Biology subjects

Crawford, J. D.

Publications and source records attributed to Crawford, J. D..

At least 19 recordsLinked to original sources

bioRxiv2026

Reach plans for grasping vs. placing objects evoke different neural dynamics within a shared cortico-cerebellar mechanism.

Many reach studies treat grasping as the endpoint of a reach, but grasping often initiates a sequence of actions, ending with placing the object. Grasping and placing both require object-specific encoding, but placing has different computational demands, introduced by the intent, sensory feedback, and tolerance for spatial error when alignment is required. Recent neuroimaging work suggests that object placement shares similar cortico-cerebellar networks with grasp, with modest increases in network segregation and cerebellar activity. Here, we ask whether Grasp and Place are better distinguished by their spatiotemporal dynamics in both behaviour and scalp-recorded EEG activity. Using high-density EEG and motion tracking, 31 participants performed alternating Grasp/Place movements of a 3D object from/toward an oriented target/template. Place movements were initiated faster but executed more slowly and with greater endpoint-orientation precision than Grasp, indicating distinct control strategies. ERP and microstate analyses revealed that Grasp and Place shared a peri-movement polarity switch, from posterior negativity/frontal positivity during preparation to posterior positivity/frontal negativity during execution. This shared pattern was amplified during Place preparation and prolonged during Place execution, with stronger expression of preparatory medial frontal/cerebellar and execution-related posterior/cerebellar microstate dynamics. Finally, SVM decoding indicated that task-specific information was primarily encoded in low-frequency EEG activity (below 6 Hz). These results confirm that grasping and placing recruit similar cortico-cerebellar mechanisms, yet different spatiotemporal dynamics are employed to support the distinct computational demands of these behaviours.

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bioRxiv2026

Eye versus hand effector-specificity in the parieto-frontal cortex and cerebellum in humans

The degree and distribution of effector-specific representations for saccade and reach movements in the human brain remain unclear, partly because overlapping regional activation and the limited temporal resolution of fMRI complicate the identification of effector-dependent signals. Using a cue-separated event-related fMRI paradigm, we examined cortical and cerebellar activity across three temporally separated phases: visual target encoding, movement planning, and movement execution in 19 adults. We combined conventional univariate analyses with multivariate analyses of spatial activity patterns to characterize overlapping and distinct neural activity associated with each effector. Univariate analyses revealed widespread overlap across parieto-frontal regions, alongside effector-dependent differences in the magnitude and distribution of activation. Reach-related activity was generally more extensive than saccade-related activity, particularly during planning, while execution revealed distinct patterns of effector-preferential activation across cortical and cerebellar regions. Despite overlapping activation, multivariate analyses identified distinguishable spatial activity patterns across cortical and cerebellar regions. These findings confirm that (1) separating sensorimotor phases improves the detection of effector-preferential signals across the brain, and (2) overlapping activation during eye and hand movements does not necessarily imply equivalent neural activity patterns. Instead, multivariate analyses reveal widespread effector-dependent differences, suggesting a greater degree of spatial differentiation between saccade- and reach-related activity across the human cortex and cerebellum than conventual activation analyses alone would indicate.

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bioRxiv2026

Heritability of leaf stable carbon isotope signature in a diversity panel of the C4 plant Sorghum bicolor

A strategy to improve agricultural water productivity is to increase water use efficiency (WUE) at the level of plant transpiration through genetic selection. This requires detectable genetic variability in WUE and the ability to phenotype and select plants with higher WUE within a population. A proxy for phenotyping leaf level WUE by measuring carbon isotope signature ({delta}13Cleaf) has been supported by theory and data in C4 species. However, the functional relationship of {delta}13Cleaf and WUE in C4 species can be driven by genetics and environment. Therefore, a wide survey of existing natural variation is needed to quantify the heritability and identify various genetic factors that influence {delta}13Cleaf and WUE. In this study a genome-wide association panel was used to quantify the heritability of {delta}13Cleaf. We measured {delta}13Cleaf across a population of 360 genetically diverse lines of the C4 species Sorghum bicolor with single nucleotide polymorphic (SNP) markers determined from whole-genome resequencing. This analysis was conducted on two independent field environments where heritability of {delta}13Cleaf was evident and was driven by small genetic effects from loci that were consistently identified across environments. Candidate genes are presented that offer insights on future targets to manipulate and explore the functional relationship between {delta}13Cleaf and WUEi in C4 plants.

