Fig. 2. Anomalous auditory brainstem responses (ABRs) in Barhl1-null mice. (A) Representative ABR evoked by 50 dB SPL click stimuli is illustrated for Barhl1^+/+ (black line) and Barhl1^–/– (red line) mice. The sensitivity, latency and waveform of the ABR response were essentially identical for Barhl1^+/+ and Barhl1^+/– mice. The auditory stimulus was presented at 0 mseconds. All Barhl1^–/– mice either had elevated thresholds or were unresponsive to sound. (B) Mean (±s.d.) click ABR thresholds are shown for Barhl1^+/+, Barhl1^+/– and responsive Barhl1^–/– mice at different ages. (C) Mean (±s.d.) ABR thresholds at different frequencies are shown for Barhl1^+/+, Barhl1^+/– and responsive Barhl1^–/– mice at 3 months of age. Because Barhl1^–/– mice did not always respond to even the loudest of the auditory stimuli presented (>70 dB at 4 kHz and >95 dB SPL for all other stimuli; Table 1), thresholds were calculated only for mice with ABR responses (clicks: n=10 out of 10 at one month, seven out 10 at 3 months, and three out of 10 at 10 months; 4 kHz: n=2 out of 10; 8 kHz: n=7 out of 10; 16 kHz: n=5 out of 10; and 32 kHz: n=5 out of 10). Every Barhl1^+/+ and Barhl1^+/– mouse exhibited responses to acoustic stimulation.