Abstract
Human cortical area MT+ (hMT+) is known to respond to visual motion stimuli, but its causal role in the conscious experience of motion remains largely unexplored. Studies in non-human primates demonstrate that altering activity in area MT can influence motion perception judgments, but animal studies are inherently limited in assessing subjective conscious experience. In the current study, we use functional magnetic resonance imaging (fMRI), intracranial electrocorticography (ECoG), and electrical brain stimulation (EBS) in three patients implanted with intracranial electrodes to address the role of area hMT+ in conscious visual motion perception. We show that in conscious human subjects, reproducible illusory motion can be elicited by electrical stimulation of hMT+. These visual motion percepts only occurred when the site of stimulation overlapped directly with the region of the brain that had increased fMRI and electrophysiological activity during moving compared to static visual stimuli in the same individual subjects. Electrical stimulation in neighboring regions failed to produce illusory motion. Our study provides evidence for the sufficient causal link between the hMT+ network and the human conscious experience of visual motion. It also suggests a clear spatial relationship between fMRI signal and ECoG activity in the human brain.
Highlights
The posterior temporal region of the non-human primate brain, and its human homologue, known as area V5 [1] or human MT complex [2,3] are responsive to visual motion [4]
Causal necessity can be established by inactivation of the brain region and observing a perceptual deficit, whereas causal sufficiency is established by modulating its activity and observing a corresponding change in the perceptual experience
During blocks of moving images, there was a significant increase in power specific to the theta (4–7 Hz) and high-gamma (50–120 Hz) bands (Figure 2A) only in the electrode directly overlapping with the functional magnetic resonance imaging (fMRI)-defined area hMT+
Summary
The posterior temporal region of the non-human primate brain (areas MT/MST), and its human homologue, known as area V5 [1] or human MT complex (hMT+) [2,3] are responsive to visual motion [4]. Electrical stimulation of this region in non-human primates can influence motion direction discriminations, suggesting that its activity is critically linked to perceptual decisions [5,6]. Fundamental to our current understanding of motion perception, studies in non-human primates cannot ascertain conscious perceptual experiences during these direct alterations of neural activity. Correlational techniques like fMRI and electroencephalography (EEG) cannot establish a causal relationship between hMT+ activity and conscious motion perception
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