Functional MRI of substantia nigra upon visual flash illumination

Abstract

In the mammalian midbrain, increasing evidence suggested a direct projection from the superior colliculus (SC) to the substantia nigra (SN), yet their functional characteristics remain largely unknown. This study explores the capability of blood oxygenation level–dependent (BOLD) fMRI to detect simultaneous activations in SC and SN upon visual flash illumination in order to understand the basic visual properties and hemodynamic responses in this functional connection. Upon monocular stimulation, activations were found predominantly in the contralateral SC and SN, whereas upon binocular stimulation activations were observed in SC and SN of both hemispheres. Significantly lower BOLD percent changes were also observed in the SN of both groups than SC before reaching similar peak heights after stimulation. The current results of having the same visual event initiating afferent inputs to both SC and SN could have important implications for interpreting the responses to biologically salient sensory events in relation to novelty, intensity or reward within the SC-SN connection.