其他摘要 | Biological motion perception is essential for individuals’ survival, development and social interaction, which is innately inherited and evolutionary conserved cross many species. The ability to recognize biological movement is so stable that the observers are able to perceive the movement of a dozen point-light attached to the joints of an actor as a moving person, and can identify gender, identity, emotion, etc. from them. Despite the substantial behavior, brain imaging and brain damaging studies regarding this topic, the neural mechanism of biological motion perception still remains unclear due to lacking of electrophysiological evidence. To investigate the neural coding mechanism of biological motion information, we used point-light biological motion, depicted by motion cues alone, to study how biological motion information is processed on the basis of kinematics alone. A plenty of electrophysiological studies have shown that MT (medial temporal area) and MST (middle superior temporal area) are two important motion sensitive brain area in the dorsal visual pathway. Therefore, we chose MT and MST in macaque to explore the neural mechanism of encoding biological motion information.
In this study, the electrophysiological recording technology for awake monkeys was used to record the electrical activity of neurons while the monkeys were passively viewing different kinds of visual stimuli. The visual stimuli used in current experiment included both biological motion and optic flow. The biological motion visual stimuli were classified into form intact and form scrambled according to form information; up and down according to inversion information; right and left according to walking direction. The optical flow stimuli included linear (8 directions with 45°apart ) and non-linear (expansion, contraction, clockwise, and counter-clockwise).
We found that MST neurons are capable of extracting form information from motion kinematic signals, and encoding inversion and discriminating walking directions. More importantly, our results revealed that biological motion information is dynamically encoded in the temporal structure of evoked spikes trains, instead of average firing rate during stimulus presentation. MT neurons cannot extract form information from biological motion, but can discriminate inversion and walking directions. Although MT and MST neurons can encode inversion, MST neurons’ modulation induced by upright biological motion was significantly higher than inverted condition, but this is not the case for MT neurons. Furthermore, the capability of MST neurons in detecting various biological motion features is closely related to the neuronal selectivity to optic flow pattern. These results suggest that macaque MST neurons is capable of encoding biological motion information in a dynamical mode, and this capability to encode biological motion features may stem from the selectivity of MST neurons for optical flow pattern. These results indicate that MST is a key brain area for biological motion recognition, and to a large extent reveal the neural coding mechanism for processing biological motion information in the dorsal visual pathway. |
修改评论