We analyzed the magnitude and interneuronal correlation of the variability in the activity of single neurons that were recorded simultaneously using a multielectrode array in the primary motor cortex and parietal areas 2/5 in rhesus monkeys. The animals were trained to move their arms in one of eight directions as instructed by a visual target. The relationship between variability (SD) and mean of the discharge rate was described by a power function with a similar exponent ( approximately 0.57), regardless of the cortical area or the behavioral condition. We examined whether the deviation from mean activity between target onset and the end of the movement was correlated on a trial-by-trial basis with variability in activity during the hold period before target onset. In both cortical areas, for about a quarter of the neurons, the neuronal noise of these two periods was positively correlated, whereas significant negative correlations were seldom observed. Overall, neurons with higher signal correlation (i.e., similar directional pattern) showed higher noise correlation in both cortical areas. On the other hand, when the data were divided according to the distance between the electrode tips from which the neurons were recorded, a consistent relationship between the signal and noise correlations was found only for pairs of neurons recorded through the same electrode. These results suggest that nearby neurons with similar directional tuning carry primarily redundant messages, whereas neurons in separate cortical columns perform more independent processing.

The visual world presents multiple potential targets that can be brought to the fovea by saccadic eye movements. These targets produce activity at multiple sites on a movement map in the superior colliculus (SC), an area of the brain related to saccade generation. The saccade made must result from competition between the populations of neurons representing these many saccadic goals, and in the present experiments we used multiple moveable microelectrodes to follow this competition. We recorded simultaneously from two sites on the SC map where each site was related to a different saccade target. The two targets appeared in rapid sequence, and the monkey was rewarded for making a saccade toward the one appearing first. Our study concentrated on trials in which the monkey made strongly curved saccades that were directed first toward one target and then toward the other. These curved saccades activated both sites on the SC map as they veered from one target to the other. The major finding was that the strongly curved saccades were preceded by sequential activity in the two neurons as indicated by three observations: the firing rate for the neuron related to the first target reached its peak earlier than did the rate of the neuron for the second target; the timing of the peak activity of the two neurons was related to the beginning and end of the saccade curvature; a weighted vector-average model based on the activity of the two neurons predicted the timing of saccade curvature. Straight averaging saccades ended between the targets so that they did not go to either target, and they were accompanied by simultaneous rather than sequential activation of the two neurons. Thus when multiple populations of neurons are active on the SC movement map, the resulting saccade is determined by the relative timing of the activity in the populations as well as their magnitude. In contrast, SC activity at the two sites did not predict the final direction of the saccade, and several control experiments found insufficient activity at other sites on the SC map to account for that final direction. We conclude that the SC neuronal activity predicts the timing of the saccade curvature, but not the final direction of the trajectory. These observations are consistent with SC activity being critical in selecting the goal of the saccade, but not in determining the exact trajectory.

We investigated the capacities of human subjects to intercept moving targets in a two-dimensional (2D) space. Subjects were instructed to intercept moving targets on a computer screen using a cursor controlled by an articulated 2D manipulandum. A target was presented in 1 of 18 combinations of three acceleration types (constant acceleration, constant deceleration, and constant velocity) and six target motion times, from 0.5 to 2.0 s. First, subjects held the cursor in a start zone located at the bottom of the screen along the vertical meridian. After a pseudorandom hold period, the target appeared in the lower left or right corner of the screen and traveled at 45 degrees toward an interception zone located on the vertical meridian 12.5 cm above the start zone. For a trial to be considered successful, the subject's cursor had to enter the interception zone within 100 ms of the target's arrival at the center of the interception zone and stay inside a slightly larger hold zone. Trials in which the cursor arrived more than 100 ms before the target were classified as "early errors," whereas trials in which the cursor arrived more than 100 ms after the target were classified as "late errors." Given the criteria above, the task proved to be difficult for the subjects. Only 41.3% (1080 out of 2614) of the movements were successful, whereas the remaining 58.7% were temporal (i.e., early or late) errors. A large majority of the early errors occurred in trials with decelerating targets, and their percentage tended to increase with longer target motion times. In contrast, late errors occurred in relation to all three target acceleration types, and their percentage tended to decrease with longer target motion times. Three models of movement initiation were investigated. First, the threshold-distance model, originally proposed for optokinetic eye movements to constant-velocity visual stimuli, maintains that response time is composed of two parts, a constant processing time and the time required for the stimulus to travel a threshold distance. This model only partially fit our data. Second, the threshold-tau model, originally proposed as a strategy for movement initiation, assumes that the subject uses the first-order estimate of time-to-contact (tau) to determine when to initiate the interception movement. Similar to the threshold distance model, the threshold-tau model only partially fit the data. Finally, a dual-strategy model was developed which allowed for the adoption of either of the two strategies for movement initiation; namely, a strategy based on the threshold-distance model ("reactive" strategy) and another based on the threshold-tau model ("predictive" strategy). This model provided a good fit to the data. In fact, individual subjects preferred to use one or the other strategy. This preference was allowed to be manifested at long target motion times, whereas shorter target motion times (i.e., 0.5 s and 0.8 s) forced the subjects to use only the reactive strategy.

I-RFA is a protective factor associated with less severe acute symptoms and shorter recovery after SRC. Conveying this message to athletes, coaches, and others involved in the care of athletes may promote timely injury reporting.

