Brain-state determines learning improvements after transcranial alternating-current stimulation to frontal cortex

Published in final edited form as: Brain Stimul. 2018 ; 11(4): 723–726. doi:10.1016/j.brs.2018.02.008BACKGROUND Theories of executive control propose that communication between medial frontal cortex (MFC) and lateral prefrontal cortex (lPFC) is critical for learning. 6-Hz phase synchronization may be the mechanism by which neural activity between MFC and lPFC is coordinated into a functional network. Recent evidence suggests that switching from eyes closed to open may induce a change in brain-state reflected by enhanced executive control and related functional connectivity. OBJECTIVE/HYPOTHESIs To examine whether causal manipulation of MFC and lPFC can improve learning according to the brain-state induced by switching from eyes closed to open. METHODS Within-subjects, sham-controlled, double-blind study of 30 healthy subjects, each receiving 6-Hz in-phase high definition transcranial alternating-current stimulation (HD-tACS) applied to MFC and right lPFC prior to performing a time estimation task. RESULTS HD-tACS with eyes open improved learning ability relative to sham, whereas HD-tACS with eyes closed had no significant effect on behavior. CONCLUSION Results suggest a phase-sensitive mechanism in frontal cortex mediates components of learning performance in a state-dependent manner.Accepted manuscrip

Characterising Testing Preorders for Finite Probabilistic Processes

In 1992 Wang & Larsen extended the may- and must preorders of De Nicola and Hennessy to processes featuring probabilistic as well as nondeterministic choice. They concluded with two problems that have remained open throughout the years, namely to find complete axiomatisations and alternative characterisations for these preorders. This paper solves both problems for finite processes with silent moves. It characterises the may preorder in terms of simulation, and the must preorder in terms of failure simulation. It also gives a characterisation of both preorders using a modal logic. Finally it axiomatises both preorders over a probabilistic version of CSP.Comment: 33 page

World Trade Flows: 1962-2000

We document a set of bilateral trade data by commodity for 1962-2000, which is available from www.nber.org/data (International Trade Data, NBER-UN world trade data). Users must agree not to resell or distribute the data for 1984-2000. The data are organized by the 4-digit Standard International Trade Classification, revision 2, with country codes similar to the United Nations classification. This dataset updates the Statistics Canada World Trade Database as described in Feenstra, Lipsey, and Bowen (1997), which was available for years 1970-1992. In that database, Statistics Canada had revised the United Nations trade data, mostly derived from the export side, to fit the Canadian trade classification and in some cases to add data not available from the export reports. In contrast, in the new NBER-UN dataset we give primacy to the trade flows reported by the importing country, whenever they are available, assuming that these are more accurate than reports by the exporters. If the importer report is not available for a country-pair, however, then the corresponding exporter report is used instead. Corrections and additions are made to the United Nations data for trade flows to and from the United States, exports from Hong Kong and China, and imports into many other countries.