Using an achiasmic human visual system to quantify the relationship between the fMRI BOLD signal and neural response

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Abstract

Achiasma in humans causes gross mis-wiring of the retinal-fugal projection, resulting in overlapped cortical representations of left and right visual hemifields. We show that in areas V1-V3 this overlap is due to two co-located but non-interacting populations of neurons, each with a receptive field serving only one hemifield. Importantly, the two populations share the same local vascular control, resulting in a unique organization useful for quantifying the relationship between neural and fMRI BOLD responses without direct measurement of neural activity. Specifically, we can non-invasively double local neural responses by stimulating both neuronal populations with identical stimuli presented symmetrically across the vertical meridian to both visual hemifields, versus one population by stimulating in one hemifield. Measurements from a series of such doubling experiments show that the amplitude of BOLD response is proportional to approximately 0.5 power of the underlying neural response. Reanalyzing published data shows that this inferred relationship is general.

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Pinglei Bao

Neuroscience Graduate Program, University of Southern California, Los Angeles, United States

Competing interests
The authors declare that no competing interests exist.
Christopher J Purington

School of Optometry, University of California, Berkeley, Berkeley, CA, United States

Competing interests
The authors declare that no competing interests exist.
Bosco S Tjan

Psychology, University of Southern California, Los Angeles, CA, United States

For correspondence
btjan@usc.edu

Competing interests
The authors declare that no competing interests exist.

Ethics

Human subjects: The Institutional Review Board of the University of Southern California approved the experimental protocol, and each subject provided written informed consent.

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This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.