actions. Using a rat focal stroke model, we perform chronic electrophysiological recordings in motor PLC and DLS during long-term recovery of a dexterous skill. We find that recovery is associated with the simultaneous emergence of reliable movement-related single-trial ensemble spiking in both structures along with increased cross-area alignment of spiking. Our study highlights the importance of consistent neural activity patterns across brain structures during recovery and suggests that modulation of cross-area coordination can be a therapeutic target for enhancing motor function post-stroke.

Double viral vector technology for selective manipulation of neural pathways with higher level of efficiency and safety

Pathway-selective gene delivery would be critical for future gene therapy against neuropsychiatric disorders, traumatic neuronal injuries, or neurodegenerative diseases, because the impaired functions depend on neural circuits affected by the insults. Pathway-selective gene delivery can be achieved by double viral vector techniques, which combine an injection of a retrograde transport viral vector into the projection area of the target neurons and that of an anterograde viral vector into their somas. In this study, we tested the efficiency of gene delivery with different combinations of viral vectors to the pathway extending from the ventral tegmental area (VTA) to the cortical motor regions in rats, considered to be critical in the promotion of motor recovery from neural injuries. It was found that retrograde recombinant adeno-associated virus 2-retro (rAAV2reto) combined with anterograde AAVDJ (type2/type4/type5/type8/type9/avian/bovine/caprine chimera) exhibited the highest transduction efficiency in the short term (3-6 weeks) but high toxicity in the long term (3 months). In contrast, the same rAAV2reto combined with anterograde AAV5 displayed moderate transduction efficiency in the short term but low toxicity in the long term. These data suggest that the combination of anterograde AAV5 and retrograde rAAV2retro is suitable for safe and efficient gene delivery to the VTA-cortical pathway.

The Role of Haptic Expectations in Reaching to Grasp: From Pantomime to Natural Grasps and Back Again

When we reach to pick up an object, our actions are effortlessly informed by the object's spatial information, the position of our limbs, stored knowledge of the object's material properties, and what we want to do with the object. A substantial body of evidence suggests that grasps are under the control of "automatic, unconscious" sensorimotor modules housed in the "dorsal stream" of the posterior parietal cortex. Visual online feedback has a strong effect on the hand's in-flight grasp aperture. Previous work of ours exploited this effect to show that grasps are refractory to cued expectations for visual feedback. Nonetheless, when we reach out to pretend to grasp an object (pantomime grasp), our actions are performed with greater cognitive effort and they engage structures outside of the dorsal stream, including the ventral stream. Here we ask whether our previous finding would extend to cued expectations for haptic feedback. Our method involved a mirror apparatus that allowed participants to see a "virtual" target cylinder as a reflection in the mirror at the start of all trials. On "haptic feedback" trials, participants reached behind the mirror to grasp a size-matched cylinder, spatially coincident with the virtual one. On "no-haptic feedback" trials, participants reached behind the mirror and grasped into "thin air" because no cylinder was present. To manipulate haptic expectation, we organized the haptic conditions into blocked, alternating, and randomized schedules with and without verbal cues about the availability of haptic feedback. Replicating earlier work, we found the strongest haptic effects with the blocked schedules and the weakest effects in the randomized uncued schedule. Crucially, the haptic effects in the cued randomized schedule was intermediate. An analysis of the influence of the upcoming and immediately preceding haptic feedback condition in the cued and uncued random schedules showed that cuing the upcoming haptic condition shifted the haptic influence on grip aperture from the immediately preceding trial to the upcoming trial. These findings indicate that, unlike cues to the availability of visual feedback, participants take advantage of cues to the availability of haptic feedback, flexibly engaging pantomime, and natural modes of grasping to optimize the movement.

Somatosensory corticospinal tract axons sprout within the cervical cord following a dorsal root/dorsal column spinal injury in the rat

The corticospinal tract (CST) is the major descending pathway controlling voluntary hand function in primates, and though less dominant, it mediates voluntary paw movements in rats. As with primates, the CST in rats originates from multiple (albeit fewer) cortical sites, and functionally different motor and somatosensory subcomponents terminate in different regions of the spinal gray matter. We recently reported in monkeys that following a combined cervical dorsal root/dorsal column lesion (DRL/DCL), both motor and S1 CSTs sprout well beyond their normal terminal range. The S1 CST sprouting response is particularly dramatic, indicating an important, if poorly understood, somatosensory role in the recovery process. As rats are used extensively to model spinal cord injury, we asked if the S1 CST response is conserved in rodents. Rats were divided into sham controls, and two groups surviving post-lesion for ~6 and 10 weeks. A DRL/DCL was made to partially deafferent one paw. Behavioral testing showed a post-lesion deficit and recovery over several weeks. Three weeks prior to ending the experiment, S1 cortex was mapped electrophysiologically, for tracer injection placement to determine S1 CST termination patterns within the cord. Synaptogenesis was also assessed for labeled S1 CST terminals within the dorsal horn. Our findings show that the affected S1 CST sprouts well beyond its normal range in response to a DRL/DCL, much as it does in macaque monkeys. This, along with evidence for increased synaptogenesis post-lesion, indicates that CST terminal sprouting following a central sensory lesion, is a robust and conserved response.

Increasing task precision demands reveals that the reach and grasp remain subject to different perception-action constraints in 12-month-old human infants

The reach and grasp follow different developmental trajectories, but are often considered to have achieved nearly adult-like precision and integration by 12 months of age. This study used frame-by-frame video analysis to investigate whether increasing precision demands, by placing small reaching targets on a narrow pedestal rather than on a flat table, would influence the reach and grasp movements of 12-month-old infants in a complementary or differential fashion. The results reveal that placing the target atop a pedestal impaired the infants's ability to direct an appropriate digit towards the small target, but did not produce a corresponding decrease in the frequency with which they used an index-thumb pincer grip to grasp the target. This was due to the fact that, although infants were more likely to contact the target with a suboptimal part of the hand in the pedestal condition, a greater proportion of these suboptimal contacts ultimately transitioned to a successful index-thumb pincer grip. Thus, increasing task precision demands impaired reach accuracy, but facilitated index-thumb grip formation, in 12-month-old infants. The differential response of the reach and grasp to the increased precision demands of the pedestal condition suggests that the two movements are not fully integrated and, when precision demands are great, remain sensitive to different perception-action constraints in 12-month-old infants.