Diana J. Gorbet

Preliminary sex differences in human cortical bold fMRI activity during the preparation of increasingly complex visually guided movements

In the past it has often been assumed that the cortical networks for visually guided movement are the same for males and females. Here we use functional magnetic resonance imaging (fMRI) to show significant sex‐related differences in human brain activity during visual‐to‐motor transformation tasks. Although the behavioural performance of the male and female groups did not differ, sex‐related differences in levels of blood oxygen level‐dependent fMRI activity are apparent in several cortical areas that have previously been demonstrated to be important for visually guided movements. These areas include the primary sensorimotor, dorsal premotor, superior parietal and lateral sulcus regions. Furthermore, the data indicate that the nature of these sex differences depends on the spatial mapping between a visual cue and the motor response that it guides.

A miniature radioimmunoassay for melatonin for use with small samples from invertebrates

Melatonin has been identified in a number of invertebrates, but little is known of its functions or its circadian control. Studies in this area are hindered by the lack of an assay for melatonin that is appropriate for use with the small sample volumes obtainable from most invertebrates and with the large numbers of sequential samples generated by circadian studies. We describe and validate a novel, miniature radioimmunoassay (RIA) protocol for these purposes. Sample volumes of c.50 microl were extracted with methanol and the extracts dried in 6 x 50 mm glass tubes. The entire assay was conducted in these tubes. The incubation volume was 200 microl. Bound ligand was precipitated and washed in these tubes, then 400 microl scintillation fluid was added and the tubes were mounted inside conventional scintillation vials for counting. Losses of material due to transfer between containers were thus eliminated. Previous RIAs for melatonin employed multiple transfers between containers and their use with small sample volumes can result in loss of substantial proportions of the sample. Two hundred samples could be processed together. The assay sensitivity was 2 pg melatonin and recovery of internal standards was c.100%. Two commercially available antisera gave closely similar results. The assay was used to quantify melatonin titers in the haemolymph of the insect Rhodnius prolixus (Hemiptera); scotophase haemolymph contained 270 pg/ml melatonin, compared with minimal values (c.40 pg/ml) during the photophase, revealing a daily rhythm. This assay opens the door for analyses of the functions and circadian regulation of melatonin in invertebrates.

Neural correlates of radial frequency trajectory perception in the human brain.

Radial frequency (RF) motion trajectories are visual stimuli that consist of a difference of Gaussians moving along a closed trajectory defined by a sinusoidal variation of the radius relative to a circular path. In the current study, multivoxel fMRI analyses demonstrated that spatial patterns of activity in visual regions V2, V3, and MT can predict RF motion trajectory shape regardless of whether an observer can behaviorally identify the shape or not. This result suggests that processing in these regions is concerned with local properties of the trajectories and not directly linked with a conscious percept of global trajectory shape. Whole-brain analyses show that RF motion trajectories also evoke premotor and posterior parietal cortical activity that may be a neural correlate of shape recognizability. Further, comparisons with activity evoked by static versions of the RF shapes reveal cue-invariant processing in regions of the posterior parietal and occipitotemporal cortices. Interestingly, the RF motion trajectories evoke patterns of dorsal visual stream cortical activity typical of visually guided movement preparation or action observation, suggesting that these stimuli may be processed as potential motor actions rather than as purely visual experiences.

An fMRI examination of the neural processing of periodic motion trajectories.

Perception of periodic or closed-circuit motion trajectories plays a crucial role in our ability to learn and perform many common skilled actions. For example, periodic trajectories are a key component of many types of biological movements when viewed relative to body translation. In the current fMRI study, we used a novel visual stimulus consisting of a target moving along a closed trajectory defined by a radial frequency (RF) pattern (i.e., a sinusoidal variation of trajectory radius relative to a circular trajectory) to determine which brain regions encode these periodic movement paths. Multivoxel pattern analyses permitted prediction of the shapes of different periodic trajectories within regions V2 and V3 indicating that these regions play a role in the processing of periodic visual motion. In addition, blood oxygen level dependent (BOLD) responses associated with the presentation of targets moving along RF trajectories compared with nonperiodic motion and static RF shapes revealed significantly greater activity in visual areas V1, V2, V3, V3A, and V4. To our knowledge, the results of this study represent the first examination of the functional brain activity underlying periodic motion processing and should inform further study.

