Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Hearing loss wikipedia , lookup
Noise-induced hearing loss wikipedia , lookup
Sound localization wikipedia , lookup
Evolution of mammalian auditory ossicles wikipedia , lookup
Auditory processing disorder wikipedia , lookup
Audiology and hearing health professionals in developed and developing countries wikipedia , lookup
Olivocochlear system wikipedia , lookup
#1561 Lateralized plastic changes in unilateral hearing loss J. T. Devlin1, K. Lanary1, J. Raley1, E. Tunbridge1, A. Floyer-Lea1, C. Narain1, P. Jezzard1, M. Burton2, D. R. Moore3, P. M. Matthews1 1Centre for Functional Magnetic Resonance Imaging of the Brain, University of Oxford, U. K. 2ENT Department, Radcliffe Infirmary, Oxford, U. K. 3MRC Institute of Hearing Research, Nottingham, U. K. Results Summary Unilateral deafness by cochlear ablation in animals produces a dramatic increase in the level of neural activity in the inferior colliculus and auditory cortex on the side of the intact ear to acoustic stimulation of that ear. Previous fMRI studies1 appear to confirm this finding in humans who have unilateral sensorineural hearing loss. Here we asked whether long term unilateral hearing loss in humans changes the symmetry of pure tone BOLD activation in the supratemporal plane. In primary auditory cortex there was a clear laterality effect. Relative to silence, tones presented to the left ear led to greater left hemisphere activity, as seen previously in normals2. Right ear stimulation, on the other hand, led to more bilateral activation – a reduction of the normal left hemisphere advantage – and this was due to an increase in ipsilateral activation. In non-primary auditory cortex unilateral hearing loss did not change the normal contralateral dominance. Table 2. Monaural tones relative to silence activated Heschl’s gyrus and adjacent non-primary areas bilaterally Figure 2: Auditory cortex activations Right hemisphere Left hemisphere PreCS IPS CS SMG PreCS PreCS IFS PT STG HG Insula PP CS IPS SMG PTr PTr STS MTG TP 7 sensorineural hearing loss (SNHL) 5 conductive hearing loss (CHL) Patients Significance 0.7% (0.10) 0.5% (0.09) 0.8% (0.08) 0.5% (0.09) n.s. n.s. Right ear stimulation L. PAC 0.9% (13.4) R. PAC 0.3% (0.10) 0.9% (0.20) 0.6% (0.12) n.s. p<0.08 Left ear stimulation L. PAC R. PAC PT Insula PP HG STG MTG TP Left ear stimulation Thus the reduction in laterality in patients with unilateral hearing loss in their left ear was due to an increase in activation in PAC ipsilateral to the stimulated (i.e. right) ear. Non-primary auditory cortex Defined as areas adjacent to PAC which were activated by the tone vs. silence comparison in the group Right ear stimulation HG removed Masked p<10-7 The upper panels display lateral views of the inflated left and right hemisphere surfaces with sulci and gyri shown in dark and light grey, respectively. The middle and bottom panels show activation in cortical auditory fields due to left and right ear stimulation. 11 patients with long term unilateral hearing loss Controls STS p<0.01 Participants Mean (±SEM) percent BOLD signal change for tones relative to silent trials in PAC. 1 2 3 Step 1: Tones vs. silence in RFX (cluster stats: Z>2.3, p<0.05) Step 2: Anatomically masked to include coordinates of human non-primary areas4 Step 3: Removed individual subject’s HG Figure 4: Laterality indices in non-primary areas 12 normal hearing controls Left ear stimulation Laterality calculations Type of Affected Duration Hearing loss Gender Ear (yrs) SNHL F R 23 SNHL M L 20 SNHL F R 16 SNHL M R 12 SNHL M R 12 SNHL F L 9 SNHL M L 8 CHL F L 2 CHL M R 6 CHL F L 20 CHL M R 18 Severity (threshold) Etiology Mod.-Sev. (65-75dB) Profound (>90dB) Profound (>95dB) Profound (>95dB) Profound (>95dB) Profound (>95dB) Profound (>95dB) Mild (36.25dB) Mild-Mod. (46.25dB) Moderate (57.5dB) Moderate (60dB) To assess relative laterality of auditory cortex responses, we computed a Laterality Index (LI): Possibly mumps Possibly mumps (Contralateral - Ipsilateral BOLD signal change) × 100 LI = (Contralateral + Ispilateral BOLD signal change) Possibly mumps +100 indicates completely contralateral activation -100 indicates completely ipsilateral activation Unknown Unknown Using mean signal change avoided biasing the laterality calculation through (1) an arbitrary statistical threshold for counting “active” voxels, or (2) differences in the volume of the ROIs across hemispheres (i.e. partial volume effects). Possibly