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
what can be measured when applying repetitive rTMS?
whether and for how long a specific cognitive task is impaired
what is the probing excitability approach?
- whats measured
- test how responsive or excitable the motor cortex is during a cognitive task
- if the motor cortex is required for a cognitive task it should already be activated when single-pulse TMS is delivered
- how strongly the motor cortex reacts to the pulse
probing excitability approach is measured by recording what, using what?
MEPs using the EMG -> electrical activity of muscles
probing excitability approach
- area stimulated
- how MEPs are processed (results)
- central sulcus
2. MEPs for each stimulation and compare average MEPs between experimental conditions
Eisenegger study:
- results
- evidence
- stimulation of M1 during mental rotation elicited stronger MEPs as compared to baseline, reading aloud and silently
- M1 more excitable during mental rotation
Bode study:
- study
- results
- > possibly..?
- does involvement of M1 depend on strategy used?
- MEPs equally high for mental rotation of all stimuli
- hands lowest
- > M1 more excitable because of adjacent brain regions?
what is the paired-pulse approach?
two pulses delivered in brief succession
- one sub-threshold, the other supra-threshold
Fitzgerald study
- study - define CSP
- results
- schizophrenia. - a period of suppression of tonic motor activity following descending excitatory activity
- compared to controls, patients with and without medication showed stronger responses to second pulse -> general deficits in motor inhibition
clinical application of TMS
- endorsed TMS as treatment for depression
- 1 hemisphere stimulated -> depression is linked to imbalance of prefrontal activity between hemispheres
- treatment is last resort
- TMS debated as treatment for other mental disorders
