Transcranial magnetic stimulation (TMS) intensity dependent alterations in regional cerebral blood flow

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  • NemoImage 13, Number 6, 2001, Part 2 of 2 Parts 10E@w PHYSIOLOGY

    Transcranial Magnetic Stimulation (TMS) Intensity Dependent Alterations in Regional Cerebral Blood Flow.

    Nitin Tandon*t, Shalini Narayanat, Frank Zamarripat, Jack Lancaster?, Peter Fox? *Division of Neurosurgery University of Texas Health Science Center - San Antonio, Texas, USA TResearch Imaging Center University of Texas Health Science Center San Antonio, Texas, USA

    The intensity of stimulation is a variable intrinsic to all TMS experiments. Stimulus intensity is a measure of the strength of the induced electrical field, a factor crucial in determining the extent of neuronal reactivity. We seek to evaluate the effect of varying TMS intensity on induced cortical neuronal responses in a direct and accurately quantifiable manner using [O-15]H20 PET.

    Methods Eight right handed volunteers underwent concurrent TMS-PET. TMS of the right supplementary motor area (SMA) was carried out at 3 Hz, at intensity levels of 75%, 100% and 125% of motor threshold (mt). A neurosurgical robot NeumMate@, was used to position and to hold the B shaped TMS coil. Scans were acquired during TMS, during sham TMS and during volitional left hand movement. Following spatial normalization, statistical parametric images of z scores (SPI{z)) were generated by contrasting real vs sham TMS for the entire group at each intensity level as well as per individual. Positive extrema in the right SMA were obvious in all SPI( z} images. Defining characteristics of extrema (z> 1.96) from the groupwise contrasts per intensity level - peak z score and cluster size were computed. SPI( z) generated per subject was used to localize the peak voxel in the SMA. Individualized regions of interest (ROIs) were then used to sample each value normalized (VN) PET injection and SPI[ z} per subject, per intensity level. Fig 1 - Locations of peak voxels in the ex-

    trema within SMA from SPI[ z) of the group (n=8) contrasting different intensities of TMS stimulation and hand movement with sham TMS (p

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