Figure 1.

Facilitatory interactions in FM specialists. A, The neuron responded to downward FM sweeps but not to upward sweeps or individual tones present in the sweep. B, Two-tone tests on the same neuron revealed asymmetric facilitation, with the high→low sequence (positive delays) producing facilitation. The solid horizontal lines near the bottom right corner indicate the response magnitude to individual tones. The horizontal dashed line shows the sum of responses to the two tones presented individually (summed response). The low→high sequence (negative delays) produced a response that was lower than the summed response showing that inhibition might enhance the asymmetry. The peak facilitation occurred at 1 ms delay. The response declined toward the summed response for longer delays. C, Histogram of the range of facilitation observed in the FM specialists. In all 46 FM specialists, the response to the two-tone sequence was at least 50% stronger than the response to the sum of individual tone responses.