Abstract
Ultra-high field MRI can functionally image the cerebral cortex of human subjects at the submillimeter scale of cortical columns and laminae. Here, we investigate both in concert, by imaging ocular dominance columns (ODCs) in primary visual cortex (V1) across different cortical depths. We ensured that putative ODC patterns in V1 (a) are stable across runs, sessions, and scanners located in different continents, (b) have a width (~1.3 mm) expected from post-mortem and animal work and (c) are absent at the retinotopic location of the blind spot. We then dissociated the effects of bottom-up thalamo-cortical input and attentional feedback processes on activity in V1 across cortical depth. Importantly, the separation of bottom-up information flows into ODCs allowed us to validly compare attentional conditions while keeping the stimulus identical throughout the experiment. We find that, when correcting for draining vein effects and using both model-based and model-free approaches, the effect of monocular stimulation is largest at deep and middle cortical depths. Conversely, spatial attention influences BOLD activity exclusively near the pial surface. Our findings show that simultaneous interrogation of columnar and laminar dimensions of the cortical fold can dissociate thalamocortical inputs from top-down processing, and allow the investigation of their interactions without any stimulus manipulation.
Highlights
Ultra-high field functional MRI (UHF-fMRI, at field strengths of 7 Tesla or more) is transforming the field of human neuroimaging (Marques and Norris, 2018; Trattnig et al, 2018; van der Zwaag et al, 2016)
Perhaps the most well-known form of cortical organization at the mesoscopic scale is columnar: ocular dominance columns (ODCs) are patches of cortex that are predominantly sensitive to input from only one of the two eyes, forming columns perpendicular to the surface of primary visual cortex, V1 (Adams and Horton, 2009;, Adams et al, 2007; Dougherty et al, 2019; Hubel and Wiesel, 1969; Tootell et al, 1988)
Models of cortical microcircuits contend that the organization orthogonal to that of cortical columns, along cortical depth, separates input-driven and feedback activity in primary sensory regions (Bastos et al, 2012; De Martino et al, 2018; Kuehn and Sereno, 2018; Rockland and Pandya, 1979; Self et al, 2019; Stephan et al, 2019)
Summary
Ultra-high field functional MRI (UHF-fMRI, at field strengths of 7 Tesla or more) is transforming the field of human neuroimaging (Marques and Norris, 2018; Trattnig et al, 2018; van der Zwaag et al, 2016). Combined laminarcolumnar UHF-fMRI could dissociate BOLD activity in V1 due to thalamocortical input (e.g., by monocular stimulation of the preferred eye of a given ODC) from activity due to higher order processes (e.g, by manipulating attention) in the same cortical columns (see Fig. 1 and Schneider et al, 2019). We speculated that humans might be able to suppress the thalamocortical input into V1 representing information that is not relevant to the task at hand (Ling et al, 2015) If this would be the case, we would expect the effect of attention to be larger in ODCs where the preferred eye is stimulated as compared to ODCs where the non-preferred eye is stimulated. There was no significant interaction between these two effects, suggesting that, in our task, thalamocortical input is not modulated by attention in an ocular-specific manner
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