On osmolality and sperm function during processing for assisted reproduction

Deep basic knowledge about sperm physiology is relevant and important to optimize the outcome of procedures used during Assisted Reproductive Technologies (ART) to select spermatozoa for fertilization. More specifically, this study examined osmolality changes and consequences for sperm motility and sperm selection in the laboratory. What kind of environmental changes occur and what challenges must the spermatozoa endure after leaving the body? How do these challenges affect the spermatozoa’s functions, fertilizing potential and the make-up of the genetic material they will deliver to the oocyte? In study I, the objective was to measure the changes in osmolality that occur after collecting the ejaculate in the laboratory. After ejaculation, the sample is mixed in order to make it homogenous. This will cause the different fractions that make up the semen sample to mix. A total of 348 individual ejaculates, 5 split ejaculates and 6 ejaculate pools were studied, and it appeared that there was an individual pattern of change in osmolality over time. At 3 hours after the ejaculation, the change in osmolality ranged from 2 mOsm/kg to 164 mOsm/kg. Furthermore, it was evident that the change in osmolality was temperature dependent. Samples stored at 37°C increased significantly more in osmolality than samples stored at 18- 22°C, than samples stored at 4-7°C and than samples stored at -20°C. Denaturising temperature (100°C) blocked any further increment in osmolality. One probable cause of the increase in osmolality is that the enzymes, which are abundant in the prostatic fluid, are degrading macro-molecules, such as the proteins that are abundant in the seminal vesicular fluid. When these two secretions are mixed, the enzymatic degradation can start (Mann and Lutwak–Mann, 1981). In study II, the markers for the different fractions of the ejaculate were measured in order to relate to the change in osmolality. As well as containing high levels of proteins, the seminal vesicular fluid also contains relatively high levels of fructose. Similarly, the prostatic fluid contains high levels of zinc. It was shown that 19% of the variation in semen osmolality covaried with the relative contribution of the prostatic fluid marker, zinc, and the seminal vesicular marker, fructose, while the epididymal marker neutral α-glucosidase did not covary. Furthermore, the results show that after removing sperm from the ejaculate, the osmolality still increased, thus, the sperm did not have an effect on the increase. In addition to the challenge of the osmotic increase occurring in the ejaculate, the preparation of the sperm for ART presents yet another challenge. Most commercial sperm preparation media, such as density gradients or swim-up media have an adjusted osmolality of 290- 300mosm/kg. Thus, depending on the individual increase in osmolality of the samples, the sperm will be exposed to varying sudden decreases in osmolality during preparation. In study III and IV, it was examined how a hypo-osmotic challenge could affect sperm motility and the outcome of sperm selection when using density gradient centrifugation. Sperm motility was assessed by Computer Assisted Sperm Analysis (CASA). When the spermatozoon was exposed to a sudden decrease in osmolality, it took up water and swelled, causing the tail to coil and fold. This in turn, resulted in a decreased motility (VCL) with as much as 20%. Furthermore, it appears that the greater the decrease in osmolality, the lower the yield was after selection of spermatozoa by density gradient centrifugation. In contrast, with further investigation, it was shown that the DNA-Fragmentation-Index (DFI), measured by flow cytometry of acridine-orange stained spermatozoa was not affected by longer incubation times. However, spermatozoa ejaculated directly into a buffer had lower values for DFI% compared to samples diluted with buffer shortly after ejaculation. The negative effect on the yield was eliminated when the ejaculate was diluted soon after ejaculation or collected directly in a buffered solution. Since the increase in osmolality in vitro is so variable, one standardized procedure for sperm preparation would not work for all ejaculates. However, if increasing osmolality can be minimized by early dilution of all samples, then the negative effects can in large be eliminated

Intelligibility benefit for familiar voices does not depend on better discrimination of fundamental frequency or vocal tract length

Speech is more intelligible when it is spoken by familiar than unfamiliar people. Two cues to voice identity are glottal pulse rate (GPR) and vocal tract length (VTL): perhaps these features are more accurately represented for familiar voices in a listener’s brain. If so, listeners should be able to discriminate smaller manipulations to perceptual correlates of these vocal parameters for familiar than unfamiliar voices. We recruited pairs of friends who had known each other for 0.5–22.5 years. We measured thresholds for discriminating pitch (correlate of GPR) and formant spacing (correlate of VTL; ‘VTL-timbre’) for voices that were familiar (friends) and unfamiliar (friends of other participants). When a competing talker was present, speech was substantially more intelligible when it was spoken in a familiar voice. Discrimination thresholds were not systematically smaller for familiar compared to unfamiliar talkers. Although, participants detected smaller deviations to VTL-timbre than pitch uniquely for familiar talkers, suggesting a different balance of characteristics contribute to discrimination of familiar and unfamiliar voices. Across participants, we found no relationship between the size of the intelligibility benefit for a familiar over an unfamiliar voice and the difference in discrimination thresholds for the same voices. Also, the intelligibility benefit was not affected by the acoustic manipulations we imposed on voices to assess discrimination thresholds. Overall, these results provide no evidence that two important cues to voice identity—pitch and VTL-timbre—are more accurately represented when voices are familiar, or are necessarily responsible for the large intelligibility benefit derived from familiar voices

Speech-evoked brain activity is more robust to competing speech when it is spoken by someone familiar

