Much of what is known about the timing of visual processing in the brain is inferred from intracranial studies in monkeys, with human data limited to mainly noninvasive methods with lower spatial resolution. Here, we estimated visual onset latencies from electrocorticographic (ECoG) recordings in a patient who was implanted with 112 subdural electrodes, distributed across the posterior cortex of the right hemisphere, for presurgical evaluation of intractable epilepsy. Functional MRI prior to surgery was used to determine boundaries of visual areas. The patient was presented with images of objects from several categories. Event-related potentials (ERPs) were calculated across all categories excluding targets, and statistically reliable onset latencies were determined, using a bootstrapping procedure over the single trial baseline activity in individual electrodes. The distribution of onset latencies broadly reflected the known hierarchy of visual areas, with the earliest cortical responses in primary visual cortex, and higher areas showing later responses. A clear exception to this pattern was a robust, statistically reliable and spatially localized, very early response, on the bank of the posterior intraparietal sulcus (IPS). The response in the IPS started nearly simultaneously with responses detected in peristriate visual areas, around 60 ms poststimulus onset. Our results support the notion of early visual processing in the posterior parietal lobe, not respecting traditional hierarchies, and give direct evidence for onset times of visual responses across the human cortex.
Bibliographical noteFunding Information:
The authors are grateful to Dr. Josef Parvizi for facilitating ECoG data collection from his patient and for fruitful discussions about the results. We acknowledge Vinitha Rangarajan and Bret Foster for assisting with data collection at the Stanford Medical Center. We thank Corentin Jacques for generously sharing with us the ECoG MT localizer data that he collected on the patient. We thank Israel Nelken for valuable consultations. This work was supported by grant 2013070 from the United States-Israel Binational Science Foundation to LYD and RTK and grant 1902_2014 from the Israel Science Foundation to LYD as well as NIH grant R01MH111417 to JW. Leon Y. Deouell is supported by the Jack A. Skirball research fund. TIR was supported by The Hoffman Leadership and Responsibility Fellowship Program at the Hebrew University of Jerusalem.
NIH, Grant/Award Number: R01MH111417; United-states Israel Binational Science Foundation, Grant Number: 2013070; Israel Science Foundation, Grant Number: 1902_2014
© 2018 Federation of European Neuroscience Societies and John Wiley & Sons Ltd
- early visual processing
- onset latency estimation