Visuomotor Pathways Research Articles

Assessing the impact of infantile hydrocephalus on visuomotor integration through behavioural and neuroimaging studies

ABSTRACT Infantile hydrocephalus considerably impacts neurodevelopment, warranting attention to potential long-term consequences on visuomotor functions. The current study investigated the impact of infantile hydrocephalus on functional connectivity within the posterior cortex. Fourteen patients, who were treated for infantile hydrocephalus, were matched for age and sex with 14 typically-developing controls. Both groups had a mean age of 9 years old. Resting-state functional MRI was used to conduct a functional connectivity analysis within the visuomotor integration network, including the inferior frontal occipital fasciculus, superior longitudinal fasciculus, and frontal aslant tract. Patients had reduced functional connectivity in visuomotor pathways compared to typically-developing children with notable impact on the left and right fusiform gyrus and precuneus. Children with infantile hydrocephalus also performed significantly lower in tasks involving visuomotor integration, visual processing, visuospatial skills, motor coordination, and fine motor manipulation. This study enhances our understanding of the multifaceted impact of infantile hydrocephalus on both neural connectivity and considering behavioral outcomes.

Short-Term Modulation of Online Monocular Visuomotor Function

Previous literature suggests that correcting ongoing movements is more effective when using the dominant limb and seeing with the dominant eye. Specifically, individuals are more effective at adjusting their movement to account for an imperceptibly perturbed or changed target location (i.e., online movement correction), when vision is available to the dominant eye. However, less is known if visual-motor functions based on monocular information can undergo short-term neuroplastic changes after a bout of practice, to improve online correction processes. Participants (n = 12) performed pointing movements monocularly and their ability to correct their movement towards an imperceptibly displaced target was assessed. On the first day, the eye associated with smaller correction amplitudes was exclusively trained during acquisition. While correction amplitude was assessed again with both eyes monocularly, only the eye with smaller correction amplitudes in the pre-test showed significant improvement in delayed retention. These results indicate that monocular visuomotor pathways can undergo short-term neuroplastic changes.

Limb Apraxias: The Influence of Higher Order Perceptual and Semantic Deficits in Motor Recovery After Stroke.

Stroke is a leading cause of disability worldwide. Limb apraxia is a group of higher order motor disorders associated with greater disability and dependence after stroke. Original neuropsychology studies distinguished separate brain pathways involved in perception and action, known as the dual stream hypothesis. This framework has allowed a better understanding of the deficits identified in Limb Apraxia. In this review, we propose a hierarchical organization of this disorder, in which a distinction can be made between several visuomotor pathways that lead to purposeful actions. Based on this, executive apraxias (such as limb kinetic apraxia) cause deficits in executing fine motor hand skills, and intermediate apraxias (such as optic ataxia and tactile apraxia) cause deficits in reaching to grasp and manipulating objects in space. These disorders usually affect the contralesional limb. A further set of disorders collectively known as limb apraxias include deficits in gesture imitation, pantomime, gesture recognition, and object use. These deficits are due to deficits in integrating perceptual and semantic information to generate complex movements. Limb apraxias are usually caused by left-hemisphere lesions in right-handed stroke patients, affecting both limbs. The anterior- to posterior-axis of brain areas are disrupted depending on the increasing involvement of perceptual and semantic processes with each condition. Lower-level executive apraxias are linked to lesions in the frontal lobe and the basal ganglia, while intermediate apraxias are linked to lesions in dorso-dorsal subdivisions of the dorsal fronto-parietal networks. Limb apraxias can be caused by lesions in both dorsal and ventral subdivisions including the ventro-dorsal stream and a third visuomotor pathway, involved in body schema and social cognition. Rehabilitation of these disorders with behavioral therapies has aimed to either restore perceptuo-semantic deficits or compensate to overcome these deficits. Further studies are required to better stratify patients, using modern neurophysiology and neuroimaging techniques, to provide targeted and personalized therapies for these disorders in the future.

