Correlation in brain networks at different time scale resolution.

Assessing brain connectivity makes up a major issue in the field of network dynamics and neuroscience. Conventional experimental techniques are based on functional imaging and magnetoencephalography, allowing to reconstruct the activity of relatively small brain volume elements. A common approach to identify networks consists in singling out sets of elements that maintain a correlated activity over time. Despite the general consensus that these networks are detectable on a time window of 10 s, no study is presently available on the distribution and thus the reliability of this time scale. In this work, we describe a new method to assess time scales on which correlations between network elements occur and to consequently identify the underlying network structures. The analysis relies on the evaluation of quasi-zero-delay cross-correlation between power sequences associated with distinct volume elements. By changing the width of the running window used to analyze successive segments of time series, the behavior of cross-correlation at different time scales was investigated. The onset of connectivity was estimated to be observable at about 30 s. The method was applied to a set of volume elements that are supposed to belong to a known resting-state network, namely the Default Mode Network. Fully connected networks were identified, provided that a sufficiently long time scale is considered. Our method makes up a new tool for the investigation of the temporal dynamics of networks.

Pancreas Transplantation From Very Small Pediatric Donor Using the "Cephalic Placement" Technique: A Case Report.

INTRODUCTION: The gap between the number of diabetic patients on the waiting list for transplantation and the number of pancreas donors is growing and it is mandatory to extend criteria for donor eligibility. Several reports showed the feasibility of pancreas transplantation from pediatric donors with comparable outcomes to adult donors in terms of long-term ß-cell function. However, there is no consensus about donor age and weight limits. CASE REPORT: We present two cases of pancreas transplantation alone (PTA) from very small pediatric donors: a 2-year-old female (weight 13 kg, height 88 cm) and a 6-year-old male (weight 29 kg, height 122 cm). We used a novel "cephalic placement" technique. The pancreas was placed upon the aortic carrefour with cephalic pole upward with 3 anchorage points: the left common iliac vein (or the inferior cava vein), the right common iliac artery, and an ileal loop. RESULTS: No postoperative thrombosis occurred and the patients gained insulin independence instantaneously. CT scan performed on postoperative day 3 showed regular organ perfusion in both cases. Graft volume and surface calculated by CT reconstruction were, respectively, 25 cc and 89 cm(2) in the first case, and 46.5 cc and 123 cm(2) in the second case. Postoperative mixed meal tolerance tests showed normal glycemic profile. Patients are actually insulin independent at 4 years and 8 months. CONCLUSIONS: Pancreases from very young pediatric donors are adequate to restore insulin independence after PTA in adult patients. The "cephalic placement" technique is feasible and effective using very small pancreases.