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By Oscar Wiksell

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By Oscar Wiksell

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  1. Neuroscience articleEvidence for impaired cortical inhibition in schizophrenia, using transcranial magnetic stimulationZafiris J. Daskalakis, MD , FRCP(C); BruceK. Christensen, PhD, Cpsych; Robert Chen, MBB Chir, MSc, FRCP(C) ; Paul B. Fitzgerald, MBBS, MPM, FRANZCP; Robert B. Zipursky, MD, FRCP (C) ; Shitij Kapur, MD, PhD, FRCP (C) By Oscar Wiksell

  2. Background • Evidence suggest that schizophrenia is a disorder associated with deficits in cortical inhibition. • This article used 3 different types of TMS to asses cortical inhibition in schizophrenic patients. • Deficits in cortical inhibition havebeen demonstrated in cognitive, motor, neurophysiologic and neuropathologic studies.

  3. Methods • Transcranial magnetic stimulation non-invasive technique to excite neurons. • 3 types used: • Paired pulseTMS • Cortical silent period • Transcallosal inhibition

  4. Methods • Paired pulse TMS • Stimulating with a lowerintensitypulse a few ms, before a higherintensitypulse. Therebyinhibitingsize of the motor evoked potential produced by higherintensitypulse. • Cortical silent period • Inhibition is reflected by the silent period duration. (duration of EMG activity cessation following a TMS induced motor evoked potential) • Transcallosal inhibition • Involves stimulation of contralateral motor cortex several ms prior to stimulation of ipsilateral motor cortex. Inhibiting size of motor evoked potential produced by ipsilateral stimulation.

  5. Methods • 15 unmedicated patients with schizophrenia. • 15 medicated patients. • 15 healthycontrols. • EMG recordings of the right and left first dorsal interosseusmuscle.

  6. Results • ppTMS • Unmedicated 31,2% less inhibtioncompared to healthy. • Medicated 15,64% less inhibtion comared to healthy. • CSP • 15,26 ms shorter in unmedicatedcompared to healthy. • 5,38 ms longer in medicatedcompared to healthy. • TCI • Unmedicated 23,25% less inhibition compared to control. • 9,92% less inhibition in medicatedcompared to healthy.

  7. Conclusion • Results demonstrateunmedicated patients with schizophrenia havesignificant deficits in CI, compared with healthycontrolsacross all 3 TMS types. • Medicationseemed to reduce CI deficits in these patients. • Results demonstrate CI deficits in ppTMSwerecorrelated with severity of psychosis. No othermeasure of CI wascorrelated with degree of psychosis. • Disrupted CI may present an importantneurophysiologicmechanismresponsible for the symptoms in patients with schizophrenia.

  8. Conclusion • Limitations to these experiments • CI differenciesbetweenumedicated & medicated patients were not significantacross all measures. Small effects, limitedsamplesize and largevariance in measures. • Not certainifdifferencesobservedwheretrulyresult of medicationeffects or related to other variables (duration of illness) • Unclearifdifferencies in CI in mediatedgroup wererelated to effects of medication on GABA, dopamine or someother neurotransmitter system.

  9. Thank you!

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