Animals control contact with surfaces when locomoting, catching prey, etc. This requires sensorily guiding the rate of closure of gaps between effectors such as the hands, feet or jaws and destinations such as a ball, the ground and a prey. Control is generally rapid, reliable and robust, even with small nervous systems: the sensorimotor processes are therefore probably rather simple. We tested a hypothesis, based on general tau theory, that closing two gaps simultaneously, as required in many actions, might be achieved simply by keeping the taus of the gaps coupled in constant ratio. tau of a changing gap is defined as the time-to-closure of the gap at the current closure-rate. General tau theory shows that tau of a gap could, in principle, be directly sensed without needing to sense either the gap size or its rate of closure. In our experiment, subjects moved an effector (computer cursor) to a destination zone indicated on the computer monitor, to stop in the zone just as a moving target cursor reached it. The results indicated the subjects achieved the task by keeping tau of the gap between effector and target coupled to tau of the gap between the effector and the destination zone. Evidence of tau-coupling has also been found, for example, in bats guiding landing using echolocation. Thus, it appears that a sensorimotor process used by different species for coordinating the closure of two or more gaps between effectors and destinations entails constantly sensing the taus of the gaps and moving so as to keep the taus coupled in constant ratio.

We studied the kinematic characteristics of arm movements and their relation to a stimulus moving with a wide range of velocity and acceleration. The target traveled at constant acceleration, constant deceleration, or constant velocity for 0.5-2.0 s, until it arrived at a location where it was required to be intercepted. For fast moving targets, subjects produced single movements with symmetrical, bell-shaped velocity profiles. In contrast, for slowly moving targets, hand velocity profiles displayed multiple peaks, which suggests a control mechanism that produces a series of discrete submovements according to characteristics of target motion. To analyze how temporal and spatial aspects of these submovements are influenced by target motion, we decomposed the vertical hand velocity profiles into bell-shaped velocity pulses according to the minimum-jerk model. The number of submovements was roughly proportional to the movement time, resulting in a relatively constant submovement frequency (approximately 2.5 Hz). On the other hand, the submovement onset asynchrony showed significantly more variability than the intersubmovement interval, indicating that the submovement onset was delayed more following a submovement with a longer duration. Examination of submovement amplitude and its relation to target motion revealed that the subjects achieved interception mainly by producing a series of submovements that would keep the displacement of the hand proportional to the first-order estimate of target position at the end of each submovement along the axis of hand movement. Finally, we did not find any evidence that information regarding target acceleration is properly utilized in the production of submovements.

During tasks requiring concentration, the IBI increased (blink rate decreased) and many blinks were incomplete without CLs. With CLs, tear film instability increased. Blinking frequency also increased, but it remained high when subjects played the game, and symptoms of ocular irritation increased. This suggests that wearing soft CLs, even when fully adapted, provides enough extrinsic ocular surface stimulation to override internal controls and affect blink parameters.

Background: Vestibular and ocular symptoms in sport-related concussions are common. The Vestibular/Ocular-Motor Screening (VOMS) tool is a rapid, free, pen-and-paper tool that directly assesses these symptoms and shows consistent utility in concussion identification, prognosis, and management. However, a VOMS validation study in the acute concussion period of a large sample is lacking. Purpose: To examine VOMS validity among collegiate student-athletes, concussed and nonconcussed, from the multisite National Collegiate Athletic Association–Department of Defense Concussion Assessment, Research and Education (CARE) Consortium. A secondary aim was to utilize multidimensional machine learning pattern classifiers to deduce the additive power of the VOMS in relation to components of the Sport Concussion Assessment Tool 3 (SCAT3). Study Design: Cohort study (diagnosis); Level of evidence, 3. Methods: Preseason and acute concussion assessments were analyzed for 419 student-athletes. Variables in the analysis included the VOMS, Balance Error Scoring System, Standardized Assessment of Concussion, and SCAT3 symptom evaluation score. Descriptive statistics were calculated for all tools, including Kolmogorov-Smirnov significance and Cohen d effect size. Correlations between tools were analyzed with Spearman r, and predictive accuracy was evaluated through an Ada Boosted Tree machine learning model’s generated receiver operating characteristic curves. Results: Total VOMS scores and SCAT3 symptom scores demonstrated significant increases in the acute concussion time frame (Cohen d = 1.23 and 1.06; P < .0001), whereas the Balance Error Scoring System lacked clinical significance (Cohen d = 0.17). Incorporation of VOMS into the full SCAT3 significantly boosted overall diagnostic ability by 4.4% to an area under the curve of 0.848 ( P < .0001) and produced a 9% improvement in test sensitivity over the existing SCAT3 battery. Conclusion: The results from this study highlight the relevance of the vestibular and oculomotor systems to concussion and the utility of the VOMS tool. Given the 3.8 million sports-related and 45,121 military-related concussions per year, the addition of VOMS to the SCAT3 is poised to identify up to an additional 304,000 athletes and 3610 servicemembers annually who are concussed, thereby improving concussion assessment and diagnostic rates. Health care providers should consider the addition of VOMS to their concussion assessment toolkits, as its use can positively affect assessment and management of concussions, which may ultimately improve outcomes for this complex and common injury.