A visuomotor circuit for evasive flight turns in Drosophila

Visual systems extract multiple features from a scene using parallel neural circuits. Ultimately, the separate neural signals must come together to coherently influence action. Here, we characterize a circuit in Drosophila that integrates multiple visual features related to imminent threats to drive evasive locomotor turns. We identified, using genetic perturbation methods, a pair of visual projection neurons (LPLC2) and descending neurons (DNp06) that underlie evasive flight turns in response to laterally moving or approaching visual objects. Using two-photon calcium imaging or whole-cell patch clamping, we show that these cells indeed respond to both translating and approaching visual patterns. Furthermore, by measuring visual responses of LPLC2 neurons after genetically silencing presynaptic motion-sensing neurons, we show that their visual properties emerge by integrating multiple visual features across two early visual structures: the lobula and the lobula plate. This study highlights a clear example of how distinct visual signals converge on a single class of visual neurons and then activate premotor neurons to drive action, revealing a concise visuomotor pathway for evasive flight maneuvers in Drosophila.

Post-traumatic headaches and vision: A review.

Post-traumatic headache is the most common sequela of brain injury and can last months or years after the damaging event. Many headache types are associated with visual concerns also known to stem from concussion. To describe the various headache types seen after head injury and demonstrate how they impact or are impacted by the visual system. We will mirror the International Classification of Headache Disorders (ICHD) format to demonstrate the variety of headaches following brain injury and relate correlates to the visual pathways. The PubMed database was searched using terms such as headache, head pain, vision, concussion, traumatic brain injury, glare, visuomotor pathways. Every type of headache described in the International Classification of Headache Disorders Edition III can be initiated or worsened after head trauma. Furthermore, there is very often a direct or indirect impact upon the visual system for each of these headaches. Headaches of every described type in the ICHD can be caused by brain injury and all are related in some way to the afferent, efferent or association areas of the visual system.

Tool use and function knowledge shape visual object processing

Perceiving the environment automatically informs how we can interact with it through affordance mechanisms. However, it remains unknown how our knowledge about the environment shapes how it is perceived. In this training study, we evaluated whether motor and function knowledge about novel objects affects visual object processing. Forty-three participants associated a usage or function to a novel object in interactive virtual reality while their EEG was recorded. Both usage and function influenced the mu-band (8–12 Hz) rhythms, suggesting that motor and function object information influence motor processing during object recognition. Learning the usage also prevented the reduction of the theta-band (4–8 Hz) rhythms recorded over the posterior cortical areas, suggesting a predominant top-down influence of tool use information on visuo-motor pathways. The modulation being specifically induced by learning an object usage, the results support further the embodied cognition approach rather than the reasoning-based approach of object processing.

Distinct saccade planning and endogenous visuospatial attention maps in parietal cortex: A basis for functional differences in sensory and motor attention

Parietal cortex activity contributes to higher-level cognitive processes, including endogenous visual attention and saccade planning. While visual attention is the process of selecting pertinent information from the environment, saccade planning may involve motor attention in the planning of a specific movement, including the process of selecting the correct path. We isolated areas in parietal cortex involved in saccade planning, while controlling visual attention, to understand the relationship between the two processes. Using our novel stimulus, participants performed a delayed saccade task and an endogenous covert visuospatial attention task with peripheral targets in identical locations. We compared multiple target locations across the two domains at the level of the individual to better understand variability in the relationship between these two maps. The anterior–posterior organization of saccade planning and visual attention maps varied among, but not within, participants, and 14–29% of the maps for each task overlapped one another across hemispheres. Interestingly, within the region of co-activation, over 67% of the voxels responded to the same location for both tasks. These cortical areas of overlap may represent regions of the brain specifically involved in the transfer of information from vision to action along the visuomotor pathway. These results further establish the relationship between maps associated with saccade planning and visual attention at the individual level, indicating the lack of a single saliency map in parietal cortex.

Photoreceptor specialization and the visuomotor repertoire of the primitive chordate Ciona.

The swimming tadpole larva of Ciona has one of the simplest central nervous systems (CNSs) known, with only 177 neurons. Despite its simplicity, the Ciona CNS has a common structure with the CNS of its close chordate relatives, the vertebrates. The recent completion of a larval Ciona CNS connectome creates enormous potential for detailed understanding of chordate CNS function, yet our understanding of Ciona larval behavior is incomplete. We show here that Ciona larvae have a surprisingly rich and dynamic set of visual responses, including a looming-object escape behavior characterized by erratic circular swims, as well as negative phototaxis characterized by sustained directional swims. Making use of mutant lines, we show that these two behaviors are mediated by distinct groups of photoreceptors. The Ciona connectome predicts that these two behavioral responses should act through distinct, but overlapping, visuomotor pathways, and that the escape behavior is likely to be integrated into a broader startle behavior.

