Figure 3. Responses of hair bundles from the rat’s cochlea.

(A) Irradiation of the hair bundle from an inner hair cell evoked motion in the direction of light propagation, here the positive direction, with a time constant of 459 μs. In this and the other panels, the bundles were stimulated at 600 nm with 18 mW of input power and the records represent the average of 25 repetitions. This number of repetitions was sufficient to diminish the noise and isolate the characteristic shape of the hair-bundle response. (B) A similar experiment with negatively directed irradiation moved the hair bundle in the opposite direction. The time constant is 258 μs. (C) Stimulation of an outer hair cell’s bundle in the positive direction evoked a response with sharp transients at both the onset and the offset of irradiation. As shown in the associated plot, the response rose with a time constant of 123 μs and peaked in less than 1 ms. (D) Negative stimulation of an outer hair cell’s bundle evoked movement in the negative direction with an onset time constant of 377 μs. (E) When a negatively directed light beam was aimed at the soma of an outer hair cell, the bundle moved with a slow time constant of 2.1 ms in the positive direction-opposite the direction of light propagation-owing to the photothermal effect.