Late-night presentation of an auditory stimulus phase delays human circadian rhythms

Although light is considered the primary entrainer of circadian rhythms in humans, nonphotic stimuli, including exercise and melatonin also phase shift the biological clock. Furthermore, in birds and nonhuman mammals, auditory stimuli are effective zeitgebers. This study investigated whether a nonphotic auditory stimulus phase shifts human circadian rhythms. Ten subjects (5 men and 5 women, ages 18-72, mean age +/- SD, 44.7 +/- 21.4 yr) completed two 4-day laboratory sessions in constant dim light (<20 lux). They received two consecutive presentations of either a 2-h auditory or control stimulus from 0100 to 0300 on the second and third nights (presentation order of the stimulus and control was counterbalanced). Core body temperature (CBT) was collected and stored in 2-min bins throughout the study and salivary melatonin was obtained every 30 min from 1900 to 2330 on the baseline and poststimulus/postcontrol nights. Circadian phase of dim light melatonin onset (DLMO) and of CBT minimum, before and after auditory or control presentation was assessed. The auditory stimulus produced significantly larger phase delays of the circadian melatonin (mean +/- SD, -0.89 +/- 0.40 h vs. -0.27 +/- 0.16 h) and CBT (-1.16 +/- 0.69 h vs. -0.44 +/- 0.27 h) rhythms than the control. Phase changes for the two circadian rhythms also positively correlated, indicating direct effects on the biological clock. In addition, the auditory stimulus significantly decreased fatigue compared with the control. This study is the first demonstration of an auditory stimulus phase-shifting circadian rhythms in humans, with shifts similar in size and direction to those of other nonphotic stimuli presented during the early subjective night. This novel stimulus may be a useful countermeasure to facilitate circadian adaptation after transmeridian travel or shift work.     

P300 from a single auditory stimulus

The P3(00) event-related brain potential (ERP) was elicited with auditory stimuli to compare 2 different discrimination tasks. The oddball paradigm presented both target and standard tones; the single-stimulus paradigm presented at target but no standard tone stimulus. Experiment 1 manipulated target stimulus probability (0.20, 0.50, 0.80) and produced highly similar P3 amplitude and latency results across probability levels for each paradigm. Experiment 2 factorially varied inter-stimulus interval (2 sec, 6 sec) and target stimulus probability (0.20, 0.80). P3 amplitude and latency were highly similar for both the oddball and single-stimulus procedures across all conditions.     

Tuning to natural stimulus dynamics in primary auditory cortex

The amplitude and pitch fluctuations of natural soundscapes often exhibit "1/f spectra", which means that large, abrupt changes in pitch or loudness occur proportionally less frequently in nature than gentle, gradual fluctuations. Furthermore, human listeners reportedly prefer 1/f distributed random melodies to melodies with faster (1/f0) or slower (1/f2) dynamics. One might therefore suspect that neurons in the central auditory system may be tuned to 1/f dynamics, particularly given that recent reports provide evidence for tuning to 1/f dynamics in primary visual cortex. To test whether neurons in primary auditory cortex (A1) are tuned to 1/f dynamics, we recorded responses to random tone complexes in which the fundamental frequency and the envelope were determined by statistically independent "1/f(gamma) random walks," with gamma set to values between 0.5 and 4. Many A1 neurons showed clear evidence of tuning and responded with higher firing rates to stimuli with gamma between 1 and 1.5. Response patterns elicited by 1/f(gamma) stimuli were more reproducible for values of gamma close to 1. These findings indicate that auditory cortex is indeed tuned to the 1/f dynamics commonly found in the statistical distributions of natural soundscapes.     

Thermal imaging of the periorbital regions during the presentation of an auditory startle stimulus

Infrared thermal imaging of the inner canthi of the periorbital regions of the face can potentially serve as an input signal modality for an alternative access system for individuals with conditions that preclude speech or voluntary movement, such as total locked-in syndrome. However, it is unknown if the temperature of these regions is affected by the human startle response, as changes in the facial temperature of the periorbital regions manifested during the startle response could generate false positives in a thermography-based access system. This study presents an examination of the temperature characteristics of the periorbital regions of 11 able-bodied adult participants before and after a 102 dB auditory startle stimulus. The results indicate that the startle response has no substantial effect on the mean temperature of the periorbital regions. This indicates that thermography-based access solutions would be insensitive to startle reactions in their user, an important advantage over other modalities being considered in the context of access solutions for individuals with a severe motor disability.     

