The involvement of the brain's motor system in action-related language processing can lead to overt interference with simultaneous action execution. The aim of the current study was to find evidence for this behavioural interference effect and to investigate its neurophysiological correlates using oscillatory MEG analysis. Subjects performed a semantic decision task on single action verbs, describing actions executed with the hands or the feet, and abstract verbs. Right hand button press responses were given for concrete verbs only. Therefore, longer response latencies for hand compared to foot verbs should reflect interference. We found interference effects to depend on verb imageability: overall response latencies for hand verbs did not differ significantly from foot verbs. However, imageability interacted with effector: while response latencies to hand and foot verbs with low imageability were equally fast, those for highly imageable hand verbs were longer than for highly imageable foot verbs. The difference is reflected in motor-related MEG beta band power suppression, which was weaker for highly imageable hand verbs compared with highly imageable foot verbs. This provides a putative neuronal mechanism for language-motor interference where the involvement of cortical hand motor areas in hand verb processing interacts with the typical beta suppression seen before movements. We found that the facilitatory effect of higher imageability on action verb processing time is perturbed when verb and motor response relate to the same body part. Importantly, this effect is accompanied by neurophysiological effects in beta band oscillations. The attenuated power suppression around the time of movement, reflecting decreased cortical excitability, seems to result from motor simulation during action-related language processing. This is in line with embodied cognition theories.

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In synesthesia, stimulation of one sensory or cognitive pathway leads to additional, involuntary experiences in a second sensory or cognitive pathway. We here review previous surveys on this neurologically based phenomenon and report the results of 63 synesthetes who completed our Internet and paper questionnaire on synesthesia. In addition to asking for personal data and information on the participant's synesthesia, the questionnaire focused on the components of the inducer that elicit or modulate synesthesia. Synesthesia was most often developmental (92%) and of the grapheme-color type (86%). Sixty-two percent of the participants perceived time-related words in a spatial configuration. Music-color synesthesia was common (41%), and synesthesia for natural and artificial sounds (33%) was higher than in previous estimates. Eighty-one percent of participants experienced more than one form of synesthesia. Multimodal synesthesia, in which inducer and concurrent belong to 2 different sensory modalities, occurred in 92% of the participants. Overall, auditory stimuli were most often reported as inducers, and visual concurrents were most common. Modulations of the synesthetic experiences such as changes of the concurrent color, expansion within the same or to a different sensory modality, or reduction of the number of inducers over time were reported by 17% of participants. This challenges the presumed consistency of synesthesia and the adequacy of the test-retest consistency score still most commonly used to assess the veracity of reported synesthesia. Implications of the high prevalence of cross-modal synesthesia and the variability of synesthesia are discussed.

The grounded cognition framework proposes that sensorimotor brain areas, which are typically involved in perception and action, also play a role in linguistic processing. We assessed oscillatory modulation during visual presentation of single verbs and localized cortical motor regions by means of isometric contraction of hand and foot muscles. Analogously to oscillatory activation patterns accompanying voluntary movements, we expected a somatotopically distributed suppression of beta and alpha frequencies in the motor cortex during processing of body-related action verbs. Magnetoencephalographic data were collected during presentation of verbs that express actions performed using the hands (H) or feet (F). Verbs denoting no bodily movement (N) were used as a control. Between 150 and 500 msec after visual word onset, beta rhythms were suppressed in H and F in comparison with N in the left hemisphere. Similarly, alpha oscillations showed left-lateralized power suppression in the H-N contrast, although at a later stage. The cortical oscillatory activity that typically occurs during voluntary movements is therefore found to somatotopically accompany the processing of body-related verbs. The combination of a localizer task with the oscillatory investigation applied to verb reading as in the present study provides further methodological possibilities of tracking language processing in the brain.

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