Fig. 5. Frequency-dependent augmentation. The same VL cell was tested with a six-shock train to the VL nucleus at 3, 5, and 10 Hz.Right, The responses to all stimuli in a train are superimposed and expanded. Top, 1,2, Responses to first and second stimuli in the train at 3 Hz; note that responses to following stimuli (3–6) did not change, compared with the response to the first stimulus. Middle, 1,2, 5, 6, Responses to the first, second, fifth, and sixth stimuli in the train at 5 Hz.Bottom, 1, 2, Responses to the first and second stimuli in the train at 10 Hz; note progressive increase in firing threshold and spike inactivation during repetitive stimulation.