Suppression of 2f1-f2 distortion product otoacoustic emissions by electrical stimulation of the inferior colliculus in guinea pigs

Electrical stimulation of certain parts of the IC resulted in the depression of the DPOAE amplitude by 0.1-2 dB. The value of maximal DPOAE suppression was similar to the DPOAE suppression produced by acoustical stimulation of the contralateral ear. Our results indicate that electrical stimulation of the external cortex of the IC can activate the efferent system and produce DPOAE suppression by similar mechanisms as does acoustical stimulation of the contralateral ear

The effect of parvalbumin deficiency on the acoustic startle response and prepulse inhibition in mice

The strength of the acoustic startle response (ASR) to short bursts of broadband noise or tone pips (4, 8 and 16 kHz) and the prepulse inhibition (PPI) of the ASR elicited by prepulse tones (4, 8 and 16 kHz) were measured in parvalbumin-deficient (PV−/−) mice and in age-matched PV+/+ mice as controls. Hearing thresholds as determined from recordings of auditory brainstem responses were found to be similar in both genotypes. The ASRs to broadband noise and tones of low and middle frequencies were stronger than the ASRs in response to high-frequency tones in both groups. In PV−/− mice, we observed smaller ASR amplitudes in response to relatively weak startling stimuli (80–90 dB sound pressure level (SPL)) of either broadband noise or 8-kHz tones compared to those recorded in PV+/+ mice. For these startling stimuli, PV−/− mice had higher ASR thresholds and longer ASR latencies. PPI of the ASR in PV−/− mice was less effective than in PV+/+ mice, for all tested prepulse frequencies (4, 8 or 16 kHz) at 70 dB SPL. Our findings demonstrate no effect of PV deficiency on hearing thresholds in PV−/− mice. However, the frequency-specific differences in the ASR and the significant reduction of PPI of ASR likely reflect specific changes of neuronal circuits, mainly inhibitory, in the auditory centers in PV-deficient mice

Relationship between the response to whistle and the response to time-reversed whistle in individual neurons (n = 502).

<p>Each dot represents one unit. The slope of the regression line (solid line) is not significantly different from one (dashed line), P>0.05.</p

Cortical Representation of Species-Specific Vocalizations in Guinea Pig

<div><p>We investigated the representation of four typical guinea pig vocalizations in the auditory cortex (AI) in anesthetized guinea pigs with the aim to compare cortical data to the data already published for identical calls in subcortical structures - the inferior colliculus (IC) and medial geniculate body (MGB). Like the subcortical neurons also cortical neurons typically responded to many calls with a time-locked response to one or more temporal elements of the calls. The neuronal response patterns in the AI correlated well with the sound temporal envelope of chirp (an isolated short phrase), but correlated less well in the case of chutter and whistle (longer calls) or purr (a call with a fast repetition rate of phrases). Neuronal rate vs. characteristic frequency profiles provided only a coarse representation of the calls’ frequency spectra. A comparison between the activity in the AI and those of subcortical structures showed a different transformation of the neuronal response patterns from the IC to the AI for individual calls: i) while the temporal representation of chirp remained unchanged, the representations of whistle and chutter were transformed at the thalamic level and the response to purr at the cortical level; ii) for the wideband calls (whistle, chirp) the rate representation of the call spectra was preserved in the AI and MGB at the level present in the IC, while in the case of low-frequency calls (chutter, purr), the representation was less precise in the AI and MGB than in the IC; iii) the difference in the response strength to natural and time-reversed whistle was found to be smaller in the AI than in the IC or MGB.</p></div

Comparisons of the rate-CF profiles (n = 502, top) and call short-term spectra (bottom) for three consecutive parts of whistle (A–C – the appropriate time interval is indicated above every rate-CF profile), for purr (D – data calculated over the first phase containing four elementary phrases), for chirp (E) and for chutter (F – calculated over the first phrase of the call).

<p>Comparisons of the rate-CF profiles (n = 502, top) and call short-term spectra (bottom) for three consecutive parts of whistle (A–C – the appropriate time interval is indicated above every rate-CF profile), for purr (D – data calculated over the first phase containing four elementary phrases), for chirp (E) and for chutter (F – calculated over the first phrase of the call).</p

Comparison of the temporal envelope of the calls and the neuronal response.

<p>A comparison of the population PSTHs (n = 502, top) and the sound envelopes (bottom) is shown for all four calls: purr (A), whistle (B), chutter (C) and chirp (D). Each population PSTH is calculated as the average PSTH of all recorded units.</p