The effect of irrelevant visual experience on visual memory

Abstract

Consolidation of memories for long term storage involves increases in excitatory synaptic strength and connectivity between neurons encoding a novel experience. The increase in neuronal excitability caused by memory consolidation could augment excitability induced by the experience of related stimuli irrelevant to the memory. Therefore, the additional neuronal excitability caused by memory consolidation could perturb neuronal activity homeostasis towards higher neuronal activation levels. Under conditions of neuronal hyperactivity, such as in Alzheimer’s disease, an increase in excitation induced by memory consolidation would further destabilize homeostasis. We hypothesize that memory deficiency, which would result in reduced neuronal excitability, is an adaptation to maintain neuronal activity homeostasis. To test this hypothesis and to identify whether experience-evoked activity contributes to memory impairments, we used a visual recognition memory (VRM) paradigm that involves synaptic plasticity in the primary visual cortex. In this paradigm, mice are repeatedly presented with a visual grating of a specific orientation and the recognition memory is assessed as a decrease in the exploration of the same stimulus over time. We tested the orientation selective behavioral habituation in a mouse model of Alzheimer’s disease (J20 line) and non-transgenic control siblings (wild type). We found that wild type mice display VRM for grating stimulus when tested one day but not at one month after the training period. In contrast, J20 mice did not display VRM even one day after the training period. To examine whether reducing neuronal excitability caused by memory irrelevant visual experience influences the long-term retention of the VRM for grating stimulus, we performed the same task in mice housed in total darkness except during the VRM task. Our preliminary data indicate that dark adaptation rescues the memory deficit in J20 mice whereas disrupts memory in control mice when tested one day after the training. These results suggest that competing experiences promote memory storage in control mice but interferes with it in APP mice.