Authors:

SHTYROV, Y., PULVERMULLER, F. & Ilmoniemi, R.J

Reference:

Year of publication:

2003

CBU number:

5743

Abstract:

Associative learning theory predicts that word form and semantics are tightly interwoven in the cortex. Action words referring to leg movements [e.g., to kick] should therefore activate cortical areas dorsal to those activated by words referring to actions performed with the upper body parts [to eat; semantic topography hypothesis; 1]. In earlier studies, action words activated different areas in the fronto-central cortex [Hauk et al., Pulvermuller et al., this volume, 2]. Here, we ask when the word-category-specific activity spreads toward fronto-central areas, and whether this differential activation is present when subjects are instructed to ignore stimulus words and watch a silent video film.

Method

16 right-handed native speakers of Finnish heard the Finnish words hotki (to eat) and potki (to kick) presented as rare (p=.17) deviant stimuli in trains of frequent standard stimuli (SOA=1.4s). Standard stimuli ended in the second syllable pi. 100-250ms after the critical stimulus divergence point (onset of second syllable), deviant stimuli elicited the magnetic Mismatch Negativity [MMNm; 3]. To reveal the cortical sources of the MMNm, Minimum Current Estimates (MCE) 4 were performed on individual subjects? data. ROIs for statistical analysis were defined so that they included superior temporal, inferior frontal, inferior central (face/hand) and superior central (leg) areas.

Results

MCEs indicated that in the left hemisphere the two words activated the four ROIs to different degrees (significant interaction Word x ROI). Planned Comparison Tests confirmed stronger activation to potki than hotki in the leg ROI, whereas the inferior frontal and central ROIs revealed stronger activation to the face/arm word hotki compared with the leg word. Time course analyses showed differences in the activation latencies of left hemispheric ROIs. Superior temporal sources sparked at 160ms after the divergence point, followed by inferior frontal (172ms) and inferior central (arm) sources, and, finally, the superior central (leg) ROI (200ms).

Conclusions:

150-200 after information about stimulus words is present in the input, a leg word activated leg areas in superior central motor and/or premotor cortex, and a face-/arm-related word activated inferior frontal areas anterior to the motor cortex, probably in premotor and prefrontal areas. Aspects of word meaning are reflected in early quasi-automatic word-evoked cortical activity. These data support the topography of meaning hypothesis [1] and may provide clues about the time-course of semantic brain processes.

References


1. Pulvermuller, F. Brain reflections of words and their meaning. Trends in Cognitive Sciences 5, 517-524 (2001).
2. Pulvermuller, F., Hummel, F. & Harle, M. Walking or Talking?: Behavioral and neurophysiological correlates of action verb processing. Brain and Language 78, 143-168 (2001).
3. Naatanen, R. The perception of speech sounds by the human brain as reflected by the mismatch negativity (MMN) and its magnetic equivalent (MMNm). Psychophysiology 38, 1-21. (2001).
4. Uutela, K., Hamalainen, M. & Somersalo, E. Visualization of magnetoencephalographic data using minimum current estimates. Neuroimage 10, 173-180 (1999).