Abstracts

Rationale: The two-streams hypothesis of visual processing suggests a dissociation between the networks underlying action naming (dorsal stream) and object naming (ventral stream). After primary visual information reaches calcarine cortex, it is processed by a hierarchically-organized set of downstream occipital regions. Visual information concerning spatial information and tool use preferentially drives activity in parietal cortex, while that concerning descriptive information and object identification preferentially drives ventral temporal activity. It is not known to what degree these streams constitute independent visual, semantic, or syntactic networks. Furthermore, the critical substrates involved in directing the stream dorsally or ventrally have not been identified. Finally, the timing of divergence to dorsal and ventral streams and convergence back to a shared articulatory network has not previously been quantified. These 3 questions will resolve outstanding questions in the role these streams play in visual processing and language production. Methods: 108 patients with either subdural surface (n = 36) or stereotactic penetrating electrodes (n = 72) completed at least one of the following language paradigms: visually cued object (n = 105) or action (n = 85) naming. Additionally, 41 of these patients underwent fMRI language lateralization with these tasks allowing comparison to a cohort of 19 volunteers without epilepsy. Studies of language production rely predominantly on data from behavioral, lesional, and functional imaging techniques – methods without access to rapid, transient, and coordinated neural processes. In contrast, human electrocorticography is uniquely suited to study the network dynamics involved in cognition with full spectrum recordings of cortical oscillations at millimeter spatial and millisecond temporal resolution. Results: We identified increased broadband gamma (60 – 120 Hz) activity (BGA) during action naming in the left, language-dominant intraparietal sulcus, posterior middle temporal gyrus, and ventral lateral prefrontal cortex. Conversely, we found increased BGA in anterolateral fusiform cortex during object naming. Furthermore, we characterized the relative timing of 9 distinct nodes defining the extent of the bilateral articulatory network: pre-SMA, SMA-proper, anterior insula, pars triangularis, pars opercularis, anterior and posterior subcentral gyrus, sylvian parietal-temporal junction, and superior temporal gyrus. We observe increased BGA in this distributed articulatory network during verb production in contrast with noun production, likely a consequence of the increased lexical and semantic demand associated with verb production. Conclusions: These experiments quantitatively characterize visual action and object naming, delineating the extent and timing of a broad bilateral language production network. Future development of improved treatment for damage to language faculties will benefit from this augmented understanding of the location and dynamics of language production. Funding: This work was supported by the National Center for Deafness and Other Communication Disorders DC014589, National Center for Research Resources Clinical and Translational Award K12-KL2 RR0224149, the Memorial Hermann Foundation, and the Hawkins Foundation Discovery Fellowship.