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We studied visual perception using an annular random-dot motion stimulus called the racetrack. We recorded neural activity using magnetoencephalography while subjects viewed variants of this stimulus that contained no inherent motion or various degrees of embedded motion. Subjects reported seeing rotary motion during viewing of all stimuli. We found that, in the absence of any motion signals, patterns of brain activity differed between states of motion perception and nonperception. Furthermore, when subjects perceived motion, activity states within the brain did not differ across stimuli of different amounts of embedded motion. In contrast, we found that during periods of nonperception brain-activity states varied with the amount of motion signal embedded in the stimulus. Taken together, these results suggest that during perception the brain may lock into a stable state in which lower-level signals are suppressed. racetrack illusion | visual motion perception doi/ 10.1073/pnas.1009857108

A study was conducted to evaluate the effects of erbium, chromium:yttrium-scandium-gallium-garnet laser irradiation on root canals. Findings indicate a disinfecting effect in the root dentin samples that was dependent on the output power but not specific for the bacterial species examined.

Directional tuning is a basic functional property of cell activity in the motor cortex. Previous work has indicated that cells with similar preferred directions are organized in columns perpendicular to the cortical surface. Here we show that these columns are organized in an orderly fashion in the tangential dimension on the cortical surface. Based on a large number of microelectrode penetrations and systematic exploration of the proximal arm area of the motor cortex while monkeys made free reaching 3D movements, it was estimated that (i) directional minicolumns are [approximately equal to] 30 [mu]m in width, (ii) minicolumns with similar preferred directions tend to occur in doublets or triplets, and (iii) such minicolumns tend to repeat every [approximately equal to] 240 [micro]m (estimated width of a column), with intermediate preferred directions represented in a gradient. These findings provide evidence for an orderly mapping of the preferred direction in the motor cortex. monkey | reaching | minicolumn

AKACID Plus, a novel polymeric guanidine with broad antimicrobial activity against multiantibiotic-resistant bacterial strains is used as a room disinfectant in a study at concentrations of 0.1, 0.25, and 0.5% for 100 min. The findings indicate that nebulized AKACID Plus at a concentration of 0.5% is a potent substance for eradication of pathogenic organisms in the hospital setting.

We visualized synchronous dynamic brain networks by using prewhitened (stationary) magnetoencephalography signals. Data were acquired from 248 axial gradiometers while 10 subjects fixated on a spot of light for 45 s. After fitting an autoregressive integrative moving average model and taking the residuals, all pairwise, zero-lag, partial cross-correlations ([PCC.sup.0.sub.ij]) between the i and j sensors were calculated, providing estimates of the strength and sign (positive and negative) of direct synchronous coupling between neuronal populations at a 1-ms temporal resolution. Overall, 51.4% of [PCC.sup.0.sub.ij] were positive, and 48.6% were negative. Positive [PCC.sup.0.sub.ij] occurred more frequently at shorter intersensor distances and were 72% stronger than negative ones, on the average. On the basis of the estimated [PCC.sup.0.sub.ij], dynamic neural networks were constructed (one per subject) that showed distinct features, including several local interactions. These features were robust across subjects and could serve as a blueprint for evaluating dynamic brain function. neural networks | synchrony | time-series analysis

We investigated the presence of short-range order (

A key idea in Lashley's formulation of the problem of serial order in behavior is the postulated neural representation of all serial elements before the action begins. We studied this question by recording the activity of individual neurons simultaneously in small ensembles in prefrontal cortex while monkeys copied geometrical shapes shown on a screen. Monkeys drew the shapes as sequences of movement segments, and these segments were associated with distinct patterns of neuronal ensemble activity. Here we show that these patterns were present during the time preceding the actual drawing. The rank of the strength of representation of a segment in the neuronal population during this time, as assessed by discriminant analysis, predicted the serial position of the segment in the motor sequence. An analysis of errors in copying and their neural correlates supplied additional evidence for this code and provided a neural basis for Lashley's hypothesis that errors in motor sequences would be most likely to occur when executing elements that had prior representations of nearly equal strength.

