Influential theories of skilled action posit that distinct cognitive mechanisms and neuroanatomic substrates support meaningless gesture imitation and tool use pantomiming, and poor performance on these tasks are hallmarks of limb apraxia. Yet prior research has primarily investigated brain-behavior relations at the group level; thus, it is unclear whether we can identify individuals with isolated impairments in meaningless gesture imitation or tool use pantomiming whose performance is associated with a distinct neuroanatomic lesion profile. The goal of this study was to test the hypothesis that individuals with disproportionately worse performance in meaningless gesture imitation would exhibit cortical damage and white matter disconnection in left fronto-parietal brain regions, whereas individuals with disproportionately worse performance in tool use pantomiming would exhibit cortical damage and white matter disconnection in left temporo-parietal brain regions. Fifty-eight participants who experienced a left cerebrovascular accident took part in a meaningless gesture imitation task, a tool use pantomiming task, and a T1 structural MRI. Two participants were identified who had relatively small lesions and disproportionate impairments on one task relative to the other, as well as below-control-level performance on one task and not the other. Using these criteria, one participant was disproportionately impaired at meaningless gesture imitation, and the other participant was disproportionately impaired at pantomiming tool use. Graph theoretic analysis of each participant's structural disconnectome demonstrated that disproportionately worse meaningless gesture imitation performance was associated with disconnection among the left inferior parietal lobule, the left superior parietal lobule, and the left middle and superior frontal gyri, whereas disproportionately worse tool use pantomiming performance was associated with disconnection between left temporal and parietal regions. Our results demonstrate that relatively focal lesions to specific portions of the Tool Use Network can be associated with distinct limb apraxia subtypes.

ObjectiveTest for a dose dependent relationship between cumulative sub-concussive head trauma loading and localised changes of brain white matter in college athletes.DesignProspective cohort studySettingNCAA Division I Women’s SoccerParticipants10 players were monitored for head impacts throughout a soccer season using wearable sensors. Linear and rotational accelerations recorded during impacts were processed to calculate the cumulative impact power. Diffusion spectrum imaging (DSI) data were acquired at season start and at 3 additional intervals. 11 age and gender matched control data sets were acquired.InterventionOne athlete suffered a concussion, was removed from play for neurocognitive testing, and entered a supervised return-to-play protocol.Outcome measuresCumulative impact power was used as a measure of the head trauma load accumulated prior to each MRI. Multi-dimensional anisotropy (MDA) values assessed localised severity of white matter changes. Session specific differences between each player’s MDA values and those of the control population were used to relate cumulative impact power and the severity of white matter changes.Main resultsHighly significant clusters of abnormal voxels were observed in athletes with no diagnosed concussion symptoms. Injury severity correlated with cumulative head impact power and demonstrated a pronounced threshold behaviour. MDA diffusion changes were located mainly within the frontal and occipital cortex at the gray-white boundary, and to a lesser degree in deep subcortical areas where there is a higher proportion of crossing fibres.ConclusionsThis cohort demonstrates dose dependent changes in white matter integrity as a function of cumulative sub-concussive head trauma.Competing interestsSG is supported, in part, by a research grant from X2 Biosystems and a General Electric-National Football League Head Health Challenge award.