The inferior colliculus of the rat: a quantitative analysis of monaural frequency response areas.
Frequency response areas (FRAs) were measured for 237 single units in the inferior colliculus (IC) of urethane-anesthetized pigmented rats using monaural pure-tone stimulation. Based on qualitative criteria [J Neurosci 21 (2001) 7303], FRAs were classified as V-shaped in 69% of neurons, non-V-shaped in 29%, and unclassifiable in the remaining 2%. Non-V-shaped FRAs were heterogeneous, comprising a number of subtypes including narrow, closed, low- and high-tilt, multipeaked, U-shaped, mosaic and inhibitory. To complement this subjective classification, we applied quantitative measures used by others (e.g. [J Neurophysiol 84 (2000) 1012]), including the inverse slope of the upper and lower FRA borders, Q-values, and other measures of bandwidth. The results suggest that FRAs in the rat IC are best described as forming a continuous distribution among subtypes, rather than clustering into discrete categories. Moreover, there is a broad range of frequency tuning characteristics and FRA types across the entire frequency spectrum. Within this general pattern, however, there are some frequency-specific differences in FRA type distribution. The relative proportion of V-shaped FRAs was greatest at the high and low ends of the auditory range, with the highest proportion of non-V-shaped FRAs in the mid-range from 6 to 12 kHz. For most neurons with multipeaked FRAs, the peak frequencies were not harmonically related. Frequency tuning in the pigmented rat IC is generally similar to that in other species. Comparison of Q values across auditory nuclei shows little evidence that FRAs are sharpened at levels above the auditory nerve. Rather, there is a broad range of frequency tuning properties at each level.
Hernández
O
O
Auditory Neurophysiology Unit, Laboratory for the Neurobiology of Hearing, Institute of Neuroscience of Castilla y León and Faculty of Medicine, University of Salamanca, Salamanca, Spain.
Espinosa
N
N
Pérez-González
D
D
Malmierca
M S
MS
D000161:Acoustic Stimulation; D000200:Action Potentials / Q000502:physiology; D000818:Animals; D001306:Auditory Pathways / Q000502:physiology*; D001309:Auditory Threshold / Q000502:physiology; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D007245:Inferior Colliculi / Q000502:physiology*; D008297:Male; D009474:Neurons / Q000502:physiology; D010898:Pitch Perception / Q000502:physiology*; D051381:Rats; D020318:Rats, Long-Evans; D013017:Sound Localization / Q000502:physiology*