We studied the performance and cortical activation patterns during a mental rotation task (Shepard & Metzler, 1971) using functional magnetic resonance imaging (fMRI) at high field (4 Tesla). Twenty-four human subjects were imaged (fMRI group), whereas six additional subjects performed the task without being imaged (control group). All subjects were shown pairs of perspective drawings of 3D objects and asked to judge whether they were the same or mirror images. The measures of performance examined included (1) the percentage of errors, (2) the speed of performance, calculated as the inverse of the average response time, and (3) the rate of rotation for those object pairs correctly identified as 'same.' We found the following: (1) Subjects in the fMRI group performed well outside and inside the magnet, and, in the latter case, before and during data acquisition. Moreover, performance over time improved in the same manner as in the control group. These findings indicate that exposure to high magnetic fields does not impair performance in mental rotation. (2) Functional activation data were analyzed from 16 subjects of the fMRI group. Several cortical areas were activated during task performance. The relations between the measures of performance above and the magnitude of activation of specific cortical areas were investigated by anatomically demarcating these areas of interest and calculating a normalized activation for each one of them. (3) We used the multivariate technique of hierarchical tree modeling to determine functional clustering among areas of interest and performance measures. Two main branches were distinguished: One comprised areas in the right hemisphere and the extrastriate and superior parietal lobules bilaterally, whereas the other comprised areas of the left hemisphere and the frontal pole bilaterally; all three performance measures above clustered with the former branch. Specifically, performance outcome ('percentage of errors') clustered with the parieto-occipital subcluster, whereas both the speed of performance and the rate of mental rotation clustered with the right precentral gyrus. We conclude that the mental rotation paradigm used involves the cooperative interaction of functional groups of cortical areas of which some are probably more specifically associated with performance, whereas others may serve a more general function within the task constraints., INTRODUCTION Shepard and his colleagues pioneered a series of tasks involving mental rotation of visual images (Shepard & Metzler, 1971; Shepard & Cooper, 1982). Typically, subjects are shown two asymmetric [...]

Many studies during the past 15 years have shown that the direction of motor output (movement or isometric force) is an important factor for neuronal activity in the motor cortex, both at the level of single cells and at the level of neuronal populations. Recent studies have investigated several new aspects of this problem including the effect of posture, the relations to time-varying movement parameters (for example, position, velocity and acceleration) and the cortical representation of memorized simple movements and complex-movement trajectories. Furthermore, the neural correlates of directional operations, such as mental rotation and memory-scanning of visuomotor directions, have also been investigated. In addition, neural networks have been used to model dynamic, time-varying, spatial motor trajectories.

A monkey was trained to respond on the basis of the serial position of a test stimulus in a sequence. First, three stimuli were presented successively on a circle. Then [...]

Use of a massively interconnected neural network model helps examine the theory that largely overlapping networks promote and store learned movement trajectories of various shapes. The core network produces externally instructed trajectories while both core and trajectory-specific region are essential for internally stored trajectories. Movement information is stored in weights of connection between the core region and specialized units and among specialized units. The core generates nearly the entire output of the network while specialized parts participate in driving dynamic behavior.

A major challenge of current neuroscience is to elucidate the brain mechanisms that underline cognitive function. There is not doubt that processing in the brainengages large populations of cells. This article explores the logic of investigating these problems by combining psychological in human subjects and neurophysiological studies of neuronal populations in the motor cortex of behaving monkeys. The results obtained show tha time-varying psychological processes can be visualized in the time-varying activity of neuronal populations. Moreover, the fucntional interactions betwen cells in the motor cortex are ver similar to those observed in a vassively interconnected artificial network performing the same computation., The recording of the activity of single cells in the brain of behaving animals provides a tool for directly studying the functional properties of single cells, interactions betwee cells, and [...]

The relation of cellular activity in the motor cortex to the direction of two-dimensional isometric force was investigated under dynamic conditions in monkeys. A task was designed so that three force variables were dissociated: the force exerted by the subject, the net force, and the change in force. Recordings of neuronal activity in the motor cortex revealed that the activity of single cells was directionally tuned and that this tuning was invariant across different directions of a bias force. Cell activity was not related to the direction of force exerted by the subject, which changed drastically as the bias force changed. In contrast, the direction of net force, the direction of force change, and the visually instructed direction all remained quite invariant and congruent and could be the directional variables, alone or in combination, to which cell activity might relate., One problem in motor physiology concerns the relation between cell activity in the motor cortex and the force exerted by a subject. This problem has been studied extensively under static [...]

