Changes in temporal acuity with age and with hearing impairment in the mouse: a study of the acoustic startle reflex and its inhibition by brief decrements in noise level.

Temporal acuity for brief gaps in noise was studied in mice of different ages (1-36 months) from strains with differing susceptibility to age-related hearing loss, using reflex modification audiometry. Prepulse inhibition of the acoustic startle reflex (ASR) increased with gap depth (GD: 10-40 dB in 70 dB SPL noise) and lead time (LT: 1-15 ms). The increase in inhibition with LT followed an exponential function in which the two parameters, asymptotic inhibition (AINH) and the time constant (tau), were both affected by GD. AINH rapidly declined from 1 to 6 and then to 18 months of age in C57BL/6J mice with progressively severe hearing loss, but first increased with maturation and then gradually declined beyond 6-12 months of age in CBA/CaJ and CBA x C57BL Fl-hybrid mice, which show no apparent change in sensory function at these ages. In contrast, tau was unaffected by hearing loss or by age, this suggesting that age-related changes in this form of temporal acuity occur because of a reduction in the efficiency with which gaps are centrally processed, not from any reduced ability to follow their rapid shift in noise level.

Nonlinear directionally selective subunits in complex cells of cat striate cortex.

1. We have analyzed receptive fields (RFs) of directionally selective (DS) complex cells in the striate cortex of the cat. We determined the extent to which the DS of a complex cell depends on spatially identifiable subunits within the RF by studying responses to an optimally oriented, three-luminance-valued, gratinglike stimulus that was spatiotemporally randomized. 2. We identified subunits by testing for nonlinear spatial RF interactions. To do this, we calculated Wiener-like kernels in a spatial superposition test that depended on two RF positions at a time. The spatial and temporal separation of light and dark bars at these two positions varied over a spatial range of 8 degrees and a temporal range of +/- 112 ms in increments of 0.5 degree and 16 ms, respectively. 3. DS responses in complex cells cannot be explained by their responses to single light or dark bars because any linear superposition of responses whose time course is uniform across space shows no directional preference. 4. Nonlinear interactions between a flashed reference bar that is fixed in position and a second bar that is flashed at surrounding positions help explain DS by showing multiplicative-type facilitation for bar pairs that mimic motion in the preferred direction and suppression for bar pairs that mimic motion in the null direction. Interactions in the preferred direction have an optimal space/time ratio (velocity), exhibited by elongated, obliquely oriented positive domains in a space-time coordinate frame. This relationship is inseparable in space-time. The slope of the long axis specifies the preferred speed, and its negative agrees with the most strongly suppressed speed in the opposite direction. 5. When the reference bar position is moved across the RF, the spatiotemporal interaction moves with it. This suggests the existence of a family of nearly uniform subunits distributed across the RF. We call the subunit interaction, as averaged across the RF, the "motion kernel" because its spatial and temporal variables are those necessary to specify the velocity, the only parameter that distinguishes a moving image from a temporally modulated stationary image. The nonlinear interaction shows a spatial periodicity, which suggests a mechanism of velocity selectivity for moving extended images.(ABSTRACT TRUNCATED AT 400 WORDS)

A signal analysis approach to rat sleep scoring instrumentation.

Automated rat sleep analysis focuses on the statistically regular waveforms of the EEG, such as theta and delta rhythms. Such stochastic processes can be quantified in several manners. Time domain statistics such as auto- and cross-correlations produce outputs that are difficult to use and are best performed in software. Frequency domain statistics like spectral density accurately quantify the sleep state by power-frequency distributions but also require sophisticated computer processing. Continuous frequency analysis, using pass-band filtering, accurately measures signal power in an on-line fashion and employs relatively inexpensive hardware to estimate power by integrating the square of the signal. This method differs substantively from other previously reported systems which rely on signal amplitude analysis. Comparison of this system with a human scorer indicates high degrees of validity and reproducibility.

Computer assisted unit data acquistion/reduction.

A computer system for unit data acquisition and reduction (CAUDAR) is presented. This system digitally processes uninterrupted, continuous unit data with attention to waveform detail. Several units in a multiunit field are recognized by evaluation of spike waveform and amplitude. High-speed computer graphics provides almost instantaneous figures of good quality for illustration. The system affords a great economy of the user's time because the computer performs all data processing.