Perception drives production across sensory modalities: A network for sensorimotor integration of visual speech

Sensory information is critical for movement control, both for defining the targets of actions and providing feedback during planning or ongoing movements. This holds for speech motor control as well, where both auditory and somatosensory information have been shown to play a key role. Recent clinical research demonstrates that individuals with severe speech production deficits can show a dramatic improvement in fluency during online mimicking of an audiovisual speech signal suggesting the existence of a visuomotor pathway for speech motor control. Here we used fMRI in healthy individuals to identify this new visuomotor circuit for speech production. Participants were asked to perceive and covertly rehearse nonsense syllable sequences presented auditorily, visually, or audiovisually. The motor act of rehearsal, which is prima facie the same whether or not it is cued with a visible talker, produced different patterns of sensorimotor activation when cued by visual or audiovisual speech (relative to auditory speech). In particular, a network of brain regions including the left posterior middle temporal gyrus and several frontoparietal sensorimotor areas activated more strongly during rehearsal cued by a visible talker versus rehearsal cued by auditory speech alone. Some of these brain regions responded exclusively to rehearsal cued by visual or audiovisual speech. This result has significant implications for models of speech motor control, for the treatment of speech output disorders, and for models of the role of speech gesture imitation in development.

Cerebral activations related to writing and drawing with each hand.

BackgroundWriting is a sequential motor action based on sensorimotor integration in visuospatial and linguistic functional domains. To test the hypothesis of lateralized circuitry concerning spatial and language components involved in such action, we employed an fMRI paradigm including writing and drawing with each hand. In this way, writing-related contributions of dorsal and ventral premotor regions in each hemisphere were assessed, together with effects in wider distributed circuitry. Given a right-hemisphere dominance for spatial action, right dorsal premotor cortex dominance was expected in left-hand writing while dominance of the left ventral premotor cortex was expected during right-hand writing.MethodsSixteen healthy right-handed subjects were scanned during audition-guided writing of short sentences and simple figure drawing without visual feedback. Tapping with a pencil served as a basic control task for the two higher-order motor conditions. Activation differences were assessed with Statistical Parametric Mapping (SPM).ResultsWriting and drawing showed parietal-premotor and posterior inferior temporal activations in both hemispheres when compared to tapping. Drawing activations were rather symmetrical for each hand. Activations in left- and right-hand writing were left-hemisphere dominant, while right dorsal premotor activation only occurred in left-hand writing, supporting a spatial motor contribution of particularly the right hemisphere. Writing contrasted to drawing revealed left-sided activations in the dorsal and ventral premotor cortex, Broca’s area, pre-Supplementary Motor Area and posterior middle and inferior temporal gyri, without parietal activation.DiscussionThe audition-driven postero-inferior temporal activations indicated retrieval of virtual visual form characteristics in writing and drawing, with additional activation concerning word form in the left hemisphere. Similar parietal processing in writing and drawing pointed at a common mechanism by which such visually formatted information is used for subsequent sensorimotor integration along a dorsal visuomotor pathway. In this, the left posterior middle temporal gyrus subserves phonological-orthographical conversion, dissociating dorsal parietal-premotor circuitry from perisylvian circuitry including Broca's area.

Neural circuits that drive binocular eye movements: implications for understanding and correcting strabismus.

