Population coding in the auditory cortex.
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Animals↗
Biomedical subjects
B H Gaese
Publications and source records attributed to B H Gaese.
Spatial attention modulates sound localization in barn owls.
Attentional influence on sound-localization behavior of barn owls was investigated in a cross-modal spatial cuing paradigm. After being cued to the most probable target side with a visual cuing stimulus, owls localized upcoming auditory target stimuli with a head turn toward the position of the sound source. In 80% of the trials, cuing stimuli pointed toward the side of the upcoming target stimulus (valid configuration), and in 20% they pointed toward the opposite side (invalid configuration). We found that owls initiated the head turns by a mean of 37.4 ms earlier in valid trials, i.e., mean response latencies of head turns were reduced by 16% after a valid cuing stimulus. Thus auditory stimuli appearing at the cued side were processed faster than stimuli appearing at the uncued side, indicating the influence of a spatial-selective attention mechanism. Turning angles were not different when owls turned their head toward a cued or an uncued location. Other types of attention influencing sound localization, e.g., a reduction of response latency as a function of the duration of cue-target delay, could not be observed. This study is the first attempt to investigate attentional influences on sound localization in an animal model.
Acoustic Stimulation↗
Anesthesia changes frequency tuning of neurons in the rat primary auditory cortex.
The vast majority of investigations on central auditory processing so far were conducted under the influence of an anesthetic agent. It remains unclear, however, to what extend even basic response properties of central auditory neurons are influenced by this experimental manipulation. We used a combination of chronic recording in unrestrained animals, computer-controlled randomized acoustic stimulation, and statistical evaluation of responses to directly compare the response characteristics of single neurons in the awake and anesthetized state. Thereby we were able to quantify the effects of pentobarbital/chloral hydrate anesthesia (Equithesin) on rat auditory cortical neurons. During Equithesin anesthesia, only a portion of central neurons were active and some of their basic response properties were changed. Only 29% of the neurons still had a frequency response area. Their tuning sharpness was increased under anesthesia. Most changes are consistent with an enhancement of inhibitory influences during Equithesin anesthesia. Thus when describing response properties of central auditory neurons, the animal's anesthetic state has to be taken into account.
Anesthetics, Combined↗
Coding for auditory space in the superior colliculus of the rat.
Although the rat is often used to determine behavioural sound-localization capabilities or neuronal computation of binaural information, the representation of auditory space in the rat brain has not been investigated so far. We obtained extracellular recordings from auditory neurons in the superior colliculus of anaesthetized rats and examined them for spatial tuning characteristics and topographical order. Many neurons (73%) showed significant tuning, with a single peak in the azimuth response profiles based on spike rates and response latencies. Best azimuth values from neurons in one SC were generally tuned to contralateral and rarely to frontal or ipsilateral directions. Tuning width was mostly broad; at supra-threshold sound pressure levels (35 dB SPL), 55% of the units had a tuning width of > 120 degrees in contralateral space. Additionally, tuning width increased with stimulation intensity. A significant but considerably scattered topographical order of best azimuth directions was observed in the deep layers of the superior colliculus with frontal directions being represented closer to the rostral pole. Tuned auditory units in the intermediate layers of the superior colliculus, however, showed no systematic spatial arrangement. This pattern was confirmed by analysing best azimuth directions from simultaneously recorded units. Our results indicate that the rat superior colliculus contains a representation of auditory space which is similar to that described for other small mammals.
Acoustic Stimulation↗
Temporal coding of amplitude and frequency modulation in the rat auditory cortex.
The rat primary auditory cortex was explored for neuronal responses to pure tones and sinusoidally amplitude-modulated (SAM) and frequency-modulated (SFM) stimuli. Units showed phase-locked responses to SAM stimulation (55%) and SFM stimulation (80%), with modulation frequencies up to 18 Hz. Tuning characteristics to the modulation frequency were mainly band-pass with best modulation frequencies (BMFs) between 4 and 15 Hz. Units with synchronized activity to SFM stimulation showed three response types with respect to the direction of the frequency modulation: 52% were selective to the upward direction, 30% to the downward direction, and 18% had no preference. Triangular frequency modulations were used to test if units were tuned to specific modulation frequencies or to specific rates of frequency change. In the vast majority of units tested the response characteristics were strongly influenced by varying the modulation frequency, whereas varying the rate of frequency change had little effect in the stimulus range used. Units that showed phase-locked responses to SAM and SFM stimulation had similar activity patterns in response to both types of stimuli. BMFs for SAM and SFM stimulation were significantly correlated. Intrinsic oscillations of up to 20 Hz could be seen in the spontaneous activity and after the stimuli independent of the stimulus type. Oscillation frequencies were significantly correlated with the BMFs of the respective units. The results are discussed in terms of a mechanism for periodicity detection based on a temporal code. This could be important for the recognition of complex acoustic signals.
Acoustic Stimulation↗