Dataset Information

Neural representations of individual stimuli in humans revealed by gamma-band electrocorticographic activity.

ABSTRACT: A fundamental question in neuroscience concerns how the human brain represents perceptual and conceptual information. Traditionally, researchers probed this issue by identifying single neurons that increased their firing rate when an animal encountered certain stimuli. Here we provide evidence of a complementary scheme in which gamma-band (25-128 Hz) electrocorticographic (ECoG) activity -- a phenomenon involving large groups of neurons -- encodes the active cognitive representation. We analyzed intracranial brain recordings from neurosurgical patients while they studied lists of visually presented letters and found that the amplitude of gamma-band activity encoded the identity of the current letter. These letter-specific patterns occurred during periods of overall increased gamma amplitude and were linked to the phase of simultaneous theta (4-8 Hz) oscillations. In occipital cortex, these patterns sometimes reflected the shape of the viewed letter, but, in other brain regions, this phenomenon was not related to letter form. Our findings show that gamma-band activity encodes a range of perceptual and conceptual information, suggesting that ECoG recordings can reveal neural correlates of specific human cognitive representations.

SUBMITTER: Jacobs J

PROVIDER: S-EPMC2752642 | biostudies-literature | 2009 Aug

REPOSITORIES: biostudies-literature

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Neural representations of individual stimuli in humans revealed by gamma-band electrocorticographic activity.

Jacobs Joshua J Kahana Michael J MJ

The Journal of neuroscience : the official journal of the Society for Neuroscience 20090801 33

A fundamental question in neuroscience concerns how the human brain represents perceptual and conceptual information. Traditionally, researchers probed this issue by identifying single neurons that increased their firing rate when an animal encountered certain stimuli. Here we provide evidence of a complementary scheme in which gamma-band (25-128 Hz) electrocorticographic (ECoG) activity -- a phenomenon involving large groups of neurons -- encodes the active cognitive representation. We analyzed ...[more]

PMID: 19692595

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Project description:Neuroimaging approaches have implicated multiple brain sites in musical perception, including the posterior part of the superior temporal gyrus and adjacent perisylvian areas. However, the detailed spatial and temporal relationship of neural signals that support auditory processing is largely unknown. In this study, we applied a novel inter-subject analysis approach to electrophysiological signals recorded from the surface of the brain (electrocorticography (ECoG)) in ten human subjects. This approach allowed us to reliably identify those ECoG features that were related to the processing of a complex auditory stimulus (i.e., continuous piece of music) and to investigate their spatial, temporal, and causal relationships. Our results identified stimulus-related modulations in the alpha (8-12 Hz) and high gamma (70-110 Hz) bands at neuroanatomical locations implicated in auditory processing. Specifically, we identified stimulus-related ECoG modulations in the alpha band in areas adjacent to primary auditory cortex, which are known to receive afferent auditory projections from the thalamus (80 of a total of 15,107 tested sites). In contrast, we identified stimulus-related ECoG modulations in the high gamma band not only in areas close to primary auditory cortex but also in other perisylvian areas known to be involved in higher-order auditory processing, and in superior premotor cortex (412/15,107 sites). Across all implicated areas, modulations in the high gamma band preceded those in the alpha band by 280 ms, and activity in the high gamma band causally predicted alpha activity, but not vice versa (Granger causality, p<1e(-8)). Additionally, detailed analyses using Granger causality identified causal relationships of high gamma activity between distinct locations in early auditory pathways within superior temporal gyrus (STG) and posterior STG, between posterior STG and inferior frontal cortex, and between STG and premotor cortex. Evidence suggests that these relationships reflect direct cortico-cortical connections rather than common driving input from subcortical structures such as the thalamus. In summary, our inter-subject analyses defined the spatial and temporal relationships between music-related brain activity in the alpha and high gamma bands. They provide experimental evidence supporting current theories about the putative mechanisms of alpha and gamma activity, i.e., reflections of thalamo-cortical interactions and local cortical neural activity, respectively, and the results are also in agreement with existing functional models of auditory processing.

Dataset Information

Neural representations of individual stimuli in humans revealed by gamma-band electrocorticographic activity.

Publications

Neural representations of individual stimuli in humans revealed by gamma-band electrocorticographic activity.

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