Neural-Metabolic Coupling in the Central Visual Pathway

Abstract

In fMRI, the blood oxygen level dependent (BOLD) signal is used to infer neural activity. One of the important limits of this method is spatial resolution. Ideally, the utility of this procedure would be vastly improved if it allowed the monitoring of neural changes at a spatial scale that would permit the resolution of columnar structure within the cerebral cortex. We have undertaken measurements that are intended to elucidate relationships between metabolic and neural functions directly. We have constructed a double barrel micropipette electrode system by which we are able to make simultaneous measurements of tissue oxygen concentrations and single-cell neural activity within the visual cortex. This approach has the advantage of enabling direct measurements of both neural and metabolic activity in a limited volume of colocalized cortical tissue. Our findings are as follows. As neural activity is raised by appropriate visual stimulation, there is an immediate proportional decrease in tissue oxygenation indicating a close link between the two functions. To pursue this finding, we used the decrease in tissue oxygenation to predict two unique functional properties of visual cortical cells in neighboring neurons: orientation selectivity and ocular dominance. These results establish a coupling between neuronal activity and
oxidative metabolism. By making certain assumptions, it is possible to apply these results to fMRI. Specifically, high resolution imaging may be enabled by use of procedures which monitor localized neural activity and this may facilitate columnar level measurements.