Linguistic correlates of asymmetric motor symptom severity in Parkinson’s Disease

Asymmetric motor severity is common in Parkinson’s Disease (PD) and provides a method for examining the neurobiologic mechanisms underlying cognitive and linguistic deficits associated with the disorder. In the present research, PD participants (N = 31) were assessed in terms of the asymmetry of their motor symptoms. Interviews with the participants were analyzed with the Linguistic Inquiry and Word Count (LIWC) program. Three measures of linguistic complexity – the proportion of verbs, proportion of function words, and sentence length – were found to be affected by symptom asymmetry. Greater left-side motor severity (and hence greater right-hemisphere dysfunction) was associated with the production of significantly fewer verbs, function words, and shorter sentences. Hence, the production of linguistic complexity in a natural language context was associated with relatively greater right hemisphere involvement. The potential neurobiological mechanisms underlying this effect are discussed.     

Role of motor processes in extrinsically encoding mental transformations

Previous research has shown that imagined perspective rotations elicit spatial and low-level cortical motor areas of the brain when participants rely on knowledge of their physical body, or body percept (Wraga, Flynn, Boyle, & Evans, 2010). The current study used functional magnetic resonance imaging (fMRI) to investigate whether recruitment of the body percept would activate low-level cortical motor areas of the brain within other classes of mental transformations. Participants performed imagined object and perspective rotations of three-dimensional Shephard-Metzler (1971) stimuli. For each task, participants used button presses serving as virtual pointers to locate a prescribed portion of the stimuli with respect to their "right" and "left." We found low-level cortical motor activation (M1) for both mental transformations; however, the degree to which such activation related to participants' performance differed, as well as the recruitment of additional nonmotoric strategies. The results are discussed in terms of recent hypotheses regarding the role of the body percept in extrinsically encoded mental transformations.     

Bimanual reaching across the hemispace: Which hand is yoked to which?

When both hands perform concurrent goal-directed reaches, they become yoked to one another. To investigate the direction of this coupling (i.e., which hand is yoked to which), the temporal dynamics of bimanual reaches were compared with equivalent-amplitude unimanual reaches. These reaches were to target pairs located on either the left or right sides of space; meaning that in the bimanual condition, one hand's contralateral (more difficult) reach accompanied by the other hand's ipsilateral (easier) reach. By comparing which hand's difficult reach was improved more by the presence of the other hand's easier ipsilateral reach, we were able to demonstrate asymmetries in the coupling. When the cost of bimanual reaching was controlled for the contralateral reaching left hand's performance was improved, suggesting that the left hand is yoked to the right during motor output. In contrast, the right hand showed the greatest improvements for contralateral reaching in terms of reaction time, pointing toward a dominant role for the left hand in the processes prior to movement onset. The results may point toward a mechanism for integrating the unitary system of attention with bimanual coordination.     

The effect of attending to motor overflow on its voluntary inhibition in young and older adults

Motor overflow refers to involuntary movement or muscle activity coinciding with voluntary movement. We examined whether 16 young adults (18-30 years) and 16 older adults (50-80 years) could voluntarily inhibit overflow. Participants performed a finger pressing task, exerting 50% of their maximal force. Overflow was concurrently recorded in the non-task hand. In the first condition, participants were not made aware of their motor overflow. Then participants, though informed of it, were asked to ignore their overflow. Finally, participants were requested to inhibit overflow with, and then without visual feedback, or vice versa. Overflow was exacerbated when older adults were unaware of it, and was reduced once they were informed. For young adults there was no significant difference between these conditions. Both Age Groups could significantly reduce overflow when so requested, independent of visual feedback. Thus motor overflow can be modulated by higher order cognitive control with directed attention.     

Fitts’ law holds for pointing movements under conditions of restricted visual feedback

Fitts’ law robustly predicts the time required to move rapidly to a target. However, it is unclear whether Fitts’ law holds for visually guided actions under visually restricted conditions. We tested whether Fitts’ law applies under various conditions of visual restriction and compared pointing movements in each condition. Ten healthy participants performed four pointing movement tasks under different visual feedback conditions, including full-vision (FV), no-hand-movement (NM), no-target-location (NT), and no-vision (NV) feedback conditions. The movement times (MTs) for each task exhibited highly linear relationships with the index of difficulty (r² > .96). These findings suggest that pointing movements follow Fitts’ law even when visual feedback is restricted or absent. However, the MTs and accuracy of pointing movements decreased for difficult tasks involving visual restriction.     

