PubMed Health⌕ Search

Biomedical subjects

J P Vasama

Publications and source records attributed to J P Vasama.

At least 19 recordsLinked to original sources
PubMed2001

Plasticity in the adult human central auditory system: evidence from late-onset profound unilateral deafness.

Experience-related changes in central nervous system (CNS) activity have been observed in the adult brain of many mammalian species, including humans. In humans, late-onset profound unilateral deafness creates an opportunity to study plasticity in the adult CNS consequent to monaural auditory deprivation. CNS activity was assessed by measuring long-latency auditory evoked potentials (AEPs) recorded from teens and adults with late-onset (post-childhood) profound unilateral deafness. Compared to monaurally stimulated normal-hearing subjects, the AEPs recorded from central electrode sites located over auditory cortical areas showed significant increases in inter-hemispheric waveform cross-correlation coefficients, and in inter-hemispheric AEP peak amplitude correlations. These increases provide evidence of substantial changes from the normal pattern of asymmetrical (contralateral > ipsilateral amplitude) and asynchronous (contralateral earlier than ipsilateral) central auditory system activation in the normal-hearing population to a much more symmetrical and synchronous activation in the unilaterally deaf. These cross-sectional analyses of AEP data recorded from the unilaterally deaf also suggest that the changes in cortical activity occur gradually and continue for at least 2 years after the onset of hearing loss. Analyses of peak amplitude correlations suggest that the increased inter-hemispheric symmetry may be a consequence of changes in the generators producing the N (approximately 100 ms peak latency) potential. These experience-related changes in central auditory system activity following late-onset profound unilateral deafness thus provide evidence of the presence and the time course of auditory system plasticity in the adult brain.

Adolescent↗
PubMed2001

Auditory pathway function after vestibular schwannoma surgery.

We studied seven patients before and after vestibular schwannoma surgery. Four patients became unilaterally profoundly deaf and three patients preserved their hearing. Cortical responses were recorded with a 122-channel whole-scalp SQUID neuromagnetometer using tone-burst stimuli to the healthy ear. Brainstem auditory evoked potentials (BAEPs) were measured using alternating clicks. Ten healthy volunteers served as a control group. In patients, preoperative cortical response latencies and strengths did not differ significantly from those of controls. However, 6 months after the operation the latency was, on average, 7 ms longer than preoperatively over both hemispheres. BAEPs were in the normal range both before and after the operation. These results suggest that unilateral lesion in peripheral auditory pathways also affects cortical reactivity to stimuli presented to the non-affected ear, possibly reflecting altered binaural interaction in the auditory pathways.

Adult↗
PubMed2000

Tympanic neurectomy and chronic parotitis.

The preoperative findings and operative outcome were evaluated in 49 patients who underwent tympanic neurectomy to treat chronic parotitis. Forty-two patients had chronic non-suppurative parotitis and 7 patients had chronic suppurative parotitis. The main symptoms prior to operation were recurrent swelling and pain of the parotid gland. After operation, 40 patients (82%) had relief of their symptoms (28 patients were totally free of symptoms and 12 patients were markedly improved). In 9 patients (18%) the symptoms remained the same. Three patients (6%) had a tympanic membrane perforation due to the operation.

Adolescent↗
PubMed2000

Auditory cortical responses in patients with Bell's palsy.

We recorded auditory evoked magnetic responses with a whole-scalp 122-channel SQUID neuromagnetometer in 14 patients with Bell's palsy (9 with left-sided and 5 with right-sided) and in 10 controls. The stimuli were 50-ms 1-kHz tone bursts, delivered first to the left and then to the right ear at interstimulus intervals (ISIs) of 1, 2 and 4 s. In patients, the N100m, the 100-ms response originating in the auditory cortices peaked, on average, 8 ms earlier and the response strengths were, on average, 7 nAm stronger over the contralateral than ipsilateral hemisphere. The response latencies and strengths did not differ significantly from those of controls and there were no significant differences in response latencies and strengths between the stimulation of the affected and healthy side. On average, the response latencies and strengths increased as a function of ISI over both hemispheres both in patients and in controls. These findings suggest that Bell's palsy is an isolated peripheral neuropathy that does not affect the function of the auditory pathways.

