Timescale-dependent shaping of correlation by olfactory bulb lateral inhibition.

Neurons respond to sensory stimuli by altering the rate and temporal pattern of action potentials. These spike trains both encode and propagate information that guides behavior. Local inhibitory networks can affect the information encoded and propagated by neurons by altering correlations between different spike trains. Correlations introduce redundancy that can reduce encoding but also facilitate propagation of activity to downstream targets. Given this trade-off, how can networks maximize both encoding and propagation efficacy? Here, we examine this problem by measuring the effects of olfactory bulb inhibition on the pairwise statistics of mitral cell spiking. We evoked spiking activity in the olfactory bulb in vitro and measured how lateral inhibition shapes correlations across timescales. We show that inhibitory circuits simultaneously increase fast correlation (i.e., synchrony increases) and decrease slow correlation (i.e., firing rates become less similar). Further, we use computational models to show the benefits of fast correlation/slow decorrelation in the context of odor coding. Olfactory bulb inhibition enhances population-level discrimination of similar inputs, while improving propagation of mitral cell activity to cortex. Our findings represent a targeted strategy by which a network can optimize the correlation structure of its output in a dynamic, activity-dependent manner. This trade-off is not specific to the olfactory system, but rather our work highlights mechanisms by which neurons can simultaneously accomplish multiple, and sometimes competing, aspects of sensory processing.

Validation of a Hearing-Related Quality-of-Life Questionnaire for Parents and Deaf or Hard-of-Hearing Infants and Toddlers.

OBJECTIVE: To design and validate a hearing-related quality-of-life questionnaire targeted toward parents and deaf or hard-of-hearing infants and toddlers: the Hearing-Related Infant/Toddler and Parent Quality of Life (HIP-QL) questionnaire. STUDY DESIGN: Cross-sectional questionnaire and prospective instrument validation. SETTING: Academic pediatric otolaryngology clinic. METHODS: A 67-question questionnaire developed from constructs of a grounded theory analysis was administered to parents of 31 deaf or hard-of-hearing children and 14 typically hearing children. Questionnaire construct validity, reliability, and discriminant validity were tested. RESULTS: Based on exploratory factor analysis, a 32-item construct composed of developmentally appropriate questions was reduced to a 17-item construct with 4 domains addressing quality of life for both child (auditory/communication behavior, temperament) and parent (management, parent-directed factors). Internal consistency measures were appropriate (Cronbach's alpha = 0.65), and test-retest reliability was high (intraclass correlation coefficient = 0.73). Total HIP-QL scores correlated significantly with related total PedsQL scores (r = 0.57, P < .001). As predicted, parents of children who are deaf or hard of hearing reported significantly lower mean HIP-QL scores but not mean PedsQL scores. HIP-QL was more sensitive than PedsQL for predicting case versus control membership (86.7% vs 76.9%). Multivariable regression confirmed a negative relationship between severity of hearing loss and HIP-QL score after controlling for age, sex, income, and maternal education. CONCLUSIONS: This context-specific questionnaire is the first validated quality-of-life instrument for parents and deaf or hard-of-hearing infants and toddlers. Previously, parental stress and functional disability questionnaires were used as proxies; therefore, this questionnaire has the potential to serve as an important tool for patient- and caregiver-centered outcomes research.

Seeking equilibrium: The experiences of parents of infants and toddlers who are deaf/hard-of-hearing.

PURPOSE: To identify key determinants of the quality of life of caregivers of infants and toddlers (< 3 years) who are deaf/hard-of-hearing (DHH). METHODS: We conducted focus groups with providers for children who are DHH as well as interviews with hearing parents of infants and toddlers who are DHH. A multi-step qualitative analysis on interview data using grounded theory was performed, and an iterative analysis to investigate codes to characterize specific topics in caring for deaf infants and toddlers was conducted. RESULTS: Four focus groups (n= 33) and six semi-structured interviews (n= 7) were conducted. The major theoretical code found was the "Search for Equilibrium" in parenting which arose from the three main categories of the caregiver role/experience: (1) being a parent - modifying parenting style as a result of their child's hearing loss, (2) being a mediator - modulating and filtering interactions between their child and their child's environment, and (3) being a navigator - managing the logistics of the medical and educational system. CONCLUSIONS: For hearing parents, the diagnosis of hearing loss requires changes in multiple domains of parenting. Support in each of these areas is critical for parents to restore a sense of equilibrium that is central to their quality of life. This framework provides a way to categorize parent experiences and may act as a template for focused interventions in the three identified domains.

Mechanisms and benefits of granule cell latency coding in the mouse olfactory bulb.

Inhibitory circuits are critical for shaping odor representations in the olfactory bulb. There, individual granule cells can respond to brief stimulation with extremely long (up to 1000 ms), input-specific latencies that are highly reliable. However, the mechanism and function of this long timescale activity remain unknown. We sought to elucidate the mechanism responsible for long-latency activity, and to understand the impact of widely distributed interneuron latencies on olfactory coding. We used a combination of electrophysiological, optical, and pharmacological techniques to show that long-latency inhibition is driven by late onset synaptic excitation to granule cells. This late excitation originates from tufted cells, which have intrinsic properties that favor longer latency spiking than mitral cells. Using computational modeling, we show that widely distributed interneuron latency increases the discriminability of similar stimuli. Thus, long-latency inhibition in the olfactory bulb requires a combination of circuit- and cellular-level mechanisms that function to improve stimulus representations.