Silent Learning

Curr Biol. 2018 Nov 5;28(21):3508-3515.e5. doi: 10.1016/j.cub.2018.09.012. Epub 2018 Oct 25.


We introduce the concept of "silent learning"-the capacity to learn despite neuronal cell-firing being largely absent. This idea emerged from thinking about dendritic computation [1, 2] and examining whether the encoding, expression, and retrieval of hippocampal-dependent memory could be dissociated using the intrahippocampal infusion of pharmacological compounds. We observed that very modest enhancement of GABAergic inhibition with low-dose muscimol blocked both cell-firing and the retrieval of an already-formed memory but left induction of long-term potentiation (LTP) and new spatial memory encoding intact (silent learning). In contrast, blockade of hippocampal NMDA receptors by intrahippocampal D-AP5 impaired both the induction of LTP and encoding but had no effect on memory retrieval. Blockade of AMPA receptors by CNQX impaired excitatory synaptic transmission and cell-firing and both memory encoding and retrieval. Thus, in keeping with the synaptic plasticity and memory hypothesis [3], the hippocampal network can mediate new memory encoding when LTP induction is intact even under conditions in which somatic cell-firing is blocked.

Keywords: AMPA receptors; GABA receptors; NMDA receptors; learning; long-term potentiation; memory encoding; memory retrieval; synaptic plasticity; watermaze.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Hippocampus / physiology
  • Learning / physiology*
  • Long-Term Potentiation / physiology*
  • Male
  • Memory / physiology*
  • Neuronal Plasticity / physiology
  • Rats
  • Receptors, N-Methyl-D-Aspartate / antagonists & inhibitors


  • Receptors, N-Methyl-D-Aspartate