Strabismus is the misalignment of the eyes and is estimated to be present in ~2% to 4% of the North American infant population. Surprisingly, to date, there is no consensus regarding the cause of strabismus. While it is commonly thought to be the result of dysfunctional orbital and/or eye muscle properties (reviewed in Refs. 1, 2), recent work emphasizes that strabismus can also be caused by the brain’s inability to transform binocular visual inputs into the motor commands required for coordinated eye motion at cortical as well as subcortical levels (reviewed in Refs. 3, 4). To gain a better understanding of the underlying changes in sensorimotor control that are responsible for strabismus, researchers have begun to perform studies in nonhuman primates. Typically, eye misalignment is induced using either surgical or visual methods (e.g., the weakening of the eye muscles or nerves versus the wearing of prism goggles). As adults, these strabismic monkeys make eye movements much like strabismus patients (i.e., consistent with estropia or exotropia). A study in this month’s issue of IOVS by Walton et al. demonstrates that when strabismus is induced in young monkeys either by the wearing of prism goggles or by medial rectus tenotomy, the activity of individual abducens nucleus neurons is reduced compared to that observed in monkeys raised with normal visual input. Since abducens neurons control the eye muscles that drive horizontal eye movements, these results provide evidence that changes in either sensory input or the eye muscles during development can have profound effects on the set point of the motor pathways required for accurate binocular control. In normal animals, the premotor and motoneurons that control eye movements preferentially encode the movement of an individual eye rather than the conjugate component of each eye movement (reviewed in Ref. 8). In their current study, Walton and colleagues found that this is also true for abducens neurons in strabismic monkeys. Moreover, both neuronal monocular tuning and eye movement sensitivities were normal. Instead, the authors’ data indicate a marked loss of tonic activity in the motoneuron input to the eye muscles. While premotor pathways are also altered in strabismic monkeys (the stimulation of premotor saccadic neurons in the pons produces abnormally disconjugate eye movements, and neurons in the supraoculomotor area [SOA] statically encode the angle of strabismus), there is currently no clear explanation for the observed loss of tonic activity in abducens. In this context, further studies of visuomotor pathways, as well as the abducens internuclear neuron to medial rectus motoneuron pathway, will likely reveal key abnormalities. For instance, Van Horn et al. recently identified a subclass of neurons in the rostral superior colliculus that robustly encode vergence angle in normal animals, suggesting this as a potentially interesting site to explore. Ultimately, such targeted experiments, comparing how the brain is normally circuited to how it develops in animals with different forms of strabismus, are needed to develop more optimally directed therapies for correcting this relatively common condition.

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

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

The parietal reach region is limb specific and not involved in eye-hand coordination

Primates frequently reach toward visual targets. Neurons in early visual areas respond to stimuli in the contralateral visual hemifield and without regard to which limb will be used to reach toward that target. In contrast, neurons in motor areas typically respond when reaches are performed using the contralateral limb and with minimal regard to the visuospatial location of the target. The parietal reach region (PRR) is located early in the visuomotor processing hierarchy. PRR neurons are significantly modulated when targets for either limb or eye movement appear, similar to early sensory areas; however, they respond to targets in either visual field, similar to motor areas. The activity could reflect the subject's attentional locus, movement of a specific effector, or a related function, such as coordinating eye-arm movements. To examine the role of PRR in the visuomotor pathway, we reversibly inactivated PRR. Inactivation effects were specific to contralateral limb movements, leaving ipsilateral limb and saccadic movements intact. Neither visual hemifield bias nor visual attention deficits were observed. Thus our results are consistent with a motoric rather than visual organization in PRR, despite its early location in the visuomotor pathway. We found no effects on the temporal coupling of coordinated saccades and reaches, suggesting that this mechanism lies downstream of PRR. In sum, this study clarifies the role of PRR in the visuomotor hierarchy: despite its early position, it is a limb-specific area influencing reach planning and is positioned upstream from an active eye-hand coordination-coupling mechanism.

A computational developmental model for specificity and transfer in perceptual learning

How and under what circumstances the training effects of perceptual learning (PL) transfer to novel situations is critical to our understanding of generalization and abstraction in learning. Although PL is generally believed to be highly specific to the trained stimulus, a series of psychophysical studies have recently shown that training effects can transfer to untrained conditions under certain experimental protocols. In this article, we present a brain-inspired, neuromorphic computational model of the Where-What visuomotor pathways which successfully explains both the specificity and transfer of perceptual learning. The major architectural novelty is that each feature neuron has both sensory and motor inputs. The network of neurons is autonomously developed from experience, using a refined Hebbian-learning rule and lateral competition, which altogether result in neuronal recruitment. Our hypothesis is that certain paradigms of experiments trigger two-way (descending and ascending) off-task processes about the untrained condition which lead to recruitment of more neurons in lower feature representation areas as well as higher concept representation areas for the untrained condition, hence the transfer. We put forward a novel proposition that gated self-organization of the connections during the off-task processes accounts for the observed transfer effects. Simulation results showed transfer of learning across retinal locations in a Vernier discrimination task in a double-training procedure, comparable to previous psychophysical data (Xiao et al., 2008). To the best of our knowledge, this model is the first neurally-plausible model to explain both transfer and specificity in a PL setting.

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.

