Fragments of a larger whole: Retrieval cues constrain observed neural correlates of memory encoding

Laying down a new memory involves activity in a number of brain regions. Here, it is shown that the particular regions associated with successful encoding depend on the way in which memory is probed. Event-related functional magnetic resonance imaging signals were acquired while subjects performed an incidental encoding task on a series of visually presented words denoting objects. A recognition memory test using the Remember/Know procedure to separate responses based on recollection and familiarity followed 1 day later. Critically, half of the studied objects were cued with a corresponding spoken word, and half with a corresponding picture. Regardless of cue, activity in prefrontal and hippocampal regions predicted subsequent recollection of a word. Type of retrieval cue modulated activity in prefrontal, temporal, and parietal cortices. Words subsequently recognized on the basis of a sense of familiarity were at study also associated with differential activity in a number of brain regions, some of which were probe dependent. Thus, observed neural correlates of successful encoding are constrained by type of retrieval cue, and are only fragments of all encoding-related neural activity. Regions exhibiting cue-specific effects may be sites that support memory through the degree of overlap between the processes engaged during encoding and those engaged during retrieval

Korshunov instantons in a superconductor at elevated bias current

Dissipation even at zero temperature reduces quantum fluctuations and tends to localize particles. A notable exception is the nonlinear dissipation due to quasiparticle tunneling in a Josephson junction. It is well known that quasiparticle dissipation does not prevent the phase particle in a superconducting junction to coherently tunnel to the next-nearest minimum even though tunneling to the nearest minimum is suppressed. The reason is that the dissipative action admits an instanton solution, the so-called Korshunov instanton. Here, we analyze this model at elevated bias current $I$. We find that besides the known regime where the logarithm of the tunneling rate scales as $I^{2/3}$ there is novel regime with a scaling $I^2$. We argue that the novel regime opens an opportunity for an experimental verification of the Korshunov instantons as the elevated bias current leads to a larger tunneling rate compared to earlier results.Comment: 10 pages, 6 figure