TMS: L1-2 Flashcards
what is TMS?
- non-invasive
- creates virtual cortical lesions
what did removing hippocampus, parahippocampal gyrus and amygdala lead to (H.M)
anterograde amnesia
what does TMS do?
-currents
- produces a rapidly changing magnetic field to induce electrical currents in the brain
- currents depolarise neurons ini a small circumscribed area of the cortex
D’arsonval (1896) discovered what?
magnetic stimulation of the visual cortex can elicit phosphenes
how is the current pulse generated?
-capacitor is charged then suddenly discharged
whats rTMS
repetitive tms, fast pulses
what are the loading times and durations of rTMS
100-200μs and <1ms
the figure 8 coil generates what?
-where’s the strongest effect?
- magnetic fields in the opposite direction = more precision
- in the centre, 3-4mm radius
What does a single TMS pulse test?
- disrupts a cognitive function, demonstrating its causal involvement (causality)
whats a way of injecting “neural noise”?
- interfere with the process of interest at exactly the time window during which the regions is requires
- regions don’t stop working completely, but are interfered
Amassian et al study
- what was the study
- what approach
- critical period
- 3 alphabetical letters as stimuli presented under difficult viewing conditions
- neural noise (rTMS)
- 40-120 ms affected letter detection
Amassian study: what was impaired
- left to right stimulation
- top to bottom stimulation
- letters in the contra-lateral visual field were impaired
2. stimulation above the reference line suppressed letters at the bottom of the display
‘visual mask’ study:
1. what did it test
- whether a visual mask can be masked using single pulse stimulation -> unmasking the stimulus
- > TMS can be used to disrupt processing of stimuli, therefore it could disrupt processing of the mask, preventing the stimulus from becoming suppressed
‘visual mask’ study results
- no TMS
- TMS
- unmasking found at what ms
-> what can this inform us?
- 100ms SOA detection rate 0.37
- detection rate 0.9
- 60-140ms stimulation after the mask
-> time-course of processing
what is the virtual lesion approach?
using repetitive TMS to interrupt or enhance cognitive processing