Saccadic suppression induces focal hypooxygenation in the occipital cortex

This study investigated how a decrease in neuronal activity affects cerebra l blood oxygenation employing a paradigm of acoustically triggered saccades in complete darkness. Known from behavioral evidence as saccadic suppressi on, electrophysiologically it has been shown in monkeys that during saccade s an attenuation of activity occurs in Visual cortex neurons (Duffy and Bur chfiel, 1975). In study A, using blood oxygen level-dependent (BOLD) contra st functional magnetic resonance imaging (fMRI), the authors observed signa l intensity decreases bilaterally at the occipital pole during the performa nce of saccades at 2 Hz. In study B.1, the authors directly measured change s in deoxyhemoglobin [deoxy-Hb] and oxyhemoglobin [oxy-Hb] concentration in the occipital cortex with near-infrared spectroscopy (NIRS). Whereas a ris e in [deoxy-Hb] during the performance of saccades occurred, there was a dr op in [oxy-Hb]. In a second NIRS study (B.2), subjects performed saccades a t different rates (1.6, 2.0, and 2.3 Hz), Here the authors found the increa se in deoxy-Kb and the decrease of oxy-Hb to be dependent on the frequency of the saccades. In summary, the authors observed a focal hypooxygenation i n the human visual cortex dependent on the saccade-frequency in an acoustic ally triggered saccades paradigm. This could be interpreted as evidence tha t corresponding to the focal hyperoxygenation observed in functional brain activation, caused by an excessive increase in cerebral blood flow (CBF) ov er the increase in CMRO2 during decreased neuronal activity CBF, is more re duced than oxygen delivery.