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We investigated some of these issues experimentally using an intact isolated turtle cerebellum\n                  <jats:italic>in vitro,<\/jats:italic>\n                  employing a novel chamber designed to deliver precisely calibrated induced electric fields along cortical depth. Our results show that single-pulse TMS can directly activate Purkinje cells and climbing fibers, and synaptically activate Purkinje cells via climbing fibers \u2013 all within the first 1.2 ms. Specifically, current source density analysis showed that TMS directly (non-synaptically) activated (1) climbing fibers near the bend with intracellular current directed toward the axonal terminals and (2) Purkinje cells directly near the axon initial segment with intracellular current directed toward the distal dendrites. The thresholds for direct activation of climbing fibers and Purkinje cells were found to be very similar, 25 \u00b1 1 V\/m. The climbing fibers synaptically activated Purkinje cells, as expected, with intracellular current originating in the proximal dendritic trunk and directed toward the distal dendrites. At higher electric fields (&gt; 58 \u00b1 17 V\/m), TMS synaptically activated dendritic currents in Purkinje cells. These results provide new insight into how TMS may activate afferent fibers and cell bodies of cortical neurons.\n                <\/jats:p>","DOI":"10.64898\/2026.05.12.724125","type":"posted-content","created":{"date-parts":[[2026,5,14]],"date-time":"2026-05-14T08:55:26Z","timestamp":1778748926000},"source":"Crossref","is-referenced-by-count":0,"title":["Cellular Mechanisms of Transcranial Magnetic Stimulation in Climbing Fibers and Purkinje Neurons in the Cerebellum"],"prefix":"10.64898","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-4372-6384","authenticated-orcid":false,"given":"Yoshio","family":"Okada","sequence":"first","affiliation":[{"name":"Division of Newborn Medicine, Department of Pediatrics, Boston Children\u2019s Hospital, Boston, MA 02115"},{"name":"Harvard Medical School, Boston, MA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Chunling","family":"Dong","sequence":"additional","affiliation":[{"name":"Athinoula. A. 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