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Biomedical subjects

A Johnen

Publications and source records attributed to A Johnen.

5 recordsLinked to original sources
PubMed2001

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↗
PubMed2000

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↗
PubMed1991

["QT" pacemaker in aggregate exchange. Do old electrodes impair functional ability?].

A "QT"-interval driven rate responsive pacemaker can also be implanted on the occasion of pacemaker replacement. To evaluate the electrophysiological properties and limitations of chronic leads, in 30 patients the evoked intracardiac electrogram was recorded via the chronic lead during pacemaker replacement (14 different types, mean interval after implantation 111 (25-171 months). T-wave detectability was evaluated with different pulse amplitudes (2.5 and 5.0 V) and two pacemaker systems (TX 915, Rhythmyx) with different "fast recharge" mechanisms. In particular, the T-wave signal was influenced by capacitor discharge effects. At 2.5 V output T-wave amplitude was greater than or equal to 1.5 mV in all (19) patients, who could be paced at this voltage. However, at 5 V in 9/30 patients T-wave was less than 1 mV and detection was not possible in 6/30 cases. During pacing with the newly developed "QT"-interval driven, rate-responsive pacemaker (Rhythmyx) with two fast recharge pulses, in nine investigated patients the T-wave was markedly better discriminable compared to the TX 915 pacemaker. Accordingly, in 37 patients with implanted "QT"-controlled pacemakers (TX 911): n = 13; TX 915: n = 21; Rhythmyx: n = 3. Indication for pacemaker therapy: high degree AV block: n = 24, sick-sinus syndrome: n = 13) reliable T-wave sensing was possible at 2.5 V/0.2 ms output, whereas at 5 V/2 ms no T-wave sensing could be achieved in 8/37 cases. On the occasion of pacemaker replacement the "QT"-controlled pacemaker can be implanted without intraoperative measurements, whenever a pulse amplitude less than 2.5 V is sufficient for stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrocardiography↗