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Biomedical subjects

M M Merzenich

Publications and source records attributed to M M Merzenich.

At least 127 records · Page 7Linked to original sources
PubMed1978

Genesis of the round window rupture syndrome; some experimental observations.

Clinical and experimental evidence has revealed that rupture of the round window membrane, by itself, is not a major cause of sensorineural hearing loss. Eighteen guinea pigs underwent removal of the round window. The status of cochlear function was determined by recording the cochlear microphonic. An average loss of only about 6 db was observed after surgery. It is felt that there must commonly be more cochlear damage concurrent with window rupture to explain the significant and often relatively immediate hearing losses seen in clinical practice. The site(s) of this primary trauma has not yet been discovered, but it would seen reasonable in the light of recent reports that the perilymphatic vessels, the vas spirale, the stria vascularis and/or the intergrity of the cochlear duct might be involved in the genesis of this hearing loss. We propose that the term "round window rupture syndrome" be used as a more accurate description of this entity. The round window damage provides evidence of more devastating trauma within the cochlea. Thus, the clinician, being alerted, should not stop his therapeutic efforts with surgical closure of the RW. Better prognosis for the patient, as well as leading into new avenues for the investigation of cochlear function, would be the result.

Animals↗
PubMed1977

Multielectrode intracochlear implants. Nerve survival and stimulation patterns.

A series of neurophysiological and anatomical experiments have been performed on cats implanted on a long-term basis with scala tympani electrodes. Auditory nerve survival was assessed for both neomycin sulfate-deafened and previously normal-hearing cats three weeks to 30 months after electrode implantation. Acute neurophysiological experiments were performed on nearly all of the cats and the spatial response to electrical stimulation was determined. The results of these experiments suggest that the auditory nerve can withstand surgical implantation and the long-term interface with scala tympani electrodes. In addition, restricted portions of the auditory nerve can be discretely excited with bipolar stimulation. Monopolar stimulation produced a very broad excitation pattern. These findings have important implications for the application of multielectrode prosthetic devices to the profoundly deaf.

Animals↗
PubMed1976

Auditory cortex in the grey squirrel: tonotopic organization and architectonic fields.

The representation of sound frequency within auditory cortex has been investigated with microelectrode mapping techniques in grey squirrels. The cyto- and myeloarchitecture of mapped cortical surfaces was examined and related to recording data. Among the results were the following: (1) A primary field can be defined on the basis of both physiological and anatomical criteria.

Animals↗
PubMed1975

Representation of cochlea within primary auditory cortex in the cat.

The representation of sound frequency (and of the cochlear partition) within primary auditory cortex has been investigated with use of microelectrode-mapping techniques in a series of 25 anesthetized cats. Among the results were the following: 1) Within vertical penetrations into AI, best frequency and remarkably constant for successively studied neurons across the active middle and deep cortical layers. 2) There is an orderly representation of frequency (and of represented cochlear place) within AI. Frequency is rerepresented across the mediolateral dimension of the field. On an axis perpendicular to this plane of rerepresentation, best-frequency (represented cochlear place) changes as a simple function of cortical location. 3) Any given frequency band (or sector of the cochlear partition) is represented across a belt of cortex of nearly constant width that runs on a nearly straight axis across AI. 4) There is a disproportionately large cortical surface representation of the highest-frequency octaves (basal cochlea) within AI. 5) The primary and secondary field locations were somewhat variable, when referenced to cortical surface landmarks. 6) Data from long penetrations passing down the rostral bank of the posterior ectosylvian sulcus were consistent with the existence of a vertical unit of organization in AI, akin to cortical columns described in primary visual and somatosensory cortex. 7) Responses to tonal stimuli were encountered in fields dorsocaudal, caudal, ventral, and rostral to AI. There is an orderly representation of the cochlea within the field rostal to AI, with a reversal in best frequencies across its border with AI. 8) Physiological definitions of AI boundaries are consistent with their cytoarchitectonic definition. Some of the implications of these findings are discussed.

Acoustic Stimulation↗
PubMedDate not supplied

Complex sound analysis (frequency resolution, filtering and spectral integration) by single units of the inferior colliculus of the cat.

