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Hiromasa SAWAMURA, Guy A Orban; Participation of different cortical networks in discriminating the number of motor acts and their targets revealed by fMRI. Invest. Ophthalmol. Vis. Sci. 2019;60(9):4376. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
The occipitotemporal, parietal and frontal cortexes participate in the observation of actions. Manipulative actions involve both the motor act itself and its target. We used functional magnetic resonance imaging (fMRI) to assess which cortical regions participate in enumeration of the motor act and of its targets.
Twenty-one right-handed healthy volunteers participated in the present study (mean age: 26 years old). The subjects were instructed to perform a two-alternative forced choice task in the scanner, in response to visual stimuli consisting of videos lasting 5.4 s presented by a head-mounted display. In the videos, a white or orange ball automatically appeared 4 times in total (ratio of 1:3 or 3:1) at regular intervals. The actor or actress performed either a push or flick motor act (ratio of 1:3 or 3:1) against the ball. The combination of the motor act and the ball appeared pseudorandomly. One of the following instructions appeared before the visual stimuli: “1 ball” or “3 balls” (Ball conditions), “1 act” or “3 acts” (Act conditions). The response was either “White” or “Orange” in the case of “Ball conditions” and either “Push” or “Flick” in the case of “Act conditions”. Eye movements were monitored using an infrared camera system. Data analysis was performed using the SPM8 software.
The accuracy was 97% on average, which did not differ across the four different conditions: “1 act”, “3 acts”, “1 ball” and “3 balls” (ANOVA, P=0.806). The average number of saccades was 4.6 times per minute, which did not differ across the four conditions (ANOVA, P=0.971). The main effect generated by the contrast “Act conditions versus Ball conditions” (FWE corrected P<0.05 at cluster level) revealed activation in the bilateral inferior parietal regions, including bilateral area PF and area phAIP in the left hemisphere. In contrast, the map generated by the contrast “Ball conditions versus Act conditions” (FWE corrected P<0.05 at cluster level) revealed activation in area PG in the right hemisphere, posterior to area PF.
The different activations observed in the present study originated from whether the subject focused on the act or on the target, even with the same visual stimuli. These observations suggest that different cortical networks are involved in enumeration of motor acts and their targets.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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