Biomedical subjects

L Z Wise

Publications and source records attributed to L Z Wise.

7 recordsLinked to original sources

PubMed1993

Effect of unilateral partial cochlear lesions in adult cats on the representation of lesioned and unlesioned cochleas in primary auditory cortex.

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.

Animals↗

PubMed1990

Retinotopic representation of the bifoveate eye of the kestrel (Falco spraverius) on the optic tectum.

Like many diurnal raptors, the American kestrel or sparrow hawk, Falco sparverius, possesses two foveae in each eye. In this study, we used fundus photography and reversed ophthalmoscopy to plot the projection of these foveae onto the visual field, together with other retinal landmarks such as the pecten and ora terminali. From such data, it was determined that the central monocular fovea (CMF) and temporal binocular fovea (TBF) were separated by 36 deg and that the kestrel has 58 deg of binocular overlap when the eyes are appropriately converged. Single-cell and multi-unit recordings were used to systematically explore the tectal surface and map receptive fields (RF) onto a hemispheric screen. A retinotopic map of the tectal surface was produced from such data and revealed an expanded representation for each fovea on the tectum and a systematic increase in RF size from fovea to periphery. The functional significance of this organization is discussed.

Animals↗

PubMed1986

Somatosensory cortical representation in the Australian ghost bat, Macroderma gigas.

Bats of the two suborders Microchiroptera and Megachiroptera have a modified hand in which the digits of the forelimb are caudally oriented to form the wing. In a previous study of a megachiropteran species, this modification of body plan was found to be reflected in the somatosensory cortical representation such that the orientation of the digit representation was reversed compared with walking mammals. This finding suggests that the precise details of arrangement of topographical maps are functionally significant and do not merely reflect an order imposed by peripheral innervation. Recent evidence for separate origins of Microchiroptera and Megachiroptera raises the question of whether the cortical somatosensory representation in Microchiroptera will also have a reversal of digit orientation compared with walking mammals. We recorded multiunit activity from the somatosensory cortex of a microchiropteran bat, Macroderma gigas. We found two orderly representations of the body surface, SI and SII, in both of which the digit orientation was opposite to the head orientation in accordance with adaptation for flight, and reversed with respect to equivalent maps in other mammals. We also found minor variations in body surface representation compared with Megachiroptera, in line with their proposed independent evolution.

Animals↗

PubMed1985

Representation of stimulus azimuth by low-frequency neurons in inferior colliculus of the cat.

The responses to changes in stimulus azimuth of 204 neurons in the inferior colliculus of the cat with best frequencies of less than 3 kHz were studied. Three main unit classes were identified: omnidirectional units uninfluenced by speaker azimuth (39%); multipeaked units with several azimuthal regions at which peak firing occurred (9%); and azimuth-selective units that showed clear preferences for a discrete range of sound-source azimuths (52%). Alterations in stimulus intensity produced little change in the shapes of profiles relating firing rate to stimulus azimuth (azimuth functions), but the peaks of these functions could shift by up to 20 degrees. Similar observations were made for a small sample of units, each of which was examined with a variety of stimulus frequencies. The pinnae were removed bilaterally in 11 cats, and azimuth functions for 35 units were measured both binaurally and with the ipsilateral or contralateral ear occluded. Evidence was found for facilitative or suppressive interactions, as a function of stimulus azimuth, between monaural inputs. The sharpness of an azimuth function was expressed by the half-width of the function, i.e., the number of degrees of azimuth between the peak of the function and the point at which 50% of maximum firing occurred on the medial side of the peak. When half-widths were plotted as a function of best frequency, it was found that the sharpest azimuth functions occurred for units with best frequencies between 1.1 and 1.5 kHz. Most units in the lowest two octaves (0.1-0.4 kHz) or having best frequencies between 2 and 3 kHz were omnidirectional. The relationship between half-width and the azimuth at which peak firing occurred (best azimuth) revealed that a range of best azimuths between 10 and 40 degrees contralateral contained the sharpest azimuth functions. When best frequency was plotted against best azimuth, it was observed that the majority of units (93%) had best azimuths in the contralateral hemifield. For frequencies between 0.7 and 1.7 kHz, best azimuths occurred relatively evenly between 10 and 60 degrees contralateral. These data suggested that for frequencies between 1.2 and 1.4 kHz, at least, the best azimuths of different units with the same best frequency collectively provide information about stimulus location across much of the contralateral hemifield.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1985

Topographic organization of interaural intensity difference sensitivity in deep layers of cat superior colliculus: implications for auditory spatial representation.

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)

Animals↗

PubMed1984

Interaural intensity difference sensitivity based on facilitatory binaural interaction in cat superior colliculus.

Sensitivity to interaural intensity difference (IID) has generally been identified as a property of neurons exhibiting inhibitory binaural interaction, viz. contralateral excitatory and ipsilateral inhibitory input (EI cells). In the deep layers of the superior colliculus, however, almost 30% of IID-sensitive cells are characterised by facilitatory or mixed facilitatory/inhibitory interactions. Such cells typically have peaked IID sensitivity functions in contrast to the step functions characteristic of EI cells. There appears to be a continuum in IID sensitivity from pure step functions to sharply-peaked functions. The observation that a given form of IID sensitivity can be associated with patterns of binaural interaction other than that by which it is most commonly produced suggests that IID-sensitive neurons are better classified on the basis of the form of their IID sensitivity than their binaural input pattern. It seems probable that IID sensitivity based on facilitatory and mixed facilitatory/inhibitory binaural interactions is a general characteristic of the primary auditory pathway, although only fragmentary data are so far available.

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↗