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Crawford, J. D.

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

33 records · Page 2Linked to original sources

bioRxiv2021

Gaze-Related Activity in Primate Frontal Cortex Predicts and Mitigates Spatial Uncertainty

A remarkable feature of primate behavior is the ability to predict future events based on past experience and current sensory cues. To understand how the brain plans movements in the presence of unstable cues, we recorded gaze-related activity in the frontal cortex of two monkeys engaged in a quasi-predictable cue-conflict task. Animals were trained to look toward remembered visual targets in the presence of a landmark that shifted with fixed amplitude but randomized direction. As simulated by a probabilistic model based on known physiology/behavior, gaze end points assumed a circular distribution around the target, mirroring the possible directions of the landmark shift. This predictive strategy was reflected in frontal cortex activity (especially supplementary eye fields), which anticipated future gaze distributions before the actual landmark shift. In general, these results implicate prefrontal cortex in the predictive integration of environmental cues and their learned statistical properties to mitigate spatial uncertainty.

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bioRxiv2021

Saccades and pre-saccadic stimulus repetition alter cortical network topology and dynamics: evidence from EEG and graph theoretical analysis

Parietal and frontal cortex are involved in saccade generation, but their output signals also modify visual signals throughout cortex. These signals produce well-documented behavioral phenomena (saccades, saccadic suppression, various perisaccadic perceptual distortions) but their underlying influence on cortical network dynamics is not known. Here, we combined electroencephalography (EEG) with frequency-dependent source localization and graph theory analysis (GTA) to understand how saccades and pre-saccadic visual stimuli interactively alter cortical network dynamics in humans. 21 participants viewed series of 1-3 vertical or horizontal grids, followed by grid with the opposite orientation just before a horizontal saccade or continued fixation. EEG signals from the presaccadic interval (cue + 200ms, or equivalent fixation period) were used for source localization. Source localization (saccade - fixation) identified bilateral dorsomedial frontoparietal activity across frequency bands, whereas stimulus repetition produced band-specific modulations in left prefrontal, posterior parietal, and central-superior frontal and/or parietal cortex, with significant saccade-repetition interactions in frontal and parietal regions. GTA analysis revealed a saccade-specific functional network with major hubs in inferior parietal cortex (alpha) and the frontal eye fields (beta), and major saccade-repetition interactions in left prefrontal (theta) and supramarginal gyrus (gamma). Overall, quantitative measures of whole-brain network topology and dynamics (segregation, integration, synchronization, complexity) were enhanced during the presaccadic interval, but repetition interactions reduced synchronization and complexity. These results show that presaccadic signals have widespread, coherent influence on cortical network dynamics, likely responsible for both saccade production and the perceptual phenomena associated with saccades. HighlightsO_LISource localization & graph theory were used to analyze presaccadic EEG signals C_LIO_LIPresaccadic signals produced band-specific modulations/hubs in parietofrontal cortex C_LIO_LIFrontal/parietal eye fields showed extensive functional connectivity across all lobes C_LIO_LIPresaccadic stimulus repetition further modulated functional network connectivity C_LIO_LISaccades and repetition both influenced network clustering, integration, & complexity C_LI

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bioRxiv2021

Medial occipital cortex participates in a cortical network for transsaccadic feature discrimination: an fMRI paradigm

Saccades change eye position and interrupt vision several times per second, necessitating neural mechanisms for continuous perception of object identity, orientation, and location. Neuroimaging studies suggest that occipital and parietal cortex play complementary roles for transsaccadic perception of intrinsic versus extrinsic spatial properties, e.g., dorsomedial occipital cortex (cuneus) is sensitive to changes in spatial frequency, whereas the supramarginal gyrus (SMG) is modulated by changes in object orientation. Based on this, we hypothesized that both structures would be recruited to simultaneously monitor identity and orientation across saccades. To test this, we merged two previous neuroimaging protocols: 21 participants viewed a 2D object and then, after sustained fixation or a saccade, judged whether the shape or orientation of the represented object changed. We, then, performed a bilateral region-of-interest analysis on identified cuneus and SMG sites. As hypothesized, cuneus showed both saccade and feature (i.e., orientation vs. shape change) modulations, and right SMG showed saccade-feature interactions. Further, the cuneus activity time course correlated with several other cortical saccade / visual areas, suggesting a functional network for feature discrimination. These results confirm the involvement of occipital / parietal cortex in transsaccadic vision and support complementary roles in spatial versus identity updating.

