Automatic domain-general processing of sound source identity in the left posterior middle frontal gyrus.

Identifying sound sources is fundamental to developing a stable representation of the environment in the face of variable auditory information. The cortical processes underlying this ability have received little attention. In two fMRI experiments, we investigated passive adaptation to (Exp. 1) and explicit discrimination of (Exp. 2) source identities for different categories of auditory objects (voices, musical instruments, environmental sounds). All cortical effects of source identity were independent of high-level category information, and were accounted for by sound-to-sound differences in low-level structure (e.g., loudness). A conjunction analysis revealed that the left posterior middle frontal gyrus (pMFG) adapted to identity repetitions during both passive listening and active discrimination tasks. These results indicate that the comparison of sound source identities in a stream of auditory stimulation recruits the pMFG in a domain-general way, i.e., independent of the sound category, based on information contained in the low-level acoustical structure. pMFG recruitment during both passive listening and explicit identity comparison tasks also suggests its automatic engagement in sound source identity processing.

Cerebral response to 'voiceness': a functional magnetic resonance imaging study.

We evaluated the response of the voice-selective areas of the auditory cortex to sound 'voiceness', that is, the degree to which an auditory stimulus resembles human voice. Normal participants were scanned using event-related functional magnetic resonance imaging while passively listening to stimuli drawn from a 'voiceness' continuum generated via auditory morphing between sounds of voice and sounds of musical instruments. The voice-selective areas of the left and right superior temporal sulcus did not show the expected relation between 'voiceness' and size effect. Instead, superior temporal sulcus activity seemed mostly driven by sound naturalness, with largest activity differences observed for the intermediate, voice-instrument hybrid stimuli.

Insulin-like growth factor 1 reduces age-related disorders induced by prenatal stress in female rats.

Stress during the prenatal period can induce permanent abnormalities in adult life such as increased anxiety-like behavior and hyperactivity of hypothalamo-pituitary-adrenal (HPA) axis system. The present study was designed to investigate whether prenatal stress could induce spatial learning impairment in aged female rats. Furthermore, since it has been recently reported that insulin-like growth factor 1 (IGF-1) attenuates spatial learning deficits in aged rats and promotes neurogenesis in the hippocampus, we assessed the impact of a chronic infusion of IGF-1 on age-related disorders. Our results show that females stressed during prenatal life exhibit learning impairments in the water maze task. Chronic IGF-1 treatment restores their spatial abilities, reduces their HPA axis dysfunction and increases plasma estradiol levels. Parallel to these effects, chronic IGF-1 up-regulates neural proliferation in the dentate gyrus of the hippocampus. These findings support the hypothesis of an early programming of the vulnerability to some neurological diseases during senescence and reinforce the potential therapeutic interest of IGF-1 during brain aging.