Partitioning age-related changes in brain activation using a virtual performance task to simulate complex movements

Event Abstract Back to Event Partitioning age-related changes in brain activation using a virtual performance task to simulate complex movements Toshiharu Nakai1*, Ayuko Tanaka1, Mitsunobu Kunimi1, Sachiko Kiyama1 and Yoshiaki Shiraishi2 1 National Center for Geriatrics and Gerontology, Neuroimaging & Informatics, Japan 2 Nagoya Institute of Technology Graduate School of Engineering, Computer Science and Engineering, Japan Aging has become a serious social issue, especially in Asian countries. In order to maintain the activities of elderly people, social programs to promote physical and mental exercises are conducted. Although some investigations have reported that those activities potentially contribute to the prevention of cognitive decline [1], the neurological background has not been systematically verified. We investigated the availability of a virtual performance task designed from such exercises as a model to test age-related changes in brain function [2]. An event-related fMRI task representing the motor behavior in the bean transfer test (BTT), which is used as one component of the test battery to evaluate the physical ability of elderly in Japan, was designed. The task consisted of two operations using a 2 by 2 turnkey system. With the left-hand key, a small, round object (bean) is pinched with two lines representing chopsticks. Then, the object with chopsticks is moved to a round target (pot) with the right-hand key to put the bean in. The behavioral data were marked with 6 checkpoints (Fig.1). The onset of each trial was determined using the sum of two jittering factors, the execution time for each trial by the subject and periodically altering the interval time before the onset of each trial. fMRI data were obtained using the EPI sequence on a 3T MR scanner, and the data sets were analyzed using SPM8. fMRI data were obtained from 11 elderly (over 60, 6 females) and 7 non-elderly (under 54) volunteers. In the activation representing the total trial, the network for the upper visuo-spatial transformation tract and higher motor control was observed in the elderly (two-sample t-test, p<0.05). Differential peaks between the two age groups were detected as augmented activation in the left BA5 ([-23 -38 59]) and bilateral BA6 ([-60 -2 47], [60 2 38]) in the elderly group (Fig.2, CPall). In the partitioned maps, it was indicated that this difference was mostly contributed to by the first task switching point (CP2) and pinching the object (CP1). Activation of these areas was not significant in the CP3 and CP4 map in the elderly. On the other hand, activation was augmented in the dorsal visuo-motor pathway in the young subjects during these steps. It was suggested that these results represent: 1) a higher demand for visuo-spatial transformation by adjusting the asymmetric (two independent) rotation of the sticks, and 2) a lower frequency of object transference to the goal than pinching it in elderly subjects. By recording self-paced object manipulation in the interactive task, complex brain activation during a combined motor processing could be more precisely attributed to cognitive elements. This feature was useful to further partitioning age-related changes in brain activation. Figure 1 Figure 2 Acknowledgements This research was supported by a Grant-in-Aid for Scientific Research (KAKENHI) # 21300196 and 24300186 supported by MEXT.

Inactivation of the Parietal Reach Region Causes Optic Ataxia, Impairing Reaches but Not Saccades

Lesions in human posterior parietal cortex can cause optic ataxia (OA), in which reaches but not saccades to visual objects are impaired, suggesting separate visuomotor pathways for the two effectors. In monkeys, one potentially crucial area for reach control is the parietal reach region (PRR), in which neurons respond preferentially during reach planning as compared to saccade planning. However, direct causal evidence linking the monkey PRR to the deficits observed in OA is missing. We thus inactivated part of the macaque PRR, in the medial wall of the intraparietal sulcus, and produced the hallmarks of OA, misreaching for peripheral targets but unimpaired saccades. Furthermore, reach errors were larger for the targets preferred by the neural population local to the injection site. These results demonstrate that PRR is causally involved in reach-specific visuomotor pathways, and reach goal disruption in PRR can be a neural basis of OA.

