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Biomedical subjects

S S Orman

Publications and source records attributed to S S Orman.

9 recordsLinked to original sources
PubMed1985

Binaural interactions in cortical area AI of cats reared with unilateral atresia of the external ear canal.

Binaural interactions were recorded in auditory cortical (AI) neurons of anesthetized adult cats that had unilateral atresias created shortly after birth by surgically ligating and cutting one external ear canal. At the time of the recording experiment, the atresia and associated debris were removed and tones were delivered to both tympanic membranes via a sealed and calibrated acoustic system. The majority of neurons recorded were in the cortex ipsilateral to the previously occluded ear. Thresholds for monaural stimulation of either the operated or unoperated ear were within normal range although thresholds to stimulation of the previously operated ear tended to occupy the upper end of the normal distribution. Monotonic and nonmonotonic spike count-vs-intensity functions derived from responses to monaural stimulation of the atretic ear were indistinguishable in their shape from those recorded in normal cats. All binaural classes were represented in our sample in proportions similar to those reported in cats with two normal ears. The forms of the functions relating spike count to interaural intensity differences and interaural phase differences were essentially the same as those seen in normal animals. The main binaural deficit observed under these conditions was a shift in the interaural intensity difference to which an AI neuron was most sensitive. The intensity needed for a stimulus to the atretic ear to participate in the binaural response was as much as 50 dB higher than that at the opposite normal ear in contrast to the nearly equal SPLs required for binaural interactions in cats with two ears intact. It was suggested that elevated thresholds at the previously operated ear could account for much of the shift observed.

Action Potentials↗
PubMed1985

Neurons in the cat's primary auditory cortex distinguished by their responses to tones and wide-spectrum noise.

In the cortex of barbiturate-anesthetized cats, area AI was identified by its tonotopic organization, and single neurons in that field were examined with regard to the shapes of their spike count-versus-intensity functions, the organization of their frequency-intensity response areas, and their responses to wide-spectrum noise, using calibrated sealed stimulating systems. Neurons whose pure tone rate intensity functions were monotonic in shape displayed V-shaped response areas that were open-ended at high tone intensities. In contrast, cells displaying nonmonotonic tone intensity functions tended to have circumscribed response areas; these cells were responsive to tones over limited ranges of both frequency and intensity. Monotonic neurons almost always responded to wide-spectrum noise stimuli, while nonmonotonic neurons often did not. The mean minimum latent period of monotonic cells (14.0 ms) was significantly shorter than that for nonmonotonic neurons (19.1 ms). For those cells that responded to both tones and noise, minimum latent periods for the two stimuli were similar or identical. Monotonic neurons tended to be horizontally segregated from nonmonotonic neurons across AI's middle cortical layers. The implications of these data for the nature of some neural mechanisms underlying the stimulus selectivity of cortical cells are discussed.

Anesthesia, General↗
PubMed1984

Responses of single neurons in posterior field of cat auditory cortex to tonal stimulation.

In the auditory cortex of barbiturate-anesthetized cats, the posterior auditory field (field P) was identified by its tonotopic organization, and single neurons in that field were studied quantitatively for their sensitivity to the frequency and intensity of tonal stimuli presented via calibrated, sealed stimulating systems. Field P neurons had narrow, V-shaped, threshold frequency tuning curves. At suprathreshold levels, spike counts were generally greatest at frequencies at or close to the neuron's threshold best frequency (BF). Eighty-six percent of posterior-field neurons displayed spike counts that were a nonmonotonic function of the intensity of a BF tone. Of these, over 90% showed at least a 50% reduction in spike count at high stimulus levels, and almost 20% of nonmonotonic cells ceased responding entirely at high stimulus intensities. The nonmonotonic shape of spike count-versus-intensity profiles was typically preserved across the range of frequencies to which any given neuron was responsive. For some neurons, this had the consequence of generating a completely circumscribed frequency-intensity response area. That is, these neurons responded to a tonal stimulus only if the stimulus was within a restricted range of both frequency and intensity. These response areas showed internal organizations that appeared to reflect one or both of two processes. For some neurons, the optimal sound pressure level for spike counts varied with tone frequency, roughly paralleling the threshold tuning curve. For other neurons, the optimal sound pressure level tended to be constant across frequency despite threshold variations of up to 20 dB. The minimum response latencies of posterior-field neurons were generally in the range of 20-50 ms, while cells in the primary auditory cortex (AI) in the same animals generally had minimum latent periods of less than 20 ms. Comparison of these data with those previously presented for neurons in two other cortical auditory fields suggests that the cat's auditory cortex might show an interfield segregation of neurons according to their coding properties.

