Childhood neighborhood context and adult substance use problems: the role of socio-economic status at the age of 30 years.

OBJECTIVES: To examine whether the (a) childhood neighborhood context predicts alcohol use disorder, nicotine dependence, and cannabis use disorder symptoms at the age of 39 years; and (b) socio-economic status during young adulthood mediates these relationships. Gender differences were also examined. STUDY DESIGN: The Seattle Social Development Project is a prospective longitudinal study of 808 individuals followed up from ages 10 to 39 years in Seattle, Washington, United States. The sample was gender balanced (51% were men). METHODS: Alcohol, nicotine, and cannabis use disorder symptoms were assessed using the Diagnostic and Statistical Manual of Mental Disorders IV-based Diagnostic Interview Schedule. Childhood neighborhood data consisted of 10 neighborhood-level variables from the 1990 national census, which were consolidated using principal component analyses. Two components with eigenvalues greater than 1 were extracted-neighborhood disadvantage and neighborhood stability. Educational attainment and employment status represented socio-economic status during young adulthood. Covariates included baseline symptoms of psychopathology, baseline substance use, gender, ethnicity, and childhood socio-economic status at the family level. Negative binomial regression was used as the primary modeling strategy. Six models for each outcome measure were estimated. The first three models examined associations between two neighborhood components and each substance use outcome measure. Next, we tested the second research question by adding unemployment and college graduate indicators at the age of 30 years as potential mediators underlying the link between the childhood neighborhood context and three substance use measures. RESULTS: Study findings revealed that childhood neighborhood stability significantly reduced alcohol and cannabis use disorder symptoms nearly 3 decades later. Path analyses suggested that socio-economic status during the transition to adulthood did not influence these relationships but rather had independent effects on problematic nicotine and cannabis use. Furthermore, the effects of childhood neighborhood factors on problematic nicotine use were stronger for men. CONCLUSIONS: Neighborhood characteristics during childhood may be important factors for alcohol and cannabis use disorder symptoms among adults and nicotine dependence disorder symptoms among men. Prevention efforts that address community stability and disadvantage can and should start in childhood, with a focus on intervention targets that might gain salience later in life to discourage the development and persistence of problematic substance use in adulthood.

General and substance-specific predictors of young adult nicotine dependence, alcohol use disorder, and problem behavior: replication in two samples.

BACKGROUND: This paper presents two replications of a heuristic model for measuring environment in studies of gene-environment interplay in the etiology of young adult problem behaviors. METHODS: Data were drawn from two longitudinal, U.S. studies of the etiology of substance use and related behaviors: the Raising Healthy Children study (RHC; N=1040, 47% female) and the Minnesota Twin Family Study (MTFS; N=1512, 50% female). RHC included a Pacific Northwest, school-based, community sample. MTFS included twins identified from state birth records in Minnesota. Both studies included commensurate measures of general family environment and family substance-specific environments in adolescence (RHC ages 10-18; MTFS age 18), as well as young adult nicotine dependence, alcohol and illicit drug use disorders, HIV sexual risk behavior, and antisocial behavior (RHC ages 24, 25; MTFS age 25). RESULTS: Results from the two samples were highly consistent and largely supported the heuristic model proposed by Bailey et al. (2011). Adolescent general family environment, family smoking environment, and family drinking environment predicted shared variance in problem behaviors in young adulthood. Family smoking environment predicted unique variance in young adult nicotine dependence. Family drinking environment did not appear to predict unique variance in young adult alcohol use disorder. CONCLUSIONS: Organizing environmental predictors and outcomes into general and substance-specific measures provides a useful way forward in modeling complex environments and phenotypes. Results suggest that programs aimed at preventing young adult problem behaviors should target general family environment and family smoking and drinking environments in adolescence.

Temporal relationship between the auditory brainstem response and focal responses of auditory nerve root and cochlear nucleus during development in the tammar wallaby (Macropus eugenii).

