Hunger and sleep recruit distinct brain systems to form spatial memory

By demonstrating that hunger consolidates spatial memory via a non-hippocampal mechanism that critically involves the retrosplenial cortex, we identify a mode of memory formation that is distinct from well-known hippocampus-dependent memory formation during sleep. Food-deprived rats encoded object locations and, during a subsequent 2-h consolidation phase, either received food and slept (Sleep-Fed) or stayed awake (Wake-Fed), or remained hungry and stayed awake (Wake-Hungry). At later retrieval testing, both Wake-Hungry and Sleep-Fed rats exhibited robust spatial memory, whereas Wake-Fed rats did not. Blocking neuropeptide-Y (NPY) signaling during the consolidation phase abolished hunger-consolidated memory. Unlike sleep-dependent consolidation, hunger-consolidated memory did not require the hippocampus during consolidation or retrieval, and not even during encoding. In contrast, inhibiting retrosplenial cortex during retrieval abolished hunger-consolidated memory but spared memory formed during sleep. Thus, recruitment of brain systems to form spatial memory is tuned to specific brain states, and fundamentally differs between sleep and hunger.