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Biomedical subjects

I Glass

Publications and source records attributed to I Glass.

27 records · Page 2Linked to original sources
PubMed1983

Responses of cells in the auditory cortex of awake squirrel monkeys to normal and reversed species-specific vocalizations.

Natural vocalizations and their artificial counterparts were found to be equally effective in evoking responses in auditory cortex units of awake squirrel monkeys. Neural responsiveness was presumably based primarily on the sensitivity of the units to acoustic transients embedded in the stimuli. For the left hemisphere, a significantly higher percentage of responding units was found in the primary compared to the secondary auditory cortex. However, the difference in the percentage of responding units between the primary and secondary auditory cortices was not significant for the right hemisphere.

Animals↗
PubMed1983

Auditory cortex responses to sequences of normal and reversed squirrel monkey vocalizations.

Responsiveness of auditory cortex (AC) units of awake squirrel monkeys to a natural sequence of species-specific calls was not significantly different from their responsiveness to a reverse playback of the sequence. No dependency was noted between the percentage of responding units and the average intensity of sounds, their spectral content or their order of presentation. The effectiveness of the sounds in eliciting responses was variable even when the sequence was produced in an unchanging behavioral context. Comparison of these findings with earlier results of individual vocalizations presented normally or backward in an isolated manner suggest that responsiveness of AC neurons to continuous sounds is lower than their responsiveness to isolated sounds, whether natural or artificial.

Animals↗
PubMed1979

Lability in the responses of cells in the auditory cortex of squirrel monkeys to species-specific vocalizations.

The activity of 28 cells located mainly in the secondary auditory cortex (A II) of awake squirrel-monkeys, was extracellularly recorded for periods of up to 6 h. Seven different species-specific vocalizations, which were repeatedly presented to the monkey, were used as auditory stimuli. Twenty-six cells responded, at least once, to one or more vocalizations; 22 cells revealed some change in their response (pattern or strength) to at least one vocalization ("change in response"). Twenty-one cells exhibited a change in the number and/or type of vocalization to which they responded during the recording period ("change in selectivity"). At some time during the recording period all the responding cells exhibited a "change in response" and/or a "change in selectivity" ("change in responsiveness"). A "change in response" of a cell to a vocalization did not necessarily exclude a "change in selectivity", associated with the same vocalization, later in time and vice-versa. A "change in responsiveness" to one vocalization was not necessarily correlated with "changes in responsiveness" to other vocalizations.

Acoustic Stimulation↗
PubMedDate not supplied

Left-right asymmetry of visual evoked potentials in brain-damaged patients: a mathematical model and experimental results.

The left-right asymmetry in the potential amplitude on the scalp was studied in poststroke patients by using flash visual evoked potential (VEP) and a numerical two-dimensional model of the head. The left-right asymmetry of the VEP was measured in three patients after thrombosis, in one after hemorrhage, and in one healthy subject. The numerical model used computed tomography images to define the different compartments of the head. The volume conductor equation for the potential distribution created by a dipole source in the occipital region was solved numerically with use of a finite volume method. Left-right asymmetry was calculated with several values of conductivity of the damaged region. The experimental results revealed a negative asymmetry in the three patients after thrombosis (i.e., the potential amplitude over the ischemic hemisphere was smaller than that over the intact hemisphere), whereas, in the patient after hemorrhage, a positive asymmetry was found. Nonsignificant left-right asymmetry was found in the healthy subject. The numerical model revealed that the electrical conductivity of the damaged tissue has a major effect on the left-right asymmetry. Negative asymmetry, such as that found for patients after thrombosis, was obtained when the conductivity of the damaged region was greater than that of the brain, whereas positive asymmetry (hemorrhage patient) was obtained when that conductivity was smaller than that of the brain. This finding indicates that the left-right asymmetry in the scalp VEP of patients after brain damage may be a result of changes in the conductivity of the volume conductor (the ischemic region) between the source and the electrodes.

Cerebrovascular Disorders↗
PubMedDate not supplied

Discrimination of complex electrical stimulation through a multichannel intracochlear implant.

A model has been developed to describe the electric fields generated in the inner ear when electrical stimuli are presented through a multichannel implant in the scala tympani of the cochlea. The model relies on the hypothesis that stimuli which excite the largest number of neural elements provide the greatest probability of successful discrimination by the implanted subject. It suggests that the effective stimulus is determined by the linear combination of electrical fields produced by the individual channels, and that excitation takes place in a spatially restricted area of the auditory nerve in the vicinity of the stimulating electrodes. The model was tested by biophysical measurements of the potential developed in the stimulated cochlea, and by a psychophysical study of the ability of a monkey to discriminate complex electrical signals using dual channel stimulation. The experimental findings are in agreement with the computer simulations.

Animals↗
PubMedDate not supplied

Impersistent execution of saccadic eye movements after traumatic brain injury.

A dynamic scoring system was developed to quantitatively resolve the ability of a subject to persistently execute a repeated motor act. Saccadic eye movements in response to pseudo-random and periodic stimuli were examined in patients with traumatic brain injury (TBI) and in normal subjects. Results indicated significantly lower dynamic persistence scores for the former group (50.5 +/- 32.2% vs 94.1 +/- 4.4%). Analysis of the patients' data revealed a stronger association of low scores with right hemisphere damage than with left hemisphere damage (39.4 +/- 28.9% vs 76.6 +/- 15.6%). Results are interpreted in terms of high-level attention impairments, not in terms of specific deficits in eye movement ability.

Adolescent↗