Investigating Mechanism Of Contour Detection With Transcranial Magnetic Stimulation

The identification of the object contours is one of the most basic functions in the advanced animal vision system.In order to identify the contours accurately,the brain of contour integration mechanism is particularly important.Over the past decades,electrophysiological research has achieved very important results.Initially,it is generally believed that the mechanism of the contours integration is a low-level processing.Later electrophysiological studies,however,have shown that there is a top-down reverse flow in the process of contour integration.In this paper,application of transcranial magnetic stimulation to interfere with the neuronal activity of the cortex,and the neural mechanisms of contour detection are studied from the bottom-up stimulation and the topdown consciousness.And investigating how top-down influences dynamically adapt neural circuits according to contour integration tasks.In the experiment 1,three kinds of stimuli,no contour,obvious contours and unobvious contours were given.The reaction time and accuracy of the three stimuli were measured when TMS was delivered at V1,V2,LOC and BA20 respectively.In addition,when the subject judged error,the contour position will be prompted,and then the subject will judge the orientation of the contour again.TMS was delivered at vertex as control site.The results show that,in accuracy,TMS over V2 does not disrupt performance in all task.TMS over V1 will disrupt the NC task,OBC task and UOBC task.TMS over LOC and BA20 does only disrupt the NC task.In the reaction time,the cortex of the TMS effect is different.TMS over V1 will disrupt the reaction time of NC,OBC and UOBCAH tasks.TMS over V2 only suppresses NC tasks.TMS over LOC dose disrupt performance in NC tasks,OBC tasks and UOBC tasks.TMS over BA20 does disrupt performance in all tasks.We remove the practice process in the experiment 2.Otherwise,the stimulation and procedure was the same as in experiment 1.The results have some differences due to lack of top-down modulation.The difference is that,in accuracy,does not only disrupt the NC task,but also the OBC task.In the reaction times,TMS effect did not cause UOBCAH task disruption in V1.And TMS over V2 cause OBC task disruption.As for the higher cortical LOC and BA20 regions,the TMS effect essentially unchanged.Finally,our evidence suggests that the mechanism of contours integration includes not only the feed-forward process but also the feedback.And the high-level cortex plays a more important role in contour detection tasks.The low-level cortex has a certain processing power for simple contour tasks,but also need further processing by the higher areas.And the difficulty of the contour task is dependent on the high-level areas.In addition,the practice of top-down modulation will strengthen the functional connection between the cerebral cortex,in particular the pathway from BA20 to the primary visual cortex.