Biology & Psychology

Natural movements towards a target show metric variations between trials. When movements combine contributions from multiple body-parts, such as head-unrestrained gaze shifts involving both eye and head rotation, the individual body-part movements may vary even more than the overall movement. The goal of this investigation was to develop a general method for both mapping sensory or motor response fields of neurons and determining their intrinsic reference frames, where these movement variations are actually utilized rather than avoided. We used head-unrestrained gaze shifts, three-dimensional (3D) geometry, and naturalistic distributions of eye and head orientation to explore the theoretical relationship between the intrinsic reference frame of a sensorimotor neuron's response field and the coherence of the activity when this response field is fitted non-parametrically using different kernel bandwidths in different reference frames. We measure how well the regression surface predicts unfitted data using the PREdictive Sum-of-Squares (PRESS) statistic. The reference frame with the smallest PRESS statistic was categorized as the intrinsic reference frame if the PRESS statistic was significantly larger in other reference frames. We show that the method works best when targets are at regularly spaced positions within the response field's active region, and that the method identifies the best kernel bandwidth for response field estimation. We describe how gain-field effects may be dealt with, and how to test neurons within a population that fall on a continuum between specific reference frames. This method may be applied to any spatially coherent single-unit activity related to sensation and/or movement during naturally varying behaviors.

Natural movements towards a target show metric variations between trials. When movements combine contributions from multiple body-parts, such as head-unrestrained gaze shifts involving both eye and head rotation, the individual body-part movements may vary even more than the overall movement. The goal of this investigation was to develop a general method for both mapping sensory or motor response fields of neurons and determining their intrinsic reference frames, where these movement variations are actually utilized rather than avoided. We used head-unrestrained gaze shifts, three-dimensional (3D) geometry, and naturalistic distributions of eye and head orientation to explore the theoretical relationship between the intrinsic reference frame of a sensorimotor neuron's response field and the coherence of the activity when this response field is fitted non-parametrically using different kernel bandwidths in different reference frames. We measure how well the regression surface predicts unfitted data using the PREdictive Sum-of-Squares (PRESS) statistic. The reference frame with the smallest PRESS statistic was categorized as the intrinsic reference frame if the PRESS statistic was significantly larger in other reference frames. We show that the method works best when targets are at regularly spaced positions within the response field's active region, and that the method identifies the best kernel bandwidth for response field estimation. We describe how gain-field effects may be dealt with, and how to test neurons within a population that fall on a continuum between specific reference frames. This method may be applied to any spatially coherent single-unit activity related to sensation and/or movement during naturally varying behaviors.

Posterior parietal cortex (PPC) participates in the planning of visuospatial behaviors, including reach movements, in gazecentered coordinates. It is not known if these representations encode the visual goal in retinal coordinates, or the movement direction relative to gaze. Here, by dissociating the intrinsic retinal stimulus from the extrinsic direction of movement, we show that PPC employs a visual code. Using delayed pointing and eventrelated functional magnetic resonance imaging, we identified a cluster of PPC regions whose activity was topographically (contralaterally) related to the direction of the planned movement. We then switched the normal visual--motor spatial relationship by adapting subjects to optical left/right reversing prisms. With prisms, movement-related PPC topography reversed, remaining tied to the retinal image. Thus, remarkably, the PPC region in each hemisphere now responded more for planned ipsilateral pointing movements. Other non-PPC regions showed the opposite world-or motor-fixed pattern. These findings suggest that PPC primarily encodes not motor commands but movement goals in visual coordinates.

Posterior parietal cortex (PPC) participates in the planning of visuospatial behaviors, including reach movements, in gazecentered coordinates. It is not known if these representations encode the visual goal in retinal coordinates, or the movement direction relative to gaze. Here, by dissociating the intrinsic retinal stimulus from the extrinsic direction of movement, we show that PPC employs a visual code. Using delayed pointing and eventrelated functional magnetic resonance imaging, we identified a cluster of PPC regions whose activity was topographically (contralaterally) related to the direction of the planned movement. We then switched the normal visual--motor spatial relationship by adapting subjects to optical left/right reversing prisms. With prisms, movement-related PPC topography reversed, remaining tied to the retinal image. Thus, remarkably, the PPC region in each hemisphere now responded more for planned ipsilateral pointing movements. Other non-PPC regions showed the opposite world-or motor-fixed pattern. These findings suggest that PPC primarily encodes not motor commands but movement goals in visual coordinates.

