Saturday, October 15, 2011

re: Thesis Overview


Supervisor: Dr. JFX DeSouza (link)
MEG Analyses Mentor: Dr. P Ferrari

Research questions

Part 1: Motion perception (fast & slow moving dots)
  • Is there different cortical representation for fast & slow motion?
  • Are there different temporal dynamics for fast & slow motion?
Part 2: Decision-making
  • Subjects need to detect a change in the motion velocity and respond with button press
  • When and where in the brain is a visual perception (velocity change) transformed into the neural signals for action?

  • Prior to the imaging sessions, I conducted a perceptual thresholds test (N=22) to acquire the minimal detectable increase and decrease in motion velocity for the subjects
  • I set up the experimental environment and collected MEG & MRI data (N=12) with the helps from S. Bells and M. Lalancette at Toronto Sickkids hospital.
    • Velocity change in the experiment was set according to each subject's perceptual thresholds, so the correct and incorrect responses could be compared
    • A delayed motor response paradigm was used to separate decision-making signals from motor related signals.



Part 1 - Motion Perception
No difference in the MT+ locations (Talairach) for fast and slow motion was found (Hotelling's T2 for two multivariate independent samples)
Fig - MT+ locations
Fig - comparing the MT+ locations with previous studies

No temporal dynamics for source peak amplitude and latency found
  • Velocity and visual display had no effects (3-way ANOVA)
  • The amplitude and latency btw the three ROIs were different (P<.05)
  • Multiple-comparison showed cuneus had higher amplitude & earlier latency than V3A & MT+

Part 2 - Decision-making
Comparing the grand average event-related beamformer images: 
  • In the correct responses, the frontoparietal sources were observed at various time points after the velocity change onset (left column, perm-test, P<.05)
  • No significant frontoparietal activations were observed in the incorrect responses (right column)

Comparing the time-frequency plots for correct and incorrect responses from IPL and SMC sources:
  • IPL source showed a beta power difference between correct and incorrect responses from 200 - 400 ms (area encircled in dotted line)
  • The initiation of IPL beta ERS was aligned with the high beta ERD increase in SMC after 400 ms (dotted line)

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