Differential Representations of Prior and Likelihood Uncertainty in the Human Brain

Uncertainty shapes our perception of the world and the decisions we make. Two aspects of uncertainty are commonly distinguished: uncertainty in previously acquired knowledge (prior) and uncertainty in current sensory information (likelihood). Previous studies have established that humans can take both types of uncertainty into account, often in a way predicted by Bayesian statistics. However, the neural representations underlying these parameters remain poorly understood. By varying prior and likelihood uncertainty in a decision-making task while performing neuroimaging in humans, we found that prior and likelihood uncertainty had quite distinct representations. Whereas likelihood uncertainty activated brain regions along the early stages of the visuomotor pathway, representations of prior uncertainty were identified in specialized brain areas outside this pathway, including putamen, amygdala, insula, and orbitofrontal cortex. Furthermore, the magnitude of brain activity in the putamen predictedindividuals' personal tendencies to rely more on either prior or current information. Our results suggest different pathways by which prior and likelihood uncertainty map onto the human brain andprovide a potential neural correlate for higher reliance on current or prior knowledge. Overall, these findings offer insights into the neural pathways that may allow humans to make decisions close to the optimal defined by a Bayesian statistical framework.

Integrity of Medial Visuomotor Pathway Predicts Better Recovery in Neglect Patients Receiving Prism Adaptation Treatment (P02.027)

Objective: To determine whether lesion location predicts functional recovery in right-hemisphere damaged (RHD) patients with neglect following prism adaptation therapy (PAT). Background PAT can produce substantial improvements in spatial neglect. Our previous studies suggested that PAT improved spatial bias in the motor-exploratory domain, which may be subserved by frontal cortico-subcortcial systems. Therefore, the current study examined whether frontal lesion involvement determined treatment response to PAT in post-stroke patients with spatial neglect, using motor-exploratory improvement in the Catherine Bergego Scale (CBS-ME) as the outcome measure. Design/Methods: Lesions of RHD patients (N=21) receiving PAT were manually mapped from clinical images (CT or MRI) using MRIcro. Based on the lesion maps, we extracted information of frontal vs. no-frontal lesion involvement and conducted a multilevel modeling analysis (MLM). Results: After controlling for age and lesion size, MLM revealed that patients with frontal lesions demonstrated better improvement trajectory (n=13) than patients without frontal involvement (n=8). Therefore, we pursued a more detailed analysis on lesion-symptom relationship to elucidate which frontal-subcortical systems strongly support PAT response. The PAT-responsive group had greater integrity of 1) subcortical vs. cortical and 2) medial vs. lateral structures. Conclusions: Our results showed that the medial visuomotor pathway critical for visually-guided movement may support PAT response. PAT may manipulate the network for visual sensorimotor adaptation, subserved by the spared thalamus and basal ganglia, which in turn may improve motor-exploratory behaviors related to spatial neglect. It is still unclear from our preliminary data whether dorsolateral prefrontal regions may account for other performance variables. Supported by: NIH Grants: R01NS055808-01-A2; K24HD062647-01; K02NS47099. Disclosure: Dr. Shah has nothing to disclose. Dr. Chen has nothing to disclose. Dr. Goedert has nothing to disclose. Dr. Foundas has nothing to disclose. Dr. Barrett has received personal compensation for activities with WebMD. Dr. Barrett has received research support from the Kessler Foundation, NIH, O9Brien Technologies, Pfizer/Eisai, and the Wallerstein Foundation for Geriatric Improvement.

Covert attention regulates saccadic reaction time by routing between different visual-oculomotor pathways

Covert attention modulates saccadic performance, e.g., the abrupt onset of a task-irrelevant visual stimulus grabs attention as measured by a decrease in saccadic reaction time (SRT). The attentional advantage bestowed by the task-irrelevant stimulus is short-lived: SRT is actually longer ~200 ms after the onset of a stimulus than it is when no stimulus appears, known as inhibition of return. The mechanism by which attention modulates saccadic reaction is not well-understood. Here, we propose two possible mechanisms: by selective routing of the visuomotor signal through different pathways (routing hypothesis) or by general modulation of the speed of visuomotor transformation (shifting hypothesis). To test them, we designed a cue gap paradigm in which a 100-ms gap was introduced between the fixation point disappearance and the target appearance to the conventional cued visual reaction time paradigm. The cue manipulated the location of covert attention, and the gap interval resulted in a bimodal distribution of SRT, with an early mode (express saccade) and a late mode (regular saccade). The routing hypothesis predicts changes in the proportion of express saccades vs. regular saccades, whereas the shifting hypothesis predicts a shift of SRT distribution. The addition of the cue had no effect on mean reaction time of express and regular saccades, but it changed the relative proportion of two modes. These results demonstrate that the covert attention modification of the mean SRT is largely attributed to selective routing between visuomotor pathways rather than general modulation of the speed of visuomotor transformation.