ABSTRACT
Sharp wave ripples (SPW-Rs) are thought to play an important role in memory consolidation. By rapid replay of previously stored information during slow wave sleep and consummatory behavior, they result from the formation of neural ensembles during a learning period. Serotonin (5-HT), suggested to be able to modify SPW-Rs, can affect many neurons simultaneously by volume transmission and alter network functions in an orchestrated fashion. In acute slices from dorsal hippocampus, SPW-Rs can be induced by repeated high frequency stimulation that induces long-lasting LTP. We used this model to study SPW-R appearance and modulation by 5-HT. Although stimulation in presence of 5-HT permitted LTP induction, SPW-Rs were "masked"--but appeared after 5-HT wash-out. This SPW-R masking was dose dependent with 100 nM 5-HT being sufficient--if the 5-HT re-uptake inhibitor citalopram was present. Fenfluramine, a serotonin releaser, could also mask SPW-Rs. Masking was due to 5-HT1A and 5-HT2A/C receptor activation. Neither membrane potential nor membrane conductance changes in pyramidal cells caused SPW-R blockade since both remained unaffected by combining 5-HT and citalopram. Moreover, 10 and 30 µM 5-HT mediated SPW-R masking preceded neuronal hyperpolarization and involved reduced presynaptic transmitter release. 5-HT, as well as a 5-HT1A agonist, augmented paired pulse facilitation and affected the coefficient of variance. Spontaneous SPW-Rs in mice hippocampal slices were also masked by 5-HT and fenfluramine. While neuronal ensembles can acquire long lasting LTP during higher 5-HT levels, lower 5-HT levels enable neural ensembles to replay previously stored information and thereby permit memory consolidation memory.
Subject(s)
Hippocampus/drug effects , Long-Term Potentiation/drug effects , Nerve Net/drug effects , Serotonin Agents/pharmacology , Serotonin/pharmacology , Animals , Biophysics , Citalopram/pharmacology , Dose-Response Relationship, Drug , Drug Interactions , Electric Stimulation , Hippocampus/physiology , In Vitro Techniques , Piperazines/pharmacology , Presynaptic Terminals/drug effects , Rats , Rats, WistarABSTRACT
Visuo-spatial attention can be directed in a top-down controlled way to search for color targets and it can be captured by color contrasts, regardless of color identity. Here we tested whether participants can both search for a particular color target (e.g., red) and make use of a color-contrast cue that predicted the target's most likely position to direct their attention voluntarily. Our results show that this was impossible for the participants. Results support that top-down search for particular colors is incommensurate with directing attention to just any color contrast. The results are discussed in light of the current debates concerning the roles of color and color contrast for visuo-spatial attention.
Subject(s)
Attention , Cues , Perceptual Masking , Visual Perception , Adult , Color Perception , Female , Humans , Male , Orientation , Pattern Recognition, Visual , Photic Stimulation , Reaction TimeABSTRACT
Salient visual singleton stimuli produce spatial cueing effects indicative of attentional capture only when they match current task sets, suggesting that capture is subject to top-down control. However, such task-set contingent capture effects could be associated with the top-down controlled disengagement of attention from non-matching stimuli that follows their initial bottom-up salience-driven selection. Using the N2pc component as an event-related potential marker of attentional capture, we demonstrate that top-down task set already controls the initial rapid selection of salient visual singleton stimuli prior to any subsequent attentional disengagement. These findings provide new evidence for the primacy of top-down control over bottom-up salience in attentional capture.
Subject(s)
Attention/physiology , Color Perception/physiology , Evoked Potentials, Visual/physiology , Orientation/physiology , Pattern Recognition, Visual/physiology , Adult , Cerebral Cortex/physiology , Cues , Discrimination, Psychological/physiology , Dominance, Cerebral/physiology , Electroencephalography , Female , Humans , Male , Reaction Time/physiology , Signal Processing, Computer-Assisted , Young AdultABSTRACT
We tested under which conditions a colour singleton of which an observer is unaware captures attention. To prevent visual awareness of the colour singleton, we used backward masking. We find that a masked colour singleton cue captures attention if it matches the observer's goal to search for target colours but not if it is task-irrelevant. This is also reflected in event-related potentials to the visible target: the masked goal-matching cue elicits an attentional potential (N2pc) in a target search task. By contrast, a non-matching but equally strong masked colour singleton cue failed to elicit a capture effect and an N2pc. Results are discussed with regard to currently pertaining conceptions of attentional capture by colour singletons.
