Auditory evoked potentials to spectro-temporal modulation of complex tones in normal subjects and patients with severe brain injury

• DOI: 10.1093/brain/123.5.1007
• Publication Date: 2002-07-26T22:45:55Z
• Authors: S. J. Jones; M. Vaz Pato; L. Sprague; M. Stokes; R. Munday; N. Haque
• Keywords: Timbre; Musical tone; Magnetoencephalography; Tone (literature); Evoked potential

In order to assess higher auditory processing capabilities, long-latency evoked potentials (AEPs) were recorded synthesized musical instrument tones in 22 post-comatose patients with severe brain injury causing variably attenuated behavioural responsiveness. On the basis of normative studies, three different types spectro-temporal modulation employed. When a continuous `clarinet' tone changes pitch once every few seconds, N1/P2 are at latencies ~90 and 180 ms, respectively. Their distribution fronto-central region is consistent generators supratemporal cortex both hemispheres. modulated much faster rate (~16 changes/s), responses each change virtually abolished but similar still elicited by changing timbre (e.g. `oboe') seconds. These appear represent cortical processes concerned spectral pattern analysis grouping frequency components form sound `objects'. Following period 16/s oscillation between two pitches, more anteriorly distributed negativity on resumption steady pitch. Various lines evidence suggest that this probably equivalent `mismatch negativity' (MMN), reflecting pre-perceptual, memory-based process for detection patterns. This method requires no off-line subtraction AEPs onset tone, MMN produced rapidly robustly considerably larger amplitude (usually >5 μV) than discontinuous pure tones. brain-injured patients, presence or complex stimuli (in combined assessment authors who `blind' clinical data) was significantly associated demonstrable possession discriminative hearing (the ability respond differentially verbal commands, further author blind AEP findings). Behavioural electrophysiological findings accordance 18/22 could be had clear hearing. The absence should not, therefore, considered indicative complete functional deafness. Conversely, substantially preserved without Although not necessarily conscious `awareness', such preservation might help identify sentient prevented motor disability from communicating their perception.