Distinct gamma-band evoked responses to speech and non-speech sounds in humans.
To understand spoken language, the human brain must have fast mechanisms for the representation and identification of speech sounds. Stimulus-induced synchronization of neural activity at gamma frequencies (20-80 Hz), occurring in humans at 200-300 msec from stimulus onset, has been suggested to be a possible mechanism for neural object representation. Auditory and visual stimuli also evoke an earlier (peak <100 msec) gamma oscillation, but its dependence on high-level stimulus parameters and, thereby, its involvement in object representation has remained unclear. Using whole-scalp magnetoencephalography, we show here that responses evoked by speech and non-speech sounds differed in the gamma-frequency but not in the low-frequency (0.1-20 Hz) band as early as 40-60 msec from stimulus onset. The gamma-band responses to the speech sound peaked earlier in the left than in the right hemisphere, whereas those to the non-speech sound peaked earlier in the right hemisphere. For the speech sound, there was no difference in the response amplitude between the hemispheres at low (20-45 Hz) gamma frequencies, whereas for the non-speech sound, the amplitude was larger in the right hemisphere. These results suggest that evoked gamma-band activity may indeed be sensitive to high-level stimulus properties and may hence reflect the neural representation of speech sounds. Consequently, speech-specific neuronal processing may commence no later than 40-60 msec from stimulus onset, possibly in the form of activation of language-specific memory traces.
Palva
Satu
S
Cognitive Brain Research Unit, Department of Psychology, FIN-00014 University of Helsinki, Finland. satu.palva@helsinki.fi
Palva
J Matias
JM
Shtyrov
Yury
Y
Kujala
Teija
T
Ilmoniemi
Risto J
RJ
Kaila
Kai
K
Näätänen
Risto
R
D000161:Acoustic Stimulation / Q000379:methods; D000704:Analysis of Variance; D001683:Biological Clocks / Q000502:physiology; D004292:Dominance, Cerebral / Q000502:physiology; D004585:Electrooculography; D005072:Evoked Potentials, Auditory / Q000502:physiology*; D006801:Humans; D015225:Magnetoencephalography; D009622:Noise; D010699:Phonation / Q000502:physiology; D011930:Reaction Time / Q000502:physiology; D012815:Signal Processing, Computer-Assisted; D013067:Speech Perception / Q000502:physiology*