Skill increase in motor performance can be defined as explicitly measuring task success but also via more implicit measures of movement kinematics. Even though these measures are often related, there ...is evidence that they represent distinct concepts of learning. In the present study, the effect of multiple tDCS-sessions on both explicit and implicit measures of learning are investigated in a pointing task in 30 young adults (YA) between 27.07 ± 3.8 years and 30 old adults (OA) between 67.97 years ± 5.3 years. We hypothesized, that OA would show slower explicit skill learning indicated by higher movement times/lower accuracy and slower implicit learning indicated by higher spatial variability but profit more from anodal tDCS compared with YA. We found age-related differences in movement time but not in accuracy or spatial variability. TDCS did not skill learning facilitate learning neither in explicit nor implicit parameters. However, contrary to our hypotheses, we found tDCS-associated higher accuracy only in YA but not in spatial variability. Taken together, our data shows limited overlapping of tDCS effects in explicit and implicit skill parameters. Furthermore, it supports the assumption that tDCS is capable of producing a performance-enhancing brain state at least for explicit skill acquisition.
The representations of the human hand in primary somatosensory cortex (SI) undergo continuous adaptational plastic processes, which arise from learning, altered use, or injury. The resulting ...reorganization affects size, extent, and position of the cortical maps, which parallels alterations of tactile behavior indicating a close relationship between map changes and perception. Here we investigate the influence of healthy aging on the cortical hand representation and on age-related changes of tactile performance. Using somatosensory evoked potential mapping in combination with electric source localization, we found that in elderly subjects aged 60–85 years the distance between the dipoles of the index and the little fingers increased indicating an expansion of the representations within SI by approximately 40%. Assessment of tactile spatial 2-point discrimination thresholds in the same subjects showed a strong decline with age. These results indicate that healthy aging strongly affects the homuncular structures of the hand representations within SI. Map expansion typically observed in young and adult subjects during learning is associated with a gain in performance. Whereas learning-related map changes are assumed to result from specific strengthening of synaptic connections, we suggest that the age-related map changes are related to the reduction of intracortical inhibition developing with age.
Patients with complex regional pain syndrome (CRPS) and intractable pain showed a shrinkage of cortical maps on primary (SI) and secondary somatosensory cortex (SII) contralateral to the affected ...limb. This was paralleled by an impairment of the two‐point discrimination thresholds. Behavioral treatment over 1 to 6 months consisting of graded sensorimotor retuning led to a persistent decrease in pain intensity, which was accompanied by a restoration of the impaired tactile discrimination and regaining of cortical map size in contralateral SI and SII. This suggests that the reversal of tactile impairment and cortical reorganization in CRPS is associated with a decrease in pain. Ann Neurol 2005;57:425–429
Computational anatomy studies typically use T1-weighted magnetic resonance imaging contrast to look at local differences in cortical thickness or grey matter volume across time or subjects. This type ...of analysis is a powerful and non-invasive tool to probe anatomical changes associated with neurodevelopment, aging, disease or experience-induced plasticity. However, these comparisons could suffer from biases arising from vascular and metabolic subject- or time-dependent differences. Differences in blood flow and volume could be caused by vasodilation or differences in vascular density, and result in a larger signal contribution of the blood compartment within grey matter voxels. Metabolic changes could lead to differences in dissolved oxygen in brain tissue, leading to T1 shortening. Here, we analyze T1 maps and T1-weighted images acquired during different breathing conditions (ambient air, hypercapnia (increased CO2) and hyperoxia (increased O2)) to evaluate the effect size that can be expected from changes in blood flow, volume and dissolved O2 concentration in computational anatomy studies. Results show that increased blood volume from vasodilation during hypercapnia is associated with an overestimation of cortical thickness (1.85%) and grey matter volume (3.32%), and that both changes in O2 concentration and blood volume lead to changes in the T1 value of tissue. These results should be taken into consideration when interpreting existing morphometry studies and in future study design. Furthermore, this study highlights the overlap in structural and physiological MRI, which are conventionally interpreted as two independent modalities.
