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D R Irvine

Publications and source records attributed to D R Irvine.

At least 55 records · Page 3Linked to original sources
PubMed1983

Some features of binaural input to single neurons in physiologically defined area AI of cat cerebral cortex.

1. In the ectosylvian cortex of 24 barbiturate-anesthetized cats, area AI was identified by its frequency organization and the responses to tonal stimuli of single neurons in that field were examined using sealed stimulating systems incorporating calibrated probe microphone assemblies. 2. The responsiveness to monaural and binaural best-frequency stimuli was examined quantitatively for 282 single units in AI. One hundred thirty-nine cells (49%) were excited by independent stimulation of only one ear and were classified as EO cells. In general, the effective monaural excitatory input was derived from the contralateral ear. One hundred ten (39%) neurons were excited by independent stimulation of each ear and were classified as EE units. For these neurons, the contralateral responses were generally stronger, shorter in latency, and lower in threshold than were their ipsilateral responses. Thirty-three cells (12%) gave weak or no responses to monaural stimuli but responded securely to binaural stimuli. These cells were classified as predominantly binaural (PB). 3. Binaural interactions were examined by comparison of the response to binaural, equally intense stimuli to the stronger monaural response. Among EO cells suppression was the most common form of interaction, while for EE cells summation was the more common. Less than 8% of cells were found to be monaural. 4. In electrode penetrations radial to the cortex surface, cells received their stronger or sole monaural excitatory input from a common ear, generally the contralateral. Within such penetrations, however, cells commonly differed with regard to the nature of their input from the other ear and/or in their binaural interactions. 5. Comparison of these data with data previously reported for subcortical auditory nuclei revealed that AI preserves many of the stimulus specificity characteristics of the lower nuclei. The reasons for the preservation of these characteristics at the cortex and the implications of the present data for the binaural column hypothesis are discussed.

Animals↗
PubMed1983

Auditory response properties of neurons in deep layers of cat superior colliculus.

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.

Acoustic Stimulation↗
PubMed1981

Plasticity of binaural interaction in the cat inferior colliculus.

Responses of single neurones in the inferior colliculus (IC) to acoustic interaural intensity difference (IID) were examined in normal, adult cats and in cats that had been reared for 3--4 months, either from birth or as adults, with unilateral ligation of the external meatus. There were significantly fewer units displaying IID sensitivity in either of the ligated groups than there were in the normal group. The loss of IID sensitivity in the ligated animals reflected a diminished inhibitory input from the non-ligated ear.

Aging↗
PubMed1981

Development of responses to acoustic interaural intensity differences in the car inferior colliculus.

Responses of single neurones in the inferior colliculus of anesthetized adult cats and kittens were studied using best-frequency stimuli of varying interaural intensity differences (IID). Two broad classes of neurone, distinguished by the predominant type of input from each ear, were examined. One class of cells received predominantly excitatory input from each er (EE cells). The other class were excited by monaural stimulation of the contralateral ear and showed no response to monaural stimulation of the ipsilateral ear, but inhibition of the excitatory response by simultaneous ipsilateral stimulation (EI cells). Fourteen of the 18 adult EI cells showed marked changes in discharge rate with variation in IID. Adult EI cells showed low response variability and were insensitive to changes in average binaural intensity. In all cases of IID sensitivity, the onset component of the response was less sensitive to IID than the sustained component. Eight out of ten EE cells were insensitive to IID over the range tested. Cells of high best-frequency in kittens younger than 28 days showed irregular changes in discharge rate with variation in IID and wide response variability. Some low-frequency EI cells in young kittens showed sensitivity to IID, but it is unlikely that these could be involved in sound localization as their frequency response was inappropriate. Many cells in kittens aged 31-40 days showed monotonic, adult-like IID functions, but the response variability of these cells remained higher than that of adult cat neurones. These data provide evidence for a developmental change of binaural interaction in the cat.