maternal rubella Possibly viral Otosclerosis Perforated ear drum Otosclerosis Current Study E.g.: The current study used sparse sampling3 to measure cortical auditory responses to monaurally presented tones Figure 3: Laterality indices in PAC Left ear stimulation Figure 1: Sparse sampling paradigm Laterality index 0.5 50 0 5 Tone 10 15 20 25 Time (seconds) Scanner Scanner Tone 30 35 Participants discriminated between high (4000Hz) and low (250Hz) frequency tones (90db SPL) by pressing one of two buttons as quickly as possible after the tone onset. Half of all trials had a silent stimulus. The purpose of the task was simply to control attention by forcing participants to attend to the tones throughout the scanning. Normal group means Right ear stimulation 0.5 50 0.3 30 0.3 30 10 0.1 10 0.1 * R -10 -0.1 -10 -0.1 -30 -0.3 -30 -0.3 -50 -0.5 Stimulation Paradigm Normal group means 0.1 10 100.1 0.0 0 0.0 0 (p<0.05) * (n.s.) -10 -0.1 -10 -0.1 -20 -0.2 -30 -0.2 In non-primary auditory cortex, there were no significant differences between the HL patients and the normal controls. Discussion Like previous studies, we observed a reduction in the normal contralateral advantage for auditory processing in patients with unilateral hearing loss1,5. The current study, however, qualifies these findings in two important ways: Primary auditory cortex The majority of primary auditory cortex (PAC) is located on Heschl’s gyrus and was therefore identified on each participant’s structural scan as an anatomic correlate of PAC. Expected BOLD signal 200.2 1. Plastic changes were limited to primary auditory cortex and not found in the adjacent non-primary regions, and Congenital atresia of external canal The threshold value represents the patient’s average for 500Hz, 1kHz, 2kHz, and 4kHz pure tone audiometry. 0.2 20 Laterality index Table 1. Patient details Right ear stimulation n.s. -50 -0.5 CHL patients SNHL patients Patient mean (±SEM) For right ear stimulation, HL patients showed a significant reduction in the normal contralateral dominance. In fact, there was no significant laterality effect in these patients. There were no significant differences between the HL patients and the normal controls for left ear stimulation. Both groups showed a strong ipsilateral (i.e. left hemisphere) dominance. 2. Only right ear stimulation led to a reduced laterality effect and this was due to an increase in ipsilateral activation rather than a reduction in contralateral activity. If BOLD signal primarily reflects synaptic metabolic demands6, then the observed changes are consistent with animal studies showing substantial sub-cortical activation increases on the side of the stimulated ear. Unlike other species, however, in humans this effect is only present for right ear stimulation. This may be due to the fact that humans appear to be unique in that they display a left hemisphere dominance for processing simple monaurally presented auditory stimuli2. In other words, a strong sub-cortical path already exists in humans leading from the left ear to left PAC which may not need to be strengthened in the event of hearing loss in the right ear. References 1. Bilecen, D., Seifritz, E., Radu, E. W., Schmid, N., Wetzel, S., Probst, R., & Scheffler, K. (2000). Cortical reorganization after acute unilateral hearing loss traced by fMRI. Neurology, 54(3), 765-767. 2. Devlin, J. T., Raley, J., Tunbridge, E., Lanary, K., Floyer-Lea, A., Narain, C., Cohen, I., Behrens, T. E. J., Jezzard, P., Matthews, P. M., & Moore, D. R. (in submission). Functional asymmetry for auditory processing in human primary auditory cortex. (See also Poster #1448.) 3. Hall, D. A., Haggard, M. P., Akeroyd, M. A., Palmer, A. R., Summerfield, A. Q., Elliot, M. R., Gurney, E. M., & Bowtell, R. W. (1999). "Sparse" temporal sampling in auditory fMRI. Human Brain Mapping, 7, 213-223. 4. Rivier, F., & Clarke, S. (1997). Cytochrome oxidase, acetylcholinesterase, and NADPH-diaphorase staining in human supratemporal and insular cortex: Evidence for multiple auditory areas. NeuroImage, 6, 288-304. 5. Scheffler, K., Bilecen, D., Schmid, N., Tschopp, K., & Seelig, J. (1998). Auditory cortical responses in hearing subjects and unliateral deaf patients as detected by functional magnetic resonance imaging. Cerebral Cortex, 8, 156-163. 6. Logothetis, N. K., Pauls, J., Augath, M., Trinath, T., & Oeltermann, A. (2001). Neurophysiological investigation of the basis of the fMRI signal. Nature, 412(6843), 150-157.