Experience-induced replay of neuronal ensembles occurs during hippocampal high-frequency oscillations, or ripples. Postlearning increase in ripple rate is predictive of memory recall, while ripple disruption impairs learning. Ripples may thus present a fundamental component of a neurophysiological mechanism of memory consolidation. In addition to systemlevel local and cross-regional interactions, a consolidation mechanism involves stabilization of memory representations at the synaptic level. Synaptic plasticity within experience-activated neuronal networks is facilitated by noradrenaline release from the axon terminals of the locus coeruleus (LC). Here, to better understand interactions between the system and synaptic mechanisms underlying "off-line" consolidation, we examined the effects of ripple-associated LC activation on hippocampal and cortical activity and on spatial memory. Rats were trained on a radial maze; after each daily learning session neural activity was monitored for 1 h via implanted electrode arrays. Immediately following "on-line" detection of ripple, a brief train of electrical pulses (0.05 mA) was applied to LC. Low-frequency (20 Hz) stimulation had no effect on spatial learning, while higher-frequency (100 Hz) trains transiently blocked generation of ripple-associated cortical spindles and caused a reference memory deficit. Suppression of synchronous ripple/spindle events appears to interfere with hippocampal-cortical communication, thereby reducing the efficiency of "off-line" memory consolidation.

Blockade of mGlu1 receptors improves working memory and reduces impulsive choice at the doses that have no effects on time perception but appear to facilitate impulsive action.

No abstract

Glutamate, the main excitatory neurotransmitter in the mammalian CNS, acts via ionotropic and metabotropic receptors. Results from in vitro studies demonstrating tight interactions between ionotropic NMDA receptors and subtype 5 metabotropic glutamate receptors (mGlu5) have shown that blockade of mGlu5 receptors increases the behavioral effects of NMDA receptor antagonists. The aim of the present work was to study the actions of the highly selective mGlu5 receptor antagonist MTEP alone and in combination with MK-801, a blocker of the NMDA receptor-associated ion channel, on performance of a delayed selection task (a test of working memory) in rats. MK-801 (0.1 mg/kg) induced a specific impairment to working memory, with proactive interference (degradation of the ability to remember current information because of the effects of previously learned material). Administration of MTEP (5.0 mg/kg) combined with both solvent and with MK-801 had no significant effects, demonstrating the small or nonexistent involvement of mGlu5 receptors in the mechanisms of working memory.

Withdrawal of antiepileptic drugs (AEDs) is a standard procedure during presurgical epilepsy assessment. Rapid and, at times, even pre‐hospital withdrawal of medication is performed in some centres to enhance the yield of recorded seizures during video‐EEG monitoring. AED withdrawal, however, affects the propensity and speed of propagation of epileptic activity, may evoke more severe seizures, and may cause pitfalls in EEG interpretation. We report a case which had been recommended to undergo intracranial EEG recordings in order to clarify apparently discordant MRI findings and ictal EEG patterns when monitoring was performed following complete AED withdrawal. Re‐evaluation to assess scalp EEG patterns at several drug levels during slow AED tapering showed a loss of localizing information with AED withdrawal due to contralateral and bitemporal spread of frontal epileptic activity. Our report demonstrates that in individual cases, rapid AED withdrawal during presurgical video‐EEG monitoring can impair the validity of EEG recordings and lead to unnecessary risks and investigations during workup.