Hand dominance influences the processing of observed bodies

In motor tasks, subgroups of lefthanders have been shown to differ in the distribution of attention about their own bodies. The present experiment examined whether similar attentional biases also apply when processing observed bodies. Sixteen right handers (RHs), 22 consistent left handers (CLHs) and 11 relatively ambidextrous inconsistent left handers (ILHs) performed an own body transformation task in which they were instructed to make speeded left–right judgements about a schematic human figure. Attentional biases associated with handedness were found to extend to observed bodies: CLHs’ judgements were faster to the figure’s left side, while ILHs, like RHs, showed facilitated performance to the figure’s right side. These results demonstrate a novel embodiment effect whereby the processing of a static schematic human figure is modulated by an individual’s personal motor capabilities. This finding suggests that motor simulation may contribute to whole body perception in the absence of actual or implied actions.     

图形型归纳推理的神经机制:一项fMRI研究

利用fMRI脑成像技术探讨图形型归纳推理的神经机制。设计了一种由图形形状和条纹方向描述的简单几何图形组成的归纳推理任务,这种图形型任务与以往研究中常用的语句型归纳推理任务是同质的。根据两个图形共享特征数量的不同设计了两种实验任务:共享两个特征(2T)和共享一个特征(1T),以休息基线(Rest)作为控制任务。2T和1T任务均为归纳推理任务,但2T任务包含知觉特征整合成分,而1T任务不包括。结果发现:与控制任务相比,归纳推理任务在前额区(BA6、9、11、46、47)、尾状核、壳核和丘脑等脑区有显著激活,反映了"前额皮层-纹状体-丘脑"通路在图形型归纳推理中的重要作用;图形型归纳推理中的知觉信息整合与右侧额下回(BA47)、双侧尾状核头部、壳核等脑区有关。     

基于神经生理学的疼痛测量

疼痛是一种受多重因素影响的复杂主观感受。临床上,疼痛测量主要依赖于患者的主观评价。然而,这种传统的疼痛测量方法具有多方面的局限。近年来,研究者借助生理记录、脑电和功能磁共振等技术,揭示疼痛的神经生理、心理机制,挖掘与疼痛相关的神经生理指标,进而构建有效、客观和精确的疼痛评价体系。在基础研究和临床实践中,这些技术有望弥补传统疼痛测量方法的不足,从而极大推动疼痛测量及其治疗等相关领域研究的发展。     

Motor asymmetry and substantia nigra volume are related to spatial delayed response performance in Parkinson disease

Studies suggest motor deficit asymmetry may help predict the pattern of cognitive impairment in individuals with Parkinson disease (PD). We tested this hypothesis using a highly validated and sensitive spatial memory task, spatial delayed response (SDR), and clinical and neuroimaging measures of PD asymmetry. We predicted SDR performance would be more impaired by PD-related changes in the right side of the brain than in the left. PD (n = 35) and control (n = 28) participants performed the SDR task. PD participants either had worse motor deficits on the right (RPD) or left (LPD) side of the body. Some participants also had magnetic resonance imaging for measurement of their substantia nigra (SN) volumes. The LPD group performed worse on the SDR task than the RPD and control groups. Right SN volume accounted for a unique and significant portion of the variance in SDR error, with smaller volume predicting poorer performance. In conclusion, left motor dysfunction and smaller right SN volume are associated with poorer spatial memory.     

Clock drawing performance and brain morphology in mild cognitive impairment and Alzheimer's disease

The Clock Drawing Test (CDT) is a widely used instrument in the neuropsychological assessment of Alzheimer's disease (AD). As CDT performance necessitates several cognitive functions (e.g., visuospatial and constructional abilities, executive functioning), an interaction of multiple brain regions is likely. Fifty-one subjects with mild cognitive impairment, 23 with AD and 15 healthy controls underwent high-resolution magnetic resonance imaging. Optimized voxel-based morphometry (VBM) was performed to investigate the putative association between CDT performance and gray matter (GM) density throughout the entire brain. In the first step of analysis (p<.001, uncorrected), VBM revealed a reduced GM density in numerous cortical (temporal lobe, frontal lobe, parietal lobe, cerebellum) and subcortical (thalamus, basal ganglia) brain regions to be associated with poorer CDT performance. When corrected for multiple comparisons (p<.01), the associations remained significant predominantly in the left temporal and--less pronounced--the right temporal lobe. VBM demonstrated CDT performance to depend on the integrity of widely distributed cortical and subcortical areas in both brain hemispheres with accentuation in the left-sided temporal lobe region.