Pigeons' timing of an arbitrary and a naturalistic auditory stimulus: tone versus cooing

Previous animal research has traditionally used arbitrary stimuli to investigate timing in a temporal bisection procedure. The current study compared the timing of the duration of an arbitrary, auditory stimulus (a 500-Hz tone) to the timing of the duration of a naturalistic, auditory stimulus (a pigeon cooing). In the first phase of this study, temporal perception was assessed by comparing psychophysical functions for the duration of tone and cooing signals. In the first set of tests, the point of subjective equality (PSE) was significantly lower for the tone than for the cooing stimulus, indicating that tones were judged longer than equivalent durations of cooing. In the second set of tests, gaps were introduced in the tone signal to match those present in the cooing signal, and no significant difference in the PSE for the tone or the cooing signal was found. A repetition of the testing conducted with gaps removed from the tone signal, failed to replicate the difference in the PSEs for the tone and cooing signals originally obtained. In the second phase of the study, memory for the duration of tone and cooing was examined, and a choose-long bias was found for both signals. Based on these results, it appears that, for pigeons, there may be no significant differences in either temporal perception or temporal memory for arbitrary, auditory signals and more complex, naturalistic, auditory signals.     

Multidimensional auditory stimulus control in a chimpanzee (Pan troglodytes)

An adolescent female chimpanzee (Pan troglodytes) was trained to discriminate auditory compound stimuli differing in tonal frequency and/or tone on-off rate. Following acquisition training and overtraining, she was shifted to multidimensional stimulus control testing using redundant relevant auditory stimulus sets with discriminability of elements in each dimension varied systematically. Although the control by both dimensions changed significantly as a function of discriminability, the degree of dimensional control was stronger in the tone on-off rate than in the tonal frequency. These results clearly demonstrated “attentional” control of the chimpanzee's auditory discrimination behavior and the interaction between two dimensions of auditory stimuli. The author is now at the Department of Psychology, Primate Research Institute, Kyoto University as a transfer student of the Doctor course.     

Effect of stimulus mode on middle latency auditory evoked potentials in humans

Middle Latency Auditory Evoked Potentials (MLAEPs) were recorded in 35 healthy subjects; all underwent monaural stimulation and 18 of them additionally underwent binaural stimulation. The aim of the study was to determine the effect of stimulus mode on MLAEP Na, Pa and Nb components and to assess normative data for clinical purposes. MLAEPs were respectively obtained from Cz-ipsilateral ear lobe (monaural mode) and from Cz-A1 and Cz-A2 (binaural mode) by twice averaging 1000 responses to 65 dBHL alternating clicks delivered at a repetition rate of 8.1 Hz. Time base was 100 msec; analogical band-pass filter setting was 5-1000 Hz (off-line digital badpass: 20-100 Hz). The statistical analyses (paired t-test, repeated measures analysis of variance) were not able to demonstrate any differences that derived from differing sides of stimulation (monaural mode) or from differing recording derivations (binaural mode); on the contrary, we demonstrated a slight increase in waveform amplitudes when the binaural mode was employed. In particular, we observed an increase in Na-Pa peak-to-peak amplitude, whereas Pa-Nb amplitude was unmodified. This finding is explicable in terms of a binaural interaction effect. Finally, we propose some guidelines for the correct performance and evaluation of MLAEPs in clinical practice.     

Music perception, pitch, and the auditory system

The perception of music depends on many culture-specific factors, but is also constrained by properties of the auditory system. This has been best characterized for those aspects of music that involve pitch. Pitch sequences are heard in terms of relative as well as absolute pitch. Pitch combinations give rise to emergent properties not present in the component notes. In this review we discuss the basic auditory mechanisms contributing to these and other perceptual effects in music.     

The otic gasbladder as an ancillary auditory structure in a mormyrid fish

Mormyrid fishes use acoustic signals for long-distance communication and a weakly electric field for short-distance interaction. Mormyrids are unique in having an otic gasbladder attached directly to the saccule on each side of the inner ear. Karl von Frisch (1938) hypothesized that the tightly coupled otic gasbladder might aid mormyrid hearing. Using the mormyrid fish (Brienomyrus brachyistius), this study manipulated gas in the otic gasbladder to test this hypothesis and histological sections were made to examine the anatomical relationship between the gasbladder and inner ear. The hearing sensitivity curves (audiograms) were obtained with the auditory brainstem response protocol. Audiograms were obtained from normal fish and from fish in which gas was withdrawn from either one or two otic gasbladders. Removal of gas from one otic gasbladder did not result in a significant change in either hearing ability or acoustically evoked brainwaves as compared to the control fish. Bilateral deflation of the otic gasbladders led to significant threshold changes. Histological sections revealed a particularly close coupling between the otic gasbladder and the saccule chamber. These results support von Frisch's hypothesis that the otic gasbladders of mormyrids assist in underwater sound detection. Accepted: 14 April 2000     

Brain-stem auditory evoked potential monitoring. Variations of stimulus artifact in brain death

Brain-stem auditory evoked potentials (BAEPs) were recorded in 20 subjects with brain death (mean age, 33.2 ± 15.1 years) and 20 healthy volunteers (mean age, 29.8 ± 6.8 years). Brain death was due to head injury (n = 14), encephalitis (n = 3), brain-stem hemorrhage (n = 1), cerebellar hemorrhage (n = 1) or cerebral infarction (n = 1). The presence, latency and amplitude of the individual BAEP components and variations of the stimulus artifact were evaluated. The mean ( ± S.D.) amplitude of the stimulus artifact was 0.26 ± 0.12 μV in the brain-dead subjects and 0.09 ± 0.05 μv in the control group (P < 0.001, t test). The causes of the phenomenon of increasing stimulus artifacts in the evolution of brain death remain unclear.     