The central nucleus of the inferior colliculus (ICC) is a center of convergence of brainstem input and is critical for auditory information processing. Here, the analysis of complex sound spectra by single neurons in the ICC is investigated. Several measures of frequency resolution (excitatory/inhibitory tuning curves, effective bandwidths, critical ratio bands, critical bands derived using narrowband masking and two-tone separation paradigms) have been obtained from the responses of these neurons at sound pressure levels (SPL) up to 80 dB above the units' response thresholds (nearly 110 dB SPL). Among our results are the following: (1) Narrowband masking measures of critical bands from ICC neurons closely parallel behavioral measures using the same stimulus paradigm. (2) Frequency resolution power as measured by critical bandwidths varies little as a function of stimulus intensity. (3) Tuning curves of ICC neurons provide no simple basis for predicting the frequency filtering of the same neurons excited by complex sound spectra. (4) There is a frequency dependence of all measures of frequency resolution similar to that found in psychophysical determinations of critical bandwidths. That is, spatial frequency resolution in the cochlea is the origin for the resolution found in the ICC and in behavioral tests. (5) Lateral inhibition at the level of the ICC clearly plays a role in frequency resolution. (6) Frequency resolution is encoded by response rate changes of ICC neurons and is independent of tone response threshold, response latency, spontaneous activity, tone response type, binaural response type. It is concluded that spectral analysis of sound is established by processes, including lateral inhibition, independent of other basic response properties of neurons at the level of the ICC.

Acoustic Stimulation↗
PubMedDate not supplied

Reorganization of cortical representations of the hand following alterations of skin inputs induced by nerve injury, skin island transfers, and experience.

Tactile experiences remodel the central nervous system representations of the body surface. The results of assessments of ten peripheral manipulations that reveal different aspects of representational plasticity are reviewed: (1) chronic peripheral denervation; (2) surgical amputation; (3) digital syndactyly and its natural behavioral equivalents; (4) peripheral nerve crush with reinnervation; (5) peripheral nerve transection and repair, with reinnervation; (6) denervation of very large skin surfaces, for very long times; (7) electrical stimulation of large-fiber afferents in the median nerve, simulating electroacupuncture; (8) implantation of always-innervated island pedicle flaps; (9) behavioral training with locationally invariant stimuli; and (10) behavioral training with moving stimuli. Focus is on the changes recorded in a primary somatosensory cortical field, area 3b, following these ten manipulations, in adult monkeys. On the basis of these findings, the following are discussed: (1) how altered schedules of activity from the skin contribute to cortical representational remodeling; (2) other factors that influence the representational remodeling; (3) where the remodeling actually occurs; and (4) some implications of these findings for sensory rehabilitation.

Amputation, Surgical↗
PubMedDate not supplied

Expansion of the cortical representation of a specific skin field in primary somatosensory cortex by intracortical microstimulation.

Intracortical microstimulation (ICMS) was applied to a single site in the middle cortical layers (III-IV) in the koniocortical somatosensory fields of sodium pentobarbital-anesthetized rats (Sml) and new world monkeys (area 3b). Low-threshold cutaneous receptive fields were defined in the cortical region surrounding the stimulation site prior to and following 2-6 hr of 5 microA ICMS stimulation. ICMS stimulation did not usually affect the receptive field location, size, or responsiveness to tactile stimulation of neurons at the stimulation site. However, the number of cortical neurons surrounding the stimulation site with a receptive field that overlapped with the ICMS-site receptive field increased in all studied animals, resulting in an enlarged cortical representation of a restricted skin region spanning several hundred microns. The mean size of receptive fields changed in some but not all cases. These results provide evidence that the responses of cortical neurons are subject to change by the introduction of locally coincident inputs into a single location, and demonstrate a capacity for representational plasticity in the neocortex in the absence of peripheral stimulation. These experimental observations are consistent with hypotheses that the cerebral cortex comprises radially oriented populations of neurons that share a common input, and that these inputs are shaped by coincident activity (see Edelman, 1978, 1987; Merzenich, 1987; Merzenich et al., 1990; von der Malsburg and Singer, 1988).

Animals↗