plant biology↗

bioRxiv2026

Transcranial Magnetic Stimulation Differentiates Egocentric vs. Allocentric Network Hubs for Memory-Guided Reach

Previous patient and imaging studies suggest that dorsal and ventral visual stream mechanisms contribute selectively to egocentric (eye-centred) and allocentric (landmark-centred) goal-directed behaviours, respectively. However, causal evidence for this ego-allocentric dissociation in healthy brains is lacking. Based on a recent neuroimaging study, we hypothesized that perturbations to dorsal stream network hubs would disrupt both egocentric and allocentric reaches, whereas perturbations to ventral hubs would affect only allocentric reaches. Sixteen participants viewed a briefly presented target in the presence of a landmark that later shifted after a memory interval. Participants were instructed to 1) ignore the landmark and reach toward / opposite the original target location (egocentric task) or 2) reach toward the targets location fixed relative to the shifted landmark (allocentric task). Transcranial magnetic stimulation (TMS) was applied during the memory period, spanning the landmark shift, at two occipital sites, based on the network hub coordinates from our previous study and individual brain anatomy. As predicted, superior occipital TMS impaired reaction time, accuracy, and precision in both tasks, whereas inferior occipital TMS only impaired allocentric performance. Further, spatial asymmetries in the resulting error patterns were influenced by TMS site and task: superior occipital TMS influenced asymmetries more strongly in the egocentric task, whereas inferior occipital TMS only influenced spatial asymmetries in the allocentric task. Finally, a functional network analysis revealed a widespread influence of TMS on network-behavior relations and another dissociation: greater influence of superior occipital TMS on the egocentric task and of inferior occipital TMS on the allocentric task. These results establish specific causal relationships between occipital hubs, widespread cortical networks, and reach behavior, confirming a default dorsal egocentric transformation for visually aimed reaches, and a role for the ventral stream for landmark-centred actions.

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bioRxiv2026

Beyond Reach I: Neuroimaging Reveals Different Cortico-cerebellar Networks for Grasp vs. Object Placement.

Object manipulation usually involves both acquisition and placement, but neuroimaging studies tend to focus on its initial reach-to-grasp component. To understand how grasp and placement are represented in the brain, we designed an event-related fMRI study in which 20 participants alternated between grasping / placing a rectangular object from / toward templates presented at variable locations and orientations on an inclined plane. Despite the similarity in target information (i.e., location and orientation), we expected to see sensory and intentional task differences, as the grasp relied on matching the hand to the object, whereas placement relied on matching the object to the template. For our analysis, we examined BOLD activation across two epochs (planning phase before movement onset and execution phase during the movement), and applied graph-theoretical analysis (GTA) of whole-brain functional connectivity based on the joint time series from these two epochs. In both tasks, we found that common activation was more focused on prefrontal regions during planning and on sensorimotor regions during execution, with a specific increase in cerebellar activation during placement. Furthermore, the greater placement activation was also found in action-related regions of interest during the planning phase, and they could accurately decode between our two tasks. GTA categorized the two networks into three identical modules (prefrontal, cerebellar-occipito-parietal, and sensorimotor) and found task-based differences in modularity scores in the prefrontal and cerebellar-occipito-parietal modules. Overall, these data show that although reach-to-grasp and reach-to-place movements share extensive neural circuitry, they also exhibit task-specific differences, likely related to differences in intentionality during planning and in sensory feedback during movement execution.

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bioRxiv2026

Cortical cognitive processing explains and predicts superior colliculus signals and timing of gaze shifts to multisensory targets.