The synoptophore was used to measure torsional interocular disparity. This, in turn, was used to compute how much the angle between the Listing's plane (LP) of the two eyes changes as a function of the vergence angle. The ratio of these two angles was defined as G. We measured G in normals and in patients suffering from intermittent horizontal strabismus. Consistent with previous search-coil experiments and with our previous visual test measures, the results using the synoptophore suggest that, for normals, G is less than 1. In the patient group the mean G was similar in magnitude but more variable. The variations in G did not appear to be related to the patient's measurement of ocular deviation. This result suggests that the vergence-related rotation of LP in these patients may be related to other factors besides the effort required to fuse the lines of sight.

Preparatory set associated with pro-saccades and anti-saccades in humans investigated with event-related fMRI. vious studies have shown that the BOLD functional MRI (fMRI) signal is increased in several cortical areas when subjects perform anti-saccades compared with pro-saccades. It remains unknown, however, whether this increase is due to an increased cortical motor signal for anti-saccades or due to differences in preparatory set between proand anti-saccade trials. To address this question, we measured eventrelated fMRI in a paradigm that allowed us to separate instructionrelated brain activity from saccade-related brain activity. In this paradigm, the instruction to either generate a pro-saccade or an antisaccade was conveyed by a switch in the color of the central fixation stimulus and preceded the presentation of a peripheral stimulus by either 6, 10, or 14 s. Cortical areas were functionally mapped using the general linear model comparing standard pro-and anti-saccade blocks with fixation blocks. When the trials were aligned on the onset of the instruction stimulus, bilateral frontal eye fields and right hemisphere dorsolateral prefrontal cortex showed an increased signal during the instruction period on anti-saccade trials as compared with pro-saccade trials. When the trials were aligned on the movement stimulus and the instruction period activity was subtracted, there were no differences between pro-and anti-saccades. This finding suggests that the increased cortical activation found in previous blocked designs originates predominately from differences in preparatory set and not from differences in the motor signal between pro-and anti-saccades.

We examined the 2D surface formed by 3D eye positions of normal subjects to determine whether the shape and thickness changed in tasks that differed in saccadic directions; random, horizontal, vertical, radial, clockwise and counter-clockwise. Eye positions during the random task did not lie precisely on Listing's plane but on a surface with a small twist. This twist was present before, during, and after saccades. The degree of twist changed with the task; becoming less twisted for horizontal tasks and more twisted in the vertical tasks. The surface thickness changed with the task becoming thicker for muitidirectional tasks. This greater thickness may occur because surfaces obtained in multidirectional tasks are the composite of surfaces with slightly different shapes.

Although both reaching and grasping require transporting the hand to the object location, only grasping also requires processing of object shape, size and orientation to preshape the hand. Behavioural and neuropsychological evidence suggests that the object processing required for grasping relies on different neural substrates from those mediating object recognition. Specifically, whereas object recognition is believed to rely on structures in the ventral (occipitotemporal) stream, object grasping appears to rely on structures in the dorsal (occipitoparietal) stream. We used functional magnetic resonance imaging (fMRI) to determine whether grasping (compared to reaching) produced activation in dorsal areas, ventral areas, or both. We found greater activity for grasping than reaching in several regions, including anterior intraparietal (AIP) cortex. We also performed a standard object perception localizer (comparing intact vs. scrambled 2D object images) in the same subjects to identify the lateral occipital complex (LOC), a ventral stream area believed to play a critical role in object recognition. Although LOC was activated by the objects presented on both grasping and reaching trials, there was no greater activity for grasping compared to reaching. These results suggest that dorsal areas, including AIP, but not ventral areas such as LOC, play a fundamental role in computing object properties during grasping.

