Ripple-associated unit firing in CA1 is delayed in slices from aged mice.

A. Top: Spontaneous sharp wave ripples recorded from CA3 stratum pyramidale. Middle: Ripple oscillations isolated from the wideband recording using a bandpass filter (100–500 Hz). Bottom: Juxtacellular unit activity recorded from a CA1 neuron near the stratum pyramidale/stratum oriens border. The unit shown on the expanded time scale is an example of a truncated waveform that resulted from low sampling resolution (5 kHz). B. Top: CA3 ripple oscillations recorded from an adult slice (left) and an aged slice (right). The corresponding CA1 unit activity is shown below (blue-adult; magenta-aged). Bottom: Histograms show normalized unit firing probability measured in 1 ms delay bins relative to the negative peak of CA3 ripples (dashed lines). Note that several peaks occur at approximately 5 ms intervals, corresponding to the period of the ripple cycle. C. Top: CA3 ripple waveform averages. Bottom: Mean normalized unit firing probabilities. Note the reduced firing probability during the earlier ripple cycles in the aged. Inset: Scatter plot of the delay bins containing the peak firing probabilities for adult neurons (blue) and aged neurons (magenta). The median delay was significantly larger in aged slices compared to adult slices. For clarity, dots were offset along the categorical axis. *p<0.05.