Thirty-two pouch-young tammar wallabies were used to discover the generators of the auditory brainstem response (ABR) during development by the use of simultaneous ABR and focal brainstem recordings. A click response from the auditory nerve root (ANR) in the wallaby was recorded from postnatal day (PND) 101, when no central auditory station was functional, and coincided with the ABR, a simple positive wave. The response of the cochlear nucleus (CN) was detected from PND 110, when the ABR had developed 1 positive and 1 negative peak. The dominant component of the focal ANR response, the N1 wave, coincided with the first half of the ABR P wave, and that of the focal CN response, the N1 wave, coincided with the later two thirds. In older animals, the ANR response coincided with the ABR's N1 wave, while the CN response coincided with the ABR's P2, N2 and P3 waves, with its contribution to the ABR P2 dominant. The protracted development of the marsupial auditory system which facilitated these correlations makes the tammar wallaby a particularly suitable model.

The social predictors of adolescent alcohol misuse: a test of the social development model.

OBJECTIVE: This study was conducted to investigate the ability of the social development model (SDM) to predict alcohol misuse at age 16 and to investigate the ability of the SDM to mediate the effects of alcohol use at age 14 on alcohol misuse at age 16. METHOD: The sample of 807 (411 males) is from the longitudinal panel of the Seattle Social Development Project which, in 1985, surveyed all consenting fifth-grade students from 18 elementary schools serving high-crime neighborhoods in Seattle, Washington. Alcohol use was measured at age 14, predictors of alcohol misuse were measured at age 15 and alcohol misuse was measured at age 16. Structural equation modeling was used to examine the fit of the model to the data. RESULTS: All factor loadings were highly significant and the measurement model achieved a good fit with the data (Comparative Fit Index [CFI] = 0.93). A second-order structural model fit the data well (CFI = 0.91) and also explained 45% of the variance in alcohol misuse at age 16. The SDM partially and significantly mediated the direct effect of age-14 alcohol use on age-16 alcohol misuse. CONCLUSIONS: The risk and protective processes specified by the SDM serve as potential targets for the prevention or reduction of adolescent alcohol misuse.

Childhood and adolescent predictors of alcohol abuse and dependence in young adulthood.

OBJECTIVE: To provide a comprehensive examination of childhood and adolescent predictors of alcohol abuse and dependence at age 21, theoretically guided by the social development model. METHOD: Data were taken from an ethnically diverse urban sample of 808 students (51% male), surveyed at age 10 and followed prospectively to age 21 in 1996. Potential predictors of alcohol abuse and dependence at age 21 were measured at ages 10, 14 and 16. Relationships between these predictors and alcohol abuse and dependence were examined at each age, to assess changes in their patterns of prediction over time. RESULTS: Strong bonding to school, close parental monitoring of children and clearly defined family rules for behavior, appropriate parental rewards for good behaviors, high level of refusal skills and strong belief in the moral order predicted a lower risk for alcohol abuse and dependence at age 21. Of these, strong bonding to school consistently predicted lower alcohol abuse and dependence from all three ages (10, 14 and 16). By contrast, youths who had a higher risk of alcohol abuse and dependence at age 21 engaged in more problem behaviors, had more opportunities to be involved with antisocial individuals and spent more time with and were more bonded to those individuals, viewed fewer negative consequences from antisocial behaviors and held more favorable views on alcohol use. Of these, prior problem behaviors and antisocial opportunities and involvements at ages 10, 14 and 16 consistently predicted alcohol abuse and dependence at age 21. CONCLUSIONS: These important malleable predictors, identifiable as early as age 10, provide potential intervention targets for the prevention of alcohol abuse and dependence in early adulthood.

Early adult outcomes of adolescent binge drinking: person- and variable-centered analyses of binge drinking trajectories.