& Everyday life typically requires behavior that involves far more than simple stimulus-response associations. Environmental cues are often ambiguous and require different actions depending on the situation. The prefrontal cortex (PFC) is thought to be crucial for this flexible control of behavior. An important task that probes this ability is the antisaccade task in which subjects have to suppress a glance towards a suddenly presented peripheral stimulus and instead look away from the stimulus to its mirror location. Here we recorded the activity of PFC neurons in monkeys trained to alternate between blocks of prosaccade and antisaccade trials with no external instruction cues. We found that the activity of many neurons was different between the two tasks during the fixation period before the peripheral stimulus was presented. These differences were already present on the first correct trials after a task switch. The activity of these neurons also discriminated between correct responses and errors. We hypothesize that the PFC provides bias signals to saccade-related areas that are necessary to preset the oculomotor system for different tasks. & D

Natural movements towards a target show metric variations between trials. When movements combine contributions from multiple body-parts, such as head-unrestrained gaze shifts involving both eye and head rotation, the individual body-part movements may vary even more than the overall movement. The goal of this investigation was to develop a general method for both mapping sensory or motor response fields of neurons and determining their intrinsic reference frames, where these movement variations are actually utilized rather than avoided. We used head-unrestrained gaze shifts, three-dimensional (3D) geometry, and naturalistic distributions of eye and head orientation to explore the theoretical relationship between the intrinsic reference frame of a sensorimotor neuron's response field and the coherence of the activity when this response field is fitted non-parametrically using different kernel bandwidths in different reference frames. We measure how well the regression surface predicts unfitted data using the PREdictive Sum-of-Squares (PRESS) statistic. The reference frame with the smallest PRESS statistic was categorized as the intrinsic reference frame if the PRESS statistic was significantly larger in other reference frames. We show that the method works best when targets are at regularly spaced positions within the response field's active region, and that the method identifies the best kernel bandwidth for response field estimation. We describe how gain-field effects may be dealt with, and how to test neurons within a population that fall on a continuum between specific reference frames. This method may be applied to any spatially coherent single-unit activity related to sensation and/or movement during naturally varying behaviors.

Natural movements towards a target show metric variations between trials. When movements combine contributions from multiple body-parts, such as head-unrestrained gaze shifts involving both eye and head rotation, the individual body-part movements may vary even more than the overall movement. The goal of this investigation was to develop a general method for both mapping sensory or motor response fields of neurons and determining their intrinsic reference frames, where these movement variations are actually utilized rather than avoided. We used head-unrestrained gaze shifts, three-dimensional (3D) geometry, and naturalistic distributions of eye and head orientation to explore the theoretical relationship between the intrinsic reference frame of a sensorimotor neuron's response field and the coherence of the activity when this response field is fitted non-parametrically using different kernel bandwidths in different reference frames. We measure how well the regression surface predicts unfitted data using the PREdictive Sum-of-Squares (PRESS) statistic. The reference frame with the smallest PRESS statistic was categorized as the intrinsic reference frame if the PRESS statistic was significantly larger in other reference frames. We show that the method works best when targets are at regularly spaced positions within the response field's active region, and that the method identifies the best kernel bandwidth for response field estimation. We describe how gain-field effects may be dealt with, and how to test neurons within a population that fall on a continuum between specific reference frames. This method may be applied to any spatially coherent single-unit activity related to sensation and/or movement during naturally varying behaviors.