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bioRxiv2020

Landmark-Centered Coding in Frontal Cortex Visual Responses

Visual landmarks influence spatial cognition [1-3], navigation [4,5] and goal-directed behavior [6-8], but their influence on visual coding in sensorimotor systems is poorly understood [6,9-11]. We hypothesized that visual responses in frontal cortex control gaze areas encode potential targets in an intermediate gaze-centered / landmark-centered reference frame that might depend on specific target-landmark configurations rather than a global mechanism. We tested this hypothesis by recording neural activity in the frontal eye fields (FEF) and supplementary eye fields (SEF) while head-unrestrained macaques engaged in a memory-delay gaze task. Visual response fields (the area of visual space where targets modulate activity) were tested for each neuron in the presence of a background landmark placed at one of four oblique configurations relative to the target stimulus. 102 of 312 FEF and 43 of 256 SEF neurons showed spatially tuned response fields in this task. We then fit these data against a mathematical continuum between a gaze-centered model and a landmark-centered model. When we pooled data across the entire dataset for each neuron, our response field fits did not deviate significantly from the gaze-centered model. However, when we fit response fields separately for each target-landmark configuration, the best fits shifted (mean 37% / 40%) toward landmark-centered coding in FEF / SEF respectively. This confirmed an intermediate gaze / landmark-centered mechanism dependent on local (configuration-dependent) interactions. Overall, these data show that external landmarks influence prefrontal visual responses, likely helping to stabilize gaze goals in the presence of variable eye and head orientations. HighlightsO_LIPrefrontal visual responses recorded in the presence of visual landmarks C_LIO_LIResponse fields showed intermediate gaze / landmark-centered organization C_LIO_LIThis influence depended on specific target-landmark configurations C_LI

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bioRxiv2020

Parietal Mechanisms for Transsaccadic Spatial Frequency Perception: An fMRI Study

Posterior parietal cortex (PPC), specifically right supramarginal gyrus, is involved in transsaccadic memory of object orientation for both perception and action. Here, we investigated whether PPC is involved in transsaccadic memory of other features, namely spatial frequency. We employed a functional magnetic resonance imaging paradigm where participants briefly viewed a grating stimulus with a specific spatial frequency that later reappeared with the same or different frequency, after a saccade or continuous fixation. Post-saccadic frequency modulation activated a region in the right hemisphere spanning medial PPC (ventral precuneus) and posterior cingulate cortex. Importantly, the site of peak precuneus activation showed saccade-specific feature modulation (compared to fixation) and task-specific saccade modulation (compared to a saccade localizer task). Psychophysiological interaction analysis revealed functional connectivity between this precuneus site and the precentral gyrus (M1), lingual gyrus (V1/V2), and medial occipitotemporal sulcus. This differed from the transsaccadic orientation network, perhaps because spatial frequency signaled changes in object identity. Overall, this experiment supports a general role for PPC in transsaccadic vision, but suggests that different networks are employed for specific features.

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bioRxiv2020

Linear vector models of time perception account for saccade and stimulus novelty interactions

Various models (e.g., scalar, state-dependent network, and vector models) have been proposed to explain the global aspects of time perception, but they have not been tested against specific visual phenomena like perisaccadic time compression and novel stimulus time dilation. Here, in two separate experiments (N=31), we tested how the perceived duration of a novel stimulus is influenced by 1) a simultaneous saccade, in combination with 2) a prior series of repeated stimuli in human participants. This yielded a novel behavioral interaction: pre-saccadic stimulus repetition neutralizes perisaccadic time compression. We then tested these results against simulations of the above models. Our data yielded low correlations against scalar model simulations, high but non-specific correlations for our feedforward neural network, and correlations that were both high and specific for a vector model based on identity of objective and subjective time. These results demonstrate the power of global time perception models in explaining disparate empirical phenomena and suggest that subjective time has a similar essence to times physical vector.

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bioRxiv2020

Spatiotemporal coding in the macaque supplementary eye fields: landmark influence in the target-to-gaze transformation

Eye-centered (egocentric) and landmark-centered (allocentric) visual signals influence spatial cognition, navigation and goal-directed action, but the neural mechanisms that integrate these signals for motor control are poorly understood. A likely candidate for ego / allocentric integration in the gaze control system is the supplementary eye fields (SEF), a mediofrontal structure with high-level executive functions, spatially tuned visual / motor response fields, and reciprocal projections with the frontal eye fields (FEF). To test this hypothesis, we trained two head-unrestrained animals to saccade toward a remembered visual target in the presence of a visual landmark that shifted during the delay, causing gaze end points to shift partially in the same direction. 256 SEF neurons were recorded, including 68 with spatially tuned response fields. Model fits to the latter established that, like the FEF and superior colliculus, spatially tuned SEF responses primarily showed an egocentric (eye-centered) target-to-gaze position transformation. However, the landmark shift influenced this default egocentric transformation: during the delay, motor neurons (with no visual response) showed a transient but unintegrated shift (i.e., not correlated with the target-to-gaze transformation), whereas during the saccade-related burst visuomotor neurons showed an integrated shift (i.e., correlated with the target-to-gaze transformation). This differed from our simultaneous FEF recordings (Bharmauria et al., 2020), which showed a transient shift in visuomotor neurons, followed by an integrated response in all motor responses. Based on these findings and past literature, we propose that prefrontal cortex incorporates landmark-centered information into a distributed, eye-centered target-to-gaze transformation through a reciprocal prefrontal circuit.