1When goal-directed movements are aimed toward multimodal stimuli, action planning differs compared to the unimodal case in both the spatial and temporal domains, as reflected in specific trends of behavioral response differences in the two conditions. This has been systematically reported in past behavioral and neurophysiological studies; however, a unified neurocognitive theory is yet to be proposed that explains all these findings together based on cognitive processes during the delay period. In our previous paper (Daemi, Harris, & Crawford, 2016) we modeled causal inference in order to determine the spatial location of the goal for saccade. Here, we extend this framework into 1) the temporal domain, and 2) the domain of neural signals. Specifically, we propose that "confidence" on selecting a winning plan, relative to other alternatives, should influence the timing of execution of the winning action plan, as reflected in known superior colliculus signals and the generated behavior. To model these concepts, we build upon our previous evidence-accumulation decision-making framework and compute an instantaneous measure of confidence based on the relative saliency of the winning motor plan compared to the alternate plans. A winning plan is only initiated when enough evidence is accumulated in its favor. This is realized by introducing an accumulative measure of confidence that integrates the instantaneous measure through time. A threshold is set on the accumulative confidence and a GO command is released whenever it reaches the threshold. We also formalize the computations of how this model may be neurally implemented in the brain, mainly in the projections between the superior colliculus (SC), the basal ganglia, and the cortex. This model produces simulations that replicate and explain several experimental multisensory observations. In the behavioral domain, our model shows how higher reaction times are predicted for multi-modal targets with higher reliability, or with higher spatial or temporal disparities, due to less confidence on a unique cause. In the neurophysiological domain, our model replicates the principal multisensory behaviors observed in SC neurons: 1) the dependence of SC neuronal activity on the spatial and temporal structure of cross-modal stimuli (i.e., spatial and temporal principles), 2) the inverse relationship between stimulus intensity and the magnitude of the elicited multisensory response (i.e., principle of inverse effectiveness). We have also simulated some novel predictions that could guide new experimental studies. Thus, our model provides a unified viewpoint to explain, for the first time, the effects of both spatial and temporal factors on reaction time variability for multisensory targets, and assigns each of these effects to a unique cognitive function upstream from sensorimotor transformations. Our model proposes cognitive significance for multisensory neural principles in SC, by linking them to how the cortex infers a causal structure and calculates confidence on its inference.

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bioRxiv2026

Modular Integration of Auditory Instructions and Visual Cues into the Cortical Reach Network

Humans often need to integrate bottom-up stimulus attributes (e.g., object shape) with top-down instructions (e.g., how to pick it up) for adaptive behavior. To investigate how such cues are integrated into the cortical reach network, we employed an fMRI paradigm where participants viewed a cube to their left or right (visual cue) and were verbally instructed to use a horizontal or vertical grip (auditory cue), in varying order. Univariate voxel-wise and region-of-interest analysis confirmed the expected order-dependent activation of sensory regions, followed by robust parietofrontal activation. Graph-theory analysis revealed two significant subnetworks (modules): an Occipital-Parietal module (likely integrating the visual cue into the reach plan) and a Temporal-Frontal module (likely integrating the auditory cue into the grasp plan), both converging in somatomotor cortex. Cue-order influenced modularity, i.e., the module corresponding to the first cue tended to dominate contralateral motor cortex, and conversely a classification model decoded cue-order based on modularity. Local network hubs were order-independent and occupied traditional reach areas, whereas global (between module) hubs were order-dependent and more distributed. Overall, these results suggest that multisensory integration of top-down and bottom-up cues for action is a network phenomenon that relies on both lateral and serial communication between parallel sensorimotor modules.

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bioRxiv2025

Associations between volumes of grey matter regions and white matter hyperintensities with cognitive empathy in oldest-old adults

OBJECTIVESTo study the differential associations of regional volumes of grey matter (GM) and white matter hyperintensities (WMH) with behavioural and informant-reported measures of cognitive empathy (CE), especially in brain regions understood to have functional connectivity involvement with CE abilities. METHODSCommunity-dwelling participants from the Sydney Memory and Ageing Study (Sydney MAS) underwent whole brain MRI. Regional cortical GM volumes were derived using FreeSurfer v7.1 for, and WMH volumes were derived using UBO Detector. On follow-up four years later, CE was indexed via the Reading the Mind in the Eyes Test (RMET; a behavioural task) and Interpersonal Reactivity Index - Perspective Taking subscale (IRI-PT; an informant-reported measure). RESULTSIn 129 participants (mean age 87.01 years), Structural equation modelling (SEM) showed associations between insula GM volumes and RMET scores (p=0.001), and between supramarginal gyrus (SMG) GM volumes and IRI-PT scores (p=0.016). Associations remained significant after inclusion of covariates accounting for age, global cognition, affective symptoms, and social networks. DISCUSSIONCE abilities assessed with RMET (a behavioural task) were positively associated with insula GM volumes. CE abilities on the IRI-PT (an informant-reported measure) were positively associated with SMG GM volumes. No associations between WMH volumes and CE measures were found. These findings may inform clinical workflows that use structural MRI investigations looking at social cognitive disturbances in older adults and provide further evidence of the divergent nature of behavioural and self-report measures of CE.

