tms in clinical practice non standard methods n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
TMS in Clinical Practice Non-Standard Methods PowerPoint Presentation
Download Presentation
TMS in Clinical Practice Non-Standard Methods

Loading in 2 Seconds...

play fullscreen
1 / 27

TMS in Clinical Practice Non-Standard Methods - PowerPoint PPT Presentation


  • 67 Views
  • Uploaded on

TMS in Clinical Practice Non-Standard Methods. SILENT PERIOD: during voluntary contraction of the target muscle TMS evokes a MEP followed by a period of inhibition of the ongoing EMG activity The SP :

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'TMS in Clinical Practice Non-Standard Methods' - thetis


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
tms in clinical practice non standard methods
TMS in Clinical PracticeNon-Standard Methods

SILENT PERIOD: during voluntary contraction of the target muscle TMS evokes a MEP followed by a period of inhibition of the ongoing EMG activity

The SP:

- is expressed in msec and measured from the onset of MEP to the restart of a constant EMG activity (approximately >25% of pre-stimulus level)

- gives information on GABA-mediated mechanisms controlling motor cortex excitability

slide3

Cortical Silent Period

  • The SP evoked in the muscles of the upper limb originates largely from activation of cortical inhibitory interneurons, although spinal mechanisms are involved in the early part
  • The SP recorded from the facial muscles originates solely in the cortex
  • SP is longest in hand muscles and is shorter in proximal arm, leg muscles facial muscles diaphragm and anal sphincter
  • In upper limb muscles, the SP can be evoked at lower stimulus intensities than the MEP
  • SP duration is related to the intensity of stimulation but is not strongly related to the size of the preceding MEP nor to the levels of background EMG activity
slide4

Cortical Silent Period

  • SP duration can be modulated by physiological phenomena that change cortical excitability,
    • hyperventilation
    • sleep deprivation
    • muscle fatigue
    • high-frequency rTMS.
  • Pharmacological studies using benzodiazepines, selective agonists of the benzodiazepine receptor subtype BZ1, baclofen, tiagabine provided evidence that the SP reflects a long-lasting cortical inhibition mediated by GABAB receptors.
  • Dopaminergic drugs lengthen the SP in normal subjects
contralateral and ipsilateral sps
Contralateral and Ipsilateral SPs

A similar period of silence can be observed also in the ongoing EMG activity of the ipsilateral muscles.

Such ipsilateral silent period probably originates from transcallosal inhibition

slide6

Il periodo silente “ipsilaterale” origina dall’attivazione di vie inibitorie transcallosali, per cui può essere utilizzato per misurare la conduzione attraverso il corpo calloso

tms in clinical practice non standard methods1
TMS in Clinical PracticeNon-Standard Methods

80-90% RMT

95% AMT

1 mV

conditioning

test

  • PAIRED TMS: two magnetic stimuli can be delivered with:
    • different intensity of stimuli
    • variable interval between them (inter-stimulus intervals)
tms in clinical practice non standard methods2
TMS in Clinical PracticeNon-Standard Methods

The test stimulus (suprathreshold) can be inhibited by a conditioning (subthreshold-80-90% RMT) stimulus given 1-5 msec before (INTRACORTICAL INHIBITION - SICI) or can be facilitated when the interval is longer than 7 msec

(INTRACORTICAL FACILITATION - SICF)

The conditioned test MEP is measured from peak-to-peak and expressed as a percentage of the unconditioned test MEP.

Kujirai et al. 1993

intracortical inhibition and facilitation
Intracortical inhibition and facilitation

These phenomena originate in the cortex from different neuronal populations:

GABAA receptors mediate the enhancement of intracortical inhibition

glutamatergic receptors mediate intracortical facilitation

slide11

Intracortical Inhibition and Facilitation

  • GABAA-agonists:> ICI
  • < ICF
  • NMDA-antagonists:> ICI
  • < ICF
  • DA-agonists:> ICI
  • < ICF
  • DA-antagonists:< ICI
  • > ICF

GLU rec.

SICF

GABAA rec.

SICI

slide12

GABA-A

GABA-B

SICI

SP

Hanajima et al. 1998

Werhahn et al. 1999

slide15

GABAA receptor subtype specific enhancement of inhibition

in human motor cortex:

SICI is not mediated by the α1-subunit-bearing subtype of the GABAAR

but by those bearing either the α2- or α3-subunit

*

*

slide16

ICF

Paired pulse transcranial magnetic stimulation at 10-25 ms ISIs

slide18

Transcranial magnetic stimulation

EMG recordings

(FDI)

Median nerve

stimulation

ISI= N20 + 2-8 ms

slide19

I1

  • Short latency afferent inhibition
slide20

Short latency afferent inhibition

Baseline After Scopolamine

Test

ISI=N20 latency + 3 ms

slide22

Gulledge AT, Stuart GJ. Cholinergic inhibition of neocortical pyramidal neurons. J Neurosci. 2005;25:10308-20

slide23

GABAA receptor subtype specific suppression of afferent inhibition in human motor cortex:

α5-subunit ?

*

*

*

*

slide27

Input-Output Curves

Cortical Maps

Measure of the number and topographical representation of excitable sites