Ignition's glow: Ultra-fast spread of global cortical activity accompanying local "ignitionsâ[euro] in visual cortex during conscious visual perception

• Published in: Consciousness and cognition Vol. 35; p. 206
• Main Authors: Noy, N, Bickel, S, Zion-Golumbic, E, Harel, M, Golan, T, Davidesco, I, Schevon, C.A, McKhann, G.M, Goodman, R.R, Schroeder, C.E, Mehta, A.D, Malach, R
• Format: Journal Article
• Language: English
• Published: San Diego Elsevier BV 01.09.2015
• Subjects: Cognition & reasoning; Consciousness; Neuropsychology; Sensory perception
• ISSN: 1053-8100; 1090-2376
• DOI: 10.1016/j.concog.2015.03.006

* Predictions of global and local models of conscious perception tested. * Large scale (>4000) intra-cranial recordings sites during a visual memory task. * Visual cortex activations, followed by ultra-fast spread into fronto-parietal areas. * Fronto-parietal responses: weak, task modulated and visual content-invariant. * Support for a local model accompanied by a global "glowâ[euro]. Despite extensive research, the spatiotemporal span of neuronal activations associated with the emergence of a conscious percept is still debated. The debate can be formulated in the context of local vs. global models, emphasizing local activity in visual cortex vs. a global fronto-parietal "workspaceâ[euro] as the key mechanisms of conscious visual perception. These alternative models lead to differential predictions with regard to the precise magnitude, timing and anatomical spread of neuronal activity during conscious perception. Here we aimed to test a specific aspect of these predictions in which local and global models appear to differ - namely the extent to which fronto-parietal regions modulate their activity during task performance under similar perceptual states. So far the main experimental results relevant to this debate have been obtained from non-invasive methods and led to conflicting interpretations. Here we examined these alternative predictions through large-scale intracranial measurements (Electrocorticogram - ECoG) in 43 patients and 4445 recording sites. Both ERP and broadband high frequency (50-150Hz - BHF) responses were examined through the entire cortex during a simple 1-back visual recognition memory task. Our results reveal short latency intense visual responses, localized first in early visual cortex followed (at ∼200ms) by higher order visual areas, but failed to show significant delayed (300ms) visual activations. By contrast, oddball image repeat events, linked to overt motor responses, were associated with a significant increase in a delayed (300ms) peak of BHF power in fronto-parietal cortex. Comparing BHF responses with ERP revealed an additional peak in the ERP response - having a similar latency to the well-studied P3 scalp EEG response. Posterior and temporal regions demonstrated robust visual category selectivity. An unexpected observation was that high-order visual cortex responses were essentially concurrent (at ∼200ms) with an ultra-fast spread of signals of lower magnitude that invaded selected sites throughout fronto-parietal cortical areas. Our results are compatible with local models in demonstrating a clear task-dependence of the 300ms fronto-parietal activation. However, they also reveal a more global component of low-magnitude and poor content selectivity that rapidly spreads into fronto-parietal sites. The precise functional role of this global "glowâ[euro] remains to be elucidated.