Figure 1. Age-related alterations in neuronal activity patterns and hub neuron dysfunction were investigated in young and aged rats. This was accomplished by combining anatomical tracing (retrograde tracer injected into the prefrontal cortex; green) and imaging neuron activity during behavior by labeling the immediate-early gene Arc (red). Thus, neurons (blue) with red and green signal are the perirhinal cortical projection cells to prefrontal cortex that were activated during behavior. Activity patterns significantly differed between aged and young rats, with changes primarily occurring within the hub neurons that have long-range projections across regions.