The overall goal of this procedure is to explore state dependency effects on phos phenic behavior as elicited through transcranial magnetic stimulation. This is accomplished by first determining baseline phos threshold and behavior over both V one, V two and V five MT plus. The second step of the procedure is to prime specific neural reactions via visual adaptation as achieved through the presentation of specific visual stimuli.
The third step of the procedure is to determine new phosphoric behavior over both V one V two and V five MT plus. The final step of the procedure is to chart and compare the second set of induced phosphines with the original baseline set of phosphines. Ultimately, results can be obtained that show specific predictable phosphine behavior can be engendered through visual adaptation to unique visual stimuli.
The implications of this technique extend to therapy for numerous neurological or physical melodies currently treated by TMS as it reveals. Guided activity undertaken before therapeutic treatment such as light physical therapy or psychotherapy may have important and predictable effects upon TMS and its outcomes. To begin, seat the subject in a comfortable chair in front of a computer screen adjacent to the TMS setup.
Take a moment to explain the details of the experiment and be sure to screen the subject to assure that there are no counter indications to TMS at this point. Both the subject and the researcher should insert earplugs for hearing protection. Now, introduce the subject to the TMS machine by discharging a few pulses so that he or she can hear the clicking sound Again.
There you go. And feel the tapping sensation so that the stimulation locations can be marked in subsequent steps. Place a swim cap over the patient's head assuring that it fits well and will not slip during the experiment.
Next, use a tape measure to ensure the distance between the computer screen and the subject's nasion is 60 centimeters. Make sure the subject can remain seated comfortably for the rest of the experiment so that this distance does not change. Finally, place a light blocking mask over the subject's eyes.
The mask should be adjusted to fit well with no light leaks so that phosphines can easily be detected and reported by the subject during the rest of the experiment. Next, the subject's phosphine threshold will need to be determined since knowing this will be important when exploring phosphoric behavior later in the protocol. To determine this threshold, first, set the TMS machine to 70%power.
Now hold the coil so the top of the figure eight faces the cranial midline and to point about three centimeters above the inion and begin single pulse stimulation. Here we are stimulating the left hemisphere. Move the coil in a small search grid around this region to determine the location where stimulation elicits consistent and unambiguous phosphine reports from the subject.
Oh, did you see anything? Yeah, it's kind of like a, like a blobby thing over here. However, keep in mind that TMS may be unable to elicit phosphines in around 40%of the population, so there is a chance that the subject will not report anything.
If this is the case. Unfortunately, this experiment will not work and the subject should be allowed to leave. If a phos phenic hotspot can be located, be sure to mark this location on the subject scalp.
Now adjust the TMS power output up and down until the subject reports phosphines for exactly three of six consecutive pulses. Record this power level as the subject's V one V two threshold. Next, using the same procedure and parameters as in the previous step, we will determine phosphine threshold over the V five mt plus complex to locate this region First, move the coil to a 0.3 centimeters dorsal and five centimeters lateral to the subjects in Ian.
Now begin single pulse stimulation. See anything? And once again, after each pulse, ask the subject to report any phostic experience.
Could you point to it and describe It's right here. It's a ball that goes Whoop. Again, using single pulses, begin a small search grid pattern.
Moving the coil until unambiguous and consistent phosphines are elicited. Mark this location as the subject's V five MT plus hotspot. Finally adjust the TMS power output up and down until the subject reports phosphines for exactly three of six consecutive pulses.
Record this power level as the subject's V five MT plus complex threshold. Once phosphine threshold has been determined for both visual areas, the subject's baseline phospho behavior will need to be measured. To do this, dim the lights in the room and remove the subject's light blocking mask.
Now instruct the subject to stare at a stable fixation cross presented in the center of the computer screen for 60 seconds. It is important that the eyes remain centered on the cross. Replace the mask and over the V one V two hotspot.
Generate a single pulse train for three seconds at 120%of the V one V two threshold. Then wait five seconds and conduct another train. Again, wait five seconds and then conduct a third train.
After the third single pulse train, ask the subject to describe the location and motive characteristics of any elicited phosphines. Yeah, I saw just the same things we were talking about earlier. Just right over here.
Just This will be the subject's baseline phosphine response Every time you zapping. Next, reset the TMS power to 120%of the V five empty plus threshold and move the coil over the V five empty plus hotspot. Repeat this same procedure in this location administering three pulse trains and record the elicited phosphine description here as well.
Now that the phosphoric baseline has been determined, her game, remove the subject's light blocking mask and instruct the subject to stare at a stable fixation cross presented in the center of the computer screen for 60 seconds. However, rather than a blank screen this time, we will embed a series of moving dots at several locations around the cross, all moving in the same direction. This stimulus should serve to engender visual adaptation so that prolonged exposure to the stimuli should serve to bias the perception of subsequently presented stimuli.
After 60 seconds, replace the mask and over the V one V two hotspot. Generate a single pulse train for three seconds at 120%of the V one V two threshold. Wait five seconds and repeat two more times.
After these three trains, ask the subject to report the locations and motive characteristics of any elicited phosphines. Continue this three train report sequence until phosphine behavior returns to baseline activity. After V one V two phosphine behavior returns to baseline remove the subject's mask and again, have him watch the stimulus after 60 seconds, replace the mask.
Finally move the stimulation coil to the V five empty plus complex hotspot and repeat this step in the protocol for this location. At 120%of the V five MT plus threshold stimulation for the second condition uses the same procedure as condition one. However, rather than presenting the subject with a series of dots moving in a single direction, present a series of dots each moving in its relative cardinal direction away from a central point similar to a starburst pattern as seen here as before.
After 60 seconds, replace the mask. Conduct a series of three, 120%threshold trains over V one V two. Ask the subject to report phosphenes and continue until baseline returns.
Once more, remove the mask and ask the subject to watch the starburst stimuli for 60 seconds. Then again, using the same stimulation parameters as the previous step, repeat this procedure for the V five mt plus hotspot.Okay. Could you describe To me what you Saw?
Sure.It was like a, a starburst type, like a like a firework thing over here going As an option. After each condition or after both conditions are completed, ask the subject to draw the region's emotive behavior of each set of phosphines onto a graph. This is not an integral step, but it will provide another set of interpretable data.
Here we again see the adapting stimuli for condition. One simple translational motion. All dots move coherently either to the left or right.
The phosphines induced from V one V two in the right and left hemisphere. During condition one should elicit an identical phospho movement over V one V two as seen here. Here we see the adapting stimuli for condition two radial motion dots moving respective cardinal directions, either towards or away from a central point, and here we see example drawings of phosphines induced from the V five mt plus complex in the right and left hemisphere during condition two.
Visual adaptation to the starburst pattern should elicit an identical starburst phospho movement from the V five mt plus complex, but should not change the V one V two baseline. After watching this video, you should have a good understanding of how to engender specific and predictable spheric behavior via visual adaptation before TMS stimulation. This is the essence of state dependency.
Identical stimulation or identical neural regions can and will elicit varied responses depending upon the initial neural state of each subject.