BACKGROUND: Many studies of the consequences of binge drinking take a variable-centered approach that may mask developmentally different trajectories. Recent studies have reported qualitatively different binge drinking trajectories in young adulthood. However, analyses of developmental trajectories of binge drinking have not been examined for an important period of drinking development: adolescence. The purpose of this study was to examine young adult outcomes of adolescent binge drinking using an approach that combines person-centered and variable-centered methods. METHODS: Data were from the Seattle Social Development Project, an ethnically diverse, gender balanced sample (n = 808) followed prospectively from age 10 to age 21. Semiparametric group-based modeling was used to determine groups of binge drinking trajectories in adolescence. Logistic regression was used to examine how well the trajectory groups predicted young adult outcomes after demographics, childhood measures, and adolescent drug use were considered. RESULTS: Four distinct trajectories of binge drinking during adolescence were identified: Early Highs, Increasers, Late Onsetters, and Nonbingers. These trajectories significantly predicted positive and negative outcomes in adulthood after controlling for demographic characteristics, early proxy measures of the outcome, and adolescent drug use. CONCLUSIONS: This integrated person- and variable-centered approach provides more information about the effects of specific patterns of binge drinking than studies that employ variable-centered methods alone.

Developmental risk factors for youth violence.

PURPOSE: To replicate earlier research findings on risk factors for youth violence and to explore the effects on violent behavior of constructs shown to increase risk for other problem behaviors, within a developmental frame. METHODS: Data were from the Seattle Social Development Project (SSDP), a prospective study involving a panel of youths followed since 1985. Potential risk factors for violence at age 18 years were measured at ages 10, 14, and 16 years. Bivariate relationships involving risk factor constructs in the individual, family, school, peer and community domains and violence were examined at each age to assess changes in their strength of prediction over time. Attention was also given to the additive strength of increasing numbers of risk factors in the prediction of violence at age 18 years. A final set of analyses explored the extent to which youths were correctly classified as having committed a violent act (or not) at age 18 years on the basis of their overall level of risk at ages 10, 14, and 16 years. RESULTS: At each age, risk factors strongly related to later violence were distributed among the five domains. Ten of 15 risk factors constructs measured at age 10 years were significantly predictive of violence at age 18 years. Twenty of 25 constructs measured at age 14 years and 19 of 21 constructs measured at age 16 years were significantly predictive of later violence. Many constructs predicted violence from more than one developmental point. Hyperactivity (parent rating), low academic performance, peer delinquency, and availability of drugs in the neighborhood predicted violence from ages 10, 14, and 16 years. Analyses of the additive effects of risk factors revealed that youths exposed to multiple risks were notably more likely than others to engage in later violence. The odds for violence of youths exposed to more than five risk factors compared to the odds for violence of youths exposed to fewer than two risk factors at each age were seven times greater at age 10 years, 10 times greater at age 14 years, and nearly 11 times greater at age 16 years. However, despite information gained from all significant risk factors, the overall accuracy in predicting youths who would go on to commit violent acts was limited. CONCLUSIONS: Findings from the study have important implications for preventive intervention programs. Prevention efforts must be comprehensive and developmentally sensitive, responding to large groups or populations exposed to multiple risks.

Developmental pathways to alcohol abuse and dependence in young adulthood.

OBJECTIVE: To determine if people who were diagnosed with alcohol abuse or dependence (AAD) at age 21 had different developmental patterns of alcohol use in adolescence than non-AAD individuals. METHOD: An ethnically diverse urban sample of 808 children was surveyed at age 10 in 1985 and followed prospectively to age 21 in 1996. AAD at age 21 was assessed following DSM-IV criteria. Latent Transition Analysis (LTA) was used to identify four statuses of alcohol use (nonuse, initiation only, current use only, heavy episodic drinking), as well as transition probabilities between these four statuses from elementary school to middle school and from middle school to high school among the AAD and non-AAD group. RESULTS: The prevalence of alcohol use statuses during elementary school was similar in the two groups. Differences in alcohol use emerged in middle school and became more pronounced in high school. In middle school, AAD individuals were more likely to have initiated or been current drinkers than non-AAD individuals. However, the two groups did not differ in the prevalence of heavy episodic drinking in middle school. In high school, most AAD individuals were in the heavy episodic drinking status (54%), while most non-AAD individuals were in the initiation only (33%) or current use only (34%) statuses. CONCLUSIONS: These findings suggest preventive intervention targets for different developmental periods. Alcohol abuse and dependence at age 21 may be prevented by delaying alcohol initiation, by reducing current use in middle school and by reducing heavy episodic drinking in high school.

