Neural mechanisms of saccadic suppression

In normal vision our gaze leaps from detail to detail, resulting in rapid image motion across the retina. Yet we are unaware of such motion, a phenomenon known as saccadic suppression. We recorded neural activity in the middle temporal and middle superior temporal cortical areas during saccades and identical image motion under passive viewing conditions. Some neurons were selectively silenced during saccadic image motion, but responded well to identical external image motion. In addition, a subpopulation of neurons reversed their preferred direction of motion during saccades. Consequently, oppositely directed motion signals annul one another, and motion percepts are suppressed.

Polymodal motion processing in posterior parietal and premotor cortex: a human fMRI study strongly implies equivalencies between humans and monkeys

In monkeys, posterior parietal and premotor cortex play an important integrative role in polymodal motion processing. In contrast, our understanding of the convergence of senses in humans is only at its beginning. To test for equivalencies between macaque and human polymodal motion processing, we used functional MRI in normals while presenting moving visual, tactile, or auditory stimuli. Increased neural activity evoked by all three stimulus modalities was found in the depth of the intraparietal sulcus (IPS), ventral premotor, and lateral inferior postcentral cortex. The observed activations strongly suggest that polymodal motion processing in humans and monkeys is supported by equivalent areas. The activations in the depth of IPS imply that this area constitutes the human equivalent of macaque area VIP.

Linear vestibular self-motion signals in monkey medial superior temporal area

The present study was aimed at investigating the sensitivity to linear vestibular stimulation of neurons in the medial superior temporal area (MST) of the macaque monkey. Two monkeys were moved on a parallel swing while single-unit activity was recorded. About one-half of the cells (28/51) responded in the dark either to forward motion (n = 10), or to backward motion (n = 11), or to both (n = 7). Twenty cells responding to vestibular stimulation in darkness were also tested for their responses to optic flow stimulation simulating forward and backward self-motion. Forty-five percent (9/20) of them preferred the same self-motion directions, that is, combined visual and vestibular signals in a synergistic manner. Thirty percent (6/20) of the cells were not responsive to visual stimulation alone. The remaining 25% (5/20) preferred directions that were antialigned. Our results provide strong evidence that neurons in the MST area are at least in part involved in the processing of self-motion.