Causal effect of disconnection lesions on interhemispheric functional connectivity in rhesus monkeys.
In the absence of external stimuli or task demands, correlations in spontaneous brain activity (functional connectivity) reflect patterns of anatomical connectivity. Hence, resting-state functional connectivity has been used as a proxy measure for structural connectivity and as a biomarker for brain changes in disease. To relate changes in functional connectivity to physiological changes in the brain, it is important to understand how correlations in functional connectivity depend on the physical integrity of brain tissue. The causal nature of this relationship has been called into question by patient data suggesting that decreased structural connectivity does not necessarily lead to decreased functional connectivity. Here we provide evidence for a causal but complex relationship between structural connectivity and functional connectivity: we tested interhemispheric functional connectivity before and after corpus callosum section in rhesus monkeys. We found that forebrain commissurotomy severely reduced interhemispheric functional connectivity, but surprisingly, this effect was greatly mitigated if the anterior commissure was left intact. Furthermore, intact structural connections increased their functional connectivity in line with the hypothesis that the inputs to each node are normalized. We conclude that functional connectivity is likely driven by corticocortical white matter connections but with complex network interactions such that a near-normal pattern of functional connectivity can be maintained by just a few indirect structural connections. These surprising results highlight the importance of network-level interactions in functional connectivity and may cast light on various paradoxical findings concerning changes in functional connectivity in disease states.
Functional Magnetic Resonance Imaging of the Brain Centre, Nuffield Department of Clinical Neurosciences, John Radcliffe Hospital, Oxford University, Oxford OX3 9DU, United Kingdom. joreilly@fmrib.ox.ac.uk
Jill X
JX
O'Reilly
Paula L
PL
Croxson
Saad
S
Jbabdi
Jerome
J
Sallet
Maryann P
MP
Noonan
Rogier B
RB
Mars
Philip G F
PG
Browning
Charles R E
CR
Wilson
Anna S
AS
Mitchell
Karla L
KL
Miller
Matthew F S
MF
Rushworth
Mark G
MG
Baxter
D000818:Animals; D001931:Brain Mapping; D058256:Brain Waves / Q000502:physiology*; D063132:Connectome; D003337:Corpus Callosum / Q000601:surgery; D005260:Female; D008253:Macaca mulatta / Q000502:physiology*; D008279:Magnetic Resonance Imaging; D008297:Male; D013997:Time Factors
fMRI; macaque; resting-state connectivity; split brain