We examined the effect of unilateral restricted cochlear lesions in adult cats on the topographic representations ("maps") of the lesioned and unlesioned cochleas in the primary auditory cortex (AI) contralateral to the lesioned cochlea. Frequency (tonotopic) maps were derived by conventional multineuron mapping procedures in anesthetized animals. In confirmation of a study in adult guinea pigs (Robertson and Irvine [1989] J. Comp. Neurol. 282:456-471), we found that 2-11 months after the unilateral cochlear lesion the map of the lesioned cochlea in the contralateral AI was altered so that the AI region in which frequencies with lesion-induced elevations in cochlear neural sensitivity would have been represented was occupied by an enlarged representation of lesion-edge frequencies (i.e., frequencies adjacent to those with elevated cochlear neural sensitivity). Along the tonotopic axis of AI the total representation of lesion-edge frequencies could extend up to approximately 2.6 mm rostal to the area of normal representation of these frequencies. There was no topographic order within this enlarged representation. Examination of threshold sensitivity at the characteristic frequency (CF, frequency to which the neurons were most sensitive) in the reorganized regions of the map of the lesioned cochlea established that the changes in the map reflected a plastic reorganization rather than simply reflecting the residue of prelesion input. In contrast to the change in the map of the lesioned contralateral cochlea, the map of the unlesioned ipsilateral cochlea did not differ from those in normal animals. Thus, in contrast to the normal very good congruency between ipsilateral and contralateral AI maps, in the lesioned animals ipsilateral and contralateral maps differed in the region of AI in which there had been a reorganization of the map of the lesioned cochlea. Outside the region of contralateral map reorganization, ipsilateral and contralateral AI maps remained congruent within normal limits. The difference between the two maps in the region of contralateral map reorganization suggested, in light of the physiology of binaural interactions in the auditory pathway, that the cortical reorganization reflected subcortical changes. Finally, response properties of neuronal clusters within the reorganized map of the lesioned cochlea were compared to normative data with respect to threshold sensitivity at CF, the size of frequency "response areas," and response latencies. In the majority of cases, CF thresholds were similar to normative data. The frequency "response areas" were slightly less sharply tuned than normal, but not significantly. Response latencies were significantly shorter than normal in three animals and significantly longer in one animal.

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The purpose of this study was to examine whether boredom proneness and/or loneliness predict problem internet use (PIU) and whether these possible associations are moderated by distress tolerance. The study used a sample of 169 undergraduate university students known to be regular internet users, and measured the impact of PIU on their life by examining the relationship between PIU and academic performance. As predicted, boredom proneness was significantly associated with PIU and was a significant predictor of PIU in a model that included loneliness and distress tolerance. Loneliness was also significantly associated with both boredom and PIU, but was not a significant predictor of PIU in the model. There was no evidence that distress tolerance moderated either of these associations. As predicted, higher levels of PIU were associated with lower levels of academic performance, leading us to the conclusion that university students who are prone to experiencing boredom tend to use the internet to seek out more stimulating and satisfying activities, which in turn can lead to problematic internet use patterns that can negatively affect their academic performance.

Sensitivity to interaural intensity difference (IID) was examined for 103 neurons in the deep layers of superior colliculus (SC) in ketamine barbiturate-anesthetized cats. Noise stimuli were presented dichotically, and IID sensitivity functions were generated while keeping the average binaural intensity (ABI) of stimulation constant. Neurons of three binaural classes were found to be IID sensitive. Neurons receiving excitatory contralateral input and inhibitory ipsilateral input (EO/I cells, 55% of sample) had steplike IID functions, with maximum response at IIDs corresponding to contralateral azimuths (positive IIDs), total suppression at IIDs corresponding to ipsilateral azimuths (negative IIDs), and cutoffs at different positions along the IID axis for different neurons. Neurons responsive only to binaural stimulation (OO/F cells, 15% of sample) had IID functions with a sharp peak in the range of 0 to 10 dB IID. Cells receiving excitatory input contralaterally and a facilitatory ipsilateral input (EO/F cells, 7% of sample) had IID functions of intermediate shape, with a peak in the range of 10 to 20 dB IID and a sharper cutoff near zero IID than at larger positive IIDs. The sharpness of IID cutoff for EO/I cells was quantified by measuring an 80% IID dynamic range. Neurons with 80% IID dynamic ranges of less than 26 dB were judged to have sharp cutoffs. The position along the IID axis of the IID cutoff for these cells was quantified by recording the IID at which the response was at 50% of maximum (half-maximal IID). A topographic organization of EO/I cells with sharp IID cutoffs was found along the rostrocaudal axis of SC, such that rostral EO/I cells had IID functions with half-maximal IIDs near zero, while increasingly caudal EO/I cells had progressively larger (positive) half-maximal IIDs. Although detailed maps could not be obtained in individual animals, the topography was observed in each of nine experiments in which EO/I cells were located in two or more rostrocaudal locations (P = 0.00002). The effect of stimulus level on the stability of IID cutoff was examined for 13 EO/I cells. The majority (85%) showed less than 10 dB variation in half-maximal IID across a range of suprathreshold ABIs, indicating that EO/I cells in SC generally exhibit stability in cutoff with changes in intensity of broadband stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)

1. The auditory responses of 207 single neurons in the intermediate and deep layers of the superior colliculus (SC) of barbiturate -or chloralose-anesthetized cats were recorded extracellularly. Sealed stimulating systems incorporating calibrated probe microphone assemblies were employed to present tone- and noise-burst stimuli. 2. All acoustically activated neurons responded with onset responses to noise bursts. Of those neurons also tested with tonal stimuli, approximately 30% were unresponsive over the frequency range tested (0.1-40 kHz), while the others had higher thresholds to tones than to noise. 3. Details of frequency responsiveness were obtained for 55 neurons; 21 were broadly tuned, while 34 were sharply tuned with clearly defined characteristic frequencies (CFs). All sharply tuned neurons had CFs greater than or equal to 10 kHz. 4. The majority of neurons (81%) responded with latencies in the range 8-20 ms; only 11% of neurons had latencies greater than 30 ms. 5. Binaural response properties were examined for 165 neurons. The great majority (79%) received monaural excitatory input only from the contralateral ear (EO). However, most EO cells were binaurally influenced, the contralateral response being either inhibited (EO/I; 96 of 131 units) or facilitated (EO/F; 33 of 131 units) by simultaneous ipsilateral stimulation. Small subgroups were monaurally excited by either ear (EE cells; 8%) or were unresponsive monaurally but responded strongly to binaural stimulation (OO/F cells; 7%). 6. EO/I, EO/F, and OO/F neurons showed characteristic forms of sensitivity to interaural intensity differences (IIDs). The IID functions of EO/I neurons would be expected to produce large contralateral spatial receptive fields with clearly defined medial borders, such as have been described in studies of deep SC neurons employing free-field stimuli. 7. Preliminary evidence suggests a possible topographic organization of IID sensitivity in deep SC, such that the steeply sloping portion of the function (corresponding to the medial edge of the receptive field) is shifted laterally for EO/I neurons located more caudally in the nucleus. 8. The auditory properties of deep SC neurons are compared with previous reports and implications for the organization of auditory input are considered. The binaural properties and auditory spatial fields of deep SC neurons suggest that any representation of auditory space in this structure is unlikely to be based on restricted spatial fields.