|Reference code: ||PT/FB/BL-2014-373.05|
|Long-range perceptual integration of visual motion revealed at high resolution 7T fMRI|
|Publication year: ||2016|
It has been suggested that activity in the human motion complex (hMT+) reflects global motion interpretation of perceptual bistability (Castelo-Branco et al., 2002). Here we investigated how the bistable perception is mapped on hMT+ columnar-like features with a paradigm in which motion coherence requires interhemispheric integration and incoherence breaks such binding across hemispheres (Wallach, 1935).
We acquired 7 Tesla fMRI data (0.8 mm isotropic resolution, TR=2000 ms, TE=26 ms, 28 slices echo planar imaging (EPI)) from 9 healthy participants, presented with a bistable (ambiguous) stimulus. The ambiguous stimulus consisted of continuously moving oblique lines forming a v-shape. With central fixation, participants alternated between two percepts: downward global motion perception (the lines are perceived moving downward as a single roof-like object) and the inward movement perception (the lines are perceived as two separate objects, one in each visual hemi-field, moving inward). An unambiguous (control) stimulus was also presented to the participants. By disambiguating the stimulus with additional moving dots the participants were biased to unambiguously perceive each kind of global percept, as induced by dot motion. In order to functionally localize direction of motion-tuned columnar-like features in hMT+, we also showed participants blocks of moving lines in different axes of motion, interleaved with static lines. Since previous studies have reliably mapped axes-of-motion, we pooled responses with opposing directions (Zimmermann et al., 2011). Analyses results were considered using only significantly activated voxel clusters at P<0.05 (corrected).
In all participants, both ambiguous and unambiguous stimulation conditions evoked stronger hMT+ bilateral activation during inward movement perception, entailing interhemispheric segregation, than downward (implying interhemispheric integration), which is to be expected if distinct neuronal assemblies are activated during inward motion, i.e. leftward plus rightward movement, compared to a common population for downward motion. Furthermore, for ambiguous stimulation the hMT+ correlation across hemispheres tend to be higher during downward coherent percept than during the inward percept. The definition of the axes of motion preference was confirmed by the successful automatic classification of each displayed movement orientation. The analysis of the ambiguous task results inside groups of voxels with different axes of motion preferences confirmed a higher activation of voxels with preference for the vertical movement during the downward movement perception than during inward movement perception. On the other hand, voxels with preference for the horizontal movement showed increased activation during inward perception, suggesting that perceptual interhemispheric representations can be found at the columnar level (Fig.1).
We conclude that perceptual representations requiring either interhemispheric segregation or integration can be localized at the columnar level in area hMT+. Accordingly, different movement percepts are bilaterally modulated by hMT+ columnar-level responses with different axes of motion preferences: the inward percept (entailing segregation) modulates activity in the columns preferring the horizontal axis of motion, and the downward percept (entailing integration) modulates activity in the columns preferring the vertical axis of motion. Our results extend to the interhemispheric domain previous studies suggesting an important role for hMT+ columns in representing bistable perception (Goebel et al., 2014; Schneider et al., 2015) and demonstrating that not only the transition of perceptual states but also the content of perception can be read-out directly from the activity patterns across axes of motion columns in hMT+ area.
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|Secondary author(s): |
|Kemper, V., Costa, G., Duarte, J., Martins, R., Goebel, R., Castelo-Branco, M.|
|Document type: |
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|Sousa, T., Kemper, V., Costa, G., Duarte, J., Martins, R., Goebel, R., & Castelo-Branco, M. (2016, June). Long-range perceptual integration of visual motion revealed at high resolution 7T fMRI. Poster presented at the 22nd Annual Meeting of the Organization for Human Brain Mapping, Geneve, Switzwerland. Abstract retrieved at https://ww5.aievolution.com/hbm1601/index.cfm?do=abs.viewAbs&abs=2467|
|Indexed document: ||No|
|Keywords: ||Functional magnetic resonance imaging (fMRI) / high field MR / Perception|