Animal models of alcohol's motivational effects.

Alcohol's positive and negative motivational effects are believed to be important influences on alcohol-seeking behavior and, therefore, key factors among the many and varied causes of alcohol abuse and dependence. Alcohol's positive effects, such as enhanced mood, and negative effects, such as hangover, are considered important factors in motivating drinkers to increase or decrease their drinking. Scientists have developed a variety of animal behavioral models to study alcohol's motivational effects. These models include "self-administration models," in which the animal controls the exposure to alcohol, and "conditioning models," in which the researcher controls the animal's exposure to alcohol. Such models have been used to study the influence of genetic differences on sensitivity to alcohol's positive and negative motivational effects, the brain mechanisms underlying alcohol's motivational effects, as well as relapse and craving.

Preventing adolescent health-risk behaviors by strengthening protection during childhood.

OBJECTIVE: To examine the long-term effects of an intervention combining teacher training, parent education, and social competence training for children during the elementary grades on adolescent health-risk behaviors at age 18 years. DESIGN: Nonrandomized controlled trial with follow-up 6 years after intervention. SETTING: Public elementary schools serving high-crime areas in Seattle, Wash. PARTICIPANTS: Of the fifth-grade students enrolled in participating schools, 643 (76%) were given written parental consent for the longitudinal study and 598 (93%) were followed up and interviewed at age 18 years. INTERVENTIONS: A full intervention provided in grades 1 through 6 of 5 days of in-service training for teachers each intervention year, developmentally appropriate parenting classes offered to parents when children were in grades 1 through 3 and 5 through 6, and developmentally adjusted social competence training for children in grades 1 and 6. A late intervention, provided in grades 5 and 6 only, paralleled the full intervention at these grades. MAIN OUTCOME MEASURES: Self-reported violent and nonviolent crime, substance use, sexual activity, pregnancy, bonding to school, school achievement, grade repetition and school dropout, suspension and/or expulsion, and school misbehavior; delinquency charges from court records; grade point average; California Achievement Test scores: and disciplinary action reports from school records. RESULTS: Fewer students receiving full intervention than control students reported violent delinquent acts (48.3% vs 59.7%; P=.04), heavy drinking (15.4% vs 25.6%; P=.04), sexual intercourse (72.1% vs 83.0%; P=.02), having multiple sex partners (49.7% vs 61.5%; P=.04), and pregnancy or causing pregnancy (17.1% vs 26.4%; P=.06) by age 18 years. The full intervention student group reported more commitment (P=.03) and attachment (P=.006) to school, better academic achievement (P=.01), and less school misbehavior (P=.02) than control students. Late intervention in grades 5 and 6 only did not significantly affect health-risk behaviors in adolescence. CONCLUSIONS: A package of interventions with teachers, parents, and children provided throughout the elementary grades can have enduring effects in reducing violent behavior, heavy drinking, and sexual intercourse by age 18 years among multiethnic urban children. Results are consistent with the theoretical model guiding the intervention and support efforts to reduce health-risk behaviors through universal interventions in selected communities or schools serving high-crime neighborhoods.

Changing teaching practices to promote achievement and bonding to school.

