Review of Coronal Oscillations - An Observer's View

Recent observations show a variety of oscillation modes in the corona. Early non-imaging observations in radio wavelengths showed a number of fast-period oscillations in the order of seconds, which have been interpreted as fast sausage mode oscillations. TRACE observations from 1998 have for the first time revealed the lateral displacements of fast kink mode oscillations, with periods of ~3-5 minutes, apparently triggered by nearby flares and destabilizing filaments. Recently, SUMER discovered with Doppler shift measurements loop oscillations with longer periods (10-30 minutes) and relatively short damping times in hot (7 MK) loops, which seem to correspond to longitudinal slow magnetoacoustic waves. In addition, propagating longitudinal waves have also been detected with EIT and TRACE in the lowest density scale height of loops near sunspots. All these new observations seem to confirm the theoretically predicted oscillation modes and can now be used as a powerful tool for ``coronal seismology'' diagnostic.Comment: 5 Figure

Microcircuits and their interactions in epilepsy: is the focus out of focus?

Epileptic seizures represent dysfunctional neural networks dominated by excessive and/or hypersynchronous activity. Recent progress in the field has outlined two concepts regarding mechanisms of seizure generation or ictogenesis. First, all seizures, even those associated with what have historically been thought of as “primary generalized” epilepsies appear to originate within local microcircuits and then propagate from that initial ictogenic zone. Second, seizures propagate through cerebral networks and engage microcircuits in distal nodes—a process that can be weakened or even interrupted by suppressing activity in such nodes. Here, we describe various microcircuit motifs, with a special emphasis on one broadly implicated in several epilepsies - feed-forward inhibition. Further, we discuss how, in the dynamic network in which seizures propagate, focusing on circuit “choke points” remote from the initiation site might be as important as that of the initial dysfunction—the seizure “focus.