Mild traumatic brain injury (mTBI), or concussion, is the most common type of traumatic brain injury. With mTBI comes symptoms that include headaches, fatigue, depression, anxiety and irritability, as well as impaired cognitive function. Symptom resolution is thought to occur within 3 months post-injury, with the exception of a small percentage of individuals who are said to experience persistent post-concussion syndrome. The number of individuals who experience persistent symptoms appears to be low despite clear evidence of longer-term pathophysiological changes resulting from mTBI. In light of the incongruency between these longer-term changes in brain pathology and the number of individuals with longer-term mTBI-related symptoms, particularly impaired cognitive function, we performed a scoping review of the literature that behaviourally assessed short- and long-term cognitive function in individuals with a single mTBI, with the goal of identifying the impact of a single concussion on cognitive function in the chronic stage post-injury. CINAHL, Embase, and Medline/Ovid were searched July 2015 for studies related to concussion and cognitive impairment. Data relating to the presence/absence of cognitive impairment were extracted from 45 studies meeting our inclusion criteria. Results indicate that, in contrast to the prevailing view that most symptoms of concussion are resolved within 3 months post-injury, approximately half of individuals with a single mTBI demonstrate long-term cognitive impairment. Study limitations notwithstanding, these findings highlight the need to carefully examine the long-term implications of a single mTBI.

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Participants were cued by an auditory tone to grasp a target object from within a size-contrast display. The peak grip aperture was unaffected by the perceptual size illusion when the target array was visible between the response cue and movement onset (vision trials). The grasp was sensitive to the illusion, however, when the target array was occluded from view when the response was cued (occlusion trials). This was true when the occlusion occurred 2.5 s before the response cue (delay), but also when the occlusion coincided with the response cue (no-delay). Unlike previous experiments, vision and occlusion trials were presented in random sequence. The results suggest that dedicated, real-time visuomotor mechanisms are engaged for the control of action only after the response is cued, and only if the target is visible. These visuomotor mechanisms compute the absolute metrics of the target object and therefore resist size-contrast illusions. In other situations (e.g. prior to the response cue, or if the target is no longer visible), a perceptual representation of the target object can be used for action planning. Unlike the real-time visuomotor mechanisms, perception-based movement planning makes use of relational metrics, and is therefore sensitive to size-contrast illusions.

. Opposite perceptual and sensorimotor responses to a size-weight illusion. J Neurophysiol 95: 3887-3892, 2006; doi:10.1152/jn.00851.2005. The perceptual size-weight illusion (SWI) occurs when two different-sized objects with equal mass are lifted in sequence: the smaller object is consistently reported to feel heavier than the larger object even after repeated lifting attempts. Here we explored the relationship between sensorimotor and perceptual responses to a SWI in which the smaller of the two target objects in fact weighed slightly less (2.7 N) than the larger object (3.2 N). For 20 consecutive lifts, participants consistently reported that the small-light object felt heavier than the large-heavy object; however, concurrently measured lifting dynamics showed exactly the opposite pattern: peak grip force, peak grip force rate, peak load force, and peak load force rate were all significantly greater for the large-heavy object versus the small-light object. The difference in peak load rate between the two objects was greatest for the initial lift but decreased significantly beyond that point, suggesting that the sensorimotor system used sensory feedback to correct for initial overand underestimations of object mass. Despite these adjustments to lifting dynamics over the early trials, the difference between the judged heaviness of the two objects did not change. The findings clearly demonstrate that the sensorimotor and perceptual systems utilize distinctly different mechanisms for determining object mass.

One of the most important functions of vision is to direct actions to objects 1 . However, every time that vision is used to guide an action, retinal motion signals are produced by the movement of the eye and head as the person looks at the object or by the motion of other objects in the scene. To reach for the object accurately, the visuomotor system must separate information about the position of the stationary target from background retinal motion signals-a long-standing problem that is poorly understood 2-7 . Here we show that the visuomotor system does not distinguish between these two information sources: when observers made fast reaching movements to a briefly presented stationary target, their hand shifted in a direction consistent with the motion of a distant and unrelated stimulus, a result contrary to most other findings 8,9 . This can be seen early in the hand's trajectory (~120 ms) and occurs continuously from programming of the movement through to its execution. The visuomotor system might make use of the motion signals arising from eye and head movements to update the positions of targets rapidly and redirect the hand to compensate for body movements.In the first experiment we investigated the role of distant motion signals in the updating of reaching movements to a stationary target. We briefly presented a stationary object while subjects fixated on a bull's-eye at the centre of a screen (see Fig. 1a and Methods). Subjects hit the position of the flashed object as quickly as possible with their index finger. A vertically drifting pattern was presented on the screen throughout the trial. Initially the pattern drifted in one direction, but, at an unpredictable moment, the direction of the drifting pattern was reversed. Figure 1b shows that the endpoints of the reaching movements were shifted either upwards or downwards in the direction of the nearby motion. Target flashes presented well before (for example −940 ms) or well after (for example 470 ms) the motion reversal (at 0 ms) produced systematic shifts in the hand's position. Because the target in these cases was presented sufficiently long before or after the motion reversal, the entire reaching movement -both programming and execution-was performed during unidirectional motion (average movement onset and movement duration were 224 and 262 ms, respectively). For this reason it is unclear whether the motion influenced the programming phase or the on-line phase of the reaching movement, or both. Competing interests statementThe authors declare that they have no competing financial interests. NIH Public Access Author ManuscriptNature. Author manuscript; available in PMC 2014 January 13. The target flash presented 235 ms before the moving pattern reversed direction addresses this question: because the average reaction time was 220 ms, motion was in one direction during most of the programming phase and in the opposite direction during the movement. This condition produced a markedly reduced shift in the movement endpoint (grey oval in Fig....

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