Natural movements towards a target show metric variations between trials. When movements combine contributions from multiple body-parts, such as head-unrestrained gaze shifts involving both eye and head rotation, the individual body-part movements may vary even more than the overall movement. The goal of this investigation was to develop a general method for both mapping sensory or motor response fields of neurons and determining their intrinsic reference frames, where these movement variations are actually utilized rather than avoided. We used head-unrestrained gaze shifts, three-dimensional (3D) geometry, and naturalistic distributions of eye and head orientation to explore the theoretical relationship between the intrinsic reference frame of a sensorimotor neuron's response field and the coherence of the activity when this response field is fitted non-parametrically using different kernel bandwidths in different reference frames. We measure how well the regression surface predicts unfitted data using the PREdictive Sum-of-Squares (PRESS) statistic. The reference frame with the smallest PRESS statistic was categorized as the intrinsic reference frame if the PRESS statistic was significantly larger in other reference frames. We show that the method works best when targets are at regularly spaced positions within the response field's active region, and that the method identifies the best kernel bandwidth for response field estimation. We describe how gain-field effects may be dealt with, and how to test neurons within a population that fall on a continuum between specific reference frames. This method may be applied to any spatially coherent single-unit activity related to sensation and/or movement during naturally varying behaviors.

Posterior parietal cortex (PPC) participates in the planning of visuospatial behaviors, including reach movements, in gazecentered coordinates. It is not known if these representations encode the visual goal in retinal coordinates, or the movement direction relative to gaze. Here, by dissociating the intrinsic retinal stimulus from the extrinsic direction of movement, we show that PPC employs a visual code. Using delayed pointing and eventrelated functional magnetic resonance imaging, we identified a cluster of PPC regions whose activity was topographically (contralaterally) related to the direction of the planned movement. We then switched the normal visual--motor spatial relationship by adapting subjects to optical left/right reversing prisms. With prisms, movement-related PPC topography reversed, remaining tied to the retinal image. Thus, remarkably, the PPC region in each hemisphere now responded more for planned ipsilateral pointing movements. Other non-PPC regions showed the opposite world-or motor-fixed pattern. These findings suggest that PPC primarily encodes not motor commands but movement goals in visual coordinates.

Natural movements towards a target show metric variations between trials. When movements combine contributions from multiple body-parts, such as head-unrestrained gaze shifts involving both eye and head rotation, the individual body-part movements may vary even more than the overall movement. The goal of this investigation was to develop a general method for both mapping sensory or motor response fields of neurons and determining their intrinsic reference frames, where these movement variations are actually utilized rather than avoided. We used head-unrestrained gaze shifts, three-dimensional (3D) geometry, and naturalistic distributions of eye and head orientation to explore the theoretical relationship between the intrinsic reference frame of a sensorimotor neuron's response field and the coherence of the activity when this response field is fitted non-parametrically using different kernel bandwidths in different reference frames. We measure how well the regression surface predicts unfitted data using the PREdictive Sum-of-Squares (PRESS) statistic. The reference frame with the smallest PRESS statistic was categorized as the intrinsic reference frame if the PRESS statistic was significantly larger in other reference frames. We show that the method works best when targets are at regularly spaced positions within the response field's active region, and that the method identifies the best kernel bandwidth for response field estimation. We describe how gain-field effects may be dealt with, and how to test neurons within a population that fall on a continuum between specific reference frames. This method may be applied to any spatially coherent single-unit activity related to sensation and/or movement during naturally varying behaviors.

Posterior parietal cortex (PPC) participates in the planning of visuospatial behaviors, including reach movements, in gazecentered coordinates. It is not known if these representations encode the visual goal in retinal coordinates, or the movement direction relative to gaze. Here, by dissociating the intrinsic retinal stimulus from the extrinsic direction of movement, we show that PPC employs a visual code. Using delayed pointing and eventrelated functional magnetic resonance imaging, we identified a cluster of PPC regions whose activity was topographically (contralaterally) related to the direction of the planned movement. We then switched the normal visual--motor spatial relationship by adapting subjects to optical left/right reversing prisms. With prisms, movement-related PPC topography reversed, remaining tied to the retinal image. Thus, remarkably, the PPC region in each hemisphere now responded more for planned ipsilateral pointing movements. Other non-PPC regions showed the opposite world-or motor-fixed pattern. These findings suggest that PPC primarily encodes not motor commands but movement goals in visual coordinates.