The Contribution of Different Cortical Regions to the Control of Spatially Decoupled Eye–Hand Coordination

Our brains ability to flexibly control the communication between the eyes and the hand allows for our successful interaction with the objects located within our environment. This flexibility has been observed in the pattern of neural responses within key regions of the frontoparietal reach network. More specifically, our group has shown how single-unit and oscillatory activity within the dorsal premotor cortex (PMd) and the superior parietal lobule (SPL) change contingent on the level of visuomotor compatibility between the eyes and hand. Reaches that involve a coupling between the eyes and hand toward a common spatial target display a pattern of neural responses that differ from reaches that require eye–hand decoupling. Although previous work examined the altered spiking and oscillatory activity that occurs during different types of eye–hand compatibilities, they did not address how each of these measures of neurological activity interacts with one another. Thus, in an effort to fully characterize the relationship between oscillatory and single-unit activity during different types of eye–hand coordination, we measured the spike–field coherence (SFC) within regions of macaque SPL and PMd. We observed stronger SFC within PMdr and superficial regions of SPL (areas 5/PEc) during decoupled reaches, whereas PMdc and regions within SPL surrounding medial intrapareital sulcus had stronger SFC during coupled reaches. These results were supported by meta-analysis on human fMRI data. Our results support the proposal of altered cortical control during complex eye–hand coordination and highlight the necessity to account for the different eye–hand compatibilities in motor control research.

The effect of concussion history on cognitive-motor integration in elite hockey players

Aim: To observe the effects of concussion history on cognitive-motor integration in elite-level athletes. Methods: The study included 102 National Hockey League draft prospects (n = 51 concussion history [CH]; n = 51 no history [NC]). Participants completed two computer-based visuomotor tasks, one involved ‘standard’ visuomotor mapping and one involved ‘nonstandard’ mapping in which vision and action were decoupled. Results: We observed a significant effect of group on reaction time (CH slower) and accuracy (CH worse), but a group by condition interaction only for reaction time (p < 0.05). There were no other deficits found. We discussed these findings in comparison to our previous work with non-elite athletes. Conclusion: Previously concussed elite-level athletes may have lingering neurological deficits that are not detected using standard clinical assessments.

Move faster, think later: Women who play action video games have quicker visually-guided responses with later onset visuomotor-related brain activity

A history of action video game (AVG) playing is associated with improvements in several visuospatial and attention-related skills and these improvements may be transferable to unrelated tasks. These facts make video games a potential medium for skill-training and rehabilitation. However, examinations of the neural correlates underlying these observations are almost non-existent in the visuomotor system. Further, the vast majority of studies on the effects of a history of AVG play have been done using almost exclusively male participants. Therefore, to begin to fill these gaps in the literature, we present findings from two experiments. In the first, we use functional MRI to examine brain activity in experienced, female AVG players during visually-guided reaching. In the second, we examine the kinematics of visually-guided reaching in this population. Imaging data demonstrate that relative to women who do not play, AVG players have less motor-related preparatory activity in the cuneus, middle occipital gyrus, and cerebellum. This decrease is correlated with estimates of time spent playing. Further, these correlations are strongest during the performance of a visuomotor mapping that spatially dissociates eye and arm movements. However, further examinations of the full time-course of visuomotor-related activity in the AVG players revealed that the decreased activity during motor preparation likely results from a later onset of activity in AVG players, which occurs closer to beginning motor execution relative to the non-playing group. Further, the data presented here suggest that this later onset of preparatory activity represents greater neural efficiency that is associated with faster visually-guided responses.