Adult↗
PubMed2000

Idiopathic sudden sensorineural hearing loss: temporal bone histopathologic study.

We microscopically examined the temporal bones of 12 ears with idiopathic sudden sensorineural hearing loss (iSSNHL), 10 ears with presbycusis, 11 ears with normal hearing, and 8 unaffected contralateral ears of patients with iSSNHL. The degeneration of the spiral ligament, vascular stria, hair cells, dendrites, and apical spiral ganglion cells was greater in ears with iSSNHL than in the other groups. The apical ganglion cells were significantly more affected than the basal ganglion cells, and the spiral ganglion cell loss increased as a function of duration of iSSNHL. Cochlear ossification was found in 1 ear with iSSNHL, and hydrops in 2. These findings suggest a viral rather than a vascular or ruptured inner ear membrane origin for iSSNHL.

Adult↗
PubMed1999

Meniere's disease and endolymphatic hydrops without Meniere's symptoms: temporal bone histopathology.

We studied temporal bone histopathology in 21 ears with Meniere's disease and 24 ears with endolymphatic hydrops without Meniere's symptoms and compared the findings to those in 10 ears with presbycusis and 11 ears with normal hearing. Normal hearing ears showed less degeneration of cochlear structures than the other ears. In ears with endolymphatic hydrops without Meniere's symptoms, the degeneration of spiral ligament, hair cells, dendrites (peripheral processes) and apical spiral ganglion cells was more severe than in the other three groups. In ears with Meniere's disease and endolymphatic hydrops without Meniere's symptoms, the hair cells and dendrites were more affected than ganglion cells and there was no correlation between hair cell and ganglion cell degeneration. These findings suggest that a permanent threshold shift in late stage endolymphatic hydrops is not related to ganglion cell loss but rather to degeneration of sensory elements.

Aged↗
PubMed1999

Effect of intratympanic gentamicin on hearing and tinnitus in Meniere's disease.

OBJECTIVE: The objective of this study was to examine the effect of intratympanically applied gentamicin (GM) (30 mg/mL) on hearing and tinnitus in patients with intractable Meniere's disease. STUDY DESIGN: A prospective study was conducted on 93 subjects treated with intratympanically applied GM. The mean pure-tone average (PTA) at speech frequencies was measured before the treatment and after 2 weeks, 1 month, 3 months, 6 months, 1 year, and 2 years after injections. Tinnitus was surveyed with a questionnaire. The mean duration of Meniere's disease was 9.8 years (range, 1-33 years). PATIENTS: The study group consisted of 28 men and 65 women. The mean age was 50.9 years (range, 19-74 years). RESULTS: The mean PTA at speech frequencies for the group worsened from 60 dB to 68 dB, which was statistically significant. Ten ears were deafened. The mean tinnitus handicap score before treatment was 2.92; 2 years after treatment, it was 2.26, indicating significant abatement of tinnitus during the course of the treatment. CONCLUSIONS: The authors found that the average frequency of deafening was 10% and it was dose dependent. GM caused alleviation of tinnitus in the majority of the patients.

Administration, Topical↗
PubMed1998

Modification of auditory pathway functions in patients with hearing improvement after middle ear surgery.

We recorded auditory-evoked magnetic responses with a whole-scalp 122-channel neuromagnetometer from seven adult patients with unilateral conductive hearing loss before and after middle ear surgery. The stimuli were 50-msec 1-kHz tone bursts, delivered to the healthy, nonoperated ear at interstimulus intervals of 1, 2, and 4 seconds. The mean preoperative pure-tone average in the affected ear was 57 dB hearing level; the mean postoperative pure-tone average was 17 dB. The 100-msec auditory-evoked response originating in the auditory cortex peaked, on average, 7 msecs earlier after than before surgery over the hemisphere contralateral to the stimulated ear and 2 msecs earlier over the ipsilateral hemisphere. The contralateral response strengths increased by 5% after surgery; ipsilateral strengths increased by 11%. The variation of the response latency and amplitude in the patients who underwent surgery was similar to that of seven control subjects. The postoperative source locations did not differ noticeably from preoperative ones. These findings suggest that temporary unilateral conductive hearing loss in adult patients modifies the function of the auditory neural pathway.