Estradiol benzoate can function as an unconditioned stimulus in a conditioned taste aversion paradigm

The extent to which gonadal steroid hormones can serve as unconditioned stimuli in a conditioned taste aversion paradigm was examined in Rockland-Swiss albino mice. With saccharin serving as the conditioned stimulus, subcutaneously injected estradiol benzoate, but not progesterone or testosterone propionate, was found to be a potent unconditioned stimulus in both male and female mice. Dose-response effects were also observed; increasing dosages of estradiol benzoate led to increasingly stronger conditioned aversions in both males and females. The aversion detected in males was more resistant to extinction than that seen in females. Prepubertal gonadectomy reversed the sex-dependent effects of estradiol benzoate in learned aversions in adulthood; castration of males promoted the extinction process, whereas ovariectomy of females retarded extinction. The results may be useful for our understanding of the mechanisms involved in conditioned taste aversion learning as well as a wide array of hormone-dependent behavioral responses.     

Coactivation during gait as an adaptive behavior after stroke

The aims of the present study were to quantify the impairment in ankle coactivation on the paretic and non-paretic sides of subjects with hemiparesis and to examine the relationship of ankle coactivation with postural instability, motor deficit of the paretic lower extremity and locomotor performance. Electromyography of the medial gastrocnemius (MG) and tibialis anterior (TA) muscles were recorded bilaterally during gait in 30 subjects (62.1±9.9 years) who had suffered a recent stroke (<6 months) as well as on one side of 17 healthy controls (59.3±9.1 years) walking at very slow speed. Ankle muscle coactivation was calculated by dividing the time of overlap between MG and TA signals (threshold of 20 μV) by the duration of the gait phases of interest: stance, swing, first and second double support sub-phases and single support sub-phase. The time spent in single support and the peak plantarflexor moment of force on the paretic side were used to measure, respectively, postural stability and dynamic strength of the paretic plantarflexors. The subjects with hemiparesis demonstrated less coactivation on the paretic side during the single support sub-phase (p<0.01) and more coactivation during first and second double support sub-phases on the non-paretic side (p<0.001) compared to control values. The patients with coactivation patterns that differed the most from controls were the patients with the more severe impairments and disabilities. While the reduced coactivation on the paretic side may contribute to poor postural stability and poor locomotor performance, the presence of excessive coactivation on the non-paretic side when both limbs were in ground contact may be an adaptation to help maintain postural stability during gait.     

Avian dependence on sound pressure level as an auditory distance cue

Sound pressure level (SPL) has received little attention as a distance cue or signal for communication because of the methodological difficulty of determining source SPL from free-ranging signallers and because SPL is presumed to be unreliable as a distance cue. Eastern towhees, Pipilo erythrophthalmus (Emberizidae, Passeriformes), in south-central Florida give a simple call during territorial interactions. I obtained measurements of call-source SPL with a calibrated microphone positioned 100+/-10 cm from caged male eastern towhees. Measurements of source SPL were highly variable, but much of this variation can be predicted from measurements of call duration or call frequency variables (spectrotemporal variables). Male towhees accurately perceived the distance of a speaker after it played synthetic calls that matched the amplitude and structure of natural 84-dB and 78-dB call types. Subjects flew further in response to an attenuated (-6 or -12 dB) version of an otherwise identical 84-dB call and flew shorter in response to an amplified (+6 dB) version of this same call. Towhees misjudged speaker distance in approximately half of the trials that included a discrepancy (-6, -12 or +6 dB SPL) between playback source SPL and predicted spectrotemporal variables. These distance errors suggest that towhees assess auditory distance partly from the difference between perceived SPL and source SPL, determined from spectrotemporal variables. Copyright 2000 The Association for the Study of Animal Behaviour.     

Emergence of tuning to natural stimulus statistics along the central auditory pathway

We have previously shown that neurons in primary auditory cortex (A1) of anaesthetized (ketamine/medetomidine) ferrets respond more strongly and reliably to dynamic stimuli whose statistics follow "natural" 1/f dynamics than to stimuli exhibiting pitch and amplitude modulations that are faster (1/f(0.5)) or slower (1/f(2)) than 1/f. To investigate where along the central auditory pathway this 1/f-modulation tuning arises, we have now characterized responses of neurons in the central nucleus of the inferior colliculus (ICC) and the ventral division of the mediate geniculate nucleus of the thalamus (MGV) to 1/f(γ) distributed stimuli with γ varying between 0.5 and 2.8. We found that, while the great majority of neurons recorded from the ICC showed a strong preference for the most rapidly varying (1/f(0.5) distributed) stimuli, responses from MGV neurons did not exhibit marked or systematic preferences for any particular γ exponent. Only in A1 did a majority of neurons respond with higher firing rates to stimuli in which γ takes values near 1. These results indicate that 1/f tuning emerges at forebrain levels of the ascending auditory pathway.