Fig. 7.

A: stimulus-evoked current source density (CSD) response for each laminar compartment, averaged across all respective channels and across sessions (n = no. of units). Green dashed line denotes stimulus onset (STIM ON), and red dashed line denotes offset (STIM OFF). Current sinks are plotted upward (i.e., as positive values). Laminar compartments are denoted at left. Repetition numbers are indicated in grayscale (bottom right). B: subtraction plot of CSD activation between the first and fourth presentations (ΔCSD; average of all channel-based subtractions). Significant differences between laminar compartments across time are indicated by color-coded horizontal bars (paired-samples t-test, P < 0.05). Stimulus repetitions yielded a similar pattern of laminar CSD as the initial presentation; however, both sinks and sources were reduced for repeated stimuli compared with the initial response. This finding suggests that the diminished spiking responses under repetitive stimulation are secondary to decreased synaptic drive.