The Journal of Neurophysiology Vol. 87 No. 1 January 2002, pp. 240-249
Copyright ©2002 by the American Physiological Society
Department of Surgery, Division of Otolaryngology, University of Rochester School of Medicine and Dentistry, Rochester, New York 14642
Wilson, Willard W. and
Joseph P. Walton.
Background Noise Improves Gap Detection in Tonically Inhibited
Inferior Colliculus Neurons. J. Neurophysiol. 87: 240-249, 2002. Single units in the inferior colliculus
(IC) in the C57Bl/6 inbred mouse strain were tested for their temporal
processing ability as measured by their minimum gap threshold (MGT),
the shortest silent interval in an ongoing white-noise stimulus which a
unit could encode. After ascertaining the MGT in quiet, units were
re-tested in various levels of background noise. The focus of this
report is on two types of tonically responding units found in the IC.
Tonically inhibited (TI) units encoded gaps poorly in quiet and low
levels of background noise as compared with tonically excited (TE)
units. In quiet, the MGTs of TI units were about an order of magnitude
longer than the MGTs typical of TE units. Paradoxically, gap encoding
was improved in high levels of background noise for TI
units. This result is unexpected from the traditional viewpoint that
noise necessarily degrades signal processing and is inconsistent with
psychophysical observations of diminished speech and gap detection
processing in noisy environments. We believe the improved feature
detection described here is produced by the adaptation of inhibitory
input. Continuous background noise would diminish the inhibitory
efficacy of the gap stimulus by increasing the latency to the onset of
inhibition and decreasing its duration. This would allow more
spontaneous activity to "bleed through" the silent gap, thus
signaling its presence. Improved feature detection in background noise
resulting from inhibitory adaptation would seem an efficient neural
mechanism and one that might be generally useful in other signal
detection tasks.