An estimation of the absolute number of axons indicates that human cortical areas are sparsely connected

Rosen, Burke Q.; Halgren, Eric

doi:10.1101/2021.06.07.447453

Cited by 5 publications

(4 citation statements)

References 76 publications

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“…A mutually-reinforcing mechanism is consistent with our previous finding of a strong dependence of phase-locking on the co-rippling of several cortical locations simultaneously, beyond the two whose ripple phase-locking is being measured (Dickey et al, 2022b). Since integration of specific information requires a high bandwidth, it could only be transmitted by direct cortico-cortical connections in humans, given that neuroanatomical calculations find that >95% of synapses on cortical cells are from the cortex (reviewed in Rosen and Halgren (2022)). In particular, the ratio of cortical neurons to thalamo-cortical projection cells is ~1400:1 (calculations based on human thalamic cell counts in Xuereb et al (1991), proportion of thalamo-cortical cells in Arcelli et al (1997), and cortical cell counts in Azevedo et al (2009)).…”

Section: Discussionsupporting

confidence: 88%

Thalamic spindles and upstates, but not ripples, coordinate cortico-cortical and hippocampo-cortical co-ripples in humans

Dickey

Verzhbinsky

Kajfez

et al. 2022

Preprint

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The co-occurrence of brief ~90 Hz oscillations (co-ripples) may be important in integrating information across the cortex and hippocampus, essential for sleep consolidation, and cognition in general. However, how such co-ripples are synchronized is unknown. We tested if cortico-cortical and hippocampal-cortical ripple co-occurrences are due to the simultaneous direct propagation of thalamic ripples, or if they are instead facilitated by lower frequency waves. Using human intracranial recordings, we found that ripples are generated in the thalamus during non-rapid eye movement sleep with similar characteristics as cortical and hippocampal ripples. However, thalamic ripples only infrequently and weakly co-occur, and never phase-lock, with cortical and hippocampal ripples. In contrast, thalamo-cortical spindles and upstates strongly facilitated cortico-cortical and hippocampo-cortical co-rippling. Thus, while thalamic ripples may not directly drive multiple cortical or hippocampal sites at ripple frequency, these sites may ripple synchronously in response to widespread activation from thalamo-cortical spindles and upstates.

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Section: Discussionsupporting

confidence: 88%

Thalamic spindles and upstates, but not ripples, coordinate cortico-cortical and hippocampo-cortical co-ripples in humans

Dickey

Verzhbinsky

Kajfez

et al. 2022

Preprint

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“…Our findings thus counter traditional views that emphasize the role of intricate patterns of long-range anatomical connections in supporting coordinated dynamics ( 33, 62, 63 ). Given the scarcity, metabolic cost, and genetic control of such connections ( 64–66 ), it will be important to determine the specific functional and evolutionary advantage that they provide beyond the dominant role of wave-like dynamics; for example, in explaining time-lagged patterns of activity ( 47 ), which are not accounted for in our current framework.…”

Section: Discussionmentioning

confidence: 99%

Geometric constraints on human brain function

Pang

Aquino

Oldehinkel³

et al. 2022

Preprint

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The brain's anatomy constrains its function, but precisely how remains unclear. Here, we show that human cortical and subcortical activity, measured with magnetic resonance imaging under spontaneous and diverse task-evoked conditions, can be parsimoniously understood as resulting from excitations of fundamental, resonant modes of the brain's geometry (i.e., its shape) rather than of its complex inter-regional connectivity, as classically assumed. We then use these modes to show that task-evoked activations across >10,000 brain maps are not confined to focal areas, as widely believed, but instead excite brain-wide modes with wavelengths spanning >60 mm. Finally, we confirm theoretical predictions that the close link between geometry and function is explained by a dominant role for wave-like dynamics, showing that such dynamics can reproduce numerous canonical spatiotemporal properties of spontaneous and evoked recordings. Our findings challenge prevailing views of brain function and identify a previously under-appreciated role of brain geometry that is predicted by a unifying and physically principled approach.

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“…The present results should be considered in light of two important methodological limitations. First, structural connectivity was estimated from diffusion MRI, a technique that is affected by systematic false positives and false negatives [21, 30, 35, 36, 57, 58, 69, 81, 99, 111, 118, 122, 132, 143, 160, 164]. We attempted to mitigate this issue by deriving a group consensus structural connectivity network that identifies consistent connections across many participants, but improvements in imaging technology and computational tractometry are still necessary.…”

Section: Discussionmentioning

confidence: 99%

Spatially heterogeneous structure-function coupling in haemodynamic and electromagnetic brain networks

Liu

Shafiei

Baillet

et al. 2022

Preprint

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The relationship between structural and functional connectivity in the brain is a key question in connectomics. Here we quantify patterns of structure-function coupling across the neocortex, by comparing structural connectivity estimated using diffusion MRI with functional connectivity estimated using both neurophysiological (MEG-based) and haemodynamic (fMRI-based) recordings. We find that structure-function coupling is heterogeneous across brain regions and frequency bands. The link between structural and functional connectivity is generally stronger in multiple MEG frequency bands compared to resting state fMRI. Structure-function coupling is greater in slower and intermediate frequency bands compared to faster frequency bands. We also find that structure-function coupling systematically follows the archetypal sensorimotor-association hierarchy, as well as patterns of laminar differentiation, peaking in granular layer IV. Finally, structure-function coupling is better explained using structure-informed inter-regional communication metrics than using structural connectivity alone. Collectively, these results place neurophysiological and haemodynamic structure-function relationships in a common frame of reference and provide a starting point for a multi-modal understanding of structure-function coupling in the brain.

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An estimation of the absolute number of axons indicates that human cortical areas are sparsely connected

Cited by 5 publications

References 76 publications

Thalamic spindles and upstates, but not ripples, coordinate cortico-cortical and hippocampo-cortical co-ripples in humans

Thalamic spindles and upstates, but not ripples, coordinate cortico-cortical and hippocampo-cortical co-ripples in humans

Geometric constraints on human brain function

Spatially heterogeneous structure-function coupling in haemodynamic and electromagnetic brain networks

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