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bioRxiv2025

Spatial task instructions and global activation trends influence functional modularity in the cortical reach network

Humans can be instructed to ignore visual cues or use them as landmarks for aiming movements (Musa et al. 2024), but it is not known how such allocentric cues interact with egocentric target codes and general planning activity to influence cortical network properties. To answer these questions, we applied graph theory analysis (GTA) to a previously described fMRI dataset (Chen et al. 2014). Participants were instructed to reach toward targets defined in egocentric or landmark-centered (allocentric) coordinates. During Egocentric pointing, cortical nodes clustered into four bilateral modules with correlated BOLD signals: a superior occipital-parietal / somatomotor module, an inferior parietal / lateral frontal module, a superior temporal / inferior frontal module, and an inferior occipital-temporal / prefrontal module. The Allocentric task showed only three modules, in part because inferior occipital nodes were incorporated into the superior occipital-parietal / somatomotor module. Both tasks engaged local (within module) and global (between module) cortical hubs, but the Allocentric task recruited additional hubs associated with allocentric visual codes and ego-allocentric integration. Removing reach-related activation trends reduced global synchrony and increased clustering, specifically diminishing dorsoventral coupling in the allocentric task. Cross-validated decoding confirmed that modularity provided the best predicter of task type and suggest that temporal / parietal modules spanning prefrontal cortex play an important role in task instruction. These results demonstrate that activation trends related to motor plans influence global network integration, whereas task instructions influence intermediate / local network properties, such as the modular integration and hub recruitment observed in our Allocentric task. HighlightsO_LIThe study explores how egocentric and allocentric cues affect cortical networks. C_LIO_LIGraph theory analysis (GTA) was applied to fMRI data from pointing tasks. C_LIO_LIEgocentric pointing formed four cortical modules; allocentric formed three. C_LIO_LIAllocentric tasks recruited additional hubs for dorsal-ventral integration. C_LIO_LIRemoving reach-related activation trends reduced global synchrony in the allocentric task. C_LI

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bioRxiv2025

A spontaneous mutation in a key C4 pathway gene significantly alters leaf δ13C uncoupling its relationship with WUE and photosynthetic performance in Zea mays

Increases in global temperature and drought are negatively impacting the yields of major crops. Therefore, targeted improvements to intrinsic water use efficiency (WUEi) are needed to reduce the water required for agricultural production. While it is very time-consuming to directly measure WUEi, stable carbon isotope ratios ({delta}13C) are a reliable high throughput proxy trait for quantifying WUEi in C3 species. While genetic studies have improved our understanding of the relationship between WUEi and {delta}13C in C4 species, the knowledge needed to implement {delta}13C in breeding schemes is incomplete. Using a Zea mays line with an extremely negative {delta}13C value, a quantitative genetics approach was used to identify a large deletion in carbonic anhydrase1 (cah1). Carbonic anhydrase is the first enzymatic step of the C4 photosynthetic pathway and is known to affect {delta}13C. Surprisingly, the line with the mutant allele has significantly higher carbonic anhydrase activity with a concurrent reduction in {delta}13C, opposite of what would be expected based on C4 carbon isotope fractionation theory. These observed decouple {delta}13C and WUEi, which calls for further investigation into carbon isotope discrimination in C4 species.

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bioRxiv2024

MEG signals reveal arm posture coding and intrinsic movement plans in parietofrontal cortex

