Post-ischemic reorganization of sensory responses in cerebral cortex

Introduction

Sensorimotor integration is critical for generating skilled, volitional movements. While stroke tends to impact motor function, there are also often associated sensory deficits that contribute to overall behavioral deficits. Because many of the cortico-cortical projections participating in the generation of volitional movement either target or pass-through primary motor cortex (in rats, caudal forelimb area; CFA), any damage to CFA can lead to a subsequent disruption in information flow. As a result, the loss of sensory feedback is thought to contribute to motor dysfunction even when sensory areas are spared from injury. Previous research has suggested that the restoration of sensorimotor integration through reorganization or de novo neuronal connections is important for restoring function. Our goal was to determine if there was crosstalk between sensorimotor cortical areas with recovery from a primary motor cortex injury. First, we investigated if peripheral sensory stimulation would evoke responses in the rostral forelimb area (RFA), a rodent homologue to premotor cortex. We then sought to identify whether intracortical microstimulation-evoked activity in RFA would reciprocally modify the sensory response.

Methods

We used seven rats with an ischemic lesion of CFA. Four weeks after injury, the rats' forepaw was mechanically stimulated under anesthesia and neural activity was recorded in the cortex. In a subset of trials, a small intracortical stimulation pulse was delivered in RFA either individually or paired with peripheral sensory stimulation.

Results

Our results point to post-ischemic connectivity between premotor and sensory cortex that may be related to functional recovery. Premotor recruitment during the sensory response was seen with a peak in spiking within RFA after the peripheral solenoid stimulation despite the damage to CFA. Furthermore, stimulation in RFA modulated and disrupted the sensory response in sensory cortex.

Discussion

The presence of a sensory response in RFA and the sensitivity of S1 to modulation by intracortical stimulation provides additional evidence for functional connectivity between premotor and somatosensory cortex. The strength of the modulatory effect may be related to the extent of the injury and the subsequent reshaping of cortical connections in response to network disruption.

Solar Energetic Particle Forecasting Algorithms and Associated False Alarms

Solar energetic particle (SEP) events are known to occur following solar flares and coronal mass ejections (CMEs). However, some high-energy solar events do not result in SEPs being detected at Earth, and it is these types of event which may be termed "false alarms". We define two simple SEP forecasting algorithms based upon the occurrence of a magnetically well-connected CME with a speed in excess of 1500 km s - 1 (a "fast" CME) or a well-connected X-class flare and analyse them with respect to historical datasets. We compare the parameters of those solar events which produced an enhancement of > 40 MeV protons at Earth (an "SEP event") and the parameters of false alarms. We find that an SEP forecasting algorithm based solely upon the occurrence of a well-connected fast CME produces fewer false alarms (28.8%) than an algorithm which is based solely upon a well-connected X-class flare (50.6%). Both algorithms fail to forecast a relatively high percentage of SEP events (53.2% and 50.6%, respectively). Our analysis of the historical datasets shows that false-alarm X-class flares were either not associated with any CME, or were associated with a CME slower than 500 km s - 1 ; false-alarm fast CMEs tended to be associated with flare classes lower than M3. A better approach to forecasting would be an algorithm which takes as its base the occurrence of both CMEs and flares. We define a new forecasting algorithm which uses a combination of CME and flare parameters, and we show that the false-alarm ratio is similar to that for the algorithm based upon fast CMEs (29.6%), but the percentage of SEP events not forecast is reduced to 32.4%. Lists of the solar events which gave rise to > 40 MeV protons and the false alarms have been derived and are made available to aid further study.

ELECTRONIC SUPPLEMENTARY MATERIAL

The online version of this article (doi:10.1007/s11207-017-1196-y) contains supplementary material, which is available to authorized users.

Invasive versus non-invasive monitoring of acute severe hypertension in women with pre-eclampsia

OBJECTIVE

To compare the accuracy of two non-invasive methods of blood-pressure measurement with intra-arterial measurement in women with pre-eclampsia and acute severe hypertension.

METHODS

This descriptive, cross-sectional study prospectively enrolled 23 women with pre-eclampsia and acute severe hypertension for continuous intra-arterial blood-pressure monitoring. Simultaneous monitoring was performed with a manual and an automated, non-invasive device during episodes of severe hypertension. The paired T-test was used to compare measured values. The accuracy of a MAP⩾125mmHg in detecting a systolic blood pressure⩾160mmHg was determined.

RESULTS

There was a weak correlation between intra-arterial and automated as well as intra-arterial and manual systolic values (r=0.34, p<0.01; r=0.41, p<0.00, respectively). Better correlation was found amongst diastolic values. The differences between the mean intra-arterial (94±11mmHg) and automated (96±12mmHg) diastolic values as well as intra-arterial and manual diastolic measurements (94±14mmHg) were not significant (p=0.20, 0.65, respectively). A mean arterial pressure⩾125mmHg was not accurate in detecting a systolic value⩾160mmHg, with low sensitivities (17.2-35.9%) and specificities (0-50%) for all three methods.

CONCLUSIONS

When compared to intra-arterial monitoring, the automated and manual methods showed weak correlation with systolic but better correlation with diastolic values. A mean arterial pressure⩾125mmHg was not accurate in detecting systolic peaks. When protection against cerebral haemorrhage is paramount, intra-arterial measurement of systolic values is best.