| Research Abstract |
Motor activities in daily life are usually guided by vision and thus involve a process whereby visual information is* transformed into plans of motor actions. To investigate, the cortical processing required for visuomotor transformation, we applied focal transcranial magnetic stimulation (TMS) over various cortical regions while the subjects performed in a visuomotor task. This was to induce a transient derangement in cortical processing ("virtual lesion") and behavioral changes.
The task was to press either of the two buttons (either left of right) with the left or right hand quickly in response to two visual cues presented successively at random intervals on a monitor screen. The first cue (precue) provided the subjects with full, partial or no advance information about the mot action to be performed, while the second cue fully specified the action and also served as the go-signal for the response. TMS was applied over 15 locations over the left and right hemisphere at various interv
… More
als (100, 150, 200, 250, 300, 350 ms) after the second cue and before the reaction time (RT) [over the dorsolateral prefrontal cortex (DLPFC), premotor cortex, motor cortex, anterior parietal cortex (apc), and posterior parietal cortex (ppc) of both hemispheres]. In control trials, TMS was delivered at locations -5, -2, 5, 0, 2.5, 5 cm anterior to Cz on the midline at the same intervals. RT was measured from the time of go-signal, and the delay induced by TMS was calculated by subtracting the control RT from test RTs with TMS delivered over lateral scalp regions.
In control trials, RT became shorter with the amount of advance information. TMS induced a delay in RT bilaterally over posterior cortical sites (APC, PPC) when applied at early intervals (100-150ms), over anterior cortical sites (DLPFC) at intermediate intervals (200-250ms), and over the left motor cortex at late intervals (300-350ms) regardless of the amount of precued information. In addition, at an intermediate interval (150-200ms), TMS induced a delay over DLPFC in partial or no information precue conditions, and the delay decreased with the increase in precued information. The results suggest a progression of cortical information flow from posterior to anterior cortical regions, and finally to the motor cortex, with a left hemispheric dominance. Less
|