Movement planning processes must account for body posture to accurately convert sensory signals into movement plans. While movement plans can be computed relative to the world (extrinsic), intrinsic muscle commands tuned for current limb posture are ultimately needed to execute spatially accurate movements. The whole-brain topology and dynamics of this process are largely unknown. Here, we use high spatiotemporal resolution magnetoencephalography (MEG) in humans combined with a Pro-/Anti-wrist pointing task with 2 opposing forearm postures to investigate this question. First, we computed cortical source activity in 16 previously identified bilateral cortical areas (Alikhanian, et al., Frontiers in Neuroscience 2013). We then contrasted oscillatory activity related to opposing wrist postures to find posture coding and test when and where extrinsic and intrinsic motor codes occurred. We found a distinct pair of overlapping networks coding for posture (predominantly in {gamma} band) vs. posture-specific movement plans ( and {beta}). Some areas (e.g., pIPS) only showed extrinsic motor coding, and others (e.g., AG) only showed intrinsic coding, but the majority showed both types of codes. In the latter case, intrinsic codes appeared slightly before extrinsic codes and persisted in parallel across different cortical areas. These findings are consistent with two cortical networks for 1) direct feed-forward sensorimotor transformations to intrinsic muscle coordinates (for rapid control) and 2) computations of extrinsic spatial coordinates, possibly for use in higher-level aspects of visually-guided action, such as spatial updating and internal performance monitoring. Significance statement / author summaryIt is thought that the brain incorporates posture into extrinsic spatial codes to compute intrinsic (muscle-centered) motor commands, but the whole-brain temporal dynamics of this process is unknown. Here we employed human magneto-encephalography (MEG) to track this process across 16 bilateral cortical sites. We identified two, largely overlapping subnetworks for posture-dependent intrinsic codes, and extrinsic spatial coding. Surprisingly, the direct transformation from sensorimotor coordinates to intrinsic commands preceded the appearance of extrinsic codes, suggesting that extrinsic motor codes are derived from intrinsic codes for higher-level cognitive purposes.

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bioRxiv2024

Saccades Influence Functional Modularity in the Human Cortical Vision Network

Visual cortex is thought to show both dorsoventral and hemispheric modularity, but it is not known if the same functional modules emerge spontaneously from an unsupervised network analysis, or how they interact when saccades necessitate increased sharing of spatial information. Here, we address these issues by applying graph theory analysis to fMRI data obtained while human participants decided whether an objects shape or orientation changed, with or without an intervening saccade across the object. BOLD activation from 50 vision-related cortical nodes was used to identify local and global network properties. Modularity analysis revealed three sub-networks during fixation: a bilateral parietofrontal network linking areas implicated in visuospatial processing and two lateralized occipitotemporal networks linking areas implicated in object feature processing. When horizontal saccades required visual comparisons between visual hemifields, functional interconnectivity and information transfer increased, and the two lateralized ventral modules became functionally integrated into a single bilateral sub-network. This network included between module connectivity hubs in lateral intraparietal cortex and dorsomedial occipital areas previously implicated in transsaccadic integration. These results provide support for functional modularity in the visual system and show that the hemispheric sub-networks are modified and functionally integrated during saccades.

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bioRxiv2024

Instruction Alters The Influence Of Allocentric Landmarks In A Reach Task

Allocentric landmarks have an implicit influence on aiming movements, but it is not clear how an explicit instruction (to aim relative to a landmark) influences reach accuracy and precision. Here, 12 participants performed a task with two instruction conditions (egocentric vs. allocentric), but with similar sensory and motor conditions. Participants fixated gaze near the centre of a display aligned with their right shoulder while a target stimulus briefly appeared alongside a visual landmark in one visual field. After a brief mask/memory delay the landmark then re-appeared at a different location (same or opposite visual field), creating an ego/allocentric conflict. In the egocentric condition, participants were instructed to ignore the landmark and point towards the remembered location of the target. In the allocentric condition, participants were instructed to remember the initial target location relative to the landmark and then reach relative to the shifted landmark (same/opposite visual field). To equalize motor execution between tasks, participants were instructed to anti-point (point to the visual field opposite to the remembered target) on 50 % of the egocentric trials. Participants were more accurate, precise, and quicker to react in the allocentric condition, especially when pointing to the opposite field. We also observed a visual field effect, where performance was worse overall in the right visual field. These results suggest that when egocentric and allocentric cues conflict, explicit use of the visual landmark provides better reach performance than reliance on noisy egocentric signals. Such instructions might aid rehabilitation when the egocentric system is compromised by disease or injury. HighlightsO_LI12 participants reached to remembered targets in the presence of a visual landmark C_LIO_LIParticipants were instructed to ignore, or point relative to, the landmark C_LIO_LIThe landmark instruction improved reaction time, precision, and accuracy C_LIO_LIThese effects were stronger when pointing was cued toward the opposite visual field C_LIO_LIKnowledge of these rules might be used to enhance performance or in rehabilitation C_LI

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bioRxiv2023

Differences in stomatal sensitivity to COC2 and light influences variation in water use efficiency and leaf carbon isotope composition in two genotypes of the C4 plant Zea mays.

