Cortical activity changes continuously during the course of the day. At a global scale, population activity varies between the ‘synchronized’ state during sleep and ‘desynchronized’ state during waking. However, whether local fluctuations in population synchrony during wakefulness modulate the accuracy of sensory encoding and behavioral performance is poorly understood. Here, we show that populations of cells in monkey visual cortex exhibit rapid fluctuations in synchrony ranging from desynchronized responses, indicative of high alertness, to highly synchronized responses. These fluctuations are local and control the trial variability in population coding accuracy and behavioral performance in a discrimination task. When local population activity is desynchronized, the correlated variability between neurons is reduced, and network and behavioral performance are enhanced. These findings demonstrate that the structure of variability in local cortical populations is not noise but rather controls how sensory information is optimally integrated with ongoing processes to guide network coding and behavior.

Post-stroke hemiparetic walking is typically asymmetric. Assessment of symmetry is often performed at either self-selected or fastest-comfortable walking speeds to gain insight into coordination deficits and compensatory mechanisms. However, how walking speed influences the level of asymmetry is unclear. This study analyzed relative changes in paretic and non-paretic leg symmetry to assess whether one speed is more effective at highlighting asymmetries in hemiparetic walking and whether there is a systematic effect of speed on asymmetry. Forty-six subjects with chronic hemiparesis walked at their self-selected and fastest-comfortable speeds on an instrumented split-belt treadmill. Relative proportions (paretic leg value/(paretic + non-paretic leg value)) were computed at each speed for step length (PSR), propulsion (PP), and joint moment impulses at the ankle and hip. Thirty-six subjects did not change their step length symmetry with speed, while three subjects changed their step length values toward increased asymmetry and seven changed toward increased symmetry. Propulsion symmetry did not change uniformly with speed for the group, with fifteen subjects changing their propulsion values toward increased asymmetry while increasing speed from their self-selected to fastest-comfortable and eleven decreasing the asymmetry. Both step length and propulsion symmetry were correlated with ankle impulse proportion at self-selected and fastestcomfortable speed (c.f., hip impulse proportion), but ratios (self-selected value / fastest-comfortable value) of the proportion measures (PSR and PP) showed that neither step length nor propulsion symmetry correlated with the ankle impulse proportions. Thus, the individual kinetic mechanisms used to increase speed could not be predicted from PSR or PP.

Brain activity during wakefulness is characterized by rapid fluctuations in neuronal responses. Whether these fluctuations play any role in modulating the accuracy of behavioral responses is poorly understood. Here, we investigated whether and how trial changes in the population response impact sensory coding in monkey V1 and perceptual performance. Although the responses of individual neurons varied widely across trials, many cells tended to covary with the local population. When population activity was in a ‘low’ state, neurons had lower evoked responses and correlated variability, yet higher probability to predict perceptual accuracy. The impact of firing rate fluctuations on network and perceptual accuracy was strongest 200 ms before stimulus presentation, and it greatly diminished when the number of cells used to measure the state of the population was decreased. These findings indicate that enhanced perceptual discrimination occurs when population activity is in a ‘silent’ response mode in which neurons increase information extraction.

Information processing in the cerebral cortex depends not only on the nature of incoming stimuli, but also on the state of neuronal networks at the time of stimulation. That is, the same stimulus will be processed differently depending on the neuronal context in which it is received. A major factor that could influence neuronal context is the background, or ongoing neuronal activity before stimulation. In visual cortex, ongoing activity is known to play a critical role in the development of local circuits, yet whether it influences the coding of visual features in adult cortex is unclear. Here, we investigate whether and how the information encoded by individual neurons and populations in primary visual cortex (V1) depends on the ongoing activity before stimulus presentation. We report that when individual neurons are in a "low" prestimulus state, they have a higher capacity to discriminate stimulus features, such as orientation, despite their reduction in evoked responses. By measuring the distribution of prestimulus activity across a population of neurons, we found that network discrimination accuracy is improved in the low prestimulus state. Thus, the distribution of ongoing activity states across the network creates an "internal context" that dynamically filters incoming stimuli to modulate the accuracy of sensory coding. The modulation of stimulus coding by ongoing activity state is consistent with recurrent network models in which ongoing activity dynamically controls the balanced background excitation and inhibition to individual neurons.

