Functional development of the inferior colliculus (IQ and its relationshipwith the auditory brainstem response (ABR) in the tammar wallaby (Macropuseugenii)

To discover the developmental relationship between the auditory brainstem r esponse (ABR) and the focal inferior colliculus (IC) response, 32 young tam mar wallabies were used, by the application of simultaneous ABR and focal b rainstem recordings, in response to acoustic clicks and tone bursts of seve n frequencies. The ic or the tammar wallaby undergoes a rapid functional de velopment from postnatal day (PND) 114 to 160. The earliest (PND 114) audit ory evoked response was recorded from the rostral IC. With development, mor e caudal parts of the IC became functional until age about PND 127, when al l parts of the IC were responsive to sound. Along a dorsoventral direction, the duration of the IC response decreased, the peak latency shortened, whi le the amplitude increased, reaching a maximum value at the central IC, the n decreased. After PND 160, the best frequency (BF) of the ventral IC was t he highest, with values between 12.5 and 16 kHz, the BF of the dorsal IC wa s the lowest, varying between 3.2 and 6.4 kHz, while the BF of the central IC was between 6.4 and 12.5 kHz. Between PND 114 and 125, the IC response d id not have temporal correlation with the ABR. Between PND 140 and 160, onl y the early components of the responses from the ventral and central IC cor related with the P4 waves of the ABR. After PND 160, responses recorded fro m different depths of the IC had a temporal correlation with the ABR. (C) 2 001 Published by Elsevier Science B.V.