When speech is masked by competing sound, people are better at understanding what is said if the talker is familiar compared to unfamiliar. The benefit is robust, but how does processing of familiar voices facilitate intelligibility? We combined high-resolution fMRI with representational similarity analysis to quantify the difference in distributed activity between clear and masked speech. We demonstrate that brain representations of spoken sentences are less affected by a competing sentence when they are spoken by a friend or partner than by someone unfamiliar—effectively, showing a cortical signal-to-noise ratio (SNR) enhancement for familiar voices. This effect correlated with the familiar-voice intelligibility benefit. We functionally parcellated auditory cortex, and found that the most prominent familiar-voice advantage was manifest along the posterior superior and middle temporal gyri. Overall, our results demonstrate that experience-driven improvements in intelligibility are associated with enhanced multivariate pattern activity in posterior temporal cortex

Natural Language Syntax Complies with the Free-Energy Principle

Natural language syntax yields an unbounded array of hierarchically structured expressions. We claim that these are used in the service of active inference in accord with the free-energy principle (FEP). While conceptual advances alongside modelling and simulation work have attempted to connect speech segmentation and linguistic communication with the FEP, we extend this program to the underlying computations responsible for generating syntactic objects. We argue that recently proposed principles of economy in language design - such as "minimal search" criteria from theoretical syntax - adhere to the FEP. This affords a greater degree of explanatory power to the FEP - with respect to higher language functions - and offers linguistics a grounding in first principles with respect to computability. We show how both tree-geometric depth and a Kolmogorov complexity estimate (recruiting a Lempel-Ziv compression algorithm) can be used to accurately predict legal operations on syntactic workspaces, directly in line with formulations of variational free energy minimization. This is used to motivate a general principle of language design that we term Turing-Chomsky Compression (TCC). We use TCC to align concerns of linguists with the normative account of self-organization furnished by the FEP, by marshalling evidence from theoretical linguistics and psycholinguistics to ground core principles of efficient syntactic computation within active inference

Preparatory and selective attention during multi-talker listening in normal and impaired hearing

One of the great challenges of hearing research is to work out how listeners can perceive what one talker is saying when other talkers are speaking at the same time. Faced with this requirement for ‘multi-talker listening’, normally-hearing listeners achieve improved speech intelligibility when they know characteristics of an upcoming talker before he or she begins to speak. One aim was to investigate the time course of this improvement in intelligibility and the brain activity that accompanies it. A task was devised in which participants had to report key words spoken by a ‘target’ talker when one or two other talkers spoke simultaneously. Before the talkers began to speak, a visual cue indicated the location (left/right) or gender (male/female) of the target talker. The accuracy and latency of reporting key words progressively improved when participants had longer to prepare for the location or gender of the target talker. Preparatory brain activity, measured with electro-encephalography, began with a short latency (< 100 ms) after the reveal of the visual cue and was sustained until the talkers began to speak. Hearing-impaired listeners, both children and adults, typically show poorer speech intelligibility during multi-talker listening than normally-hearing listeners. One advantage of the experimental design was that brain activity during preparatory attention (before the onset of acoustical stimuli) could be compared between normally-hearing and hearing-impaired listeners and atypical attention identified, without confounding differences in transduction at the auditory periphery. This thesis demonstrates atypical preparatory EEG activity in children, aged 7-16 years, with bilateral moderate cochlear hearing loss, which provides evidence for atypical preparatory attention. Therefore, atypical preparatory attention might be one factor that contributes to poorer speech intelligibility in noisy environments. An implication is that acoustic hearing aids may not have the potential alone to restore normal processing of acoustical stimuli in hearing-impaired listeners

Peripheral hearing loss reduces the ability of children to direct selective attention during multi-talker listening

Restoring normal hearing requires knowledge of how peripheral and central auditory processes are affected by hearing loss. Previous research has focussed primarily on peripheral changes following sensorineural hearing loss, whereas consequences for central auditory processing have received less attention. We examined the ability of hearing-impaired children to direct auditory attention to a voice of interest (based on the talker’s spatial location or gender) in the presence of a common form of background noise: the voices of competing talkers (i.e. during multi-talker, or “Cocktail Party” listening). We measured brain activity using electro-encephalography (EEG) when children prepared to direct attention to the spatial location or gender of an upcoming target talker who spoke in a mixture of three talkers. Compared to normally-hearing children, hearing-impaired children showed significantly less evidence of preparatory brain activity when required to direct spatial attention. This finding is consistent with the idea that hearing-impaired children have a reduced ability to prepare spatial attention for an upcoming talker. Moreover, preparatory brain activity was not restored when hearing-impaired children listened with their acoustic hearing aids. An implication of these findings is that steps to improve auditory attention alongside acoustic hearing aids may be required to improve the ability of hearing-impaired children to understand speech in the presence of competing talkers

Familiar voices are more Intelligible, even if they are not recognized as familiar

This research has demonstrated that it’s easier to understand someone who is familiar to us (compared to someone unfamiliar) even if we can’t recognize them from their voice. As listeners, we focus on certain parts of speech sounds for specific purposes. For example, there may be some situations in which you can understand words spoken by your mother very well, better than you could understand a stranger in the same situation, even if you can’t tell that it’s your mother speaking.https://ir.lib.uwo.ca/brainscanresearchsummaries/1001/thumbnail.jp