Functional MRI mapping neuronal inhibition and excitation at columnar level in human visual cortex

Abstract

The capability of non-invasively mapping neuronal excitation and inhibition at the columnar level in human is vital in revealing fundamental mechanisms of brain functions. Here, we show that it is feasible to simultaneously map inhibited and excited ocular dominance columns (ODCs) in human primary visual cortex by combining high-resolution fMRI with the mechanism of binocular inhibitory interaction induced by paired monocular stimuli separated by a desired time delay. This method is based on spatial differentiation of fMRI signal responses between inhibited and excited ODCs that can be controlled by paired monocular stimuli. The feasibility and reproducibility for mapping both inhibited and excited ODCs have been examined. The results conclude that fMRI is capable of non-invasively mapping both excitatory and inhibitory neuronal processing at the columnar level in the human brain. This capability should be essential in studying the neural circuitry and brain function at the level of elementary cortical processing unit.

Fig. 1

Illustration of a high-resolution GE-EPI image (0.5 × 0.5 mm² in-plane resolution), a selection of ROI and an ODC map created using the proposed fMRI method

Fig. 2

Histogram of ODCI of all activated ROI voxels from a one subject; and b averaged results of all three subjects. The activated ROI pixels clearly cluster into two populations: an inhibited population (ODCI<1) and an excited population (ODCI>2)

Fig. 3

ODC maps in the first subject. a ODC map generated the whole data set acquired in one fMRI session. b ODC map generated from the first half of data. c ODC map generated from the second half of data acquired within the same fMRI session as (b). d Overlap of reproducible pixels from (b) and (c). The lower row is blurred version of the corresponding upper row

Fig. 4

ODC maps in the second subject. a ODC map generated the whole data set acquired in one fMRI session. b ODC map generated from the first half of data. c ODC map generated from the second half of data acquired within the same fMRI session as (b). d Overlap of reproducible pixels from (b) and (c). The lower row is blurred version of the corresponding upper row

Fig. 5

ODC maps in the third subject. a ODC map generated the whole data set acquired in one fMRI session. b ODC map generated from the first half of data. c ODC map generated from the second half of data acquired within the same fMRI session as (b). d Overlap of reproducible pixels from (b) and (c). The lower row is blurred version of the corresponding upper row

Fig. 6

a Correlation of ODCI of all activated ROI pixels between the first and second half of data in one subject. b Correlation of ODCI of all reproducible pixels between the first and second half of data in the first subject. c Correlation of ODCI of all reproducible pixels between the first and second half of data in the second subject. d Correlation of ODCI of all reproducible pixels between the first and second half of data in the third subject. e Correlation of ODCI of all reproducible pixels between the first and second half of data in all three subjects