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bioRxiv2019

Dynamic light experiments and semi-automated plant phenotyping enabled by self-built growth racks and simple upgrades to the IMAGING-PAM

BackgroundOver the last years, several plant science labs have started to employ fluctuating growth light conditions to simulate natural light regimes more closely. Many plant mutants reveal quantifiable effects under fluctuating light despite being indistinguishable from wild-type plants under standard constant light. Moreover, many subtle plant phenotypes become intensified and thus can be studied in more detail. This observation has caused a paradigm shift within the photosynthesis research community and an increasing number of scientists are interested in using fluctuating light growth conditions. However, high installation costs for commercial controllable LED setups as well as costly phenotyping equipment can make it hard for small academic groups to compete in this emerging field. ResultsWe show a simple do-it-yourself approach to enable fluctuating light growth experiments. Our results using previously published fluctuating light sensitive mutants, stn7 and pgr5, confirm that our low-cost setup yields similar results as top-prized commercial growth regimes. Moreover, we show how we increased the throughput of our Walz IMAGING-PAM, also found in many other departments around the world. We have designed a Python and R-based open source toolkit that allows for semi-automated sample segmentation and data analysis thereby reducing the processing bottleneck of large experimental datasets. We provide detailed instructions on how to build and functionally test each setup. ConclusionsWith material costs well below USD$1000, it is possible to setup a fluctuating light rack including a constant light control shelf for comparison. This allows more scientists to perform experiments closer to natural light conditions and contribute to an emerging research field. A small addition to the IMAGING-PAM hardware not only increases sample throughput but also enables larger-scale plant phenotyping with automated data analysis.

plant biology↗

bioRxiv2019

Integration of eye-centered and landmark-centered codes in frontal eye field gaze responses

The visual system is thought to separate egocentric and allocentric representations, but behavioral experiments show that these codes are optimally integrated to influence goal-directed movements. To test if frontal cortex participates in this integration process, we recorded primate frontal eye field (FEF) activity during a cue-conflict memory delay saccade task. To dissociate egocentric and allocentric coordinates, we surreptitiously shifted a visual landmark during the delay period, causing saccades to deviate by 37% in the same direction. To assess the cellular mechanisms, we fit neural response fields against an egocentric (eye centered target-to-gaze) continuum, and an allocentric shift (eye-to-landmark centered) continuum. Initial visual responses best fit target position. Motor responses (after the landmark shift) predicted future gaze position but embedded within the motor code was a 29% shift toward allocentric coordinates. This shift appeared transiently in memory-related visuomotor activity, and then reappeared in motor activity before saccades. Notably, fits along the egocentric and allocentric shift continua were initially independent, but became correlated just before the motor burst. Overall, these results implicate frontal cortex in the integration of egocentric and allocentric visual information for goal-directed action, and demonstrate the cell-specific, temporal progression of signal multiplexing for this process in the gaze system.