•Increased blood volume leads to overestimation of grey matter thickness and volume.•Changes in O2 concentration and blood volume lead to changes in the T1 of tissue.•Changes in grey matter from blood volume cover most of cortex and are bilateral.•The impact of blood volume is on a similar scale as aging and diseases changes.
Cortical activity during simple unimanual actions is typically lateralized to contralateral sensorimotor areas, while a more bilateral pattern is observed with an increase in task demands. In ...parallel, increasing task demands are associated with subtle mirror muscle activity in the resting hand, implying a relative loss in motor selectivity. The corpus callosum (CC) is crucially involved in unimanual tasks by mediating both facilitatory and inhibitory interactions between bilateral motor cortical systems, but its association with mirror motor activity is yet unknown. Here we used diffusion-weighted imaging (DWI) and bilateral EMG measurements during a unimanual task to investigate potential relationships between white matter microstructure of the CC and mirror EMG activity. Participants performed a unimanual pinch force task with both hands. 4 parametrically increasing force levels were exerted while electromyographic (EMG) activity was recorded bilaterally from first dorsal interosseus muscles. Consistent with previous findings, mirror EMG activity increased as a function of force. Additionally, there was a significant relationship between the slope of mirror EMG increases and fractional anisotropy in transcallosal fibres connecting both primary motor cortices. No significant relationships were found for fibres connecting dorsal premotor cortices or supplementary motor area, indicating the local specificity of the observed brain–physiology relationship.
Physiological mirror activity (pMA), observed in healthy human adults, describes the involuntary co-activation of contralateral homologous muscles during unilateral limb movements. Here we provide ...novel evidence, using neuromuscular measurements (electromyography; EMG), that the amplitude of pMA can be voluntarily inhibited during unilateral isometric contractions of intrinsic hand muscles after informing human participants (10 male, 10 female) about its presence and establishing a basic understanding of pMA mechanisms through a standardized protocol. Importantly, significant suppression of pMA was observed immediately after participants were asked to inhibit it, despite the absence of any online feedback during task execution and without special training. Moreover, we observed that the decrease of pMA was specifically accompanied by an increase in relative frontal δ power recorded with electroencephalography (EEG). Correlation analysis further revealed an inverse association between the individual amplitude of pMA and frontal δ power that reached significance once participants started to inhibit. Taken together, these results suggest that δ power in frontal regions might reflect executive processes exerting inhibitory control over unintentional motor output, in this case pMA. Our results provide an initial reference point for the development of therapeutic applications related to the neurorehabilitation of involuntary movements which could be realized through the suppression of pMA observed in the elderly before it would fully manifest in undesirable overt movement patterns.
Introduction Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique used to modulate cortical excitability. In the motor domain, there is consensus that anodal ...tDCS increases cortical excitability, whereas cathodal tDCS decreases it. On the other hand, inconsistent results of tDCS-induced effects in the sensory domain have been reported. Objective The aim of the present study was to investigate (A) changes in cortical excitability within primary somatosensory cortex (S1) by means of single-pulse somatosensory evoked potentials (SEPs) and (B) intracortical inhibition by means of paired-pulse SEPs when tDCS was applied over left SM1. Materials and Methods 10 min of anodal, cathodal or sham tDCS was applied over the left SM1 using saline-soaked sponge electrodes (35 cm2 electrodes, 1 mA, current density 0.028 mA/cm2 ). Before, immediately after as well as 10 min after termination of tDCS, single-and paired-pulse SEP recordings were performed. We hypothesized that tDCS will induce polarity specific changes in cortical excitability within left S1. Furthermore, we reasoned that anodal tDCS will reduce paired-pulse inhibition within left S1 while cathodal tDCS will result in an augmentation of inhibition relative to sham stimulation. Results 10 min of anodal and cathodal tDCS over SM1 did not result in any significant excitability changes within left S1. However, anodal tDCS resulted in a reduction of paired-pulse inhibition within left S1 10 min after termination of stimulation. No change in paired-pulse inhibition could be observed after cathodal tDCS. Conclusion Here we provide novel evidence that anodal tDCS affects inhibitory processing within S1, a finding that might improve our understanding about the underlying neural mechanisms of tDCS on somatosensory processing.
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