Robotic interventional neuroradiology is an emerging field with the potential to enhance patient safety, reduce occupational hazards, and expand systems of care. Endovascular robots allow the operator to precisely control guidewires and catheters from a lead-shielded cockpit located several feet (or potentially hundreds of miles) from the patient. This has opened up the possibility of expanding telestroke networks to patients without access to life-saving procedures such as stroke thrombectomy and cerebral aneurysm occlusion by highly-experienced physicians. The prototype machines, first developed in the early 2000s, have evolved into machines capable of a broad range of techniques, while incorporating newly automated maneuvers and safety algorithms. In recent years, preliminary clinical research has been published demonstrating the safety and feasibility of the technology in cerebral angiography and intracranial intervention. The next step is to conduct larger, multisite, prospective studies to assess generalizability and, ultimately, improve patient outcomes in neurovascular disease.

Acute platelet transfusion after intracerebral hemorrhage (ICH) given in efforts to reverse antiplatelet medication effects and prevent ongoing bleeding does not appear to improve outcome and may be associated with harm. Although the underlying mechanisms are unclear, the influence of ABO-incompatible platelet transfusions on ICH outcomes has not been investigated. We hypothesized that ICH patients who receive ABO-incompatible platelet transfusions would have worse platelet recovery (using absolute count increment [ACI]) and neurological outcomes (mortality and poor modified Rankin Scale [mRS 4-6]) as compared to those receiving ABO-compatible transfusions. In a single center cohort of consecutively admitted ICH patients, we identified 125 patients receiving acute platelet transfusions, of whom 47 (38%) received an ABO-incompatible transfusion. Using quantile regression, we identified an association of ABO-incompatible platelet transfusion with lower platelet recovery (ACI: 2x103cells/mL vs 15x103cells/mL; adjusted coefficient b:-19; 95%CI:-35.55 to -4.44; p=0.01). ABO-incompatible platelet transfusion was also associated with increased odds of mortality (adjusted OR 2.59; 95%CI: 1.00-6.73; p=0.05) and poor mRS (adjusted OR 3.61; 95%CI: 0.97-13.42; p=0.06), however these estimates were imprecise. Together, these findings suggest the importance of ABO-compatibility for platelet transfusions for ICH; however, further investigation into the mechanism(s) underlying these observations is required.

Background and Purpose Osseous pseudoprogression (OPP) on MRI can mimic true progression in lesions treated with spine stereotactic radiosurgery (SSRS). Our aim is to describe the prevalence and time course of OPP, in order to assist radiologists in assessment of post-SSRS patients. Materials and Methods A secondary analysis of two prospective trials was performed. MRIs before and after SSRS were assessed for response. OPP was defined as transient growth in signal abnormality centered at the lesion with a sustained decline on follow-up MRI that was not attributable to chemotherapy. Results From the initial set of 223 patients, 37 lesions in 36 patients met inclusion criteria and were selected for secondary analysis. Five of the 37 lesions (14%) demonstrated OPP and 9 demonstrated progressive disease. There was significant association between single-fraction therapy and the development of OPP (p=0.01), and there was a significant difference in OPP-free survival between single- and multi-fraction regimens (p=0.0052). In lesions demonstrating OPP, time to peak size occurred between 9.7 and 24.4 weeks after SSRS (mean: 13.9 weeks, 95% CI: 8.6–19.1 weeks). The peak lesion size was between 4–10 mm larger than baseline. Most lesions returned to baseline size between 23–52.4 weeks following SSRS. Conclusions Progression on MRI obtained between 3 and 6 months following SSRS should be treated with caution, as OPP may be seen in > 1/3 of these lesions. Single-fraction SSRS may be associated with OPP. The possibility of OPP should be incorporated into prospective criteria for assessment of local control following SSRS.

Drowsiness may be defined as the progressive loss of cortical processing efficiency that occurs with time passing while awake. This loss of cortical processing efficiency is reflected in focal changes to the electroencephalogram, including islands of increased delta power concurrent with drop-offs in neuronal activity (i.e., focal cortical inactivity). The authors hypothesized that these focal changes are evidenced at individual electrodes by combination of increased instantaneous amplitude in delta band and decreased instantaneous frequency in theta-alpha band, permitting their categorization as "active" and "inactive." An analysis of records from six patients with refractory epilepsy undergoing video-electrocorticographic monitoring was conducted. Feature extraction and state classification on multiple recordings revealed focal changes consistent with the hypothesis, as well as progressively increased numbers of inactive electrodes with time awake. The implications of these findings on the study of sleep, and particularly local sleep, are discussed.