The ratio of net CO2 uptake (Anet) and stomatal conductance (gs) is an intrinsic measurement of leaf water use efficiency (WUEi) however its measurement can be challenging for large phenotypic screens. Measurements of leaf carbon isotope composition ({delta}13Cleaf) may be a scalable tool to approximate WUEi for screening because it in part reflects the competing influences of Anet and gs on the CO2 partial pressure (pCO2) inside the leaf over time. However, in C4 photosynthesis the CO2 concentrating mechanism complicates the relationship between {delta}13Cleaf and WUEi. Despite this complicated relationship, several studies have shown genetic variation in {delta}13Cleaf across C4 plants. Yet there has not been a clear demonstration of whether Anet or gs are the causal mechanisms controlling WUEi and {delta}13Cleaf. Our approach was to characterize leaf photosynthetic traits of two Zea mays recombinant inbred lines (Z007E0067 and Z007E0150) which consistently differ for {delta}13Cleaf even though they have minimal confounding genetic differences. We demonstrate that these two genotypes contrasted in WUEi driven by differences in the speed of stomatal responses to changes in pCO2 and light that lead to unproductive leaf water loss. These findings provide support that differences in {delta}13Cleaf in closely related genotypes do reflect greater WUEi and further suggests that differences in stomatal kinetic response to changing environmental conditions is a key target to improve WUEi.

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bioRxiv2023

Multiunit frontal eye field activity codes the visuomotor transformation, but not gaze prediction or target memory, in a delayed saccade task

Single-unit (SU) activity - action potentials isolated from one neuron -- has traditionally been employed to relate neuronal activity to behavior. However, recent investigations have shown that multi-unit (MU) activity - ensemble neural activity recorded within the vicinity of one microelectrode - may also contain accurate estimations of task-related neural population dynamics. Here, using a well-established model-fitting approach, we compared the spatial codes of SU response fields with corresponding MU response fields recorded from the frontal eye fields (FEF) in head-unrestrained monkeys (Macaca mulatta) during a memory-guided saccade task. We focused on characterizing the visuomotor transformation from Target-in-Eye coordinates to future Gaze-in-Eye coordinates (Sajad et al., 2015). Most SU visual response fields coded targets (with some predicting Gaze), whereas the MU population only coded targets. Most SU motor responses coded Gaze, but many still retained a target code. In contrast, MU motor activity predominantly coded Gaze with very little target coding. Finally, both SU and MU populations showed a progressive transition through intermediate Target-to-Gaze codes during the delay period, but the MU activity showed a smoother transition. These results confirm the theoretical and practical potential of MU activity recordings as a biomarker for fundamental sensorimotor transformations (e.g., Target-to-Gaze coding in the oculomotor system), while also highlighting the importance of SU activity for coding more cognitive (e.g., predictive / memory) aspects of sensorimotor behavior. SIGNIFICANCE STATEMENTMulti-unit recordings (undifferentiated signals from several neurons) are relatively easy to record and provide a simplified estimate of neural dynamics, but it is not clear which single-unit signals are retained, amplified, or lost. Here, we compared single-/multi-unit activity from a well-defined structure (the frontal eye fields) and behavior (memory-delay saccade task), tracking their spatial codes through time. The progressive transformation from target to gaze coding observed in single-unit activity was retained in multi-unit activity, but gaze prediction (in the visual response) and target memory (in the motor response) were lost. This suggests that multi-unit activity provides an excellent biomarker for healthy sensorimotor transformations, at the cost of missing more subtle cognitive signals.

