title: Distinct kinetics of synaptic structural plasticity, memory formation, and memory decay in massed and spaced learning.
abstract: Long-lasting memories are formed when the stimulus is temporally distributed (spacing effect). However, the synaptic mechanisms underlying this robust phenomenon and the precise time course of the synaptic modifications that occur during learning remain unclear. Here we examined the adaptation of horizontal optokinetic response in mice that underwent 1 h of massed and spaced training at varying intervals. Despite similar acquisition by all training protocols, 1 h of spacing produced the highest memory retention at 24 h, which lasted for 1 mo. The distinct kinetics of memory are strongly correlated with the reduction of floccular parallel fiber-Purkinje cell synapses but not with AMPA receptor (AMPAR) number and synapse size. After the spaced training, we observed 25%, 23%, and 12% reduction in AMPAR density, synapse size, and synapse number, respectively. Four hours after the spaced training, half of the synapses and Purkinje cell spines had been eliminated, whereas AMPAR density and synapse size were recovered in remaining synapses. Surprisingly, massed training also produced long-term memory and halving of synapses; however, this occurred slowly over days, and the memory lasted for only 1 wk. This distinct kinetics of structural plasticity may serve as a basis for unique temporal profiles in the formation and decay of memory with or without intervals.
authors.affiliation: Division of Cerebral Structure, National Institute for Physiological Sciences, Okazaki 444-8787, Japan.
authors.forename: Wajeeha
authors.initials: W
authors.lastname: Aziz
authors.forename: Wen
authors.initials: W
authors.lastname: Wang
authors.forename: Sebnem
authors.initials: S
authors.lastname: Kesaf
authors.forename: Alsayed Abdelhamid
authors.initials: AA
authors.lastname: Mohamed
authors.forename: Yugo
authors.initials: Y
authors.lastname: Fukazawa
authors.forename: Ryuichi
authors.initials: R
authors.lastname: Shigemoto
mesh_terms: D000818:Animals; D049229:Dendritic Spines / Q000502:physiology; D005133:Eye Movements; D007858:Learning / Q000502:physiology*; D008297:Male; D057567:Memory, Long-Term / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D009473:Neuronal Plasticity / Q000502:physiology*; D011689:Purkinje Cells / Q000166:cytology; D018091:Receptors, AMPA / Q000378:metabolism; D013569:Synapses / Q000502:physiology*; D013997:Time Factors
chemical_list: D018091:Receptors, AMPA
keywords: AMPA receptor reduction; cerebellar motor learning; synapse shrinkage and elimination