Infant isoflurane exposure affects social behaviours, but does not impair specific cognitive domains in juvenile non-human primates.

BACKGROUND: Clinical studies show that children exposed to anaesthetics for short times at young age perform normally on intelligence tests, but display altered social behaviours. In non-human primates (NHPs), infant anaesthesia exposure for several hours causes neurobehavioural impairments, including delayed motor reflex development and increased anxiety-related behaviours assessed by provoked response testing. However, the effects of anaesthesia on spontaneous social behaviours in juvenile NHPs have not been investigated. We hypothesised that multiple, but not single, 5 h isoflurane exposures in infant NHPs are associated with impairments in specific cognitive domains and altered social behaviours at juvenile age. METHODS: Eight Rhesus macaques per group were anaesthetised for 5 h using isoflurane one (1×) or three (3×) times between postnatal days 6 and 12 or were exposed to room air (control). Cognitive testing, behavioural assessments in the home environment, and provoked response testing were performed during the first 2 yr of life. RESULTS: The cognitive functions tested did not differ amongst groups. However, compared to controls, NHPs in the 3× group showed less close social behaviour (P=0.016), and NHPs in the 1× group displayed increased anxiety-related behaviours (P=0.038) and were more inhibited towards novel objects (P<0.001). CONCLUSIONS: 5 h exposures of NHPs to isoflurane during infancy are associated with decreased close social behaviour after multiple exposures and more anxiety-related behaviours and increased behavioural inhibition after single exposure, but they do not affect the cognitive domains tested. Our findings are consistent with behavioural alterations in social settings reported in clinical studies, which may guide future research.

Binaural Pitch Fusion in Children With Normal Hearing, Hearing Aids, and Cochlear Implants.

OBJECTIVES: Binaural pitch fusion is the perceptual integration of stimuli that evoke different pitches between the ears into a single auditory image. Adults who use hearing aids (HAs) or cochlear implants (CIs) often experience abnormally broad binaural pitch fusion, such that sounds differing in pitch by as much as 3 to 4 octaves are fused across ears, leading to spectral averaging and speech perception interference. The main goal of this study was to measure binaural pitch fusion in children with different hearing device combinations and compare results across groups and with adults. A second goal was to examine the relationship of binaural pitch fusion to interaural pitch differences or pitch match range, a measure of sequential pitch discriminability. DESIGN: Binaural pitch fusion was measured in children between the ages of 6.1 and 11.1 years with bilateral HAs (n = 9), bimodal CI (n = 10), bilateral CIs (n = 17), as well as normal-hearing (NH) children (n = 21). Depending on device combination, stimuli were pure tones or electric pulse trains delivered to individual electrodes. Fusion ranges were measured using simultaneous, dichotic presentation of reference and comparison stimuli in opposite ears, and varying the comparison stimulus to find the range that fused with the reference stimulus. Interaural pitch match functions were measured using sequential presentation of reference and comparison stimuli, and varying the comparison stimulus to find the pitch match center and range. RESULTS: Children with bilateral HAs had significantly broader binaural pitch fusion than children with NH, bimodal CI, or bilateral CIs. Children with NH and bilateral HAs, but not children with bimodal or bilateral CIs, had significantly broader fusion than adults with the same hearing status and device configuration. In children with bilateral CIs, fusion range was correlated with several variables that were also correlated with each other: pure-tone average in the second implanted ear before CI, and duration of prior bilateral HA, bimodal CI, or bilateral CI experience. No relationship was observed between fusion range and pitch match differences or range. CONCLUSIONS: The findings suggest that binaural pitch fusion is still developing in this age range and depends on hearing device combination but not on interaural pitch differences or discriminability.

Binaural pitch fusion: Comparison of normal-hearing and hearing-impaired listeners.

Binaural pitch fusion is the fusion of dichotically presented tones that evoke different pitches between the ears. In normal-hearing (NH) listeners, the frequency range over which binaural pitch fusion occurs is usually <0.2 octaves. Recently, broad fusion ranges of 1-4 octaves were demonstrated in bimodal cochlear implant users. In the current study, it was hypothesized that hearing aid (HA) users would also exhibit broad fusion. Fusion ranges were measured in both NH and hearing-impaired (HI) listeners with hearing losses ranging from mild-moderate to severe-profound, and relationships of fusion range with demographic factors and with diplacusis were examined. Fusion ranges of NH and HI listeners averaged 0.17 ± 0.13 octaves and 1.7 ± 1.5 octaves, respectively. In HI listeners, fusion ranges were positively correlated with a principal component measure of the covarying factors of young age, early age of hearing loss onset, and long durations of hearing loss and HA use, but not with hearing threshold, amplification level, or diplacusis. In NH listeners, no correlations were observed with age, hearing threshold, or diplacusis. The association of broad fusion with early onset, long duration of hearing loss suggests a possible role of long-term experience with hearing loss and amplification in the development of broad fusion.

Theoretical Considerations for Optimizing the Use of Optogenetics with Complex Behavior.

Optogenetic approaches have allowed researchers to address complex questions about behavior that were previously unanswerable. However, as optogenetic procedures involve a large parameter space across multiple dimensions, it is crucial to consider such parameters in conjunction with the behaviors under study. Here, we discuss strategies to optimize optogenetic approaches with complex behavior by identifying critical experimental design considerations, including frequency specificity, temporal precision, activity-controlled optogenetics, stimulation pattern, and cell-type specificity. We highlight potential limitations or theoretical considerations to be made when manipulating each of these factors of optogenetic experiments. This overview emphasizes the importance of optimizing optogenetic study design to enhance the conclusions that can be drawn about the neuroscience of behavior. © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC.

Binaural pitch fusion: Effects of sound level in listeners with normal hearing.

Pitch is an important cue that allows the auditory system to distinguish between sound sources. Pitch cues are less useful when listeners are not able to discriminate different pitches between the two ears, a problem encountered by listeners with hearing impairment (HI). Many listeners with HI will fuse the pitch of two dichotically presented tones over a larger range of interaural frequency disparities, i.e., have a broader fusion range, than listeners with normal hearing (NH). One potential explanation for broader fusion in listeners with HI is that hearing aids stimulate at high sound levels. The present study investigated effects of overall sound levels on pitch fusion in listeners with NH. It was hypothesized that if sound level increased, then fusion range would increase. Fusion ranges were measured by presenting a fixed frequency tone to a reference ear simultaneously with a variable frequency tone to the opposite ear and finding the range of frequencies that were fused with the reference frequency. No significant effects of sound level (comfortable level ± 15 dB) on fusion range were found, even when tested within the range of levels where some listeners with HI show large fusion ranges. Results suggest that increased sound level does not explain increased fusion range in listeners with HI and imply that other factors associated with hearing loss might play a larger role.