Gamma activity modulated by naming of ambiguous and unambiguous images: intracranial recording.

OBJECTIVE: Humans sometimes need to recognize objects based on vague and ambiguous silhouettes. Recognition of such images may require an intuitive guess. We determined the spatial-temporal characteristics of intracranially-recorded gamma activity (at 50-120Hz) augmented differentially by naming of ambiguous and unambiguous images. METHODS: We studied 10 patients who underwent epilepsy surgery. Ambiguous and unambiguous images were presented during extraoperative electrocorticography recording, and patients were instructed to overtly name the object as it is first perceived. RESULTS: Both naming tasks were commonly associated with gamma-augmentation sequentially involving the occipital and occipital-temporal regions, bilaterally, within 200ms after the onset of image presentation. Naming of ambiguous images elicited gamma-augmentation specifically involving portions of the inferior-frontal, orbitofrontal, and inferior-parietal regions at 400ms and after. Unambiguous images were associated with more intense gamma-augmentation in portions of the occipital and occipital-temporal regions. CONCLUSIONS: Frontal-parietal gamma-augmentation specific to ambiguous images may reflect the additional cortical processing involved in exerting intuitive guess. Occipital gamma-augmentation enhanced during naming of unambiguous images can be explained by visual processing of stimuli with richer detail. SIGNIFICANCE: Our results support the theoretical model that guessing processes in visual domain occur following the accumulation of sensory evidence resulting from the bottom-up processing in the occipital-temporal visual pathways.

Cooing- and babbling-related gamma-oscillations during infancy: intracranial recording.

We determined the spatio-temporal dynamics of intracranially-recorded gamma-oscillations modulated by spontaneous cooing and babbling, which are considered to embody pre-linguistic language behaviors during infancy. Electrocorticographic (ECoG) signals were recorded from 110 cortical sites in the right hemisphere of a 10-month-old girl with focal epilepsy. Electrocorticographic signals were time-locked to the onset of cooing or babbling. The amplitudes of gamma-oscillations during vocalizations were compared to those during preceding silent reference periods. Cooing and babbling elicited significant gamma-augmentation at 30-100 Hz at distinct sites of the inferior Rolandic region, whereas both forms of vocalizations elicited gamma-augmentation at an identical superior temporal site. The spatial, temporal and spectral characteristics of gamma-augmentation elicited by cooing and babbling were similar to those elicited by phoneme vocalization in older children and adults. Differential activation within the right inferior Rolandic region during cooing and babbling may reflect the mechanical or developmental difference between these two forms of vocalizations. The right superior temporal gyrus may participate in an auditory feedback system during vocalization.