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bioRxiv2023

Influence of Gaze, Vision, and Memory on Hand Kinematics in a Placement Task

People usually reach for objects to place them in some position and orientation, but the placement component of this sequence is often ignored. For example, reaches are influenced by gaze position, visual feedback, and memory delays, but their influence on object placement is unclear. Here, we tested these factors in a task where participants placed and oriented a trapezoidal block against 2D visual templates displayed on a frontally located computer screen. In Experiment 1, participants matched the block to three possible orientations: 0{degrees} (horizontal), +45{degrees} and -45{degrees}, with gaze fixated 10{degrees} to the left/right. The hand and template either remained illuminated (closed-loop), or visual feedback was removed (open-loop). In Experiment 2, a memory delay was added, and participants sometimes performed saccades (centripetal, centrifugal, or opposite side). In Experiment 1, the hand consistently overshot the template relative to gaze (similar to reaching), especially in the open-loop task. After a memory delay, location errors were influenced by both template orientation and gaze position. Based on previous reach experiments, we expected these errors to be independent of the previous eye position, but placement overshoot also depended on previous saccade metrics. Hand orientation over-rotated relative to template orientation (all conditions). Orientation was influenced by gaze position in Experiment 1, but this vanished in the presence of a memory delay. These results demonstrate interactions between gaze, location, and orientation signals in the planning and execution of hand placement and suggest different neural mechanisms for closed-loop, open-loop, and memory delay placement. NEW & NOTEWORTHYEye-hand coordination studies usually focus on object acquisition, but placement is equally important. Here, we investigated how gaze position influences object placement toward a 2D template, with different levels of visual feedback. Like reach, placement overestimated goal location relative to gaze, but was also influenced by previous saccade metrics. Gaze also modulated hand orientation, which generally overestimated template orientation. Gaze influence was feedback-dependent, with location errors increasing but orientation errors decreasing after a memory delay.

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bioRxiv2022

Parieto-frontal Oscillations Show Hand Specific Interactions with Top-Down Movement Plans

To generate a hand-specific reach plan, the brain must integrate hand-specific signals with the desired movement strategy. Although various neurophysiology / imaging studies have investigated hand-target interactions in simple reach-to-target tasks, the whole-brain timing and distribution of this process remain unclear, especially for more complex, instruction-dependent motor strategies. Previously, we showed that a pro/anti-pointing instruction influences magnetoencephalographic (MEG) signals in frontal cortex that then propagate recurrently through parietal cortex (Blohm et al., 2019). Here, we contrasted left versus right hand pointing in the same task to investigate 1) which cortical regions of interest show hand specificity, and 2) which of those areas interact with the instructed motor plan. Eight bilateral areas - the parietooccipital junction (POJ), superior parietooccipital cortex (SPOC), supramarginal gyrus (SMG), middle / anterior interparietal sulcus (mIPS/aIPS), primary somatosensory / motor cortex (S1/M1), and dorsal premotor cortex (PMd) - showed hand-specific changes in beta band power, with four of these (M1, S1, SMG, aIPS) showing robust activation before movement onset. M1, SMG, SPOC, and aIPS showed significant interactions between contralateral hand specificity and the instructed motor plan, but not with bottom-up target signals. Separate hand / motor signals emerged relatively early and lasted through execution, whereas hand-motor interactions only occurred close to movement onset. Taken together with our previous results, these findings show that instruction-dependent motor plans emerge in frontal cortex and interact recurrently with hand-specific parietofrontal signals before movement onset to produce hand-specific motor behaviors. Impact StatementThe brain must generate different motor signals, depending which hand is used. The distribution and timing of hand use / instructed motor plan integration is not understood at the whole-brain level. Using whole-brain MEG recordings we show that different sub-networks involved in action planning code for hand usage (alpha and beta frequencies) and integrating hand use information into a hand-specific motor plan (beta band). The timing of these signals indicates that frontal cortex first creates a general motor plan and then integrates hand-specific frontoparietal information to produce a hand-specific motor plan.

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bioRxiv2021

Integration of allocentric and egocentric visual information in a convolutional / multilayer perceptron network model of goal-directed gaze shifts

Allocentric (landmark-centered) and egocentric (eye-centered) visual codes are fundamental for spatial cognition, navigation, and goal-directed movement. Neuroimaging and neurophysiology suggest these codes are segregated initially, but then reintegrated in frontal cortex for movement control. We created and validated a theoretical framework for this process using physiologically constrained inputs and outputs. To implement a general framework, we integrated a Convolutional Neural Network (CNN) of the visual system with a Multilayer Perceptron (MLP) model of the sensorimotor transformation. The network was trained on a task where a landmark shifted relative to the saccade target. These visual parameters were input to the CNN, the CNN output and initial gaze position to the MLP, and a decoder transformed MLP output into saccade vectors. Decoded saccade output replicated idealized training sets with various allocentric weightings, and actual monkey data where the landmark shift had a partial influence (R2 = 0.8). Furthermore, MLP output units accurately simulated prefrontal response field shifts recorded from monkeys during the same paradigm. In summary, our model replicated both the general properties of the visuomotor transformations for gaze and specific experimental results obtained during allocentric-egocentric integration, suggesting it can provide a general framework for understanding these and other complex visuomotor behaviors.

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