Transcranial Magnetic Stimulation (TMS) Rapid magnetic field changes >> electric current Magnetic field created at scalp with figure-8 coil Electric current induced in neurons in cortex –Adds noise, disrupts coordinated activity –Temporary “lesion” Without the kind of compensation that develops w/ long-term lesions Apply to different areas of scalp & see what functions disrupted –Disruption does NOT mean brain regions directly under coil responsible for function –Only that it’s involved somehow in the function –OR connected to regions involved in the function Get distal effects through connections (“diaschisis”)

TMS Coil Maximum magnetic field at center of figure-8 Naeser et al. (2004), Fig 2, p 100

Rapid-onset brief electrical current generated in coil Produces rapid-onset brief magnetic field pulse (up to 2 Tesla) Induces rapid-onset brief electrical field Induces rapid-onset brief electrical current in brain (mostly cortex) Which has an effect on some task Walsh & Cowey (2000), Fig 2, p 76

Repetitive TMS (rTMS) Most studies so far have used rapidly repeated trains of magnetic pulses –Because single pulses weren’t found to have much effect on gross measures of behavior early on But more recently, single pulse studies have found effects when have constrained hypotheses & more sensitive behavioral measures –Can time single pulse at different steps in a process to see when it has the most effect Very little so far Mostly studying vision & motor processes

TMS & Language Stewart et al. (2001) Stewart, Walsh, Frith, & Rothwell (2001), Neuroimage, 13, –rTMS during speech –Monitored speech, EMG, & videotaped –rTMS at a more posterior frontal region of both the LH & RH produced both Speech arrest & EMG in mentalis muscle –At a more anterior frontal region, only LH stimulation produced Speech arrest But no EMG in mentalis –So, probably different causes of the 2 kinds of speech arrest, & only LH stim leads to the non-muscular type

More TMS & Language Knecht et al. (2002) Knecht, Floel, Drager, Breitenstein, Sommer, Henningsen, Ringelstein, & Pascual-Leone (2002), Nature Neuroscience, 5, –Goal: Evaluate the functional significance of varying degrees of language lateralization –Evaluated lateralization in large sample during silent word production task w/ Functional transcranial Doppler sonography (fTCD) fMRI Grouped subjects into 5 categories from very strongly left lateralized to very strongly right lateralized –Many more subjects w/ L than w/ R lat –Task: Picture-word verification

Knecht et al. cont’d rTMS applied during task to –L & R language areas (CP5 & CP6, ~ Wernicke’s area) –Midline occipital region (Oz) Control, not expected to affect task performance –1 Hz for 10 min*, w/ 30 min* rest between trains Produces disruption lasting up to several minutes –Significant correlation between degree of slowdown & inaccuracy in task w/ degree of lateralization More strongly L-lateralized, more disruption w/ LH stim More strongly R-lateralized, more disruption w/ RH stim Less lateralized, less disruption w/ either H stim * Notice corrections since in-class presentation

TMS vs Wada Test Neurosurgeons routinely use pre-surgical Wada Test to determine gross lateralization of language –So can spare language-related tissue –Risky – occasionally causes stroke TMS less risky, & some proponents argue it should replace Wada test –But others argue that Wada & TMS on the same person disagree too often to rely on TMS yet

TMS as Therapeutic Tool Already used in treatment of depression Naeser et al. (2004) Naeser, Martin, Nicholas, Baker, Seekins, Kobayashi, Theoret, Fregni, Maria-Tormos, Kurland, Doron, & Pascual- Leone (2004), Brain & Language, 93, –Functional imaging studies on non-fluent aphasics often show more activation in RH homologues of LH language areas than normals do Does this represent some kind of adaptive strategy? Is it actually maladaptive? Could TMS suppress this activity, & lead to better language??

Naeser et al. cont’d 4 non-fluent patients, 5-11 years post-stroke Naeser et al. (2004), Fig 1, p 99; (Radiological convention = L & R reversed)

Naeser et al. cont’d rTMS over RH homologue of Broca’s area –Daily for 10 days, 20 min each time Tested picture naming speed & accuracy –Immediately after 10 th session All patients reliably faster & more accurate than their pre-treatment baseline measures –2 months later & 8 months later Effects decreased over time, but continued through 8 mos for 3 of 4 patients

The Right Hemisphere (RH) & Language The RH –Retrieves & holds onto infrequent & contextually inappropriate meanings of ambiguous words Long after the LH settles on what seems to be the contextually appropriate meaning –Plays critical role in understanding non-literal language Puns, idioms, metaphors, sarcasm, etc. Maybe it’s the RH’s job to hold onto stuff that might be relevant, just in case things don’t turn out as the LH thought they would –LH’s job to make quick decisions, which means it’s sometimes going to be wrong & need what RH has kept

TMS Study I’d Like to See What would happen if apply TMS to RH during the comprehension of ambiguous words or idioms or sarcasm? –How much would effects depend on timing of pulse(s)? –How would pulse(s) earlier vs later during the processing of ambiguous words influence whether get priming for targets related to contextually irrelevant meanings of ambiguous words? –How would pulse(s) earlier vs later during idiom comprehension influence whether you get the idiom? –…–…