Effect of amantadine on motor memory consolidation in humans

The Effects of Post-Learning Alcohol Ingestion on Human Motor Memory Consolidation

The neurochemical mechanisms underlying motor memory consolidation remain largely unknown. Based on converging work showing that ethyl alcohol retrogradely enhances declarative memory consolidation, this work tested the hypothesis that post‐learning alcohol ingestion would enhance motor memory consolidation. In a within‐subject and fully counterbalanced design, participants (n = 24; 12M; 12F) adapted to a gradually introduced visual deviation and ingested, immediately after adaptation, a placebo (PBO), a medium (MED) or high (HIGH) dose of alcohol. The alcohol doses were bodyweight‐ and gender‐controlled to yield peak breath alcohol concentrations of 0.00% in the PBO, ~0.05% in the MED and ~0.095% in the HIGH condition. Retention was evaluated 24 h later through reach aftereffects when participants were sober. The results revealed that retention levels were neither significantly nor meaningfully different in both the MED and HIGH conditions as compared to PBO (all absolute Cohen's d_z values < ~0.2; small to negligible effects), indicating that post‐learning alcohol ingestion did not alter motor memory consolidation. Given alcohol's known pharmacological GABAergic agonist and NMDA antagonist properties, one possibility is that these neurochemical mechanisms do not decisively contribute to motor memory consolidation. As converging work demonstrated alcohol's retrograde enhancement of declarative memory, the present results suggest that distinct neurochemical mechanisms underlie declarative and motor memory consolidation. Elucidating the neurochemical mechanisms underlying the consolidation of different memory systems may yield insights into the effects of over‐the‐counter drugs on everyday learning and memory but also inform the development of pharmacological interventions seeking to alter human memory consolidation.

An N-methyl-D-aspartate receptor agonist facilitates sleep-independent synaptic plasticity associated with working memory capacity enhancement

Working memory (WM) capacity improvement is impacted by sleep, and possibly by N-methyl-D-aspartate (NMDA) agonists such as D-cycloserine (DCS), which also affects procedural skill performance. However, the mechanisms behind these relationships are not well understood. In order to investigate the neural basis underlying relationships between WM skill learning and sleep, DCS, and both sleep and DCS together, we evaluated training-retest performances in the n-back task among healthy subjects who were given either a placebo or DCS before the task training, and then followed task training sessions either with wakefulness or sleep. DCS facilitated WM capacity enhancement only occurring after a period of wakefulness, rather than sleep, indicating that WM capacity enhancement is affected by a cellular heterogeneity in synaptic plasticity between time spent awake and time spent asleep. These findings may contribute to development, anti-aging processes, and rehabilitation of higher cognition.

D-cycloserine facilitates procedural learning but not declarative learning in healthy humans: a randomized controlled trial of the effect of D-cycloserine and valproic acid on overnight properties in the performance of non-emotional memory tasks

Although D-cycloserine (DCS), a partial agonist of the N-methyl-d-aspartate (NMDA) receptor, and valproic acid (VPA), a histone deacetylase inhibitor, have been investigated for their roles in the facilitation of emotional learning, the effects on non-emotional declarative and procedural learning have not been clarified. We performed a randomized, blind, placebo-controlled, 4-arm clinical trial to determine the effects of DCS and VPA on the overnight properties of declarative and procedural learning in 60 healthy adults. Subjects were orally administrated a placebo, 100 mg DCS, 400 mg VPA, or a combination of 100 mg DCS and 400 mg VPA before they performed declarative and procedural learning tasks. Subjects then had their performance retested the following day. We observed that DCS facilitated procedural but not declarative learning and that VPA did not contribute to learning. Surprisingly, however, VPA attenuated the enhancement effect of DCS when coadministered with it. These results suggest that DCS acts as an enhancer of hippocampus-independent learning and that VPA may have an extinguishing pharmacological effect on excitatory post-synaptic action potentials that NMDA receptors regulate within procedural learning.