Figure 8.

Strong duty cycle preference in PM receptive fields of sustained neurons from aged animals. A, Variance in PM receptive fields of sustained neurons from young adult and aged animals explained by PCs. PCs were computed from PM receptive fields of young adult and aged animals separately. For sustained neurons from young adult animals, 50% of the variance is explained by the first, 30% by the second, and ∼10% by the third PC. In contrast, in the aged population, 90% of the variance is explained by the first and only 10% by the second PC. B, First, second, and third PC of PM receptive fields of sustained neurons from young adult and aged animals. In all the 3-D plots, dark red depicts strong responses and dark blue weak responses. Distributions of weights for principal components of individual PM receptive fields are shown in the right. Weights for the second PC tend to more positive values for young adult than for aged animals (not significant). Weights for the third PC tend to cluster around 0 for aged but are spread to positive and negative values for young adult animals (Ansari-Bradley test, p = 0.02). C, Mean PM receptive fields of neurons from young adult and aged animals. Neurons were clustered based on their representation in three-dimensional principal component space (weights). Note that cluster 2 comprises neurons that showed a strong preference in discharge for short duty cycles and was mostly dominated by neurons from aged animals. Cluster 3 comprised neurons that showed a clear preference for pulse trains with short to medium pulse and pause durations. This cluster was dominated by sustained neurons from young adult animals.