Negative BOLD in the Lateral Geniculate Nucleus: Neuronal Implications and Cortico-Thalamic Feedback

Previous research has demonstrated a sustained negative BOLD response (NBR) that is negatively correlated with the spatio-temporal properties of a visual stimulus. Whilst it has been suggested that the NBR surrounding the positive BOLD response (PBR) may reflect blood-stealing, evidence indicates that the extensive NBR distal to the PBR is a manifestation of neuronal suppression. This study aimed to evaluate NBR in the lateral geniculate nucleus (LGN), and to explore the source of the NBR. fMRI data were obtained from six subjects, while they viewed a grating stimulus. The NBR was identified in the LGN ipsilateral to the stimulus. The results also verified the NBR in V1 ipsilateral to the stimulus and revealed the PBR in bilateral V5. It was concluded that the NBR can be found in the LGN, and is most likely driven by feedback from ipsilateral V1. The finding that the stimulus that stimulates the LGN in one hemisphere can cause extensive suppression in the LGN of the opposite hemisphere rejects the notion that the effect is purely a blood-stealing effect as the two LGN have different blood supplies. The results, together with previous research, indicate that the NBR may reflect neuronal suppression.