An intervention to modify teaching practices in grades five and six was evaluated. Results showed that higher levels of teacher implementation of the modified practices favorably influenced students' levels of classroom opportunity, involvement, reinforcement, and bonding to school. Levels of academic achievement were also increased. The importance of assessing implementation in theory-guided experimental studies is discussed.

Taste reactivity to alcohol and basic tastes in outbred mice.

The taste reactivity test was used to determine the response of outbred mice to orally infused taste solutions. For the initial measures, mice (n = 10) were tested with 3%, 6%, 9%, and 12% (v/v) alcohol and four taste solutions: sucrose, sodium chloride, hydrochloric acid, and quinine hydrochloride (a single concentration of each). A second group of naive mice (n = 16) was tested with 5%, 10%, 20%, 30%, and 40% alcohol. The final set of measures with naive mice (n = 26) was taken with a range of sucrose concentrations: 0.01 M, 0.05 M, 0.1 M, 0.5 M, and 1.0 M. In general, mice made similar reactivity responses to all solutions tested. A predominant component of the mouse response to all infused fluids was forelimb flailing; gaping was also a common response to all solutions. Despite the large number of aversive-type responses, mice rejected very little fluid via passive drip or fluid expulsion. The single, significant difference in responding to the four taste stimuli was that mice made fewer aversive responses to sucrose. Differential responding to the 5 to 40% alcohol concentrations and sucrose concentrations was observed. Mice increased ingestive responding as the concentration of alcohol and sucrose increased. Aversive responding decreased reliably only with increases in the sucrose concentration. Data provide the first reported taste reactivity responses of mice to orally infused taste solutions. These results can be compared with the extant data available in rats and can also be used as a basis for exploring taste factors in genetically defined mouse populations.

Development of auditory function in the tammar wallaby Macropus eugenii.

Auditory brainstem responses (ABRs) were evoked in developing wallabies by click and tone burst stimuli delivered by bone conduction and air conduction, at progressive stages of post-natal (pouch) life. ABRs were recorded through the onset of auditory responses (95-110 days), the opening of the external ear canal (125-130 days) and the maturation of ABR thresholds and latencies to values corresponding to those in adults ( > 180 days). ABRs were evoked in response to bone-conducted clicks some days prior to the age at which an acoustically evoked response was first observed (around 95 days of pouch life). ABRs could be evoked by bone-conducted and intense air-conducted stimuli prior to opening of the ear canal. A trend of decreasing threshold and latency with age was observed for both modes of stimulation. The morphology of the ABR became more complex, according to both increased age and increased stimulus intensity. The ABR waveforms indicated relatively greater mechanosensitivity to bone-conducted stimuli than to air-conducted stimuli, prior to opening of the ear canal. Following opening of the ear canal, thresholds to air-conducted clicks and tones were substantially reduced and decreased further over the next 10-20 days, while thresholds to bone-conducted clicks continued slowly to decrease. Thresholds to tone bursts in the centre frequency range (4-12 kHz) remained less than those for low (0.5-1.5 kHz) and higher (16 kHz) frequencies. Latencies of an identified peak in ABR waveforms characteristically decreased with age (at constant stimulus intensity) and with stimulus intensity (for a given age). ABR waveforms obtained at progressive ages, but judged to be at corresponding sensation levels, underwent maturational changes, independent of conductive aspects of the wallabies' hearing, for 2-3 weeks after opening of the ear canal.

Basilar membrane motion in relation to two-tone suppression.

