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Abstract:
An essential need of brain function is the detection of living entities, and one of the major characteristics for their identification is their motion. Humans are very good at recognizing living entities from their motion, and attribute animacy to even very simple objects displaying self-propelled or goal-directed motion. Our previous results (1) show that increasing correlation between the movements of two simple interacting objects leads to A) an increase in the impression of goal-directed motion and of animacy and B) to increasing BOLD signal in the superior temporal sulcus (STS), suggesting that STS is involved in decoding the information leading to the percept of animacy. This is consistent with previous studies implicating the posterior part of the STS in recognition of biological motion. In the current study, 7 volunteering patients undergoing investigations prior to epilepsy surgery observed the animate motion stimuli used in (1). Simultaneously, we recorded multichannel subdural electrocorticogram data from healthy cortex surrounding the STS and performed trial-by-trial frequency decomposition over time. We found that power in the 30-60Hz frequency band (gamma band) between 1 and 2 seconds after stimulus onset showed a significant parametric response to the amount of goal-directed motion, paralleling our previous BOLD signal findings (1). Furthermore, due to the high temporal resolution of these data, we were able to localize at which time points during the animations the strongest response in the STS occurred. Our results confirm the importance of the STS in processing of visual characteristics of animate entities, and suggest that neuronal activity in this area changes over the duration of the animations. We are currently comparing time-varying attributes of the stimuli to the time-course of gamma-band activity to reveal which events in the stimuli drive STS activity.
