Responses generated in the prelimbic-infralimbic cortices (areas 32 and 25) by stimulation of the basolateral amygdala were studied by means of laminar field potential recordings. Based on the analysis of wave forms and depth potential profiles of the responses, three constituent responses were identified: (1) a surface-positive potential with a short onset latency (mean, 4.5 ms) and a long duration (ca. 70 ms) that reversed the polarity at a depth of 400 microns; (2) a surface-positive potential with a mean onset latency of 15 ms and a duration of 20 ms that reversed to a negative potential at a depth of 300 microns; and (3) a long-latency (ca. 20 ms) superficial-negative potential that reversed to a positive potential at depths below 400 microns. Lesion experiments ruled out the possibility that impulse traffic via the thalamic mediodorsal nucleus (MD) contributed to the responses. Amygdala stimulation also produced responses in the insular cortex, but they did not contaminate the responses in the mesial cortex. It is proposed that impulses originating from the amygdala provide excitation for cortical pyramidal cells at a short latency at deeper layers, but with considerable delays at upper and superficial layers, in the medial prefrontal cortex (mPFC).