FIG. 4.

Characteristics of responses to outer molecular layer stimulation. A: variability of evoked responses. Five responses of a spiny hilar cell to stimulation of the outer molecular layer are shown. Stimulus strength was the lowest level that would evoke a response, yet responses were evoked in only 3 of 5 trials. Stimulus strength = 60 μA, 40 μs. Note that no response was ever elicited by a 60-nA, 30-μs stimulus in 20 consecutive trials. Stimulus frequency = 0.1 Hz. Membrane potential = −63 mV. Small circles: stimulus artifact. B: effects of stimulus strength and voltage on evoked responses. Top: responses to stimulation of the outer molecular layer of a spiny hilar cell at −61 mV. On the left is a response to a 30-μS duration stimulus (50 nA). The response to a 50-μS stimulus is shown in the next column. Longer-duration stimuli (100 μs) triggered action potentials at −61 mV and are not shown. Stimuli occurred at the dots. Center: responses of the same cell as in A to the same stimuli at −77 mV membrane potential. Bottom: responses of the same cell to the same stimuli at −93 mV membrane potential.