Presentation is loading. Please wait.

Presentation is loading. Please wait.

Stimulating language: Insights from TMS Joseph T. Devlin MSc Neuroscience, Language & Communication 16 November 2011.

Similar presentations


Presentation on theme: "Stimulating language: Insights from TMS Joseph T. Devlin MSc Neuroscience, Language & Communication 16 November 2011."— Presentation transcript:

1 Stimulating language: Insights from TMS Joseph T. Devlin MSc Neuroscience, Language & Communication 16 November 2011

2 Lack of animal models I say, is that a banana?

3 Neurology of language Intra-cortical mappingStrokes & Disease

4 MRI studies of brain structure PET and MRI studies of brain function Non-invasive methods

5 Magnusson & Stevens (1911-1912) Magnetic stimulation elicited phosphenes Magnetic stimulation

6 Barker, Jalinous & Freeston (1985). Lancet, 11, 1106-7.

7 Transcranial magnetic stimulation

8 TMS coil current 8kA Magnetic field pulse 2.5T Rate of change of magnetic field 30kT/s Induced tissue current 15mA/cm 2 Induced electric field 500v/m How does it work?

9 Its fun -- really!

10 Speech arrest with TMS

11 Semantic decision (Synonyms?) Sentence completion: Meaning Categorisation (man-made?) Meaning preferentially engages anterior, ventral Brocas area Brocas area re-visited

12 Phonological decision (Homophones?) Sentence Completion: Rhymes Two syllables? Sounds of words (or sentences) preferentially engage posterior, dorsal parts of Brocas area

13 Common activations BUT… both sound and meaning engage all of Brocas area relative to low level baselines Word pairsSentencesSingle words

14 Two possibilities 1.Necessary processing quantitative difference 2.Incidental processing qualitative difference Semantic Phonological

15 rTMS None Rostral Caudal Semantic Phonological Gough et al (2005). J Neuroscience rTMS None rTMS None rTMS None Subdividing Brocas area Is there a double dissociation in LIFC for semantic and phonological processing? Are both areas engaged by both types of processing?

16 TMS Results

17 Rostral:-52, 35, -74 × 6cm Caudal:-52, 15, 82 × 3cm Mean distance in cortex of 2.3cm apart Sites on scalp separated by 3.5cm, on average MNI coordinatesRelative to C-T line Anatomic localisation

18 * Single pulse TMS Devlin et al (2003). J of Cognitive Neuroscience No TMS

19 Motor evoked potentials

20 Functional connectivity Seyal et al. (1999). Clin Neurophysiol, 110(3), 424-429. MEP magnitude in hand during reading Before +

21 Functional connectivity Seyal et al. (1999). Clin Neurophysiol, 110(3), 424-429. MEP magnitude in hand during reading Before After officer

22 Implications Evolutionary link? Or inexplicable link between hand gestures and language (most refined in Italian speakers)?

23 Actions and motor cortex Buccino et al. (2005). Brain Res Cogn Brain Res, 24(3), 355-363. He turned the key. He kicked the ball. He forgot the name.

24 Speech comprehension Watkins et al. (2003). Neuropsychologia, 41(8), 989-994.

25 Somatotopy of speech Results DAusilio et al. (2009). Current Biology, 19, 381-5.

26 Disrupting speech perception Meister et al. (2007). Current Biology, 17, 1692-6. TMS Results

27 Recovery from aphasia L R peri-lesional activation Contralateral activation

28 Stimulating IFG in patients Thiel et al. (2006). Brain Lang. 98(1): 57-65. No effect

29 Pre-morbid differences? Knecht et al. (2000). Brain, 123 ( Pt 1), 74-81. Lateralisation in 324 normal adults by fTCD Left Right

30 Laterality affects susceptibility Knecht et al. (2002). Nat Neurosci, 5(7), 695-699.

31 Theraputic TMS? Naeser et al. (2005) Neurocase, 11(3), 182-193; Naeser et al. (2005) Brain Lang, 93(1), 95-105

32 Long term enhancement

33 Relation to other methods Walsh and Cowey (2000). Nat Revs Neurosci.

34 PET and TMS Paus et al. (1997). J Neurosci.

35 EEG and TMS Ilmoniemi et al. (1997). NeuroReport

36 Designing experiments for TMS

37 Design considerations 1.Type of stimulation 2.Choosing control conditions 3.Targeting stimulation 4.Choosing parameters 5.Ethical considerations

38 Design considerations 1.Type of stimulation 2.Choosing control conditions 3.Targeting stimulation 4.Choosing parameters 5.Ethical considerations

39 Choosing a type of TMS On-line stimulation occurs while the subject performs a task and the effects last for approximately the duration of stimulation. Eg: Virtual lesions Chronometrics Functional connectivity Off-line stimulation occurs without a task and the length of effect is typically measured in minutes. Eg: 1Hz stimulation Theta burst

40 Repetitive or chronometric? Repetitive stimulation typically involves trains of three or more pulses evenly spaced in time Effect lasts approx. duration of stimulation Dont need to know exactly when to stimulate Lots of pulses Chronometric studies use either single or paired-pulses to examine the processing time course in a region Requires far more trials!!! Subjects tolerate stimulation better How to best order trials?

41 Single pulse TMS No TMS

42 Ordering timing trials No TMS

43 Design considerations 1.Type of stimulation 2.Choosing control conditions Control sites Control tasks Control stimuli Sham stimulation 3.Targeting stimulation 4.Choosing parameters 5.Ethical considerations

44 Control site: Vertex

45 Choosing another control site

46 Control task(s)

47 Sham TMS… …is a sham

48 Design considerations 1.Type of stimulation 2.Choosing control conditions 3.Targeting stimulation Functional localizers Anatomically guided: MRI based stereotaxy Heuristics 4.Choosing parameters 5.Ethical considerations

49 Ventral occipito- temporal cortex Area sensitive to reading words Functionally localize w/ fMRI

50 Rostral site Task: Same category? potato + turnip Caudal site Task: Rhyme? vein + pane 41 ms* 52 ms* Functionally localize w/ TMS

51 Identifying corresponding positions on the subject and subjects MRI scan for registration Frameless stereotaxy

52 Rostral:-52, 35, -74 × 6cm Caudal:-52, 15, 82 × 3cm Mean distance in cortex of 2.3cm apart Sites on scalp separated by 3.5cm, on average MNI coordinatesRelative to C-T line Scalp coordinates

53 International 10-20 system

54 Design considerations 1.Type of stimulation 2.Choosing control conditions 3.Targeting stimulation 4.Choosing parameters 5.Ethical considerations

55 Choosing parameters Stimulation intensity / duration / rate Inter-stimulation interval Type of coil Type of stimulation / stimulator Accessibility Number of trials per condition? Number of subjects in a study? Analysis methods?

56 Design considerations 1.Type of stimulation 2.Choosing control conditions 3.Targeting stimulation 4.Choosing parameters 5.Ethical considerations

57 Ethics of TMS Although the risk is small, it is always present, so there is an obligation on the experimenter to always consider the value of a given experiment How can you minimize risk & discomfort? What is the minimal stimulation necessary? Is the TMS information clear and consent informed? Are subjects always screened? Are the experimenters safety trained? Are emergency procedures clear & in place? Would YOU do this experiment?

58


Download ppt "Stimulating language: Insights from TMS Joseph T. Devlin MSc Neuroscience, Language & Communication 16 November 2011."

Similar presentations


Ads by Google