ABSTRACT
Abstract With the current emphasis on atypical patterns of connectivity in the brain hypothesized to be a core feature of autism spectrum disorders (ASDs), there has been a considerable focus over the last decade or so
Contents Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 457 22.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 458 22.2 Autism spectrum disorder. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 459
22.2.1 ASD characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . 459 22.2.2 Neurocognitive models of ASD . . . . . . . . . . . . . . . . . . 461
22.2.2.1 Excitation-inhibition in autism . . . . . . . . . . . 461 22.2.2.2 Aberrant cortical connectivity in ASD . . . . . 462
22.3 Gamma activity in the human brain. . . . . . . . . . . . . . . . . . . . . 463 22.3.1 Measuring gamma . . . . . . . . . . . . . . . . . . . . . . . . . . . . 463 22.3.2 Gamma metrics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 464
22.3.2.1 Gamma frequencies . . . . . . . . . . . . . . . . . . . . 464 22.3.2.2 Task-related gamma . . . . . . . . . . . . . . . . . . . . 466 22.3.2.3 Task-free (resting-state) gamma. . . . . . . . . . . 471
22.3.3 Gamma and connectivity measures . . . . . . . . . . . . . . . 471 22.3.4 GBA as a measure of GABA . . . . . . . . . . . . . . . . . . . . 473 22.3.5 Functional signicance of gamma oscillations . . . . . . 474
22.4 Gamma activity in autism. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 474 22.4.1 Visual gamma in ASD . . . . . . . . . . . . . . . . . . . . . . . . . 475 22.4.2 Auditory gamma in ASD . . . . . . . . . . . . . . . . . . . . . . . 479 22.4.3 Resting-state, “task-free” gamma activity . . . . . . . . . . 483
22.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 485 22.5.1 Further renements and future focus . . . . . . . . . . . . . . 486
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 487
on high-frequency (gamma) band activity (GBA) in both the human and the non-human brain as a measure of connectivity. This chapter provides an overview of the measurement, analysis, and interpretation of GBA and links this to existing neurocognitive and neurophysiological models of ASD. A review of GBA research in ASD, particularly focussing on visual and auditory atypicalities, reveals some consistencies and some inconsistencies, generally arising from the application of different methodologies. It is concluded that, in parallel with emerging theoretical and analytical improvements, the study of GBA and GBA-related processes will continue to offer signicant insights into ASD atypicalities at every level, additionally offering the possibility of identifying diagnostic biomarkers, serving as indices of therapeutic progress or contributing to the identication of endophenotypes.
