Dwight Sutton

Neocortical and limbic lesion effects on primate phonation.

Abstract Five monkeys were individually trained to emit a relatively prolonged call of specified loudness in order to obtain a preferred food. At the completion of training each animal gave the required call in response to a signal cue light and withheld calls during periods in which no cue light was present. Sequential bilateral removal of the homolog of Brocas area, transitional parieto-occipital cortex, and temporal association cortex in 3 monkeys had no influence on performance of the discriminative call. There was no change in sound spectral properties of the call as a result of surgery. Bilateral removal of anterior cingulate/subcallosal gyrus in the remaining two monkeys was accompanied by loss of phonatory performance. Postoperative calls given by each of these animals in the test situation were weak and infrequent. The data indicate that control over learned, discriminative phonation in monkeys is not mediated by neorcortical regions homologous to human ‘speech’ areas.

Relation of psychophysical data to histopathology in monkeys with cochlear implants.

Psychophysical measures of threshold and dynamic range for electrical stimulation were made in macaque monkeys that had electrodes implanted in the scala tympani. At the completion of psychophysical testing the monkeys were sacrificed and the cochleas and brain steins examined. Low thresholds and large dynamic ranges were associated with minimal damage to the organ of Corti and minimal brain stem degeneration. whereas thresholds were high and dynamic ranges small in subjects showing a high degree of sensorineural cochlear damage and brain stem degeneration. Three different implant orientations were observed. but orientation did not seem to have a major effect on threshold.

Clinical experience with the tracheoesophageal anastomosis for intractable aspiration.

Clinical experience in six patients in whom the tracheoesophageal diversion procedure or a modification thereof has been performed is presented. Two of these patients have been reconstructed with resulting normal laryngeal and esophageal function. Three of the patients have successfully undergone tracheoesophageal anastomosis and are candidates for reconstruction. One patient in whom the tracheoesophageal anastomosis has been present for 2K years may never demonstrate neurological return sufficient for reversal of the procedure. On the basis of these six cases, we consider the tracheoesophageal anastomosis to be an effective, yet reversible, procedure for intractable aspiration.

Single Cell Activity in the Auditory Cortex of Rhesus Monkeys: Behavioral Dependency

The response to repetitive stimulation of single cells in the auditory cortex of the monkey is dependent upon behavioral performance and training of the subject in a simple auditory discrimination task. In the trained, performing animal, single cells are more responsive than in the animal that is trained but not performing in the task. In the naive monkey, evoked responses are labile and are maintained only with nonrepetitive auditory stimuli.

Vocalization in rhesus monkeys: Conditionability

Three rhesus monkeys were individually trained to emit relatively prolonged calls in an experimental arrangement which required that intensity of each call be maintained within prescribed limits. Each animal learned to produce the calls when a stimulus signaled the appropriate occasion. Stimulus control over the calls was demonstrated by increased number of calls and increased average duration of calls when the signal was present, together with diminished number of calls when the signal was not present.

RELATION OF COCHLEAR IMPLANT FUNCTION TO HISTOPATHOLOGY IN MONKEYSa

Although a number of patients are currently benefiting from cochlear implants, it is widely believed that considerable improvement can be made in this method of providing hearing to the deaf. Many investigators are currently gathering data with this goal in mind. We believe that one of the most fruitful approaches is to examine the relations between implant function, measured psychophysically, and the condition of the implanted cochlea, measured histologically. This approach yields data that are applicable at several levels: (1 ) Observing the relation of implant function to various levels and types of pathology will aid in establishing criteria for selection and treatment of implant candidates. (2 ) These observations yield data relevant to physiological models of implant function. If we can model what neural elements are being excited by electrical stimulation, and how various percepts are encoded, we will be in a much better position to specify optimal electrode placements and parameters for electrical stimulation. ( 3 ) Studies of hearing in the absence of hair cells and basilar membrane mechanics, and in many cases in the absence of a large percentage of the normal complement of eighth nerve fibers, provide unique opportunities to analyze central neural mechanisms. A better understanding of central auditory processing would be of great benefit to those who are trying to devise paradigms for translating acoustic stimuli into electrical signals that can be delivered by singleor multichannel cochlear implants. Realistically, achievement of these goals will require data from both implanted human patients and laboratory animals. The human data ultimately demonstrate the relevance of the animal data, and in addition, some percepts are more readily tested in humans than in animals. On the other hand, the procurement of human histological data is naturally very slow, and the human psychophysical data are often inadequate owing to a variety of complicating factors. For example, human data are usually collected from patients who have been deaf for a number of years and whose ability to perform the required psychophysical experiments is not known, whereas animal data can often be obtained from a deafened, implanted ear and a normal hearing

Wound Tension and Blood Flow in Skin Flaps

The relationship between wound-closing tension, blood flow, and flap viability is examined using piglets as an experimental model. Twenty-seven rectangular skin flaps with random-pattern blood flow were created and closed under varying tensions. Closing tensions were accurately measured using a stabilized mechanical force gauge. In flaps with an impaired blood supply, there was a statistically significant increase in flap necrosis for those flaps closed with greater than 250 g of tension. The laser Doppler demonstrated a clear-cut inverse relationship between flap tension and blood flow in these flaps which correlated well with the experimental flap necrosis seen.

A finite element model of skin deformation. II. An experimental model of skin deformation.

Skin flap design has traditionally been based on geometric models which ignore the elastic properties of skin and its subcutaneous attachments. This study reviews the theoretical and experimental mechanics of skin and soft tissues (I) and proposes a mathematical model of skin deformation based on the finite element method (III). Finite element technique facilitates the modeling of complex structures by analyzing them as an aggregate of smaller elements.

Intensity discrimination with cochlear implants

Intensity difference limens were measured for various frequencies and intensities of sinusoidal and pulsatile electrical stimulation in monkeys with electrodes implanted in the scala tympani, scala vestibuli, modiolus, or middle ear. Difference limens decreased, as a function of initial stimulus intensity, from values of 1.5-3 dB near threshold to as low as 0.5 dB near the upper limit of the dynamic range. If sensation level was held constant, difference limens decreased as a function of frequency up to about 500 Hz, and then remained constant. They were similar across a variety of electrode placements and separations if differences in threshold and dynamic range were taken into account. However, difference limens measured in severely damaged ears were slightly smaller than those in moderately damaged ears. The near miss to Webers law, characteristic of acoustic difference limens, was not seen with electrical stimuli. Differences limens for electrical stimuli were roughly one-half those for acoustic stimuli; thus, part of the deficit in dynamic range for electrical stimulation compared with acoustic stimulation is countered by the smaller intensity differences limens for electrical stimuli.

Cochlear implant effects on the spiral ganglion

To evaluate the effects of chronic intrascalar implants on spiral ganglion cells, we studied 15 monkey cochleas that had had implants for periods ranging from 1 to 28 months. All cases exhibited loss or ongoing degeneration of cells. Cell loss typically was greater in the basal turn, where the implants were located, than at more apical locations. Increasing apical damage was a function of postimplant survival time. Preimplant local treatment of the inner ear with neomycin did not influence the loss of spiral ganglion cells. Osteoneogenesis occurred in the majority of cases, appearing in the basal turn with occasional extension into middle and apical turns. Cell loss was inconsistently associated with new bone formation. Electrical stimulation had no obvious influence on cell survival.