Functional MRI activity in the thalamus and occipital cortex of anesthetized dogs induced by monocular and binocular stimulation

The neuroanatomy of the mammalian visual system has received considerable a ttention through electrophysiological study of cats and non-human primates, and through neuroimaging of humans. Canine neuroanatomy, however, has rece ived much less attention, limiting our understanding of canine vision and v isual pathways. As an early step in applying blood oxygenation level depend ant (BOLD) functional magnetic resonance imaging (fMRI) for veterinary use, we compared visual activity in the thalamus and occipital cortex of anesth etized dogs presented with binocular and monocular visual stimuli. Activity in the left and right thalamus and occipital cortex during monocular stimu lation was also compared. Six beagles were presented with a vertical gratin g visual stimulus and scanned at 4 Tesla. Each dog was scanned twice under each of 3 anesthetic protocols (isoflurane, propofol, and fentanyl/midazola m). We found: 1) significant BOLD activation in the lateral geniculate nucl eus (LGN) of the thalamus and the occipital cortex; 2) a significantly larg er area of activation in the LGN during monocular stimulation than during b inocular stimulation; and 3) that activity in the hemisphere contralateral to the stimulus was not significantly greater than that ipsilateral to it.