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bioRxiv2019

Parietal Cortex Integrates Visual and Oculomotor Signals to Update Grasp Plans

Coordinated reach-to-grasp movements are often accompanied by rapid eye movements (saccades) that displace the desired object image relative to the retina. Parietal cortex compensates for this by updating reach goals relative to current gaze direction, but its role in the integration of oculomotor and visual orientation signals for updating grasp plans is unknown. Based on a recent perceptual experiment, we hypothesized that inferior parietal cortex (specifically supramarginal gyrus; SMG) integrates saccade and visual signals to update grasp plans in more superior parietal areas. To test this hypothesis, we employed a functional magnetic resonance adaptation paradigm, where saccades sometimes interrupted grasp preparation toward a briefly presented object that later reappeared (with the same/different orientation) just before movement. Right SMG and several parietal grasp areas, namely left anterior intraparietal sulcus (aIPS) and bilateral superior parietal lobe (SPL), met our criteria for transsaccadic orientation integration: during movement preparation, they showed task-dependent saccade modulations and, during grasp execution, they were specifically sensitive to changes in object orientation that followed saccades. Finally, SMG showed enhanced functional connectivity with both prefrontal saccade areas (consistent with oculomotor input) and aIPS / SPL (consistent with sensorimotor output). These results support the general role of parietal cortex for the integration of visuospatial perturbations, and provide specific cortical modules for the integration of oculomotor and visual signals for grasp updating. Significance StatementThe cortical mechanisms that update reach goals during eye movements are well documented, but it is not known how object features are linked to oculomotor signals when updating grasp plans. Here, we employed functional magnetic resonance imaging adaptation (fMRIa) and functional connectivity analysis to identify a cluster of inferior parietal (supramarginal gyrus) and superior parietal (intraparietal and superior parietal) regions that show functional connectivity with frontal cortex saccade centers, and also show saccade-specific modulations during unexpected changes in object / grasp orientation. This provides a network - complementary to the goal updater network - that integrates visuospatial updating into grasp plans, and may help explain some of the more complex symptoms associated with parietal damage such as constructional ataxia.

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bioRxiv2018

Action-specific feature processing in the human visual cortex

Sensorimotor integration involves feedforward and reentrant processing of sensory input. Grasp-related motor activity precedes and is thought to influence visual object processing. Yet, while the importance of reentrant feedback is well established in perception, the top-down modulations for action and the neural circuits involved in this process have received less attention. Do action-specific intentions influence the processing of visual information in the human cortex? Using a cue-separation fMRI paradigm, we found that action-specific instruction (manual alignment vs. grasp) influences the cortical processing of object orientation several seconds after the object had been viewed. This influence occurred as early as in the primary visual cortex and extended to ventral and dorsal visual stream areas. Importantly, this modulation was unrelated to non-specific action planning. Further, the primary visual cortex showed stronger functional connectivity with frontal-parietal areas and the inferior temporal cortex during the delay following orientation processing for align than grasping movements, strengthening the idea of reentrant feedback from dorsal visual stream areas involved in action. To our knowledge, this is the first demonstration that intended manual actions have such an early, pervasive, and differential influence on the cortical processing of vision.

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bioRxiv2018

Cortical Mechanisms for Reaches Versus Saccades: Progression of Effector-Specificity Through Target Memory to Movement Planning and Execution

Effector-specific cortical mechanisms can be difficult to establish using fMRI, in part because low time resolution might temporally conflate different signals related to target representation, motor planning, and motor execution. Here, we used an event-related fMRI protocol and a cue-separation paradigm to temporally separate these three major sensorimotor stages for saccades vs. reaches. In each trial, subjects (N=12) 1) briefly viewed a target 4-7{degrees} left or right of midline fixation on a touchscreen, followed by an 8 second delay (effector-independent target memory phase), 2) were instructed by an auditory cue to perform a reach or a saccade, followed by a second delay of 8 seconds (effector-specific planning phase), and finally 3) were prompted to move by reaching-to-touch or performing a saccade towards the remembered target (effector-specific execution phase). Our analysis of saccade and reach activation (vs. a non-spatial control task) revealed modest effector-agnostic target memory activity (left AG, bilateral mIPS) followed by independent effector parietofrontal sites and time courses during the motor components of the task, specifically: more medial (pIPS, mIPS, M1, and PMd) activity during both reach planning and execution, and more lateral (mIPS, AG, and FEF) activity only during saccade execution. These motor activations were bilateral, with a left (contralateral) preference for reach. A conjunction analysis revealed that left mIPS and right AG, PCu, SPOC, FEF/PMv and LOTC showed activation for both saccades and reaches. Overall, effector-preference contrasts (reach vs. saccade) revealed significantly more parietofrontal activation for reaches than saccades during both planning and execution, with the exception of FEF. Cross-correlation of reach, saccade, and reach-saccade activation through time revealed correlated activation both within and across effectors in each hemisphere, but with a tendency toward higher correlations in the right hemisphere, especially between the eye and hand. These results demonstrate substantially independent but temporally correlated cortical networks for human eye, hand, and eye-hand control, that follow explicit spatiotemporal rules for effector-specific timing, medial-lateral distribution, and hemispheric lateralization.

