Neurophysiological origin of human brain asymmetry for speech and language.
The physiological basis of human cerebral asymmetry for language remains mysterious. We have used simultaneous physiological and anatomical measurements to investigate the issue. Concentrating on neural oscillatory activity in speech-specific frequency bands and exploring interactions between gestural (motor) and auditory-evoked activity, we find, in the absence of language-related processing, that left auditory, somatosensory, articulatory motor, and inferior parietal cortices show specific, lateralized, speech-related physiological properties. With the addition of ecologically valid audiovisual stimulation, activity in auditory cortex synchronizes with left-dominant input from the motor cortex at frequencies corresponding to syllabic, but not phonemic, speech rhythms. Our results support theories of language lateralization that posit a major role for intrinsic, hardwired perceptuomotor processing in syllabic parsing and are compatible both with the evolutionary view that speech arose from a combination of syllable-sized vocalizations and meaningful hand gestures and with developmental observations suggesting phonemic analysis is a developmentally acquired process.
Morillon
Benjamin
B
Institut National de la Santé et de la Recherche Médicale U960-Ecole Normale Supérieure, 75005 Paris, France.
Lehongre
Katia
K
Frackowiak
Richard S J
RS
Ducorps
Antoine
A
Kleinschmidt
Andreas
A
Poeppel
David
D
Giraud
Anne-Lise
AL
D000328:Adult; D001303:Auditory Cortex / Q000502:physiology; D001921:Brain / Q000033:anatomy & histology / Q000502:physiology*; D004292:Dominance, Cerebral / Q000502:physiology*; D004569:Electroencephalography; D006801:Humans; D007802:Language; D008279:Magnetic Resonance Imaging; D008297:Male; D009044:Motor Cortex / Q000502:physiology; D013060:Speech / Q000502:physiology*; D055815:Young Adult