Animals↗
PubMed1984

Binaural interactions of single neurons in posterior field of cat auditory cortex.

In the auditory cortex of barbiturate-anesthetized cats, the posterior auditory field (area P) was identified by its tonotopic organization, and single neurons in that field were studied quantitatively with regard to their binaural interactions at their respective best frequencies, using calibrated, sealed stimulating systems. Almost 60% of the neurons studied displayed " summative " binaural interactions in that their responses to binaural, equally intense stimulation of the two ears were stronger than were their responses to monaural stimuli of the same intensity. For these neurons, latent periods were shorter for binaural stimuli than for monaural stimuli. Some field P neurons were sensitive to interaural intensity disparities and manifested that sensitivity in one of two forms. Cells that were excited by stimulation of one ear and inhibited by stimulation of the other typically displayed a sigmoidal relation of spike count to intensive disparity, with spike counts being larger when the disparity favored the contralateral ear. Cells that were unresponsive to monaural stimuli but responded securely to binaural stimuli usually displayed a peaked, nonmonotonic relation of spike count to interaural intensity disparity, with maximal responses being elicited by stimuli with zero or near-zero disparity. Some neurons of low best frequency were sensitive to variations in interaural phase delay. In all cases, this sensitivity was manifested as a cyclical relation of spike count to interaural delay, with the period of the cycle being that of the stimulating tone. The fact that the binaural interactions of field P neurons were similar to those of cells in the primary auditory cortex suggests that the previously described heightened spectral-amplitude selectivity of field P neurons has been achieved without cost to their sensitivity to a variety of parameters of binaural stimulation. The particular sensitivity of cortical neurons to variations in interaural disparities associated with midline or near-midline azimuths might constitute a neural mechanism for the behavioral finding that animals and humans show their greatest acuity in sound localization for stimulus locations in or near the midsagittal plane.

Animals↗
PubMed1981

Effects of changes in cortical arousal and of auditory cortex cooling on neuronal activity in the medial geniculate body.

The activity of cells in the medial geniculate body (MGB) of adult cats was recorded during different states of cortical arousal with and without cooling of the auditory cortex. In the absence of auditory cortex cooling, the overall mean unit spontaneous discharge rate was 49% higher during desynchroized Electrocorticogram (ECoG) periods (high cortical arousal). Responses to sound were somewhat more prominent vis-à-vis the spontaneous activity during periods of high arousal. Changes in spontaneous discharge rate associated with arousal shifts were significantly reduced during auditory cortex cooling. When the ECoG changed from desynchronized to synchronized activity, MGB cells showed a change in discharge pattern, typically characterized by an increase in both high-rate bursts and long-interval pauses. These changes were duplicated for most cells by cooling of the auditory cortex. Corticofugal fiber discharge thus has an effect on MGB neuronal activity which is dependent on the level of cortical arousal. This effect is most likely a result of direct corticogeniculate activity, though indirect auditory cortex - brainstem - MGB routes may also be involved.

Animals↗
PubMedDate not supplied

Removable, conforming device for cooling the cortical surface.

A technique for cooling the cerebral cortex is described. It makes use of a neoprene bladder through which cold fluids is circulated. The flexible bladder is contained within a cylinder permanently attached to the skull. The bladder itself can be quickly installed and removed and conforms to the cortical surface with minimal pressure.

Animals↗
PubMedDate not supplied

Guinea pig tectorial membrane profile in an in vitro cochlear preparation.

The guinea pig cochlea was examined under high-magnification light microscopy in an in vitro preparation. After extraction of the otic capsule, the bulla was opened widely and a small hole made into the fourth turn of the scala vestibuli. The organ of Corti was visualized under artificial endolymph at 600 X magnification. Added 1-micron titanium dioxide particles settled on the upper surface of the transparent tectorial membrane. Particle positions showed that much of this upper surface lay in a flat sheet that extended centrifugally almost to the Hensen's cells, giving the impression it was attached there. The sheet extended at least to the level of the inner hair cells, where a tectorial membrane thickness of about 40 micron was reached. Titanium dioxide particles were seen regularly in immediate proximity to the hair cell cilia, indicating that scala media is continuous with the subtectorial space. Upon mechanical manipulation, Hensen's cells proved to be extremely cohesive and elastic. It is suggested that hair cell stereocilia provide major mechanical connections for the tectorial membrane.

Animals↗