It is proposed that two-tone suppression of rate responses in auditory-nerve fibres by a low-side suppressor cannot be explained in terms of basilar membrane motion. In a model, the amplitude of the mechanical response, either to the tone at characteristic frequency (CF), or to the CF tone combined with a second, lower frequency tone (a suppressor), is taken as the effective stimulus to inner hair cells (IHC), the voltage response of which is considered responsible for excitatory drive to auditory-nerve fibres. Many empirical mechanical and physiological effects are simulated accurately by the model, particularly phenomena observed in two-tone experiments using low-side suppressor tones, that authors have described as two-tone suppression. It is argued in this paper, however, that such phenomena strictly do not constitute suppression in the cochlear response and provide no explanation for rate suppression in nerve fibres. According to the model presented here and consistent with experimental data, suppression of the spike response to a CF tone in an auditory-nerve fibre by a low-side suppressor cannot be explained in terms of the mechanics of the BM. Conclusions by others that experiments support a mechanical explanation for low-side rate suppression are shown to be questionable. It is concluded that low-side suppression of neural responses is explicable only in terms of a non-mechanical factor derived from the response to the low frequency tone, that depresses responsiveness in fibres at the CF location. Adherence to the model of low-side neural rate suppression depending on reduced net mechanical response of the BM is contrary to experimental evidence; furthermore it overlooks a profound influence additional to synaptic drive, that is implied in the shaping of responses in auditory-nerve fibres.

Naltrexone treatment increases the aversiveness of alcohol for outbred rats.

Acute naltrexone treatments (0.0, 0.5, 1., or 3.0 mg/kg body weight) were administered to separate groups of rats and alcohol taste reactivity and consumption were measured. Rats were given daily naltrexone injections and then tested for taste reactivity to 10% alcohol 30 and 60 min after injection. Each reactivity trial (total of 4) was 60 sec during which 1 ml of fluid was infused. The rats' orofacial and body movements were videotaped and scored later. In the final measure, rats were placed on a restricted fluid access schedule and given naltrexone treatments 10 min before being presented with the 10% alcohol solution in the home case (60-min drinking period). After 4 days of consumption tests under the drug condition, the rats were given 4 more daily tests without the drug. Results indicated that the two highest naltrexone doses significantly decreased ingestive responding and increased aversive responding, particularly at the 30-min test. Both the 1.0 and 3.0 mg/kg body weight doses also significantly decreased alcohol consumption as measured during the free access tests. Alcohol consumption returned to control levels immediately after the drug treatments were stopped. The data show that dosages of naltrexone 1.0 mg or higher significantly alter both alcohol taste reactivity (increased aversiveness and decreased palatability) and alcohol consumption (decreased intake) in outbred rats. These results are discussed in relation to naltrexone treatment as a means for decreasing alcohol use and abuse.

Exploring the effects of age of alcohol use initiation and psychosocial risk factors on subsequent alcohol misuse.

OBJECTIVE: This study examines whether the age of initiation of alcohol use mediates the effects of other variables that predict alcohol misuse among adolescents and also whether the age of initiation of alcohol use accounts for known gender differences in the severity of alcohol misuse. METHOD: Data were taken from an ethnically diverse sample of 808 (412 male) students who were recruited in grade 5 at age 10-11 and followed prospectively on an annual basis for the next 7 years to age 17-18. State-of-the-art missing data methodology was used to address nonresponse due to noninitiation of alcohol use. Structural equation modeling was used to examine hypotheses for the prediction of alcohol misuse. RESULTS: A younger age of alcohol initiation was strongly related to a higher level of alcohol misuse at age 17-18 and fully mediated the effects of parent drinking, proactive parenting, school bonding, peer alcohol initiation and ethnicity, all measured at age 10-11, and perceived harmfulness of alcohol use, measured at age 10-11 and age 11-12. However, age of alcohol initiation did not fully account for gender differences in the level of alcohol misuse at age 17-18. To further examine the role of gender, interactions between gender and school bonding, and gender and friend's alcohol initiation, were evaluated. However, neither of the interaction terms had direct effects on either age of initiation or level of alcohol-related problems. CONCLUSIONS: Most measured risk factors for alcohol misuse were mediated through age of alcohol initiation. Only gender differences in alcohol misuse at age 17-18 were not mediated by age of alcohol initiation. Variables associated with these differences require further study. The results of this study indicate the importance of prevention strategies to delay the age of initiation of alcohol use.