Looking up while reaching out: the neural correlates of making eye and arm movements in different spatial planes

Standard visually guided reaching begins with foveation of a target of interest followed by an arm movement to the same spatial location. However, many visually guided arm movements, as well as a majority of imaging studies examining such movements, require participants to perform non-standard visuomotor mappings where the locations of gaze and arm movements are spatially dissociated (e.g. gaze fixation peripheral to the target of a reaching movement, or use of a tool such as a joystick while viewing stimuli on a screen). In this study, we compare brain activity associated with the production of standard visually guided arm movements to activity during a visuomotor mapping where saccades and reaches were made in different spatial planes. Multi-voxel pattern analysis revealed that while spatial patterns of voxel activity remain quite similar for the two visuomotor mappings during presentation of a cue for movement, patterns of activity become increasingly more discriminative throughout the brain as planning progresses toward motor execution. Decoding of the visuomotor mappings occurs throughout visuomotor-related regions of the brain including the premotor, primary motor and somatosensory, posterior parietal, middle occipital, and medial occipital cortices, and in the cerebellum. These results show that relative to standard visuomotor tasks, activity differs substantially in areas throughout the brain when a task requires an implicit sensorimotor recalibration.

Measuring cognitive-motor integration to detect prolonged performance declines post-concussion

Objective There is a higher risk of re-injury for athletes with concussion history when returning to play, despite being asymptomatic and cleared for activity. One possible explanation is that current return to play assessments test thinking and moving separately, but sport activities often require their concurrent processing (cognitive-motor integration, CMI). The aim of this research is to characterize CMI performance across a range of ages and skill levels following concussion. We hypothesize that there will be CMI impairment, even when cognition and motor action measured separately are deemed recovered, and that impairment level is affected by age and skill level. Methods 133 participants with concussion history (mix of youth, adolescent, university, and elite athletes) and 130 no-concussion controls (age/sex/skill matched) performed two eye-hand coordination tasks. Participants displaced a cursor from a central to peripheral targets by either sliding their finger on a vertically-oriented touchscreen or with decoupled eye-hand coordination (targets/cursor viewed on vertical screen but finger slid on second horizontal touchscreen with 180° cursor feedback rotation). Results Children, young adult, and elite athletes with concussion history all had CMI performance deficits in movement planning, timing and execution, despite being asymptomatic and returned to play. Younger and less skilled athletes were more impaired relative to older/elite performers. Conclusions Cognitive-motor integration tasks are successful in detecting performance post-concussion relative to established assessment tools that test these domains separately. We propose that testing CMI performance, a skill crucial in sport, is important to comprehensively assess function post-concussion and to prevent re-injury. Competing interests None.

White matter integrity and its relationship to cognitive-motor integration in females with post-concussion syndrome

Objective Cognitive-motor integration (CMI) is required in sport when performing movements where a rule is used to align the required motor output and the guiding visual information. Previous research has shown CMI declines in young athletes with a concussion history, deemed recovered at the time of evaluation. The purpose of this study was to characterise differences in symptoms, CMI, and white matter integrity (fractional anisotropy, FA) in those with post-concussion syndrome (PCS) and healthy controls. We hypothesised that those with PCS would have decreased FA and CMI performance, with increased symptom scores. Participants Twelve females were included; 6 with PCS for 6 months or more, and 6 age-matched healthy controls with no concussion history. Methods Participants were administered the SCAT3, four visuomotor CMI tasks, and diffusion weighted images were acquired. Participants displaced a cursor from a central target to peripheral targets by sliding their finger on a horizontally placed tablet either directly to the viewed target or with decoupled eye-hand coordination (targets viewed on a vertical monitor, 180° feedback rotation, or both). Results We observed worse symptom scores and impaired performance in CMI tasks, as well as decreased mean FA in bilateral corticospinal tracts beneath the premotor and primary motor cortices and in the white matter underlying the right superior parietal lobule, in those with PCS compared to healthy controls. Conclusions CMI decline may be related to decreased FA within the frontal-parietal-subcortical network. Measuring CMI, a skill crucial to athletes, provides an effective behavioural means for detection of brain alterations associated with concussion. Competing interests None.