Adaptation, Physiological↗
PubMed1998

Microvascular decompression of the cochlear nerve in patients with severe tinnitus. Preoperative findings and operative outcome in 22 patients.

We evaluated the operative outcome in 22 consecutive patients who underwent microvascular decompression (MVD) of the intracranial portion of the cochlear nerve to relieve incapacitating tinnitus and related it to preoperative findings. The patients were selected for operation from the following criteria: severe tinnitus with sensorineural hearing loss and/or changes in brainstem auditory evoked potentials (BAEPs). Fifty percent had unilateral tinnitus. Before operation, 17 patients (77%) had sensorineural hearing loss in their affected ear. BAEPs were abnormal in 21 patients (95%) and acoustic middle ear reflex response was abnormal in six patients (27%). Vascular compression of the cochlear nerve was found in all patients during the operation. After the operation, 33% had relief of their tinnitus (two patients were totally free of tinnitus and five were markedly improved). Eight patients were slightly improved (38%), and the tinnitus did not change in four patients; two patients (10%) became worse. Of the patients with unilateral tinnitus, 63% had relief of their tinnitus. In one patient hearing was noticeably improved after the operation. Five patients (23%) had mild to moderate sensorineural hearing loss due to the operation. No other complications were detected.

Adult↗
PubMed1997

Auditory cortical responses in humans with profound unilateral sensorineural hearing loss from early childhood.

We recorded auditory evoked magnetic fields from five patients with profound unilateral sensorineural hearing loss from early childhood, using a 122-channel whole-scalp neuromagnetometer. The stimuli were 50-ms 1-kHz tone bursts delivered to the healthy ear at interstimulus intervals (ISI) of 1, 2, and 4 s. As the normal-hearing controls, four patients had shorter latencies of N100m, the 100-ms response, over the hemisphere contralateral to the stimulation than over the ipsilateral hemisphere. With 1-s ISI, three patients had, instead of N100m, a deflection of opposite polarity at about 100 ms (P100m) after the stimulus onset. A 10-year-old patient had a prominent P100m response, did not produce a clear N100m at any ISI, but had a clear N50m at the 4-s ISI. Four patients had bilateral N200m deflections peaking about 200 ms after the stimulus onset; the fifth patient showed N200m over the right hemisphere. N200m was also observed in the three youngest controls in both hemispheres. The ISI dependence of N100m amplitude and latency was similar in controls and patients. The amplitudes and latencies of N200m did not show any ISI dependence. In patients, the appearance of P100m-N200m deflections of auditory evoked fields, normally present in children, is more pronounced than in controls. The defect apparently delays the development of N100m, possibly by interfering with function of callosal connections.

Acoustic Stimulation↗
PubMed1995

Abrupt unilateral deafness modifies function of human auditory pathways.

We studied nine patients with unilateral abrupt deafness caused by acoustic neuroma surgery. Cortical responses to tones delivered to the intact ear were recorded postoperatively with a 122-channel whole-scalp neuromagnetometer. In three patients, followed for 12 months with 2-4 measurements, evoked responses originating in the auditory cortices were weak and delayed one month after the operation in both hemispheres. During the follow-up, the amplitudes reached the control level. No response abnormalities were found in patients who were studied 1.5-4.5 years after the operation. Our findings suggest that abrupt unilateral deafness causes immediate changes in the function of auditory pathways of adult humans and that reorganization takes place within 1 year.

Adolescent↗
PubMed1995

Auditory pathway plasticity in adult humans after unilateral idiopathic sudden sensorineural hearing loss.