Aging↗
PubMed1981

Responses of single neurons in physiologically defined area AI of cat cerebral cortex: sensitivity to interaural intensity differences.

In 15 cats, cortical area AI was defined by its frequency organization, and cells within that field were tested for sensitivity to interaural intensity differences (IIDs) using sealed stimulus delivery systems. Of 39 cells tested quantitatively, 26 were sensitive to IIDs. In 70% of cases, sensitivity to IIDs reflected suppressive binaural interactions, and was manifested as a sigmoidal relation of spike count to IID. For 8 other cells, facilitative binaural interactions generated unit sensitivity to IIDS; three of these neurons demonstrated nonmonotonic dependency of spike count on IID, with peak firing rates at or near 0 dB IID. Analysis of spike count versus IID functions in terms of the auditory azimuths known to generate the IIDs used revealed that the majority of cells were most sensitive to IIDs associated with azimuths in the contralateral sound field. These data are compatible with other evidence on the sensitivity of cortical and brainstem cells to binaural sound localization cues, and suggest that each side of the auditory brain is independently capable of localizing sound sources in the contralateral field.

Animals↗
PubMed1980

Afferent and efferent connections between the claustrum and parietal association cortex in cat: a horseradish peroxidase and autoradiographic study.

Combined injections of [3H]proline and horseradish peroxidase (HRP) were made into acoustically responsive cortical association areas on the middle suprasylvian gyrus (MSA) and anterior lateral gyrus (ALA) in the cat. Sources and terminations of cortical axons were located within the claustrum. There are three findings: (1) MSA and ALA project to and receive fibers from restricted areas of the dorsal claustrum. The locations of the projection fields within the claustrum are different for the two cortical areas; (2) the afferent and efferent projection fields in the claustrum are coextensive suggesting a reciprocal claustral-cortical relationship and (3) the projections are bilateral with the ipsilateral projection predominating.

Afferent Pathways↗
PubMed1979

The development of some peripheral and central auditory responses in the neonatal cat.

The development of cochlear nerve action potential thresholds at different frequencies (AP audiograms) and inferior colliculus (IC) single unit thresholds and tuning was examined in barbiturate-anaesthetized kittens. AP thresholds decreased over the whole frequency spectrum during the first 5 weeks of life. Thresholds to high-frequency stimulation remained higher in 7-week-old animals than in adults. These results are in contrast to previous reports which have suggested that the AP response and gross cochlear anatomy are mature by the end of the second week. These differences may be due to the fact that the AP audiogram technique provides a measure of the activity of discrete regions along the cochlear partition. IC units in animals younger than 3.5 weeks had significantly elevated thresholds and broader tuning than those of the adult cat. Comparison of AP audiogram and IC unit thresholds in the adult revealed that these indices show similar frequency-dependent sensitivity. The slower maturation revealed by the AP audiogram may be due to the greater number and/or synchrony of cochlear nerve discharges needed to produce the gross AP. If this were the case, perception of suprathreshold sounds might not develop as quickly as thresholds for sound detection.

Acoustic Stimulation↗
PubMed1979

Bone conduction mechanisms: Mössbauer measurements on the role of ossicular inertia.

The Mössbauer technique was used to measure displacements of the stapes footplate and adjacent temporal bone during bone conduction stimulation at frequencies from 250 to 400 Hz in anaesthetized guinea pigs. The stapes was found not to be driven at amplitudes or phases that differed significantly from those of the temporal bone. Measurement of stapes displacements during air conduction stimulation, and of temporal bone displacements during bone conduction stimulation producing matching cochlear microphonic amplitude, enabled calculation of limiting values of amplitude and phase difference necessary to produce the required relative displacement. The obtained values (less than 1 dB for amplitude and 1--4 degrees for phase) were beyond the resolution of the measurement system employed for reasonable nuclear counting times. The results provide quantitative estimates of the magnitude of inertial effects, but do not establish whether ossicular inertia is an important factor in bone conduction stimulation.

