Figure 7

Distribution of memory performance and hippocampal volumes for individual animals and their evolution over time.

Each pair of circles connected by a line represents a single animal (black and red represent unstressed and stressed animals respectively). The y-axis represents the performance in the Object displacement task on day13 and x-axis represents the total hippocampal volume. The hollow circle represents the hippocampal volume on day3 and the solid circle the hippocampal volume on day11. The arrowhead shows the direction of the shift in total hippocampal volume from day3 to day11 for each individual animal. The brown line represents the median (50 percentile) of performance in Object displacement task on day13. The green line represents the median (50 percentile) of the total hippocampal volume on day3. A majority of the animals possessing hippocampal volumes (x-axis) above the median (i.e. larger hippocampal volumes) are also primarily located above the median along the y-axis (i.e. superior performance in the object displacement task). Conversely, a majority of those that are under the median value for hippocampal volumes are also located below the median value for memory performance. Moreover, a majority of the points in the upper right quadrant (above the median for both volume and performance) are unstressed animals (black circles), while a majority of those located in the lower left quadrant (below the median for both volume and performance) are stressed animals. The direction of the individual black arrows (connecting black circles) for the unstressed animals is a mixed population – some volumes increase (rightward shift), while others decrease or remain unchanged. In striking contrast, all the red arrows (connecting red circles) show a leftward shift (decrease in volume from day3 to day11).