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bioRxiv2018

Transsaccadic feature interactions in multiple reference frames: an fMRIa study

Transsaccadic integration of visual features can operate in various frames of reference, but the corresponding neural mechanisms have not been differentiated. A recent fMRIa (adaptation) study identified two cortical regions in supramarginal gyrus (SMG) and extrastriate cortex that were sensitive to transsaccadic changes in stimulus orientation (Dunkley et al., 2016). Here, we modified this paradigm to identify the neural correlates for transsaccadic comparison of object orientations in: 1) Spatially Congruent (SC), 2) Retinally Congruent (RC) or 3) Spatially Incongruent (SI)) coordinates. Functional data were recorded from 12 human participants while they observed a grating (oriented 45{degrees} or 135{degrees}) before a saccade, and then judged whether a post-saccadic grating (in SC, RC, or SI configuration) had the same or different orientation. Our analysis focused on areas that showed a significant repetition suppression (Different > Same) or repetition enhancement (Same > Different) BOLD responses. Several cortical areas were significantly modulated in all three conditions: premotor/motor cortex (likely related to the manual response), and posterior-middle intraparietal sulcus. In the SC condition, uniquely activated areas included left SMG and left lateral occipitotemporal gyrus (LOtG). In the RC condition, unique areas included inferior frontal gyrus and the left lateral BA 7. In the SI condition, uniquely activated areas included the frontal eye field, medial BA 7, and right LOtG. Overall, the SC results were significantly different from both RC and SI. These data suggest that different cortical networks are used to compare pre- and post-saccadic orientation information, depending on the spatial nature of the task.\n\nSignificance StatementEvery time one makes a saccade, the brain must compare and integrate stored visual information with new information. It has recently been shown that transsaccadic integration of visual object orientation involves specific areas within parietal and occipital cortex (Dunkley et al., 2016). Here, we show that this pattern of cortical activation also depends on the spatial nature of the task: when the visual object is fixed relative to space, the eye, or relative to neither space nor the eye, different frontal, parietal, and occipital regions are engaged. More generally, these findings suggest that different aspects of trans-saccadic integration flexibly employ different cortical networks.

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bioRxiv2018

Timing Determines Tuning: a Rapid Spatiotemporal Transformation in Superior Colliculus Neurons During Reactive Gaze Shifts.

Gaze saccades -rapid shifts of the eyes and head toward a goal-- have provided fundamental insights into the neural control of movement. For example, it has been shown that the superior colliculus (SC) transforms a visual target (T) code to future gaze (G) location commands after a memory delay. However, this transformation has not been observed in reactive saccades made directly to a stimulus, so its contribution to normal gaze behavior is unclear. Here, we tested this using a quantitative measure of the spatial continuum between T and G coding based on variable gaze errors. We demonstrate that a rapid T-G transformation occurs between SC visual and motor responses during reactive saccades, even within visuomotor cells, with a continuous spatiotemporal shift in coding occurring in cell types (visual, visuomotor, motor). We further show that the primary determinant of this spatial code was not the intrinsic visual-motor index of different cells or populations, but rather the timing of the response in all cells. These results suggest that the SC provides a rapid spatiotemporal transformation for normal gaze saccades, that its motor responses contribute to variable gaze errors, and that those errors arise from a noisy spatiotemporal transformation involving all SC neurons.\n\nSignificance StatementOculomotor studies have demonstrated visuomotor transformations in structures like the superior colliculus with the use of trained behavioral manipulations, like the memory delay and antisaccades tasks, but it is not known how this happens during normal saccades. Here, using a spatiotemporal model fitting method based on endogenous gaze errors in reactive gaze saccades, we show that the superior colliculus provides a rapid spatiotemporal transformation from target to gaze coding that involves visual, visuomotor, and motor neurons. This technique demonstrates that SC spatial codes are not fixed, and may provide a quantitative biomarker for assessing the health of sensorimotor transformations.

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bioRxiv2018

Neuromagnetic signatures of the spatiotemporal transformation for reaching

Movement planning involves transforming the sensory goal representation into a command in motor coordinates. Surprisingly, the real-time dynamics of sensorimotor transformations at the whole brain level remain unknown, in part due to the spatiotemporal limitations of fMRI and neurophysiological recordings. Here, we used magnetoencephalography (MEG) during pro-/anti-wrist pointing to determine (1) the cortical areas involved in transforming visual signals into appropriate hand motor commands, and (2) how this transformation occurs in real time, both within and across the regions involved. We computed sensory, motor, and sensorimotor indices in 16 bilateral brain regions for direction coding based on hemispherically lateralized de/synchronization in the (7-15Hz) and {beta} (15-35Hz) bands. We found a visuomotor progression, from pure sensory codes in early occipital-parietal areas, to a temporal transition from sensory to motor coding in the majority of parietal-frontal sensorimotor areas, to a pure motor code, in both the and {beta} bands. Further, the timing of these transformations revealed a top-down pro/anti cue influence that propagated backwards from frontal through posterior cortical areas. These data directly demonstrate a progressive, real-time transformation both within and across the entire occipital-parietal-frontal network that follows specific rules of spatial distribution and temporal order.

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