Cross-Spectral Channel Gap Detection in the Aging CBA Mouse

1
Cross-Spectral Channel Gap Detection in the Aging
CBA Mouse Jason T. Moore, Paul D. Allen, James R.
Ison Department of Brain Cognitive Sciences,
University of Rochester, Rochester, NY
ARO 2005 432
Experiment 1 High frequency within-channel gaps
have the lowest detection thresholds
Experiment 2 Aging-related loss of
cross-spectral channel gap detection
Introduction
Gap detection is optimal when the auditory
stimuli preceding and following the gap are
spectrally similar (within-channel signals), but
can still occur to a lesser extent with
between-channel signals (Formby and Forrest,
1991 Oxenham, 2000). More recent studies using
within-channel signals have shown that temporal
acuity degrades with age in mice as it does in
humans (Barsz et al, 2002 Allen et al., 2003
and note that age does not affect noise pulse
detection). To our knowledge nothing is known
about how aging affects between-channel gap
detection. This series of experiments was
performed in order, first, to compare the aging
CBA mouses performance on within- and
between-channel detection tasks (Expt 1) second,
to determine how between-channel gap detection
is affected by the spectral components of the
auditory signals (Expt 2) and third, to provide
data directly comparing the spectral dependence
of between-channel and within-channel gap
detection (Expt 3).
Within-Channel The 2- and 12-month old CBAs
performed similarly on both within-channel
conditions, with the low-frequency condition
requiring a longer gap to achieve a comparatively
lower level of maximal inhibition. The 24-month
CBAs exhibited inhibition from gaps only in the
high-frequency within-channel condition, and the
gap detection threshold was higher than that of
the younger mice.
Inhibition Due to Gaps Old mice showed no
consistent inhibition in the between-channel
conditions. The 2-month old mice were better
able to detect low-to-high spectral swaps than
the 12-month old mice, while the two age groups
performed similarly in high-to-low spectral swaps.
Methods
Subjects Three groups, each containing 16
CBA/CaJ mice young adult (2 months), middle-aged
(12 months), and old (24 months). Auditory
Stimuli and Recording Gap detection was
quantified by measuring the magnitude of a
mouses acoustic startle reflex (ASR) via reflex
modification. All stimuli were ½-octave band
filtered pink noise and were presented at 70 dB
SPL in the presence of a constant 50 dB pink
noise background. The eliciting stimulus (ES)
was a 30 ms, 110 dB noise burst and was always
presented 50 ms after the end of the gap. 10
trials were performed for each condition, with a
mean inter-trial interval of 20 sec.
Between-Channel The old mice were not able to
detect gaps in either between-channel condition.
Both of the younger groups performed better in
the low-to-high frequency condition than in the
high-to-low condition.
Inhibition Due to Frequency Swap While within
each age group the spectral contents of the
markers had little effect on the amount of
swap-induced inhibition, the frequency swap
proved to be a salient inhibitory stimulus with a
strong interaction between frequency and age.
When M1 was a low frequency, both the young and
middle-aged mice perform very similarly, while
when M1 was a high frequency, the frequency swap
was less inhibitory to the young mice.
ES
Experiment 3 Within-channel gap detection across
frequencies
Discussion
M1
M2
Gap detection is dependent on the spectral
contents of the pre- and post-gap auditory
stimuli. Within-channel gaps were easier for the
mice to detect at shorter gap durations and these
gaps resulted in greater inhibition of the
startle reflex than between-channel gaps. For
young and middle-aged mice, the preferable
between-channel condition was a low frequency
marker preceding the gap and a higher frequency
marker following the gap, compared to the
reverse, and a high-frequency M2 was most
important for gap detection. However, aging
leads to an almost complete loss of the ability
to detect gaps between spectrally dissimilar
signals old mice were only able to appreciably
detect gaps in high-frequency within-channel
conditions. While mice have their best ABR
thresholds at 12-16 kHz, they performed best at
gap detection when the markers contained higher
frequency components (22-26 kHz), providing
further support to the hypothesis that the
aging-related loss of temporal acuity is at least
partly independent of sensorineural hearing loss.
Despite elevated ABR thresholds for high
frequencies, older mice require the presence of
higher frequencies to perform gap detection,
indicating that aging virtually eliminates the
mouses ability to use low and mid frequencies as
cues for gap detection.
Within-Channel Gap Detection (left) Young and
middle-aged mice had significant inhibition to
all conditions except for the lowest center
frequency (6.7 kHz), while the old mice detected
the 10ms gap only when the two markers were
centered at higher frequencies (22.6-38 kHz
). Comparison with ABR Thresholds (right) The
frequency range that provides the lowest ABR
thresholds (12-16 kHz) is spectrally distinct
from the range that provides best temporal acuity
(22.6 and 26.9 kHz). The mice that were used to
determine ABR thresholds (N23, 31, 41 for 2mo,
12mo, 24mo) were not tested in the behavioral
portion of this experiment. Solid lines
represent the frequency range of best
within-channel gap detection.
Experiment 1 The pre-gap marker (M1) and the
post-gap marker (M2) were centered at either 8 or
32 kHz, yielding two within-channel conditions
and two between-channel conditions. The gap
duration ranged from 0 to 30 ms. Experiment 2 M1
was centered at either 9.51, 16, or 26.91 kHz,
while the center frequency for M2 ranged from 6.7
to 38 kHz, yielding 3 within-channel condition
and 30 between-channel conditions for each M1
frequency. The gap duration was either 0 or
10ms. Experiment 3 M1 and M2 were always
centered at the same frequency, but this center
frequency ranged from 6.7 to 38 kHz, yielding 11
within-channel conditions. The gap duration was
either 0 or 10 ms.
Supported by NIA Grant AG09524 and the de
Kiewiet Fellowship