A study published online in Brain Advance Access (Brain, doi:10.1093/brain/awn308) may provide new insight into cortical plasticity. The abstract is provided here;to access the full article or for a subscription to Brain, please visit: https://brain.oxfordjournals.org/
Authors: Brian C. J. Moore, Department of Experimental Psychology, Cambridge University, Downing Street, Cambridge CB2 3EB, UK.
Vinay, Department of Audiology, All India Institute of Speech and Hearing, Manasagangothri, Mysore 570 006, India
Research using animals suggests that a lesion in the basal portion of the cochlea, causing a high-frequency 'dead region', leads to cortical reorganization, such that frequencies just below the edge frequency of the dead region, fe, become over-represented. We set out to determine if this reorganization has functional benefits. Two groups of subjects were tested, with and without acquired high-frequency dead regions, as assessed using the TEN(HL) test. For the ears with dead regions, the value of fewas close to 1000 or 1500 Hz. The two groups were matched in terms of audiometric thresholds for frequencies below feand in terms of age. Three subjects with unilateral dead regions (with matched low-frequency audiometric thresholds across ears) were also tested. Three tasks were used: (i) frequency discrimination of sinusoidal tones. The level of every stimulus was roved over a 12-dB range to reduce the salience of loudness cues. The center frequencies used ranged from 250 Hz to just below fe;(ii) detection of sinusoidal amplitude modulation of a sinusoidal carrier. Carrier frequencies of 500 and 800 Hz were used with all subjects, and an additional carrier frequency of 1200 Hz was used for ears with feclose to 1500 Hz and their matched counterparts. Modulation frequencies were 4, 50 and 100 Hz;(iii) identification of consonants in nonsense syllables. The syllables were lowpass filtered at 1000 or 1500 Hz (depending on the value of fe) and complementary highpass-filtered noise was presented to prevent use of information from neurons tuned above fe. For the frequency-discrimination task, the ears with dead regions showed a significant local improvement ('enhanced' thresholds) for frequencies just below fe, as has been reported previously. For the subjects with unilateral dead regions, the enhancement occurred only for the ears with dead regions. For the amplitude-modulation detection task, thresholds were generally lower for the ears with dead regions than for the ears without, and this effect was statistically significant. For the subjects with unilateral dead regions, thresholds were lower for the ears with dead regions than for the ears without. Consonant identification was significantly better for the ears with than without dead regions, and this was true for the subjects with unilateral dead regions. We conclude that a dead region at high frequencies is associated with a better ability to process information at low frequencies. These effects may reflect cortical plasticity induced by the dead regions.
Abbreviations: CD, compact disk;CF, characteristic frequency;F, step used in frequency discrimination task;DLF, difference limen for frequency;ERBN, equivalent rectangular bandwidth of the auditory filter for normal-hearing listeners;fcut-off, cut-off frequency of hearing loss;fe, edge frequency of a dead region;IHC, inner hair cell;LE, left ear;m, modulation index;RE, right ear;SD, standard deviation;SL, sensation level;SII, speech intelligibility index;TEN, threshold-equalizing noise
Enhanced Discrimination of Low-frequency Sounds for Subjects with High-frequency Dead Regions
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