Auditory-visual integration in fields of the auditory cortex.

While multimodal interactions have been known to exist in the early sensory cortices, the response properties and spatiotemporal organization of these interactions are poorly understood. To elucidate the characteristics of multimodal sensory interactions in the cerebral cortex, neuronal responses to visual stimuli with or without auditory stimuli were investigated in core and belt fields of guinea pig auditory cortex using real-time optical imaging with a voltage-sensitive dye. On average, visual responses consisted of short excitation followed by long inhibition.

Spatiotemporal dynamics of neural activity related to auditory induction in the core and belt fields of guinea-pig auditory cortex.

Auditory induction is a continuity illusion in which missing sounds are perceived under appropriate conditions, for example, when noise is inserted during silent gaps in the sound. To elucidate the neural mechanisms underlying auditory induction, neural responses to tones interrupted by a silent gap or noise were examined in the core and belt fields of the auditory cortex using real-time optical imaging with a voltage-sensitive dye. Tone stimuli interrupted by a silent gap elicited responses to the second tone following the gap as well as early phasic responses to the first tone.

Dynamic spatiotemporal inhibition in the guinea pig auditory cortex.

Real-time optical imaging was conducted in the guinea pig auditory cortex to study spatiotemporal interrelations of excitation and inhibition in response to tone stimulation. Tone stimulation elicited responses consisting of three phases in the anterior field (the primary auditory cortex of guinea pig) and in the dorsocaudal field of the auditory cortex. An early depolarization was followed by a late hyperpolarization and an even later depolarization both in the maximum excitatory regions and in the lateral regions beside and/or between them.

Optical imaging of binaural interaction in multiple fields of the guinea pig auditory cortex.

Locating the source of a sound is an important function of the auditory system and interaural intensity differences are one of the most important cues. To study the functional pathways of sound localisation processing in the auditory cortex, activity in multiple fields of the guinea pig auditory cortex during stimulation with interaural intensity differences was studied using optical imaging with a voltage-sensitive dye. Of the auditory core (primary and dorsocaudal) and the belt fields which surround them, the posterior and ventroposterior belt fields were the most sensitive to interaural intensity differences.

Spatial focusing of neuronal responses induced by asynchronous two-tone stimuli in the guinea pig auditory cortex.

Spatiotemporal patterns of neuronal responses to asynchronous two-tone stimuli in the anterior field of the auditory cortex of anesthetized guinea pigs were studied using an optical recording method (12 x 12 photodiode array, voltage sensitive dye RH795). Interactions between the onset response to the first tone (masker; 5, 8, 10, 12 and 15 kHz, 200 ms) and to the second tone (probe; 10 kHz, 30 ms) with onset delays relative to the masker onset (0, 5, 10, 15 and 20 ms) were investigated. In general, two-tone interaction was suppressive rather than facilitative.