Auditory brainstem response in tammar wallaby (Macropus eugenii).

Auditory brainstem responses (ABR) elicited by click and tonal stimuli were recorded from the tammar wallaby (Macropus eugenii), a marsupial mammal. The morphology, threshold, amplitude, and latency of ABRs recorded in the tammar wallaby are similar to those of other marsupials and mammals used in auditory research, including humans. Thresholds determined by an algorithm employing cross-correlation and by conventional visual detection methods were comparable. The findings from this study indicate that tammar wallaby is a suitable model for auditory research and that algorithms employing cross-correlation are useful for detection of the ABR waveform.

Neural responses to free-field auditory stimulation in the superior colliculus of the wallaby (Macropus eugenii).

Auditory responses to free-field broad band stimulation from different directions were recorded from clusters of neurones in the superior colliculus (SC) of the anaesthetized tammar wallaby. The auditory responses were found approximately 2 mm beneath the first recording of visually evoked responses in the superficial layers, the vast majority being solely auditory in nature; only one recording responded to both auditory and visual stimulation. Responses to suprathreshold intensities displayed sharp spatial tuning to sound in the contralateral hemifield. Those from the rostral pole of the SC disclosed a preference for auditory stimuli in the azimuthal anterior field, whereas those in the caudal SC preferentially responded to sounds in the posterior field. A continuum of directionally tuned responses was seen along the rostrocaudal axis of the SC so that the entire azimuthal contralateral auditory hemifield was represented in the SC. Furthermore, tight spatial alignment was evident between the best position of the visual responses in the superficial layers in azimuth and the peak angle of the auditory response in the deeper layers.

The Work Preference Inventory: assessing intrinsic and extrinsic motivational orientations.

The Work Preference Inventory (WPI) is designed to assess individual differences in intrinsic and extrinsic motivational orientations. Both the college student and the working adult versions aim to capture the major elements of intrinsic motivation (self-determination, competence, task involvement, curiosity, enjoyment, and interest) and extrinsic motivation (concerns with competition, evaluation, recognition, money or other tangible incentives, and constraint by others). The instrument is scored on two primary scales, each subdivided into 2 secondary scales. The WPI has meaningful factor structures, adequate internal consistency, good short-term test-retest reliability, and good longer term stability. Moreover, WPI scores are related in meaningful ways to other questionnaire and behavioral measures of motivation, as well as personality characteristics, attitudes, and behaviors.

Two-tone suppression, excitation and the after effect in rate responses in auditory nerve fibres in the cat.

Responses were recorded from single, auditory nerve fibres in the anaesthetized cat. Acoustic stimuli consisted of two tones, one of which was at characteristic frequency (CF), the other (the suppressor) was at considerably lower frequency. Tones were presented in simultaneous and sequential configurations. For simultaneous presentations, well-known response properties were observed. The rising limb of the two-tone rate-intensity function closely matched that of the appropriately adapted response to the suppressor tone presented alone. Also, whether strongly suppressed relative to CF-driven rate, or equal to CF-driven rate, rate responses to the two-tone stimuli persisted unchanged when the CF tone was terminated and the suppressor tone continued alone. These results support the hypothesis that the suppressor tone has dual influences, suppressive and excitatory, that are distinct and additive. Peristimulus response histograms confirm in the cat that depression and slow recovery of sensitivity to CF may follow termination of the suppressor tone, as reported for the guinea pig [Hill, K.G. and Palmer, A.R. (1991) Hear. Res. 55, 167-176]. This delay in recovery of normal sensitivity to CF appeared to be directly related to the amount of excitation of the fibre that is attributable to the suppressor tone. A similar, delayed re-establishment of sensitivity also occurred in the response to a tone at CF, presented immediately following excitation by a suppressor tone. However, no delay occurred in the onset of response to the suppressor when preceded by the CF tone.(ABSTRACT TRUNCATED AT 250 WORDS)