Acoustic Stimulation↗
PubMed1979

Acoustic response characteristics of neurons in nonspecific areas of cat cerebral cortex.

1. Acoustic properties of single neurons in pericruciate, anterior lateral, and medial suprasylvian "association" areas were studied in chloralose-anesthetized cats using sealed stimulating systems incorporating probe microphone assemblies. 2. A total of 652 cells were isolated. Approximately 70% of the cells in each area were responsive to acoustic stimulation, and the majority of these cells were also driven by visual and/or somatosensory stimulation. 3. Association cortex neurons responded to tone- or noise-burst stimulation with an onset response of 16--50 ms latency. The onset response was found to be followed by a long period of suppression in those cases in which spontaneous activity was sufficiently high for this to be detected. 4. The majority of 56 units for which detailed frequency-tuning data were obtained had broad, irregular tuning curves extending over 5--6 octaves or more. A small proportion of association cortex cells exhibited sharp tuning comparable to that obtained in control recordings from cells in primary auditory cortex (AI). Although a number of broadly tuned units were rather insensitive, many cells--both broadly and sharply tuned--were of comparable sensitivity to AI cells. 5. Of the association cortex cells examined for binaural properties, 95% received excitatory input from each ear, and the dominant mode of binaural interaction in these cells was one of occlusion. The occurrence of occlusion at suprathreshold intensities reflected a tendency for monoaural and binaural intensity functions to asymptote at the same level. 6. The broad tuning, lability, and polysensory convergence exhibited by association cortex cells are similar to those of the so-called auditory lemniscal adjunct system. However, the binaural properties of association cells differ significantly from those of both the lemniscal line and adjuct components of the auditory pathway. 7. The homogeneity of acoustic and polysensory input to the three association fields is compatible with their input being derived from the single subcortical nonspecific projection system (reticular formation and medial/intralaminar thalamus) postulated by previous investigators. However, both neuroanatomical and neurophysiological evidence suggest that the lemniscal adjunct system and certain areas of periauditory cortex might also contribute to this input.

Acoustic Stimulation↗
PubMed1979

Acoustic input to single neurons in pulvinar-posterior complex of cat thalamus.

1. Extracellular microelectrode recordings have been made of 429 single neurons in the pulvinar-posterior (Pul-PO) complex and adjacent regions of the thalamus of cats anesthetized with either sodium pentobarbital or alpha-chloralose. Controlled acoustic stimuli were presented by sealed systems incorporating probe microphone assemblies. 2. Neurons in pulvinar, lateralis posterior, and nucleus posterior were unresponsive to acoustic stimulation. Few cells in medial PO were observed to receive acoustic input, while sensitivity to tonal stimuli was a general feature of driven cells in other PO divisions. 3. Cells in lateral PO were generally sharply tuned to stimulus frequency, while the majority of cells in magnocellular medial geniculate and intermediate division of PO were broadly tuned. 4. Neurons in lateral PO and magnocellular medial geniculate had short response latencies to acoustic stimulation. Cells in intermediate division of PO were more often long latency. 5. Divisions of PO could not be differentiated on the basis of their binaural properties. Cells receiving excitatory input from solely the contralateral ear (E/O) or fros with onset discharge patterns showed occlusive binaural interaction properties. For cells with multiple-component discharge patterns, individual response components frequently had different patterns of binaural input and/or interaction. 6. On the basis of their discharge patterns, short latency, and frequency-tuning properties, it is suggested that lateral PO and magnocellular medial geniculate might derive their acoustic input from different divisions of the inferior colliculus. In contrast, the long latencies of units in PO intermediate division suggests a corticofugal input. 7. These data support anatomical parcelations of the Pul-PO complex, and the suggestion that this complex might provide acoustic input to the association cortices is evaluated.

Acoustic Stimulation↗