L. Aitkin et al., THE RESPONSES OF NEURONS IN SUBDIVISIONS OF THE INFERIOR COLLICULUS OF CATS TO TONAL, NOISE AND VOCAL STIMULI, Experimental Brain Research, 98(1), 1994, pp. 53-64
The aim of this study was to gain information from anesthetized cats a
bout the differential coding properties of neurons in the three major
subdivisions of the inferior colliculus: the central (CNIC) and extern
al (EN) nuclei and dorsal cortex (DC). Stimuli were presented in the f
ree field from a speaker facing the contralateral pinna. For each unit
, the characteristic frequency (CF, where threshold was lowest) was de
termined, and impulse rates to CF tone bursts, noise bursts and four f
eline vocal stimuli were measured as a function of increasing sound pr
essure level (rate/level functions). Peristimulus-time histograms were
computed for responses to all stimuli. Sustained firing patterns to C
F stimuli were observed for 81% of units in CNIC, for 50% of units in
EN and 27% of units in DC. Sustained discharges were evoked by noise i
n 78-100% of units in all regions, and by at least one vocal stimulus
in 86% of units in CNIC, 82% in EN and 55% in DC. In the CNIC, non-mon
otonic rate/level functions to CF stimuli were more common (41%) than
either monotonic or plateau functions, whereas the reverse was the cas
e with noise and vocal stimuli. Non-monotonic functions were uncommon
to any stimulus in EN and DC (21-24%). Vocal stimuli were more effecti
ve in terms of higher firing rates than noise or CF stimuli in 27% of
units in CNIC, 82% in EN and 72% in DC. There were no units that respo
nded exclusively to one vocal stimulus, but a high proportion of units
in EN responded strongly to broad band stimuli, and some of these sho
wed clear preferences for one vocal stimulus over others.