We recorded auditory evoked magnetic fields from 8 patients with unilateral, idiopathic, sudden, sensorineural hearing loss and from 8 healthy controls, using a 122-channel whole-scalp neuromagnetometer. The stimuli were 50-ms l-kHz tone bursts, delivered to the healthy ear at interstimulus intervals (ISIs) of 1, 2, 4, 8, and 16 s. On average, as in normal-hearing controls, the dipole moments and the latencies of N100m, the 100-ms response, increased as a function of ISI over both hemispheres to left- and right-ear stimulation. Four patients had shorter response latencies and 4 had stronger dipole moments over the hemisphere ipsilateral to the stimulation. In 3 patients, one additional source was observed over the anterolateral right hemisphere and another near head midline. These findings suggest that unilateral sensorineural hearing loss may modify information processing in the central auditory pathways.

Acoustic Stimulation↗
PubMed1995

Effects of intensity variation on human auditory evoked magnetic fields.

We recorded auditory evoked magnetic fields from 6 healthy subjects with a 122-channel whole-head neuromagnetometer. The stimuli were 200-ms 1-kHz tones delivered at 4 different intensities (40, 50, 60, and 65 dB HL). The tones were given once every second, binaurally in the first session, and monaurally to each ear in the second one. The four intensities were presented randomly and equiprobably within a single sequence. In both stimulus conditions, the 100-ms response (N100m) decreased in latency and increased in amplitude as a function of intensity in both hemispheres. No systematic dependence was found between stimulus intensity and the N100m source location in the auditory cortex. Our study illustrates a noninvasive method to examine the functional properties of human auditory cortex, allowing simultaneous comparison between signals arising from both hemispheres.

Acoustic Stimulation↗
PubMed1994

Auditory cortical responses in humans with congenital unilateral conductive hearing loss.

We recorded auditory evoked magnetic fields from 6 patients with congenital unilateral conductive hearing disorder with a 122-channel whole-head neuromagnetometer. The stimuli were 50-ms 1-kHz tones delivered to the better ear at interstimulus intervals (ISIs) of 2 and 8 s at two different intensities (50 and 70 dB HL). As in normal-hearing subjects, the amplitudes of N100m, the 100-ms response, were larger in 5 patients and the latencies were shorter in 3 patients over the hemisphere contralateral to stimulation. However, in one patient N100m peaked already at 61 ms over the contralateral hemisphere and amplitudes were larger over the ipsilateral hemisphere, possibly reflecting reorganization of the auditory pathways. In 3 patients the latencies were shorter over the ipsilateral hemisphere. The effects of ISI and intensity were similar over both hemispheres and did not differ from those in controls. It seems that congenital unilateral conductive hearing loss does not necessarily lead to any gross disturbances in the human auditory cortex.

Acoustic Stimulation↗
PubMed1994

Human auditory cortical mechanisms of sound lateralisation: III. Monaural and binaural shift responses.

Neuromagnetic responses were recorded over the whole head with a 122-channel gradiometer. A pair of 150-ms 1-kHz tones separated by an interval of 150 ms was presented to one ear every 2 s. The other ear received either no input, an identical pair simultaneous to the first, an identical pair alternating with the first or a continuous 600-ms tone. The 'monaural shift' condition in which stimuli alternated between ears produced a clear perception of changing lateralisation, but the evoked response could be explained as merely the sum of simple monaural onset and offset responses; thus we found no evidence for a separate response to interaural intensity difference in this condition. The 'binaural shift' condition, in which intensity changed in one ear while the other received a continuous tone, evoked a transient response (N130m) at a latency of about 130 ms. N130m was larger over the hemisphere contralateral to the direction of shift, and larger than the corresponding monaural response, whether to an onset or an offset. We concluded that N130m also was not a separate directional response, but was analogous to a simple monaural response, the prolonged latency being due to masking and the enhanced amplitude to facilitation by the sustained response to the continuous tone.

Adult↗