The effect of unpredicted visual feedback on activation in the secondary somatosensory cortex during movement execution

BACKGROUND: A mechanism that monitors the congruence between sensory inputs and motor outputs is necessary to control voluntary movement. The representation of limb position is constantly updated on the basis of somatosensory and visual information and efference copy from motor areas. However, the cortical mechanism underlying detection of limb position using somatosensory and visual information has not been elucidated. This study investigated the influence of visual feedback on information processing in somatosensory areas during movement execution using magnetoencephalography. We used an experimental condition in which the visual information was incongruent despite the motor execution and somatosensory feedback being congruent. Subjects performed self-paced bimanual movements of both thumbs, either symmetric or asymmetric, under normal visual and mirrored conditions. The mirror condition provided a visual feedback by showing a reflection of the subject’s right hand in place of the left hand. Therefore, in the Asymmetric task of the Mirror condition, subjects saw symmetric movements despite performing asymmetric movements. RESULTS: Activation in the primary somatosensory area (SI) revealed inhibition of neural activity and that in the secondary somatosensory area (SII) showed enhancement with voluntary movement. In addition, the SII contralateral to the side of stimulation was significantly enhanced in the Asymmetric task of the Mirror condition, which provided non-veridical visual feedback. CONCLUSIONS: These results suggested that visual information influenced the neuronal activity concerning sensorimotor interaction in the SII during motor execution. The SII contributes to the detection of unpredicted visual feedback of movement execution

Do Gravity-Related Sensory Information Enable the Enhancement of Cortical Proprioceptive Inputs When Planning a Step in Microgravity?

International audienceWe recently found that the cortical response to proprioceptive stimulation was greater when participants were planning a step than when they stood still, and that this sensory facilitation was suppressed in microgravity. The aim of the present study was to test whether the absence of gravity-related sensory afferents during movement planning in microgravity prevented the proprioceptive cortical processing to be enhanced. We reestablished a reference frame in microgravity by providing and translating a horizontal support on which the participants were standing and verified whether this procedure restored the proprioceptive facilitation. The slight translation of the base of support (lateral direction), which occurred prior to step initiation, stimulated at least cutaneous and vestibular receptors. The sensitivity to proprioceptive stimulation was assessed by measuring the amplitude of the cortical somatosensory-evoked potential (SEP, over the Cz electrode) following the vibration of the leg muscle. The vibration lasted 1 s and the participants were asked to either initiate a step at the vibration offset or to remain still. We found that the early SEP (90–160 ms) was smaller when the platform was translated than when it remained stationary, revealing the existence of an interference phenomenon (i.e., when proprioceptive stimulation is preceded by the stimulation of different sensory modalities evoked by the platform translation). By contrast, the late SEP (550 ms post proprioceptive stimulation onset) was greater when the translation preceded the vibration compared to a condition without pre-stimulation (i.e., no translation). This suggests that restoring a body reference system which is impaired in microgravity allowed a greater proprioceptive cortical processing. Importantly, however, the late SEP was similarly increased when participants either produced a step or remained still. We propose that the absence of step-induced facilitation of proprioceptive cortical processing results from a decreased weight of proprioception in the absence of balance constraints in microgravity

Visuomotor Tracking Task for Enhancing Activity in Motor Areas of Stroke Patients

Recovery of motor function following stroke requires interventions to enhance ipsilesional cortical activity. To improve finger motor function following stroke, we developed a movement task with visuomotor feedback and measured changes in motor cortex activity by electroencephalography. Stroke patients performed two types of movement task on separate days using the paretic fingers: a visuomotor tracking task requiring the patient to match a target muscle force pattern with ongoing feedback and a simple finger flexion/extension task without feedback. Movement-related cortical potentials (MRCPs) were recorded before and after the two motor interventions. The amplitudes of MRCPs measured from the ipsilesional hemisphere were significantly enhanced after the visuomotor tracking task but were unchanged by the simple manual movement task. Increased MRCP amplitude preceding movement onset revealed that the control of manual movement using visual feedback acted on the preparatory stage from motor planning to execution. A visuomotor tracking task can enhance motor cortex activity following a brief motor intervention, suggesting efficient induction of use-dependent cortical plasticity in stroke

Differences in Microphytobenthos and Macrofaunal Abundances Associated with Groundwater Discharge in the Intertidal Zone

We investigated the impact of intertidal groundwater seepage on benthic microalgae and macrofauna in 4 study sites located in 2 large tidal flat ecosystems along the western coast of Korea by comparing the chemical, physical, and biological characteristics of ‘glossy’ seepage sites with those of nearby areas without visually distinct groundwater discharge (dry sediment surface). At 3 of the 4 sites, sediment properties as well as pore water chemistry were similar in groundwater seepage and dry areas. At the 4th study site, the groundwater seepage areas were more coarsegrained compared to the dry areas. Here, the groundwater seepage also had lower salinity and higher nutrient concentrations than the pore water of the dry area and the seawater in a nearby tide pool. Although diatoms were the dominant algal class in seepage and dry areas alike, the seepage areas in 3 of the sites had elevated contributions of other marker pigments such as chlorophyll (chl) b compared to the dry areas. Chl a concentrations were higher in all seepage areas compared to dry areas, and all dry areas had high pheophytina:chla ratios, indicating a substantial amount of degraded algal material. In the seepage areas of 3 of the sites, we found large numbers of the snail Batillaria cumingi, while crab burrows of Scopimera sp. were only present in the neighboring dry areas. Correlations of sediment chl a concentrations with physicochemical properties of the ambient pore water indicated that microphytobenthos responded specifically to groundwater seepage, which may provide shelter from desiccation and salt stress during emersion of the tidal flat. Our results suggest that globally common groundwater seepage significantly impacts the ecosystem structures and microphytobenthos production of the tidal flats