A hemispheric asymmetry in the functional activation of the human motor cortex during contralateral (C) and ipsilateral (1) finger movements, especially in right-handed subjects, was documented with nuclear magnetic resonance imaging at high field strength (4 tesla). Whereas the right motor cortex was activated mostly during contralateral finger movements in both right-handed (C/I mean area of activation = 36.8) and left-handed (C/I = 29.9) subjects, the left motor cortex was activated substantially during ipsilateral movements in left-handed subjects (C/I = 5.4) and even more so in right-handed subjects (C/I = 1.3)., Two basic aspects of human motor function are hemispheric dominance and handedness. The dominant roles of the left hemisphere for speech and the right hemisphere for visuospatial tasks and for [...]

Abstract * Two rhesus monkeys were trained to intercept a moving target at a fixed location with a feedback cursor controlled by a 2-D manipulandum. The direction from which the [...]

Abstract * The single-unit activity of 831 cells was recorded in the arm area of the motor cortex of two monkeys while the monkeys intercepted a moving visual stimulus (interception [...]

Apostolos P. Georgopoulos [1,2] Kenneth Whang [1,2] Maria-Alexandra Georgopoulos [1,2] Georgios A. Tagaris [1,2] Bagrat Amirikian [1,2] Wolfgang Richter [2] Seong-Gi Kim [2] Kamil Ugurbil [2] Abstract We studied the [...]

Abstract * We sought to determine how a visual maze is mentally solved. Human subjects (N = 13) viewed mazes with orthogonal, unbranched paths; each subject solved 200-600 mazes in [...]

Abstract * The functional equivalence of overt movements and dynamic imagery is of fundamental importance in neuroscience. Here, we investigated the participation of the neocortical motor areas in a classic [...]

The neural encoding of serial order was studied in the motor cortex of monkeys performing a context-recall memory scanning task. Up to five visual stimuli were presented successively on a circle (list presentation phase), and then one of them (test stimulus) changed co[or; the monkeys had to make a single motor response toward the stimulus that immediately followed the test stimulus in the list. Correct performance in this task depends on memorization of the serial order of the stimuli during their presentation. It was found that changes in neural activity during the list presentation phase reflected the serial order of the stimuli; the effect on cell activity of the serial order of stimuli during their presentation was at least as strong as the effect of motor direction on cell activity during the execution of the motor response. This establishes the serial order of stimuli in a motor task as an important determinant of motor cortical activity during stimulus presentation and in the absence of changes in peripheral motor events, in contrast to the commonly held view of the motor cortex as just an 'upper motor neuron.', Ever since Lashley's famous paper in 1951 (1), the imagination of psychologists and neuroscientists alike has been captured by the problem of serial order in behavior. Accurate representation of temporal [...]

Neuronal Population Coding of Movement Direction FOR MANY FUNCTIONS CONTROLLED by the brain or variables represented in the brain, the relevant unit is the neuronal population rathr than the individual [...]

STEPHEN M. KOSSLYN. MIT Press, Cambridge, MA, 1994. x, 516 pp., illus. $45 or 38.50°. Kosslyn's Image and Brain is a tour de force in the analysis of visual perception [...]

Mental imagery paradigms can be used to study properties of representations of movement. Such studies of mental representations of movement parameters can provide information on properties of motor representations not only at the macroscopic but also at the microscopic level. Moreover, if the brain is capable of representing movement parameters, then one should be able to observe neural activity related to these parameters when the movement is intended.

Mental Rotation of the Neuronal Population Vector A FUNDAMENTAL PROBLEM IN COGNITIVE neuroscience is the identification and elucidation of brain events underlying cognitive operations. The technique of recording the activity [...]

This paper discusses work on the function of the motor cortex as revealed by single cell recordings in monkeys and artificial neural network modelling. Our key conceptual approach both in behavioural neuroscience and neural network modeling of motor cortical function relies on reconstructing, visualizing, and modelling the activity in neuronal populations, indeed a key concept advanced by Hebb (1949). The behaviour investigated ranges from exertion of isometric force to pointing movements to complex cognitive processing. The functional properties of single cells with respect to the direction of movement in space are described as well as a population code which provides a unique measure for this direction. Finally, the results of modeling studies are discussed in which directional population activity is used as an input to an artificial neural network to drive a simulated arm.